Integrative and Comparative Biology - recent issues

Does new technology inspire new directions? Examples drawn from pelagic visual ecology

Johnsen, S. — 2007-11-18

Oceanography has seen the recent development of many new tools and techniques. The subfield of pelagic visual ecology in particular has benefited from the development of more reliable, portable, and economic tools and techniques that can be taken to sea including spectrometers, microspectrophotometery, electroretinography, and ultraviolet and polarization imaging systems. These advances have led to a relative wealth of data on the visual physiology of pelagic species and on the optical properties of these species and their environment. These data, particularly in combination with computational methods, have tested long-standing hypotheses in pelagic ecology and led to new hypotheses and research directions. While the ability to study pelagic species still lags far behind what is possible in terrestrial and coastal environments, a renaissance may be developing in the study of the integrative biology of pelagic species.

Comparative visual acuity of coleoid cephalopods

Sweeney, A. M., Haddock, S. H. D., Johnsen, S. — 2007-11-18

The pelagic realm of the ocean is characterized by extremely clear water and a lack of surfaces. Adaptations to the visual ecology of this environment include transparency, fluorescence, bioluminescence, and deep red or black pigmentation. While the signals that pelagic organisms send are increasingly well-understood, the optical capabilities of their viewers, especially for predators with camera-like vision such as fish and squid, are almost unknown. Aquatic camera-like vision is characterized by a spherical lens focusing an image on the retina. Here, we measured the resolving power of the lenses of eight species of pelagic cephalopods to obtain an approximation of their visual capabilities. We did this by focusing a standard resolution target through dissected lenses and calculating their modulation transfer functions. The modulation transfer function (MTF) is the single most complete expression of the resolving capabilities of a lens. Since the optical and retinal capabilities of an eye are generally well-matched, we considered our measurements of cephalopod lens MTF to be a good proxy for their visual capabilities in vivo. In general, squid have optical capabilities comparable to other organisms generally assumed to have good vision, such as fish and birds. Surprisingly, the optical capability of the eye of Vampyroteuthis infernalis rivals that of humans.

Phylogenetic analysis of lineage relationships among hyperiid amphipods as revealed by examination of the mitochondrial gene, cytochrome oxidase I (COI)

Browne, W. E., Haddock, S. H. D., Martindale, M. Q. — 2007-11-18

Among metazoans, crustaceans display the greatest disparity between body plans and are second only to the insects in overall species diversity. Within the crustaceans, the Amphipoda rank as one of the most speciose extant orders. Amphipods have successfully invaded a variety of ecosystems, including the pelagic midwater environment. Despite their abundance in varied and dissimilar habitats, and the use of traditional morphological and systematic comparative analyses, phylogenetic relationships among amphipods remain uncertain. The pelagic amphipods, hyperiids, have highly divergent life histories and morphological attributes in comparison to more familiar benthic, nearshore, intertidal, and terrestrial amphipods. Some of these adaptations are likely correlated with their pelagic life history and include features such as hypertrophied olfactory and visual systems, duplications of the eyes, and an array of modifications to the appendages. Many of these morphological features may represent homoplasies, thus masking the true phylogenetic relationships among extant hyperiid amphipods. Here, we sample a wide range of amphipod taxa for the COI gene and present the first preliminary molecular phylogeny among the hyperiids.

The prevalence and implications of copepod behavioral responses to oceanographic gradients and biological patchiness

Woodson, C. B., Webster, D. R., Weissburg, M. J., Yen, J. — 2007-11-18

Several species and developmental stages of calanoid copepods were tested for responses to environmental cues in a laboratory apparatus that mimicked conditions commonly associated with patches of food in the ocean. All species responded to the presence of phytoplankton by feeding. All species responded by increasing proportional residence time in one, but not both, of the treatments defined by gradients of velocity or density. Most species increased swimming speed and frequency of turning in response to the presence of chemical exudates or gradients of velocity. Only one species, Eurytemora affinis, increased proportional time of residence in response to gradients in density of the water. Responses of E. affinis to combined cues did not definitively demonstrate a hierarchical use of different cues as previously observed for Temora longicornis and Acartia tonsa. A simple foraging simulation was developed to assess the applicability in the field of the behavioral results observed in the laboratory. These simulations suggest that observed fine-scale behaviors could lead to copepod aggregations observed in situ. The present study demonstrates that behavioral response to cues associated with fine-scale oceanographic gradients and biological patchiness is functionally important and prevalent among copepods and likely has significant impacts on larger-scale distributional patterns.

Comparative feeding behavior of planktonic ctenophores

Haddock, S. H. D. — 2007-11-18

The phylum Ctenophora (known as comb jellies) consists of gelatinous marine carnivores found from the surface to several thousand meters depth. Their morphology can be simple or complex, ranging from a sac-like shape with no tentacles to large lobed forms with sinuous "auricles," papillae, and two different kinds of tentacles. This diversity appears to reflect adaptations to many different diets. For example, some species can continuously "graze" on small crustaceans or larvae, others engulf larger jellies, and some are able to snare individual larger prey through a variety of strategies. Thus feeding behavior can help explain the high morphological diversity in this relatively small phylum. Because of their fragility, comb jellies are difficult to study alive and the natural histories of many types, especially those found in the deep sea, have not been examined. This account categorizes ctenophore feeding methods using published reports as well as new observations using submersibles and blue-water scuba diving.

The Hox gene complement of a pelagic chaetognath, Flaccisagitta enflata

Matus, D. Q., Halanych, K. M., Martindale, M. Q. — 2007-11-18

Chaetognaths are transparent marine animals that are ubiquitous and abundant members of oceanic zooplanktonic communities. Their phylogenetic position within the Metazoa, however, has remained obscure since their discovery. Morphology and embryology have traditionally allied chaetognaths with deuterostomes, but molecular evidence suggests otherwise. Two recent multigene expressed sequence tag (EST) molecular phylogenomic studies suggest that chaetognaths are either sister to the Lophotrochozoa (Matus et al. 2006) or to all protostomes (Marlétaz et al. 2006). We have isolated eight Hox genes, one Parahox gene, and Mox, a related homeodomain gene, from the pelagic chaetognath, Flaccisagitta enflata. Although chaetognath central class Hox genes lack the Lox5 or "spiralian" parapeptide, a diagnostic amino-acid motif that has been utilized previously to assign lophotrochozoan affinity, they do possess a central class Hox gene that has a partial "Ubd-A peptide" found in both ecdysozoan and lophotrochozoan Ubx/Abd-A/Lox2/Lox4 genes. Additionally, we report the presence of two distinct chaetognath posterior Hox genes that possess both ecdysozoan and lophotrochozoan signature amino-acid motifs. The phylogenetic position of chaetognaths, as well as the evolution of the Hox cluster, is discussed in light of these data.

Homology of ciliary bands in Spiralian Trochophores

Henry, J. Q., Hejnol, A., Perry, K. J., Martindale, M. Q. — 2007-11-18

A number of hypotheses have been presented regarding the origins of the metazoans and, more specifically, the Bilateria. Using various phylogenetic analyses, characteristics have been mapped on phylogenetic trees to infer ancestral body plans and life history strategies of those ancestors. Many arguments on the evolution of the Bilateria are based on the presumed homology of certain characteristics of extant larva and adults, including various ciliated bands involved in feeding and locomotion. This article considers a recent study indicating that the second, downstream-collecting, ciliated band in the veliger larva of the gastropod mollusc, Crepidula fornicata, is actually derived from secondary trochoblasts (derived from second quartet micromeres), that normally form part of the prototrochal band found in other spiralian phyla (Hejnol et al. 2007). Despite previous arguments, these new findings suggest that the second ciliated band in the veliger larva is not homologous to the metatroch found in the trochophore larva of some other spiralians, such as the annelid, Polygordius lacteus. In the latter case, the metatroch was reported to be formed by a different set of lineage precursors (derived from third quartet micromeres) (Woltereck 1904). These findings have important implications for the interpretation of various hypotheses related to the evolution of metazoan phyla.

A brief review of holopelagic annelids

Halanych, K. M., Cox, L. N., Struck, T. H. — 2007-11-18

Annelids are one of the most successful major animal lineages in terms of number of species and of habitats occupied. Despite annelids being common in terrestrial, aquatic, and marine environments, only a limited number of lineages have evolved a holopelagic existence. Most of these holopelagic lineages belong to Phyllodocida (nereidids, syllids, scale worms, and jawed worms) and more particularly often within the family Phyllodocidae. These worms generally appear to retain many characteristics of adult annelids. Moreover, we provide molecular evidence showing that the well-known alciopids are derived from within Phyllodocidae. In contrast, at least two lineages, Poeobius meseres/Flota flabelligera and probably Chaetopterus pugaporcinus, are derived through paedomorphic processes acting on larvae from lineages that have sedentary adult forms. Herein, we will briefly review the known diversity of holopelagic annelids with discussion of their evolutionary origins.

Metabolic temperature compensation and coevolution of locomotory performance in pteropod molluscs

Seibel, B. A., Dymowska, A., Rosenthal, J. — 2007-11-18

Gymnosomatous pteropods are highly specialized planktonic predators that feed exclusively on their thecosomatous relatives. Feeding behavior and the morphology of gymnosome feeding structures are diverse and have evolved in concert with the size, shape, and consistency of the thecosome shell. Here, we show that the metabolic capacity and locomotory behaviors of gymnosomes are similarly diverse and vary with those of their prey. Both gymnosomes and thecosomes range from gelatinous sit-and-wait forms to active predators with high-performance locomotory muscles. We find more than 10-fold variation in size-adjusted and temperature-adjusted metabolic rates within both the Gymnosomata and Thecosomata and a strong correlation between the metabolic rates of predators and of prey. Furthermore, these characteristics are strongly influenced by environmental parameters and predator and prey converge upon similar physiological capacities under similar selection. For example, compensation of locomotory capacity in cold waters leads to elevated metabolic rates in polar species. This highly coevolved system is discussed in terms of a predator–prey "arms race" and the impending loss of both predator and prey as elevated atmospheric carbon dioxide levels threaten to dissolve prey shells via oceanic acidification.

The Evolution of Death: Why We Are Living Longer. Stanley Shostak.

Blackstone, N. W. — 2007-11-18

Emerging Threats to Tropical Forests. William F. Laurance and Carlos A. Peres, editors.

Lowman, M. — 2007-11-18

Design and Information in Biology: From Molecules to Systems. J. A. Bryant, M. A. Atherton and M. W. Collins, editors.

Wiegmann, B. M. — 2007-11-18

Evolutionary Ecology of Parasites. Robert Poulin.

Grimes, L. R. — 2007-11-18

Microbial Life, Second Edition. James T. Stanley, Robert P. Gunsalus, Stephen Lory, and Jerome J. Perry.

Keen, M. G. — 2007-11-18

Darwinian Reductionism Or, How to Stop Worrying and Love Molecular Biology. Alexander Rosenberg.

Stegmann, U. — 2007-11-18

The Biology of the Threespine Stickleback. Sara Ostlund-Nilsson, I. Mayer, and F.A. Huntingford, editors.

Foster, S. A. — 2007-11-18

Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral and Symbolic Variation in the History of Life. Eva Jablonka and Marion Lamb.

Newman, S. A. — 2007-11-18

Key transitions in animal evolution

DeSalle, R., Schierwater, B. — 2007-10-16

In order to address this subject further and to assess progress in the examination of animal origins and transitions, an international group of scientists was convened at the Society for Comparative Biology meeting in January 2007.

Can we ever identify the Urmetazoan?

Schierwater, B., DeSalle, R. — 2007-10-16

Unraveling the root of the metazoan tree of life has been a difficult task since the time of Haeckel and the invention of phylogenetics. Even considerable amounts of recent molecular data have not provided a generally accepted answer. Here, we review the major problems of this phylogenetic conundrum and provide some directions for solving it.

Field biology of placozoans (Trichoplax): distribution, diversity, biotic interactions

Pearse, V. B., Voigt, O. — 2007-10-16

The goal of this review is to highlight what little is known, and point to the bulk of what is yet to be learned, about the natural history of placozoans in the field—in order to stimulate a broader search for placozoans and a fuller exploration of their distribution, diversity, and all other aspects of their enigmatic lives. The documented geographic distribution of placozoans lies mostly in the nearshore, warm, marine waters of the tropics and subtropics. Although placozoans have long been viewed as benthic organisms, they can be more readily collected from the water column, well above the sea bottom. The full life-history of placozoans is unknown, including the nature of this abundant pelagic phase and all details of sexual reproduction and development. We note observations on the biota associated with placozoans in field collections, in particular the other regular members of the microcommunity in which placozoans occur on our collecting plates and on some factors influencing this assemblage. Among the animals found are some potential predators against which placozoans appear to be defended, although the mechanisms are still to be examined. Also yet to be uncovered is the full breadth of diversity in this phylum, certainly underrepresented by its single named species. We report here greatly expanded distributions for known haplotypes and fresh specimens that include a new haplotype, and we review the evidence that many more almost certainly await discovery. We also describe some methods for collecting and handling these small, fragile animals.

Cnidarian milestones in metazoan evolution

Boero, F., Schierwater, B., Piraino, S. — 2007-10-16

Cnidarians display most of the characters considered as milestones of metazoan evolution. Whereas a tissue-level organization was probably already present in the multicellular common ancestor of all animals, the Urmetazoa, the emergence of important animal features such as bilateral symmetry, triploblasty, a polarized nervous system, sense organs (eyes, statocysts), and a (chitinous or calcium-based) continuous skeleton can be traced back before the divergence between cnidarians and bilaterians. Modularity and metamery might be also regarded as two faces of the same medal, likely involving conserved molecular mechanisms ruling animal body architectures through regional specification of iterated units. Available evidence indicates that the common ancestor of cnidarians and bilaterians, the UrEumetazoa, was a surprisingly complex animal with nerve cell differentiation. We suggest that paedomorphic events in descendants of this ancestor led to the array of diversity seen in the main extant animal phyla. The use of molecular analyses and identifying the genetic determinants of anatomical organizations can provide an integrative test of hypotheses of homologies and independent evidence of the evolutionary relationships among extant taxa.

Implications of cnidarian gene expression patterns for the origins of bilaterality is the glass half full or half empty?

2007-10-16

The past two years have seen a dramatic increase in the available data on gene sequence and gene expression for cnidarians and other "lower" Metazoa, and a flurry of recent papers has drawn on these to address the origins of bilaterality. Cnidarian homologs of many genes that play key roles in the specification of both the A/P and D/V axes of bilaterians have been characterized, and their patterns of expression determined. Some of these expression patterns are consistent with the possibility of conservation of function between Cnidaria and Bilateria, but others clearly differ. Moreover, in some cases very different interpretations have been made on the basis of the same, or similar, data. In part, these differences reflect the inevitable uncertainties associated with the depth of the divergence between cnidarians and bilaterians. In this article, we briefly summarize the cnidarian data on gene expression and organization relevant to axis formation, the varying interpretations of these data, and where they conflict. Our conclusion is that the presently available data do not allow us to unequivocally homologize the single overt axis of cnidarians with either of the bilaterian axes.

Evolution of sensory structures in basal metazoa

2007-10-16

Cnidaria have traditionally been viewed as the most basal animals with complex, organ-like multicellular structures dedicated to sensory perception. However, sponges also have a surprising range of the genes required for sensory and neural functions in Bilateria. Here, we: (1) discuss "sense organ" regulatory genes, including; sine oculis, Brain 3, and eyes absent, that are expressed in cnidarian sense organs; (2) assess the sensory features of the planula, polyp, and medusa life-history stages of Cnidaria; and (3) discuss physiological and molecular data that suggest sensory and "neural" processes in sponges. We then develop arguments explaining the shared aspects of developmental regulation across sense organs and between sense organs and other structures. We focus on explanations involving divergent evolution from a common ancestral condition. In Bilateria, distinct sense-organ types share components of developmental-gene regulation. These regulators are also present in basal metazoans, suggesting evolution of multiple bilaterian organs from fewer antecedent sensory structures in a metazoan ancestor. More broadly, we hypothesize that developmental genetic similarities between sense organs and appendages may reflect descent from closely associated structures, or a composite organ, in the common ancestor of Cnidaria and Bilateria, and we argue that such similarities between bilaterian sense organs and kidneys may derive from a multifunctional aggregations of choanocyte-like cells in a metazoan ancestor. We hope these speculative arguments presented here will stimulate further discussion of these and related questions.

A food's-eye view of the transition from basal metazoans to bilaterians

Blackstone, N. W. — 2007-10-16

Living things invariably consist of some kind of compartmentalized redox chemistry. Signaling pathways mediated by oxidation and reduction thus derive from the nature of life itself. The role of such redox or metabolic signaling broadened with major transitions in the history of life. Prokaryotes often use redox signals to deploy one or more variant electron carriers and associated enzymes to better utilize environmental energy sources. Eukaryotes transcend the strong surface-to-volume constraints inherent in prokaryotic cells by moving chemiosmotic membranes internally. As a consequence, eukaryotic redox signaling is frequently between these organelle membranes and the nucleus, thus potentially involving levels-of-selection synergies and antagonisms. Gradients of oxygen and substrate in simple multicellular organisms similarly associated metabolic signaling with levels of selection, now at the level of the cell and the organism. By allowing sequestration of large amounts of food, the evolution of the animal mouth was a pivotal event in metabolic signaling, leading to "multicellular" redox regulation. Because concentrated food resources may be patchy in time and space, long-lived sedentary animals with mouths employ such metabolic signaling and phenotypic plasticity in ways that adapt them to the changing availability of food. Alternatively, if the mouth is coupled to a battery of sensory equipment, the organism can actively seek out and sequester patches of food. In these early bilaterians, competition for food resources may have favored rapid development with little subsequent plasticity and metabolic signaling. With rapid dispersal and colonization, such "assembly-line" animals could effectively compete for patchy resources. Limiting metabolic signaling, however, resulted in a cascade of seemingly unrelated changes. These changes derive from the effectiveness of metabolic signaling in policing variation at the cellular level. If the signals an organism uses to control cellular replication are the same as the signals a cell uses to control its own metabolism, then cells that ignore these signals and carry out selfish replication will pay a fitness cost in terms of inefficient metabolism. Bilaterians with limited metabolic signaling thus require other mechanisms to police cell-level variation. Bilaterian features such as restricted somatic cell potency, a sequestered germ line, and determinate growth should be viewed in this context. Bilaterian senescence evolved as a by-product of restricted potency of somatic cells, itself a mechanism of cell policing required by limited metabolic signaling.

Key transitions in animal evolution: a mitochondrial DNA perspective

Lavrov, D. V. — 2007-10-16

Animal mitochondrial DNA (mtDNA) is usually depicted as a small and very economically organized molecule with almost invariable gene content, stable gene order, a high rate of sequence evolution, and several unorthodox genetic features. Sampling across different animal phyla reveals that such a description applies primarily to mtDNA of bilaterian animals (such as arthropods or chordates). By contrast, mitochondrial genomes of nonbilaterian animals (phyla Cnidaria, Placozoa, and Porifera) display more variation in size and gene content and, in most cases, lack the genetic novelties associated with bilaterian mtDNA. Outside the Metazoa, mtDNA of the choanoflagellate Monosiga brevicollis, the closest unicellular out-group, is a much larger molecule that contains a large proportion of noncoding DNA, 1.5 times more genes, as well as several introns. Thus, changes in animal mtDNA organization appear to correlate with two main transitions in animal evolution: the origin of multicellularity and the origin of the Bilateria. Studies of mtDNA in nonbilaterian animals provide valuable insights into these transitions in the organization of mtDNA and also supply data for phylogenetic analyses of the relationships of early animals. Here I review recent progress in the understanding of nonbilaterian mtDNA and discuss the advantages and limitations of mitochondrial data sets for inferences about the phylogeny and evolution of animals.

Fossils and phylogenies: integrating multiple lines of evidence to investigate the origin of early major metazoan lineages

Cartwright, P., Collins, A. — 2007-10-16

Understanding the nature and timing of metazoan origins is one of the most important, yet elusive, questions in evolutionary biology. Fossil data provide the most tangible evidence for the origin of early animal lineages, although additional evidence from molecular phylogenetics, molecular clock studies, and development has contributed to our current understanding. We review several lines of evidence to explore the nature and timing of early metazoan evolution and discuss how these data, when considered together, provide a more cohesive picture of the origin of animal diversity. We discuss how trace fossils and biomarkers provide compelling evidence for the origins of Bilateria and siliceous sponges. Using a molecular phylogenetic framework for metazoans, we discuss how fossils can be used to date the origin of clades. We use these fossil dates to perform a relaxed molecular clock analysis for estimating dates of nodes when no fossils are available. We also discuss current data from developmental biology that suggest that early metazoans possessed a sophisticated molecular toolkit for building complex body plans. We conclude that the best evidence for the origin of major metazoan lineages lies in the careful interpretation of the fossil record and that these data, when considered with phylogenetic and developmental evidence, support the notion that the Cambrian radiation is a real phenomenon that marks a critically important time in the history of life.

Origin and evolution of a myxozoan worm

Jimenez-Guri, E., Okamura, B., Holland, P. W. H. — 2007-10-16

Buddenbrockia plumatellae is an active, muscular, worm-shaped parasite of freshwater bryozoans. This rare and enigmatic animal has been assigned to the Myxozoa on the basis of 18S ribosomal DNA sequences and the presence of malacosporean spores. Here we report cloning of four homologous protein-coding genes from Buddenbrockia worms, the putatively conspecific sac-shaped parasite originally described as Tetracapsula bryozoides and the related sac-shaped parasite Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease in salmonid fish. Analyses are consistent with the hypothesis that Buddenbrockia is indeed a malacosporean myxozoan, but do not provide support for conspecificity with either T. bryozoides or T. bryosalmonae. Implications for the evolution of worm-like body plans in the Myxozoa are discussed.

Key transitions during the evolution of animal phototransduction: novelty, "tree-thinking," co-option, and co-duplication

Plachetzki, D. C., Oakley, T. H. — 2007-10-16

Biologists are amazed by the intricacy and complexity of biological interactions between molecules, cells, organisms, and ecosystems. Yet underlying all this biodiversity is a universal common ancestry. How does evolution proceed from common starting points to generate the riotous biodiversity we see today? This "novelty problem"—understanding how novelty and common ancestry relate—has become of critical importance, especially since the realization that genes and developmental processes are often conserved across vast phylogenetic distances. In particular, two processes have emerged as the primary generators of diversity in organismal form: duplication plus divergence and co-option. In this article, we first illustrate how phylogenetic methodology and "tree-thinking" can be used to distinguish duplication plus divergence from co-option. Second, we review two case studies in photoreceptor evolution—one suggesting a role for duplication plus divergence, the other exemplifying how co-option can shape evolutionary change. Finally, we discuss how our tree-thinking approach differs from other treatments of the origin of novelty that utilized a "linear-thinking" approach in which evolution is viewed as a linear and gradual progression, often from simple to complex phenotype, driven by natural selection.

Evolution of the bilaterian germ line: lineage origin and modulation of specification mechanisms

Extavour, C. G. M. — 2007-10-16

A key focus of evolutionary developmental biology (evo–devo) in recent years has been to elucidate the evolution of developmental mechanisms as a means of reconstructing the hypothetical last common ancestors of various clades. Prominent among such reconstructions have been proposals as to the nature of the mysterious "Urbilateria," originally defined as the last common ancestor of the extant Bilateria (protostomes and deuterostomes). Indeed, drawings of this animal can now be found, as well as detailed information on the genetics and morphological processes that it used to construct its gut, heart, eyes, appendages, segments, and body regions. Perhaps surprisingly, however, no explanations have yet been offered as to how this animal might have achieved the successful reproduction that must have been necessary for it to give rise to those lineages that are ancestral to today's diverse clades. The present article examines the comparative data available to date on the specification of the only cells containing the genetic hereditary material, the germ cells, and speculates on the possible evolutionary and developmental origin of the Urbilaterian germ line.

The Natural History of Weasels and Stoats: Ecology, Behavior and Management, Second Edition. Carolyn M. King and Roger A. Powell.

Holmes, T. — 2007-10-16

Handbook of Avian Hybrids of the World. Eugene M. McCarthy.

Hamel, P. B. — 2007-10-16

Reproductive Biology and Phylogeny of Annelida * Volume edited by Greg Rouse and Fredrik Pleijel Series edited by Barrie G.M. Jamieson.

Hutchings, P. — 2007-10-16

Reproductive Biology and Phylogeny of Gymnophiona (Caecilians). Jean-Marie Exbrayat, editor.

Rastogi, R. K. — 2007-10-16

Extinction & Biogeography of Tropical Pacific Birds. David W. Steadman.

Gochfeld, M. — 2007-10-16

Reproductive Biology and Phylogeny of Birds: Phylogeny, Morphology, Hormones, Fertilization (Volume 6A of Series). Barrie G. M. Jamieson, editor. * Reproductive Biology and Phylogeny of Birds: Sexual Selection, Behavior, Conservation, Embryology and Genetics (Volume 6B of Series). Barrie G. M. Jamieson, editor.

Bock, W. J. — 2007-10-16

The Cell Cycle, Principles of Control. David O. Morgan.

Lubischer, J. L. — 2007-10-16

Reproductive Biology and Early Life History of Fishes in the Ohio River Drainage: Aphredoderidae through Cottidae, Moronidae, and Sciaenidae, Volume 5. Robert Wallus and Thomas P. Simon, editors.

Starnes, W. C. — 2007-10-16

Recent developments in neurobiology: introduction to the symposium to honor Professor Douglas G. Stuart

Satterlie, R. A. — 2007-09-20

The role of postinhibitory rebound in the locomotor central-pattern generator of Clione limacina

Pirtle, T. J., Satterlie, R. A. — 2007-09-20

In animals, networks of central neurons, called central-pattern generators (CPGs), produce a variety of locomotory behaviors including walking, swimming, and flying. CPGs from diverse animals share many common characteristics that function at the system level, circuit level, and cellular level. However, the relative roles of common CPG characteristics are variable among different animal species, in ways that suit different forms of locomotion in different environmental contexts. Here, we examine some of these common features within the locomotor CPG in a model system used to investigate changes in locomotory speed—the swim system of the pteropod mollusk, Clione limacina. In particular, we discuss the role of one cellular characteristic that is essential for locomotor pattern generation in Clione, postinhibitory rebound.

Contextual learning and obstacle memory in the walking cat

McVea, D.A., Pearson, K.G. — 2007-09-20

Animals in their natural environments display a remarkably diverse variety of walking patterns. Although some of this diversity is generated by alterations in feedback from the moving limbs, animals can modify their walking in many ways that cannot be directly attributed to this sensory feedback. For example, animals and humans can learn to associate a particular environment with disturbances that were experienced there earlier, and alter their stepping accordingly even after the disturbance has ceased. Another relevant example is that walking animals are aware of the locations of obstacles around them, and use this awareness to alter their stepping patterns even when there is no visual information available about the location of the obstacles relative to the body. In this article, we discuss recent work from our laboratory that addresses these two topics. First, we report that perturbing walking cats in a consistent manner evokes long-lasting changes to the walking pattern that are expressed only in the context in which walking was disturbed. Secondly, we show that cats that have stepped over an obstacle remember the location of that obstacle relative to the body during long delays, and can use that memory to guide stepping. The general theme of this research is that sensory inputs that signal context—the visual and auditory environment that surrounds an animal—play an important role in shaping the basic pattern of locomotion.

The neurobiology of muscle fatigue: 15 years later

Barry, B. K., Enoka, R. M. — 2007-09-20

This brief review summarizes progress that has been made in the study of muscle fatigue since a review published 15 years ago (Enoka RM, Stuart DG. 1992. Neurobiology of muscle fatigue. J Appl Physiol 72:1631–48.). The present review first discusses progress on the four themes identified in the 1992 review and then describes a new approach that can be used to identify the functionally significant physiological adjustments that occur during fatiguing contractions. As described in the previous review, it is currently not possible to develop a comprehensive model of muscle fatigue because the prevailing mechanism that impairs performance varies with the characteristics of the task that is being performed. An alternative approach is to focus on the mechanisms that cause failure to complete the task. This task-failure approach involves comparing two performances and identifying the adjustments that limit the rate for the more difficult condition. With this approach, initial studies have demonstrated that the time to failure of a sustained contraction can be influenced by such variables as the type of load supported by the limb, the posture of the limb, and the group of muscles involved in the task. The challenge is to identify the mechanisms that enable these different variables influence the time to task failure.

Predictive and reactive tuning of the locomotor CPG

Prochazka, A., Yakovenko, S. — 2007-09-20

The neural control of locomotion involves a constant interplay between the actions of a central pattern generator (CPG) and sensory input elicited by bodily movement. With respect to the CPG, recent analysis of fictive locomotion has shown that durations of flexion and extension tend to covary along specific lines in plots of phase duration versus cycle duration. The slopes of these lines evidently depend on internal states that vary among preparations, but, within a preparation, remain rather steady from one sequence to the next. These relationships can be reproduced in a simple oscillator model having two pairs of preset parameters, suggesting that steady internal drives to flexor and extensor half-centers determine how phase durations covary. Regarding the role of sensory inputs, previous experiments have revealed state-dependent rules that govern phase-switching independently of the CPG rhythm. In addition, sensory input is known to modulate motoneuronal activation through stretch reflexes. To explore how sensory input combines with the locomotor CPG, we used a neuromechanical model with muscle actuators, proprioceptive feedback, sensory phase-switching rules, and a CPG. Interestingly, sequences of stable locomotion were always associated with phase durations that conformed to an extensor-dominated phase-duration characteristic (where extension durations vary more than flexion durations). This is the characteristic seen in normal animals, but not necessarily in fictive locomotion, where movement and associated sensory input are absent. This suggests that to produce the biomechanical events required for stability, an extensor-dominated phase-duration characteristic is required. In the model, when the preset CPG phase durations were well matched to coincide the biomechanical requirements, CPG-mediated phase switching produced stable cycles. When CPG phase durations were too short, phases switched prematurely and the model soon fell. When CPG phase durations were too long, sensory rules fired and overrode the CPG, maintaining stability. We posit that under normal circumstances, descending input from higher centers continually adjusts the operating point of the CPG on the preset phase-duration characteristic according to anticipated biomechanical requirements. When the predictions are good, CPG-generated phase durations closely match those required by the kinetics and kinematics, and little or no sensory adjustment occurs. We propose the term "neuromechanical tuning" to describe this process of matching the CPG to the biomechanical requirements.

Reflections on integrative and comparative movement neuroscience

Stuart, D. G. — 2007-09-20

Integrative movement neuroscience involves blending "inside-out" and "outside-in" approaches in the study of posture and movement. The former is characterized by determining the properties of single cells within the central nervous system (CNS) and then ascertaining how these properties influence the operation of CNS microcircuits, single reflexes, groups of reflexes, and generators of central pattern. This information is then used to theorize about CNS control of overt motor behavior. In contrast, the outside-in approach begins with analysis of the biomechanics of posture and movement and then uses this information to theorize how the mechanics are solved by the CNS and its pathways, circuitry, and even single cells. Studies conducted in the 1960s on CNS circuitry generating locomotor patterns in several invertebrate and vertebrate species, together with work on the treadmill locomotion of brain-stimulated decerebrate cats, led to a subsequent convergence of inside-out and outside-in understanding of the neural control of locomotion in invertebrates, nonmammalian vertebrates, and mammalian vertebrates, even including humans. This convergence of integrative and comparative approaches has been facilitated by modeling and simulation studies. These developments have important implications for doctoral and postdoctoral training programs in movement neuroscience. They can profit greatly by use of a multidisciplinary university-wide faculty who place a strong emphasis on integrative and comparative biology. Furthermore, the next generation of movement neuroscientists will require more familiarity with modeling and simulation than are being provided in most current training programs. To achieve the above, it will be advantageous if university culture and structure truly champion university-wide interdisciplinary research.

Introduction to special section on respiratory biology

Perry, S. F., Schmitz, A., Spinelli Oliveira, E. — 2007-09-20

Why respiratory biology? The meaning and significance of respiration and its integrative study

Perry, S. F., Burggren, W. W. — 2007-09-20

Traditionally the process of respiration is divided into three phases: (1) cellular respiration, (2) transport of respiratory gases and (3) ventilation of the gas exchange organs (breathing). Thereby organisms assimilate chemical energy from the environment, and within their cells transfer it from molecule to molecule in a stepwise fashion. Although studied separately, these phases represent a continuum and cellular respiration in all life forms has much in common. Ironically, these respiratory foci have been artificially delineated by their own practitioners, who tend to publish in their own journals, and attend their own conferences. The goal of modern respiratory biology should be to understand biological connectivity and complexity by viewing an organism as a series of interconnecting systems from molecule to ecosystem. The future of science in general, and biology in particular, lies in disciplinary networking: combining the results of traditional disciplines to better understand the whole. Because of its universality, Respiratory Biology can best provide this bridge and improve interdisciplinary studies in biology generally. To this end, the First International Congress of Respiratory Biology was held from August 14 to 16, 2006, at Bonn, Germany. As evident from the success of this inaugural meeting, these are exciting times for Respiratory Biology. The explosion of "X-omics" and systems biology, the powerful genetic approaches to disease treatment, and the long-standing and newly emerging questions in evolutionary biology and ecology; all portend a continuing role of respiratory biology as a key integrative discipline.

Devonian climate change, breathing, and the origin of the tetrapod stem group

Clack, J. A. — 2007-09-20

The diversification of the tetrapod stem group occurred during the late Middle through the Late Devonian, that is from the Givetian to Famennian stages about 385–365 million years ago. The relationships between the known taxa representing this radiation have currently reached a reasonable consensus so that interpretations of the order of appearance of tetrapod characters is possible. The immediate fish relatives of the earliest limbed tetrapods show what is interpreted as a progressive increase in the spiracular chamber and its opening to the outside. Here, this is inferred to be associated with an increased capacity for air-breathing. Lungs are thought to have been present in most early bony fishes, and were most likely ventilated by air-gulping. This could have brought about a facultative capacity for air-breathing, which the tetrapod stem group exploited to the greatest degree. These adaptations are shown not only in freshwater forms but also in estuarine and marginal marine forms. Estimates of oxygen levels during this period suggest that they were unprecedentedly low during the Givetian and Frasnian periods. At the same time, plant diversification was at its most rapid, changing the character of the landscape and contributing, via soils, soluble nutrients, and decaying plant matter, to anoxia in all water systems. The co-occurrence of these global events may explain the evolution of air-breathing adaptations in at least two lobe-finned groups, contributing directly to the rise of the tetrapod stem group. In contrast to recent studies, low atmospheric oxygen is not considered to be a causal factor in the lack of fossils documenting the evolution of Early Carboniferous tetrapods.

Coping with cyclic oxygen availability: evolutionary aspects

Fluck, M., Webster, K. A., Graham, J., Giomi, F., Gerlach, F., Schmitz, A. — 2007-09-20

Both the gradual rise in atmospheric oxygen over the Proterozoic Eon as well as episodic fluctuations in oxygen over several million-year time spans during the Phanerozoic Era, have arguably exerted strong selective forces on cellular and organismic respiratory specialization and evolution. The rise in atmospheric oxygen, some 2 billion years after the origin of life, dramatically altered cell biology and set the stage for the appearance of multicelluar life forms in the Vendian (Ediacaran) Period of the Neoproterozoic Era. Over much of the Paleozoic, the level of oxygen in the atmosphere was near the present atmospheric level (21%). In the Late Paleozoic, however, there were extended times during which the level of atmospheric oxygen was either markedly lower or markedly higher than 21%. That these Paleozoic shifts in atmospheric oxygen affected the biota is suggested by the correlations between: (1) Reduced oxygen and the occurrences of extinctions, a lowered biodiversity and shifts in phyletic succession, and (2) During hyperoxia, the corresponding occurrence of phenomena such as arthropod gigantism, the origin of insect flight, and the evolution of vertebrate terrestriality. Basic similarities in features of adaptation to hyopoxia, manifest in living organisms at levels ranging from genetic and cellular to physiological and behavioral, suggest the common and early origin of a suite of adaptive mechanisms responsive to fluctuations in ambient oxygen. Comparative integrative approaches addressing the molecular bases of phenotypic adjustments to cyclic oxygen fluctuation provide broad insight into the incremental steps leading to the early evolution of homeostatic respiratory mechanisms and to the specialization of organismic respiratory function.

Respiratory plasticity in response to changes in oxygen supply and demand

2007-09-20

Aerobic organisms maintain O₂ homeostasis by responding to changes in O₂ supply and demand in both short and long time domains. In this review, we introduce several specific examples of respiratory plasticity induced by chronic changes in O₂ supply (environmental hypoxia or hyperoxia) and demand (exercise-induced and temperature-induced changes in aerobic metabolism). These studies reveal that plasticity occurs throughout the respiratory system, including modifications to the gas exchanger, respiratory pigments, respiratory muscles, and the neural control systems responsible for ventilating the gas exchanger. While some of these responses appear appropriate (e.g., increases in lung surface area, blood O₂ capacity, and pulmonary ventilation in hypoxia), other responses are potentially harmful (e.g., increased muscle fatigability). Thus, it may be difficult to predict whole-animal performance based on the plasticity of a single system. Moreover, plastic responses may differ quantitatively and qualitatively at different developmental stages. Much of the current research in this field is focused on identifying the cellular and molecular mechanisms underlying respiratory plasticity. These studies suggest that a few key molecules, such as hypoxia inducible factor (HIF) and erythropoietin, may be involved in the expression of diverse forms of plasticity within and across species. Studying the various ways in which animals respond to respiratory challenges will enable a better understanding of the integrative response to chronic changes in O₂ supply and demand.

From critters to cancers: bridging comparative and clinical research on oxygen sensing, HIF signaling, and adaptations towards hypoxia

2007-09-20

The objective of this symposium at the First International Congress of Respiratory Biology (ICRB) was to enhance communication between comparative biologists and cancer researchers working on O₂ sensing via the HIF pathway. Representatives from both camps came together on August 13–16, 2006, in Bonn, Germany, to discuss molecular adaptations that occur after cells have been challenged by a reduced (hypoxia) or completely absent (anoxia) supply of oxygen. This brief "critters-to-cancer" survey discusses current projects and new directions aimed at improving understanding of hypoxic signaling and developing therapeutic interventions.

Implications of dealing with airborne substances and reactive oxygen species: what mammalian lungs, animals, and plants have to say?

2007-09-20

A gas-exchange structure interacts with the environment and is constantly challenged by contaminants that may elicit defense responses, thus compromising its primary function. It is also exposed to high concentrations of O₂ that can generate reactive oxygen species (ROS). Revisiting the lung of mammals, an integrative picture emerges, indicating that this bronchi-alveolar structure deals with inflammation in a special way, which minimizes compromising the gas-exchange role. Depending on the challenge, pro-inflammatory or antiinflammatory responses are elicited by conserved molecules, such as surfactant proteins A and D. An even broader picture points to the participation of airway sensors, responsive to inflammatory mediators, in a loop linking the immunological and nervous systems and expanding the role played by respiratory organs in functions other than gas-exchange. A byproduct of exposure to high concentration of O₂ is the formation of superoxide ( ), hydrogen peroxide (H₂O₂), hydroxyl radical (HO^•), and other ROS, which are known to be toxic to different types of cells, including the lung epithelium. A balance between antioxidants and oxidants exists; in pulmonary epithelial cells high intracellular and extracellular levels of antioxidants are found. Antioxidant adaptations related to plant and animal life-styles involve a broad range of overlapping strategies based on well-conserved molecules. Glutathione (GSH) is an abundant and ubiquitous thiol-tripeptide antioxidant, also present in lungs, whose role in providing information on the intracellular redox state of animals and plants is well established. In these organisms, GSH influences gene expression associated with stress, maximizing defense responses. Several enzymatic antioxidants, such as glutathione peroxidase (GPx), glutathione reductase, glutathione S-transferase, and glucose 6-phosphate dehydrogenase participate in the redox system; in animals that are stress-tolerant GPx is a key element against oxidative assaults. Most importantly, alternative roles of ROS as signaling molecules have been found in all plants and animals. For example, alveolar macrophages produce that act as second messengers, in addition to having a bactericidal role. The nonradical ROS H₂O₂ signals inflammation in mammalian lungs, apoptosis in different animal tissues, and is also involved in stomatal closure, root development, gene expression, and defense responses of plants. Antioxidant adaptations in some water-breathing animals involve the excretion of H₂O₂ by diffusion through gas-exchange structures. The fine balance among a multitude of factors and cells makes the difference between damage and protection in animals and plants. Knowledge about the mechanisms and consequences of these molecular interactions is now starting to be integrated.

Respiratory chemoreceptor function in vertebrates comparative and evolutionary aspects

2007-09-20

The sensing of blood gas tensions and/or pH is an evolutionarily conserved, homeostatic mechanism, observable in almost all species studied from invertebrates to man. In vertebrates, a shift from the peripheral O₂-oriented sensing in fish, to the central CO₂/pH sensing in most tetrapods reflects the specific behavioral requirements of these two groups whereby, in teleost fish, a highly O₂-oriented control of breathing matches the ever-changing and low oxygen levels in water, whilst the transition to air-breathing increased the importance of acid–base regulation and O₂-related drive, although retained, became relatively less important. The South American lungfish and tetrapods are probably sister groups, a conclusion backed up by many similar features of respiratory control. For example, the relative roles of peripheral and central chemoreceptors are present both in the lungfish and in land vertebrates. In both groups, the central CO₂/pH receptors dominate the ventilatory response to hypercarbia (60–80%), while the peripheral CO₂/pH receptors account for 20–30%. Some basic components of respiratory control have changed little during evolution. This review presents studies that reflect the current trends in the field of chemoreceptor function, and several laboratories are involved. An exhaustive review on the previous literature, however, is beyond the intended scope of the article. Rather, we present examples of current trends in respiratory function in vertebrates, ranging from fish to humans, and focus on both O₂ sensing and CO₂ sensing. As well, we consider the impact of chronic levels of hypoxia—a physiological condition in fish and in land vertebrates resident at high elevations or suffering from one of the many cardiorespiratory disease states that predispose an animal to impaired ventilation or cardiac output. This provides a basis for a comparative physiology that is informative about the evolution of respiratory functions in vertebrates and about human disease. Currently, most detail is known for mammals, for which molecular biology and respiratory physiology have combined in the discovery of the mechanisms underlying the responses of respiratory chemoreceptors. Our review includes new data on nonmammalian vertebrates, which stresses that some chemoreceptor sites are of ancient origin.

Deconvoluting lung evolution: from phenotypes to gene regulatory networks

2007-09-20

Speakers in this symposium presented examples of respiratory regulation that broadly illustrate principles of evolution from whole organ to genes. The swim bladder and lungs of aquatic and terrestrial organisms arose independently from a common primordial "respiratory pharynx" but not from each other. Pathways of lung evolution are similar between crocodiles and birds but a low compliance of mammalian lung may have driven the development of the diaphragm to permit lung inflation during inspiration. To meet the high oxygen demands of flight, bird lungs have evolved separate gas exchange and pump components to achieve unidirectional ventilation and minimize dead space. The process of "screening" (removal of oxygen from inspired air prior to entering the terminal units) reduces effective alveolar oxygen tension and potentially explains why nonathletic large mammals possess greater pulmonary diffusing capacities than required by their oxygen consumption. The "primitive" central admixture of oxygenated and deoxygenated blood in the incompletely divided reptilian heart is actually co-regulated with other autonomic cardiopulmonary responses to provide flexible control of arterial oxygen tension independent of ventilation as well as a unique mechanism for adjusting metabolic rate. Some of the most ancient oxygen-sensing molecules, i.e., hypoxia-inducible factor-1alpha and erythropoietin, are up-regulated during mammalian lung development and growth under apparently normoxic conditions, suggesting functional evolution. Normal alveolarization requires pleiotropic growth factors acting via highly conserved cell–cell signal transduction, e.g., parathyroid hormone-related protein transducing at least partly through the Wingless/int pathway. The latter regulates morphogenesis from nematode to mammal. If there is commonality among these diverse respiratory processes, it is that all levels of organization, from molecular signaling to structure to function, co-evolve progressively, and optimize an existing gas-exchange framework.

The anatomy, physics, and physiology of gas exchange surfaces: is there a universal function for pulmonary surfactant in animal respiratory structures?

2007-09-20

(Orgeig and Daniels) This surfactant symposium reflects the integrative and multidisciplinary aims of the 1st ICRB, by encompassing in vitro and in vivo research, studies of vertebrates and invertebrates, and research across multiple disciplines. We explore the physical and structural challenges that face gas exchange surfaces in vertebrates and insects, by focusing on the role of the surfactant system. Pulmonary surfactant is a complex mixture of lipids and proteins that lines the air–liquid interface of the lungs of all air-breathing vertebrates, where it functions to vary surface tension with changing lung volume. We begin with a discussion of the extraordinary conservation of the blood–gas barrier among vertebrate respiratory organs, which has evolved to be extremely thin, thereby maximizing gas exchange, but simultaneously strong enough to withstand significant distension forces. The principal components of pulmonary surfactant are highly conserved, with a mixed phospholipid and neutral lipid interfacial film that is established, maintained and dynamically regulated by surfactant proteins (SP). A wide variation in the concentrations of individual components exists, however, and highlights lipidomic as well as proteomic adaptations to different physiological needs. As SP-B deficiency in mammals is lethal, oxidative stress to SP-B is detrimental to the biophysical function of pulmonary surfactant and SP-B is evolutionarily conserved across the vertebrates. It is likely that SP-B was essential for the evolutionary origin of pulmonary surfactant. We discuss three specific issues of the surfactant system to illustrate the diversity of function in animal respiratory structures. (1) Temperature: In vitro analyses of the behavior of different model surfactant films under dynamic conditions of surface tension and temperature suggest that, contrary to previous beliefs, the alveolar film may not have to be substantially enriched in the disaturated phospholipid, dipalmitoylphosphatidylcholine (DPPC), but that similar properties of rate of film formation can be achieved with more fluid films. Using an in vivo model of temperature change, a mammal that enters torpor, we show that film structure and function varies between surfactants isolated from torpid and active animals. (2) Spheres versus tubes: Surfactant is essential for lung stabilization in vertebrates, but its function is not restricted to the spherical alveolus. Instead, surfactant is also important in narrow tubular respiratory structures such as the terminal airways of mammals and the air capillaries of birds. (3). Insect tracheoles: We investigate the structure and function of the insect tracheal system and ask whether pulmonary surfactant also has a role in stabilizing these minute tubules. Our theoretical analysis suggests that a surfactant system may be required, in order to cope with surface tension during processes, such as molting, when the tracheae collapse and fill with water. Hence, despite observations by Wigglesworth in the 1930s of fluid-filled tracheoles, the challenge persists into the 21st century to determine whether this fluid is associated with a pulmonary-type surfactant system. Finally, we summarize the current status of the field and provide ideas for future research.

The integrative and evolutionary biology of gas-binding copper proteins: an introduction

Decker, H., Terwilliger, N., Portner, H.-O. — 2007-09-20

This article summarizes the contributions given at the symposium "The Benefits of Gas-binding Proteins. Integrative and Evolutionary Physiology of Copper Proteins: Molecules to Organisms and their Environment," presented at the First International Congress of Respiratory Biology, August 14–16, at Bad Honnef/Bonn, Germany.

Minireview: Recent progress in hemocyanin research

Decker, H., Hellmann, N., Jaenicke, E., Lieb, B., Meissner, U., Markl, J. — 2007-09-20

This review summarizes recent highlights of our joint work on the structure, evolution, and function of a family of highly complex proteins, the hemocyanins. They are blue-pigmented oxygen carriers, occurring freely dissolved in the hemolymph of many arthropods and molluscs. They are copper type-3 proteins and bind one dioxygen molecule between two copper atoms in a side-on coordination. They possess between 6 and 160 oxygen-binding sites, and some of them display the highest molecular cooperativity observed in nature. The functional properties of hemocyanins can be convincingly described by either the Monod–Wyman–Changeux (MWC) model or its hierarchical extension, the Nested MWC model; the latter takes into account the structural hierarchies in the oligomeric architecture. Recently, we applied these models to interpret the influence of allosteric effectors in detailed terms. Effectors shift the allosteric equilibria but have no influence on the oxygen affinities characterizing the various conformational states. We have shown that hemocyanins from species living at different environmental temperatures have a cooperativity optimum at the typical temperature of their natural habitat.

Besides being oxygen carriers, some hemocyanins function as a phenoloxidase (tyrosinase/catecholoxidase) which, however, requires activation. Chelicerates such as spiders and scorpions lack a specific phenoloxidase, and in these animals activated hemocyanin might catalyse melanin synthesis in vivo. We propose a similar activation mechanism for arthropod hemocyanins, molluscan hemocyanins and tyrosinases: amino acid(s) that sterically block the access of phenolic compounds to the active site have to be removed. The catalysis mechanism itself can now be explained on the basis of the recently published crystal structure of a tyrosinase.

In a series of recent publications, we presented the complete gene and primary structure of various hemocyanins from different molluscan classes. From these data, we deduced that the molluscan hemocyanin molecule evolved ca. 740 million years ago, prior to the separation of the extant molluscan classes. Our recent advances in the 3D cryo-electron microscopy of hemocyanins also allow considerable insight into the oligomeric architecture of these proteins of high molecular mass. In the case of molluscan hemocyanin, the structure of the wall and collar of the basic decamers is now rapidly becoming known in greater detail. In the case of arthropod hemocyanin, a 10-Å structure and molecular model of the Limulus 8 x 6mer shows the amino acids at the various interfaces between the eight hexamers, and reveals histidine-rich residue clusters that might be involved in transferring the conformational signals establishing cooperative oxygen binding.

Role of blood-oxygen transport in thermal tolerance of the cuttlefish, Sepia officinalis

Melzner, F., Mark, F. C., Portner, H. O. — 2007-09-20

Mechanisms that affect thermal tolerance of ectothermic organisms have recently received much interest, mainly due to global warming and climate-change debates in both the public and in the scientific community. In physiological terms, thermal tolerance of several marine ectothermic taxa can be linked to oxygen availability, with capacity limitations in ventilatory and circulatory systems contributing to oxygen limitation at extreme temperatures. The present review briefly summarizes the processes that define thermal tolerance in a model cephalopod organism, the cuttlefish Sepia officinalis, with a focus on the contribution of the cephalopod oxygen-carrying blood pigment, hemocyanin. When acutely exposed to either extremely high or low temperatures, cuttlefish display a gradual transition to an anaerobic mode of energy production in key muscle tissues once critical temperatures (T_crit) are reached. At high temperatures, stagnating metabolic rates and a developing hypoxemia can be correlated with a progressive failure of the circulatory system, well before T_crit is reached. However, at low temperatures, declining metabolic rates cannot be related to ventilatory or circulatory failure. Rather, we propose a role for hemocyanin functional characteristics as a major limiting factor preventing proper tissue oxygenation. Using information on the oxygen binding characteristics of cephalopod hemocyanins, we argue that high oxygen affinities (= low P₅₀ values), as found at low temperatures, allow efficient oxygen shuttling only at very low venous oxygen partial pressures. Low venous PO₂s limit rates of oxygen diffusion into cells, thus eventually causing the observed transition to anaerobic metabolism. On the basis of existing blood physiological, molecular, and crystallographical data, the potential to resolve the role of hemocyanin isoforms in thermal adaptation by an integrated molecular physiological approach is discussed.

Negative cooperativity in Root-effect hemoglobins: role of heterogeneity

Decker, H., Nadja, H. — 2007-09-20

In some animals, the oxygen transport capacity of blood decreases when pH is lowered, yielding oxygen binding curves with Hill-coefficients smaller than unity. This so-called Root effect is observed in several fishes and is important for creating large oxygen partial pressures locally, for example in the swim bladder. While there is general agreement on the physiological advantages of this effect, its molecular basis remains ambiguous. Various studies show that isoforms of hemoglobins usually are present in the hemolymph, when the Root effect is observed. Here, we show that in such a case the mixture of these isoforms can exhibit apparent negative cooperativity, although each component taken separately can be described by the MWC model. In other cases, isolated isoforms exhibit true negative cooperativity. The well established MWC model describes many cooperative phenomena of enzymes and respiratory proteins but is not capable of describing negative cooperativity. In order to model negative cooperativity within a single molecular species a decoupling model might be employed, as pointed out previously. However, simulations show that it is not mandatory to have species with negative cooperativity, in order to obtain the binding curves typically seen for whole blood. These two aspects of the Root effect will be discussed on the basis of data from the literature.

Hemocyanins and the immune response: defense against the dark arts

Terwilliger, N. B. — 2007-09-20

The innate immune response is a conserved trait shared by invertebrates and vertebrates. In crustaceans, circulating hemocytes play significant roles in the immune response, including the release of prophenoloxidases. Activated phenoloxidase (tyrosinase) participates in encapsulation and melanization of foreign organisms as well as sclerotization of the new exoskeleton after wound-repair or molting. Hemocyanin functions as a phenoloxidase under certain conditions and thus also participates in the immune response and molting. The relative contributions of hemocyte phenoloxidase and hemocyanin in the physiological ratio at which they occur in hemolymph have been investigated in the crab Cancer magister. Differences in activity, substrate affinity, and catalytic ability between the two enzymes indicate that hemocytes are the predominant source of phenoloxidase activity in crabs. In contrast, hemocyanin is the primary source of phenoloxidase activity in isopods and chelicerates whose hemocytes show no phenoloxidase activity. Quantitative PCR studies on the distribution of prophenoloxidase mRNA in the tissues of Carcinus maenas showed little effect relative to salinity stress. Phylogenetic analysis of hemocyanin, phenoloxidase, and other members of this arthropod gene family are consistent with the possibility that a common ancestral molecule had both phenoloxidase and oxygen-binding capabilities.