IBC2000-3 Genetics

Genetics and Public Herds in the 21st Century

James Derr, Ph.D
Associate Professor and Chair, Faculty of Genetics
Department of Veterinary Pathobiology
The College of Veterinary Medicine
Texas A&M University
College Station, TX USA 

The following article was originally presented at the International Bison Conference in Edmonton, Alberta in August 2000.  The conference covered a wide array of bison topics including production, marketing, genetics, history and much more.  This article has been reprinted with the permission of the IBC2000 Chairman.

Abstract

For North American Bison, the Canadian and US public herds represent the genetic foundation from which virtually all private herds developed.  Therefore, the management of these historically important herds is paramount to the preservation of bison genetic diversity.  Because of the significance of these herds, management decisions must be squarely based in sound scientific information.  The application of genetic biotechnology to the understanding of the historical structure of these herds, their genetic architecture and their genetic potential is absolutely critical in assuring the public herds are successful in fulfilling the mandate of conscientious stewardship of this species.

Keywords

bison, genetics, research, hybridization, conservation, mtDNA, nuclear DNA.

Introduction

My research program and that of others at Texas A&M University have been involved in molecular genetic investigations of public and private bison herds for a number of years.  These studies are funded through various federal and state agencies and by private bison owners.  Based on our current findings and the guidelines provided by the organizers of this workshop, I will comment on the following: what might be the next developments in DNA and where might this technology lead us, how should DNA purity issues affect public policy and, what should the role of public herds be regarding conservation genetics?

What might be the next developments in DNA and where might they lead us?

First, before we concern ourselves with future advancements, it is important to understand and fully utilize the technology currently available.  Therefore, I will review recent advancements in our understanding of bison genetics and outline the significant results of these studies.

The first reports using modern DNA level analyses of bison populations revealed that at least one public herd (Polziehn et al. 1995) contained animals with domestic cattle mitochondrial DNA (mtDNA).  Subsequently, a more detailed study (Ward et al. 1999) found a number of both public and private bison herds (40% of the herds tested) with cattle mtDNA.  This study went further to describe that there were at least five different cattle mtDNAs in North American bison and developed a simple test for cattle mtDNA in bison.  One major conclusion of this study was that bison herds that contain cattle mtDNA should be maintained in reproductive isolation from other bison herds that have no evidence of past hybridization with cattle.  In addition, because mtDNA is inherited solely through the female lineage, it seemed logical to define the genetic differences in bison and cattle Y-chromosomes and look for cattle Y-chromosomes in these herds with confirmed hybridization histories.  This second study (Ward et al. 2000, in press) found no evidence of the cattle Y-chromosome in any bison herds.  The major implications therefore are consistence with other reports that first generation hybrid males are usually sterile and the direction of hybridization between these two species favors matings between male bison and female domestic cattle.

Although the presence of cattle mtDNA in bison indicates past hybridization, this information alone can not be used to determine the length of time since the hybridization event or the amount of nuclear genetic material from cattle present in an individual bison. That requires a detailed analysis of the nuclear genome.  My laboratory has relied heavily on the advancements from the cattle genome project (outlined by Womack 1997) to develop a set of 400 linked and mapped nuclear markers known as microsatellites.  We now have a very detailed genetic map of the nuclear genome in bison that includes each chromosome and we are using these markers to: 1. determine the size, location and frequency of introgressed segments of cattle chromosomes into bison genomes (Ward 2000), 2. develop a powerful set of molecular markers to use for gene mapping as well as parentage and purity testing (Schnabel et al. 2000) and, 3. produce reverse pedigrees in bison for breeding and management strategies (Derr and Templeton 2000).  In order to accomplish this level of understanding, advanced genetic biotechnologies must be developed and employed.  This has been highlighted as a priority for bison conservation, preservation and utilization research at Texas A&M University.

The future of genetic technology and its application with bison is rich with excitement and opportunities.  We will use technology: 1. to understand gene expression for economically important traits, 2. for disease resistance and vaccine response, 3. to diagnosis infectious diseases, and 4. to determine the metabolic cost to bison that possess domestic cattle genes.  These technologies will include analysis of DNA on microchips to determine single nucleotide polymorphisms (i.e. digital DNA identification) and define the specific genetic differences among bison as well as between bison and other related species. 

How should DNA purity issues affect public herd policy?

Based on the information outlined in the previous section regarding the genetic evidence for hybridization between domestic cattle and bison and due to the fact that some bison herds appear to have no influence from cattle, the following strategy seems prudent. 

Public bison herds with a history that includes domestic cattle should be managed in reproductive isolation from herds with no historical or genetic evidence of hybridization.  Economical, reliable and non-invasive (hair follicle) DNA tests are now available to determine the presence of cattle genes in bison (Ward et al. 1999; Ward 2000) and this information should be considered in the overall management profiles of public bison herds.

What should the role of public herds be regarding conservation genetics?

Because the public bison herds represent the genetic foundation of virtually all private herds, the management of these historically important herds is crucial for the preservation of bison genetic diversity.  Modern genetic biotechnology can provide information regarding the history of these herds, the extent and type of hybridization that has occurred with domestic cattle, their genetic diversity, breeding structures and their genetic potential to respond to challenges.  Therefore, it is important for public herd managers to be the leaders in employing genetic biotechnology to insure the long-term conservation of bison germplasm. 

The US Department of Interior and Texas A&M University recently initiated a study to accomplish these goals in the five National Parks (NP) that contain bison (Derr and Templeton 2000).  These parks include Badlands NP, Teddy Roosevelt NP, Grand Teton NP, Windcave NP, and Yellowstone NP. 

The objectives of this four-year study include:

1. Test for cattle gene introgression - cattle-bison hybrids, in all five NPS bison herds.

2. Determine the effect of nonrandom culling on the genetic architecture of each of the five NP bison herds using mapped microsatellites and parentage testing in order to estimate relatedness for the culled animals compare to a random sampling of each herd. 

3. Test for the prevalence of genes that have a major effect on control of natural resistance to brucellosis and most likely tuberculosis and paratuberculosis in the Yellowstone and Grand Teton National Park's bison herds. 

4. Evaluate the predicted effects, through model simulation, of various population sizes and removal scenarios on gene frequencies, rare alleles, heterozygosity and inbreeding through time in order to develop long-term management strategies for the conservation of bison germplasm.

When completed, results from this study will assist the managers of these historically important herds in making management decisions to insure to long-term conservation and preservation of North American bison.

Summary and Recommendations

University laboratories have already provided a great deal of knowledge regarding molecular and conservation genetics of North American bison.  We know that hybridization occurred in the past with domestic cattle and this hybridization resulted in some public herds having both cattle mtDNA and cattle nuclear genes.  So, based on this knowledge, how can the managers of public herds contribute to the genetic conservation of bison?  First, by using modern genetic biotechnology to clarify the genetic history and structure of their populations and make this information available to policy makers and the public; second, by assuring that management and policy decisions are founded on a broad knowledge base that includes genetic information; third, by helping to educate the public in the application of this technology to meet their specific needs; forth, to realize that the conservation of a species is the conservation and preservation of germplasm and not individuals; and fifth, public bison herds with a history that includes domestic cattle should be managed in reproductive isolation from herds with no historical or genetic evidence of hybridization.

In fact, this is exactly what the National Park Service in the US, and others, have done by identifying germplasm purity and conservation as a high priority and funding long-term projects to insure the genetic health of the herds under their management.  With the use of genetic biotechnology, the mandate is becoming clear, for the long-term conservation of a species, the most important consideration must be the preservation of its germplasm.  If this germplasm is lost through extinction, genetic drift or hybridization it can never be fully recovered.

Acknowledgements

The author would like to acknowledge the following for intellectual contributions, laboratory expertise and sound advice; L.G. Adams, D. Davis, S. Davis, P. Grogan, R. Hiebert, N. Halbert, C. Kolenda, R.D Schnabel, J.W. Templeton, T. J. Ward, J.E. Womack and numerous managers of public and private bison herds for providing DNA samples.  This research was supported through grants from the National Science Foundation-US, the Department of Interior-US, Texas Parks and Wildlife, the Texas Agriculture Experiment Station and private bison owners.

References

Derr, J.N., Templeton, J.W. 2000.  The application of conservation genetics to the long-term management of bison in National Parks.  A grant proposal for research funded for four years through the DOI, USGS, and NPS. 

Polziehn, R.O., Strobeck, C., Sheraton, J. & Beech, R. 1995. Bovine mtDNA discovered in North American bison populations. Conservation Biology 9:1638-1643. 

Schnabel, R.D., Ward, T.J., Derr, J.N.  2000 (in press).  Validation of 15 microsatellites for parentage testing in North American bison, Bison bison L. and domestic cattle.  In Press,  Animal Genetics.

Ward, T.J., Bielawski, J.P., Davis, S.K., Templeton, J.W. and Derr, J.N. 1999. Identification of domestic cattle hybrids in wild cattle and bison species: a general approach using mtDNA markers and the parametric bootstrap. Animal Conservation 2: 51-57.

Ward, T.J. 2000.  An evaluation of the outcome of interspecific hybridization events coincident with a dramatic demographic decline in North American bison.  Ph.D dissertation (J.N. Derr advisor - Genetics) Texas A&M University.

Ward, T.J., Skow, L.C., Gallagher, D.S., Schnabel, R.D., Kolenda, C.E., Nall, C., & Derr, J.N. 2000a (in press). Differential Introgression of Uniparentally-Inherited Markers in Bison Populations with Hybrid Ancestries.  In Press, Animal Genetics.

Womack, J.E. 1997. Mapping animal genomes. Pages 157 – 189 in Advances in Veterinary Medicine, vol. 40. Academic Press.