Integrative and Comparative Biology - current issue

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