A major question in conservation biology is why some populations with low levels of genetic variation remain relatively stable while others decline in size. Stable populations may not have lost genetic variation related to disease resistance, such as the suite of resistance genes known as the Major Histocompatibility Complex (MHC). Theory suggests that natural selection is more likely to maintain functionally important MHC variation in populations that have experienced declines in size. This study will make direct estimates of natural selection on the MHC and other immunity genes using data from both historic and contemporary populations of the greater prairie-chicken, which is one of the most threatened species of bird in North America. This project will also examine the association between variation at MHC genes and parasites, immunity and survival in two small populations that are undergoing augmentation with translocations (Wisconsin) and captive breeding (Texas) to increase genetic variation.
The results of this study will valuable for biologists studying the effects of population size on disease and parasite resistance, and it will provide management guidelines for captive breeding and translocating animals, practices that are likely to increase with continuing loss of prairie habitat. Graduate students and a post-doctoral researcher will be trained in immunogenetics, and the project should lead to valuable new genetic markers for studying immunity-related genes in other species. The PIs will work with environmental education centers in Milwaukee and Dallas-Fort Worth on citizen science and teacher education projects that focus on the health of wildlife. The results will be broadly disseminated to state and federal wildlife agencies, environmental groups and the general public.
There is increasing concern that the ability of threatened and endangered species to combat pathogens may be compromised due to a loss of diversity at genes important to immunity. It is well established that populations often loose non-functional, or neutral, genetic diversity due to drift following a significant decline in population abundance, yet it is less clear if a similar pattern occurs with functional genes important for immunity. In this study, we documented a significantly reduced level of genetic diversity at immune genes in the critically endangered Attwater’s Prairie-chicken (Tympanuchus cupido attwateri) compared to populations of larger size with its conspecific, the Greater Prairie-chicken (T. c. pinnatus), suggesting that reduced immunocompetence may be an important factor limiting survival in the wild. Less than 100 Attwater’s Prairie-chicken currently exist in the wild after experiencing a precipitous decline in abundance over the past century from over a million individuals. The wild population is almost entirely dependent on supplementation from a captive bred population with over 200 individuals released on an annual basis. In this study we determined that survivorship post-release over a two-year period was not correlated with individual immunocompetence, but was influenced by their level of inbreeding. Individuals with higher inbreeding coefficients (i.e., more inbred) had lower survival to 1-month post-release, while the opposite pattern was observed at 9-months with those with higher inbreeding coefficients survived longer, suggesting a purging effect. These results therefore suggest that levels of inbreeding appear more important than immunocompetence relative to their influence on survival post-release from a captive environment, at least for the two years studied. It is important to note, however, that our study was focused on birds post-release from a captive environment after they were at least three months of age. We do not know if immuncompetence is correlated with survival prior to release or with chicks produced in the wild. This aspect of the study certainly deserves future study and will be the focus of ongoing research with this population. We have shown that individual immunocompetence did not explain survival post-release in the Attwater's Prairie-chicken captive–release program, yet level of inbreeding was shown to be an important factor. These findings have resulted in a more focused effort to prevent errors in the pedigree used to assign breeding pairs in the captive population, which has also resulted in increased chick survival and the number of birds available for population supplementation for the past three consecutive years. This work exemplified how genetic management of a critically endangered species can improve fitness of the remaining population, thereby assisting in efforts to prevent extinction and conserve biodiversity.
