© 2003 by The Society for Integrative and Comparative Biology
Integrative Biology and Genetic Resources Management1
1 Centre de Génétique Moléculaire, CNRS, 91198, Gif-sur-Yvette, France
2 Station d'Amélioration Génétique des Animaux, INRA, BP 27, 31326, Castanet-Tolosan, France
 |
SYNOPSIS |
|---|
TOP
 SYNOPSIS INTRODUCTIONRESULTS AND INFERENCESDISCUSSIONReferences |
|---|
Integrative Biology is exemplified by a diversity of recently established collaborations to study the genetic diversity of the European rabbit, Oryctolagus cuniculus. Molecular markers were developed and used to investigate the link between wild population decreases or domestication procedures and possible losses of genetic diversity. Simultaneously, a European programme was launched for the management of genetic resources. The Integrative Biology approach shows that changes in genetic diversity are often buffered by the flexibility of rabbit reproductive systems. It appears, also, that all domestic animals belong to a subset of the wild genetic pool of their species without major loss of diversity despite exposure to severe viral infections. Consequently, management of genetic resources for production purposes and conservation or protection of declining Iberian wild populations require different approaches and measures.
|
INTRODUCTION |
|---|
|
TOP
SYNOPSISINTRODUCTIONRESULTS AND INFERENCESDISCUSSIONReferences |
|---|
The example of the ecological maintenance and commercial production of European rabbits illustrates the Integrative Biology perspective and shows how such an approach is able to capitalize on the multidisciplinary input of classical approaches (zoology, genetics and molecular biology, reproduction and developmental biology, ecology and ethology) to provide the kind of dynamic biological knowledge needed to support the management of genetic resources. Driven by the continuously evolving expectations of societies, the practice of genetic resource management builds upon existing biodiversity and makes deliberate choices regarding selective conservation, multiplication, and the production and commercial exploitation of "useful" biological items (animals, plants or microorganisms). In doing so, it renews the process of domestication, started long ago by farmers, by adding the input of modern science and biotechnology. Operating within the ethical and judicial framework of national rules and international conventions (World Trade Organisation Agreements, Intellectual Property Rights and Biological Diversity Convention) genetic resource management has a global impact upon today's world.
The European Rabbit, Oryctolagus cuniculus, is a species that emerged in the Iberian Peninsula a few million years ago. It experienced a series of expansions and reductions in conjunction with successive glacial waves. At the end of the last ice age, rabbits moved from their refuges to resume the colonization of southern France. Further expansion through the European continent was complicated by the impact of domestication efforts from the time of the Middle Ages onwards (Arnold, 1994
; Callou, 1995 and 2000 and Fig. 1). Indeed, meat and pelts are a resource, but rabbits also destroy crops. The species acquired a plural status: game to be hunted, farm animals to be produced, pests to eradicate, and recently also pets. In their laboratories, biologists discovered that rabbit evolution has explored a diversity of molecular and physiological mechanisms in terms of genetics, immunology, reproductive biology, social organization, ecology and interactions with parasites. These inventions warrant chapters devoted specifically to rabbits in biology books and the use of rabbits as biological models for research in, for example, immunology or embryo transplantation.
|
Today, Western Europe accounts for 70% of the world's commercial rabbit production but still imports carcasses to cover its demand for meat. Briefly stated: rabbit production is mainly based on commercial strains, extracted from a few breeds and strongly selected for production traits. Purebreeding is decreasing, whereas more than 60 breeds exist and are maintained by amateurs (fancy breeders) for curiosity's sake or as hobbies or pets. Finally, wild populations thrive in many locations all over Western Europe. Their status rests on an unstable equilibrium between destruction as pests and protection as game. Genetic exchanges between wild and domestic animals, whether spontaneous or directed by breeders, have long been recognized, and local institutions have moved animals around to maintain game resources, especially when viral epidemics reduce animal numbers.
In 1995, a research program called RESGEN-CT95-60 was launched by the European Union to federate scientists and managers working on the inventory, evaluation, conservation and utilization of European rabbit genetic resources, to promote a strategy of integrative management (Bolet et al., 1999 and 2000). The agenda set out the following objectives: inventory of currently used domestic breeds to constitute the core of the future data bank; selection of thirteen breeds on the basis of their potential economic importance in order to promote conservation, both in situ and by cryoconservation; thorough zootechnical evaluation of these breeds to prepare the implementation of breeding development; thorough evaluation of genetic diversity within and among breeds, comparison with the reservoir diversity observed among other breeds and in wild populations; constitution of an extended data bank to be included in the FAO Programme for the Global Management of Animal Genetic Resources.
The existence of this programme and the call for added scientific knowledge prompted biologists to formulate and bring forth cross-disciplinary research projects. Three such projects illustrate how results of a purely fundamental but integrative approach stand by themselves as well as being relevant to husbandry or data bank elaboration. A fourth example shows how such research feeds the field of evolutionary biology which is, in its essence, rather far removed from everyday life on the farm.
|
RESULTS AND INFERENCES |
|---|
|
TOP
SYNOPSISINTRODUCTIONRESULTS AND INFERENCESDISCUSSIONReferences |
|---|
1. Microsatellite analysis of reproduction and social organization in the European rabbit
The European rabbit is a social and territorial species. Populations are subdivided into small, independent social groups. Social groups occupy defined territories and restrain the arrival of individuals from other groups. The social organisation of a group is based on dominance relationships in the access to feeding and breeding resources (Daly, 1981
; Cowan and Roman, 1985). The apparent stability of the group during a breeding season suggests its reproductive isolation. The breeding system was in consequence thought to be a major determinant of the organisation of genetic diversity in general. A more quantitative understanding of this is necessary, especially with regard to limits and resilience, since it is directly relevant to the questions of size and numbers of populations involved in an in situ conservation programme.
An experimental optimisation and multiplexing of 16 polymorphic microsatellite loci was performed for systematic parentage testing in a well-defined wild population (Marshall et al., 1998; Queney, 2000; Queney et al., 2001). Potential adult breeders and young animals born each breeding season were sampled over three years (Marchandeau et al., 1995). The genotypes of 223 new-borns were compared to 135 candidate parents, and 103 litters were thus "identified" over three years. As expected from the theory on dominance relationships, 20% of the breeders sired half of the litters. But nearly all the adults participated in the reproduction (from one to six litters each, Fig. 2), and interbreeding was observed between social groups. This means that social organisation and hierarchy within groups do not lead necessarily to genetic structuring of wild rabbit populations. Such results should not be generalized without care however, since rigorous paternity assignments depend on the relative homozygosity of the population and on the choice and number of microsatellite loci used.
|
2. Absence of genetic bottleneck in a free-living population exposed to a severe viral epizootic
Over the last five decades, rabbit populations have suffered two severe epizootics: myxomatosis and rabbit viral haemorraghic disease (RVHD). Mortality rates were high, and, in line with the general understanding of such situations (O'Brien and Evermann, 1998
), the impacts on genetic diversity were said to be important, although not thoroughly assessed. It happens that, since the beginning of the 1980s, a particular isolated free-living population, localized in northern France, has been the subject of an ecological and genetic survey. An outbreak of RVHD occurred in 1995, followed by a demographic crash (mortality rate of 90%). Polymorphic microsatellite loci examination was carried out to test a putative reduction in genetic diversity (Queney et al., 2000). A net decrease in effective population size (Ne) was recorded, but without evidence of genetic diversity loss (Fig. 3). The temporal change in allele frequencies fits with classical panmictic evolution under genetic drift. Indeed the remnant population size stayed high enough (around 50 animals) to maintain diversity at the level it was before the demographic crash. These data give an indication of the minimal investments needed when a genetic resources management program is launched. Yet they do not say at what level they should amount since the possibility of selective removal of genetic variation of the immune response loci has not been excluded. Additional integrative research on such a question is necessary to help decision making.
|
3. On the origin of domestic breeds
Oryctolagus cuniculus arose in the Iberian Peninsula a few MYR ago and then moved through the Pyrenees barrier to Mediterranean France some 500,000 years later (Pages, 1980
). About 1,500 years ago, the species embarked upon a remarkable process of expansion in connection with human interventions (Arnold, 1994; Callou, 1995 and 2000). In the last few years, a number of studies using a panel of molecular markers (protein polymorphism, immunoglobin diversity, nuclear and mitochondrial DNA variation) have mapped the extent and the geographical distribution of the species genetic diversity. It is organised into two population groups, one in the south western part of the Iberian Peninsula, the second over the northern part of the peninsula and all of western Europe. The data suggest that two independent lineages evolved separately for a significant period of time and that a hybrid zone formed following recent secondary contacts.
A survey of 13 domestic breeds and 3 inbred strains was carried out (Queney, 2000; Queney et al., 2001). Their microsatellites were analysed and compared to that of wild populations. All domestic genotypes, including breeds from Spain and France, are very close to those found among the wild populations of northern France (Fig. 1). The genetic diversity of both domestic animals and wild ones of northern France populations represents only some 38% of that of the whole species. This provides evidence for a unique genetic origin of domestication efforts, followed by a general dispersal of domestic stocks, even back to the Iberian Peninsula. Moreover, when drawing animals from that particular genetic pool, domestications sampled genetic diversity without significant loss.
Looking towards the future two types of problems are to be considered. On one hand the way the Iberian wild populations and their diversity evolve is a socially recognized question. The guidelines of dynamic and long-term policies have been agreed upon at a European institutional level. Financial and technical supports are available under the supervision of European Authorities to develop local and regional wild life management programmes through habitat preservation measures. Rabbits are included in these operations in Spain and Portugal.
On the other hand European societies express diverse and rapidly changing production needs (meat, game). Efficiency in the response implies short-term direct technical interventions. Resources for these can only be found in the available stocks of domestic animals and in the adaptation of husbandry techniques. The two questions of species fate and production objectives are obviously related, but answers cannot be found on the same time, space and biological scales.
4. Strong constraint on a microsatellite locus through leporid evolution
Running genetic studies on a large scale resulted in building up a set of data on an important number of microsatellite loci, their variations, their mendelian transmission and their allele frequencies in Oryctolagus cuniculus. One is then able to ask whether they all follow the same molecular dynamics and whether they are equivalent markers for demographic studies (Queney, 2000; Queney et al., 2001). Alternatively, differences in patterns among loci may reveal peculiar genomic situations. In the panel of 16 loci, the sat 12 locus exhibits specific characteristics: a smaller number of alleles, a smaller range of variation and a lower level of heterozygosity. This suggests that it is local molecular processes rather than population effects that drive the sat 12 locus polymorphism. A comparative study of sat 12 was consequently carried out, covering five species of hare (Andersson et al., 1999; Queney, 2000). The repeated perfect motif (TCTA)n has been conserved across the 12–29 MYR of divergence of these leporids (Halanych and Robinson, 1999; Su and Nei, 1999). Essentially no variation on flanking regions (1 nucleotide among 49 distinguishes rabbits from hares in these sequences) has been observed. This situation fulfils the conditions of the step-wise mutation model for repeated sequences. As the mean expansion of sat 12 is different in the various species, data have been introduced in the formal model of Xu et al. (2000) for three of them (Fig. 4). It is suggested that the sat 12 mutation rate is about 0.0004 per generation in rabbits. In this species, expansion and contraction processes of sat 12 repeated motives are somewhat compensated, whereby the expansion process is just beginning in mountain hare and somewhat further advanced in brown hare. As the model postulates that the sat 12 locus existed in those leporids' common ancestor, differences in reproductive biology (generation times longer in hares) and demographic differences (small size of hare populations with genetic bottlenecks) may explain the present situation.
|
|
DISCUSSION |
|---|
|
TOP
SYNOPSISINTRODUCTIONRESULTS AND INFERENCESDISCUSSIONReferences |
|---|
In the course of this research, some light has been shed on two persistant questions, namely the correlation between population dynamics and genetic diversity, and the constrained evolution of repeated sequences. Briefly, the results are consistent with the well-established view that genetic diversity depends on population size and reproductive systems. In the case of leporids, changes in genetic diversity are buffered by the adaptability of the social organisation of reproductive groups of animals and the reproductive specificity of species. The relevance of the data stems the case by case quantifications and the subsequent identification of new scientific questions: for instance the differences in sat 12 sequences dynamics in hares and rabbits suggest major differences in their biological history. Whether the explanations given here are acceptable remains to be explored and needs new Integrative Biology approaches.
Both the results and the techniques presented in this paper are of direct relevance for programmes of conservation and of genetic resources management. The methodology used joins ecological and molecular genetic approaches; its main advantage is that it allows the assessment of the genetic identity of an animal, the identification of its parents and of the strain, the breed and the local wild population that it belongs to. Very clearly, measures to be taken (number of animals and populations to protect, or action to develop in cases of disease, for instance) and investments to be made (areas concerned, techniques to use, personnel to hire) are different depending upon whether a conservation goal or the breeding of strains adapted to evolving husbandry conditions is pursued. Whereas all domestic animals analysed today derive from the northern France subset of the genetic pool of all wild animals, the conservation of the species has to be organised over the entire area, with special attention given to the declining Iberian wild populations, while short-term breeding efforts should focus on a more thorough management of those races and strains that have hitherto only attracted the interest of a few amateurs.
As indicated previously, the RESGEN programme involved many more integrative research projects besides the ones presented here, where the approach was mainly from the points of view of molecular biology, population genetics, ecology and population biology. On the whole, most of the inventory operations are complete, and the data bank is accessible on EAAP (European Association for Animal Production) website http://www.tiho-hannover.de/einricht/zucht/eaap/index.htm, but not yet on the FAO networks (http://dad.fao.org) for some abstruse reasons. Assessments of breeding conditions and reproduction techniques have highlighted the necessity for more careful management of genetic resources and sanitary controls. New questions have emerged, and more research is needed to fulfil the challenges faced by biologists and breeders. An illustration is provided by host-parasite interactions: Apart from their own pests and viruses, rabbits harbour some parasites they transfer to humans (Pneumocystis carini for instance, Guillot et al., 1999) under poorly known conditions.
In brief, scientists fulfil new roles when they participate in such a programme, and Integrative Biology holds even greater promise when it extends its approach to the biological problems that society faces.
|
ACKNOWLEDGMENTS |
|---|
We wish to thank Vivienne Reuter for help in correcting English writing.
|
FOOTNOTES |
|---|
1 From the Symposium The Promise of Integrative Biology presented at the Annual Meeting of the Society for Integrative and Comparative Biology, 2–6 January 2002, at Anaheim, California.
2 E-mail: mounoloujcm{at}wanadoo.fr
|
References |
|---|
|
TOP
SYNOPSISINTRODUCTIONRESULTS AND INFERENCESDISCUSSIONReferences |
|---|
Andersson, A., C. Thulin, and H. Tegelström. 1999. Applicability of rabbit microsatellite primers for studies of hybridisation between introduced and a native hare species. Hereditas, 130:309-315.[Medline]
Arnold, J. 1994. Historique de l'élevage du lapin. C. R. Acad. Agric. France, 80:3-12.
Bolet, G., M. Monnerot, C. Arnal, J. Arnold, D. Bell, G. Bergoglio, U. Besenfelder, S. Bosze, S. Boucher, J. M. Brun, N. Chanteloup, M. C. Ducourouble, M. Durand-Tardif, P. J. Esteves, N. Ferrand, G. Hewitt, T. Joly, P. F. Koelh, M. Laube, S. Lechevestrier, M. Lopez, G. Masoero, R. Piccinin, G. Queney, G. Saleil, A. Surridge, W. van der Loo, J. Vanhommerig, J. S. Vicente, G. Virag, and J. M. Zimmermann. 1999. A programme for the inventory, characterisation, evaluation, conservation and utilisation of European rabbit (Oryctolagus cuniculus) genetic resources. Animal Genetic Resources Information Bulletin, 25:57-70.
Bolet, G., J. M. Brun, M. Monnerot, F. Abeni, C. Arnal, J. Arnold, D. Bell, G. Bergoglio, U. Besenfelder, S. Bosze, S. Boucher, N. Chanteloup, M. C. Ducourouble, M. Durand-Tardif, P. J. Esteves, N. Ferrand, A. Gautier, C. Haas, G. Hewitt, N. Jehl, T. Joly, P. F. Koehl, T. Laube, S. Lechevestrier, M. Lopez, G. Masoero, J. J. Menigoz, R. Piccinin, G. Queney, G. Saleil, A. Surridge, W. van der Loo, J. S. Vicente, M. P. Viudes de Castro, J. S. Virag, and J. M. Zimmermann. 2000. Evaluation and conservation of European rabbit (Oryctolagus cuniculus) genetic resources. First results and inferences. Seventh World Rabbit Conference, 4–7th July 2000, Valencia, Spain. Vol. A:281–316.
Callou, C. 1995. Modification de l'aire de repartition du lapin (Oryctolagus cuniculus) en France et en Espagne, du Pleistocène à l'époque actuelle. Etat de la question. Anthropozoologica, 21:95-114.
Callou, C. 2000. La diffusion du lapin (Oryctolagus cuniculus) en Europe occidentale: Aspects historiques, biogéographiques, évolutifs et anthropologiques. Ph.D. Thesis, Université Paris I—Panthéon–Sorbonne, UFR Art et Archéologie, Paris.
Cowan, D., and E. Roman. 1985. The construction of life-tables with special reference to the European wild rabbit (Oryctolagus cuniculus). J. Zool., Ser A4, 207:607-609.
Daly, J. 1981. Effects of social organization and environmental diversity on determining the genetic structure of a population of the wild rabbit, Oryctolagus cuniculus. Evolution, 4:689-706.
Guillot, J., V. Chevalier, G. Queney, M. Berthelemy, B. Polack, P. Lacube, P. Roux, and R. Chermette. 1999. Acquisition and biodiversity of Pneumocystis carini in a colony of wild rabbits (Oryctolagus cuniculus). J. Euk. Microbiol, 46:100s-101s.
Halanych, K., and T. Robinson. 1999. Multiple substitutions affect the phylogenetic utility of cytochrome b and 12S rDNA data: Examining a rapid radiation in Leporid (Lagomorpha) evolution. J. Mol. Evol, 48:369-379.[CrossRef][ISI][Medline]
Marchandeau, S., M. Guenezan, and J. Chantal. 1995. Utilisation de la croissance ponderale pour la détermination de l'âge de jeunes lapins de garenne (Oryctolagus cuniculus). Gibier Faune Sauvage, 12:289-302.
Marshall, T., J. Slate, L. Kruuk, and J. Pemberton. 1998. Statistical confidence for likehood-based paternity in natural populations. Molecular Ecology, 7:639-655.[CrossRef][Medline]
O'Brien, S. J., and J. F. Evermann. 1998. Interactive influence of infectious disease and genetic diversity in natural populations. Trends in Ecology and Evolution, 10:254-259.
Pages, M. V. 1980. Essai de reconstitution de l'histoire du lapin de garenne en Europe. Bull. Mens. Off. Natl. Chasse, Sp. Scien. Techn., Decembre 1980; 13–21.
Queney, G. 2000. Histoire des populations et organisation sociale du lapin européen (Oryctolagus cuniculus) à travers l'étude de marqueurs microsatellites. Ph.D. Thesis, University Paris 7- Denis Diderot, Paris.
Queney, G., N. Ferrand, S. Marchandeau, M. Azevedo, F. Mougel, M. Branco, and M. Monnerot. 2000. Absence of a genetic bottleneck in a wild rabbit population exposed to a severe viral epizootic. Molecular Ecology, 9:1253-1264.[Medline]
Queney, G., N. Ferrand, S. Weiss, F. Mougel, and M. Monnerot. 2001. Stationary distributions of microsatellite loci between divergent population groups of the European rabbit (Oryctolagus cuniculus). Mol. Biol. Evol, 18:2162-2168.
Su, C., and M. Nei. 1999. Fifty-million-year-old polymorphism at an immunoglobin variable region gene locus in the rabbit evolutionary lineage. Proc. Nat. Acad. Sci. U.S.A, 96:9710-9715.
Xu, X., M. Peng, Z. Fang, and X. Xu. 2000. The direction of microsatellite mutations is dependant upon allele length. Nature Genetics, 24:396-399.[CrossRef][ISI][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||