A Genetic Test for Vulnerability to Inbreeding Depression in Right Whales and Elephant Seals

EPA Grant Number: R827110
Title: A Genetic Test for Vulnerability to Inbreeding Depression in Right Whales and Elephant Seals
Investigators: Hare, Matthew P. , Palumbi, Stephen R.
Institution: University of Maryland , Harvard University
EPA Project Officer: Manty, Dale
Project Period: May 5, 1999 through May 4, 2001 (Extended to May 4, 2002)
Project Amount: $152,274
RFA: Exploratory Research - Environmental Biology (1998) RFA Text |  Recipients Lists
Research Category: Biology/Life Sciences , Health , Ecosystems

Description:

The intensity of realized inbreeding depression after a severe population size reduction (bottleneck) is quite variable among species, and this unpredictability of inbreeding effects makes it difficult to gauge whether the poor post-bottleneck recovery of an endangered species is due to inbreeding depression or extrinsic factors such as habitat degradation. Our objective is to explore the conditions under which the history of a natural population will influence its vulnerability to inbreeding depression during a demographic bottleneck. A recent and severe demographic bottleneck is well documented for North Atlantic right whales and northern elephant seals, and in each species contemporary genetic diversity is low. Yet elephant seals are making $strong recovery and right whales are not. We propose to test whether today's low genetic diversity was caused by over harvesting, and therefore likely to be causing inbreeding depression, or whether genetic diversity was historically low in pre-harvest populations. A simple explanation for the post-harvest recovery of elephant seal populations compared to low reproductive fitness in right whales is that elephant seals had a previous history of bottlenecks in which heterozygosity was reduced and its mutational load of deleterious alleles was purged. In contrast, pre-harvest northern right whales may have had relatively high heterozygosity so that their decimation to small numbers unmasked deleterious recessive alleles and caused reduced fitness. Thus, differences in population history potentially explain these variable inbreeding effects, and we propose to test this by measuring ancestral levels of heterozygosity in these two extreme cases.

Approach:

The genealogical stream of hereditary information that has remained unbroken from ancestral populations to today holds within it information about the ancestor's level of heterozygosity, and therefore about its susceptibility to inbreeding depression. Alleles at each locus transit the extended population pedigree by taking slightly different paths because of the action of genetic drift. Because larger populations show more variation in these paths in among-locus comparisons, the among-locus variance in transit properties can reveal a great deal about contemporary and ancestral populations. In particular, the among-locus variance in genetic divergences between two sister species can be used to generate a maximum likelihood estimate of genetic diversity in their most recent common ancestor if we have data from enough independent loci. Because the northern right whale and elephant seal both have closely related sister species, we propose to use this analytical framework to provide the most direct comparison of pre- and post-harvest heterozygosity presently possible. The strength of this analytical approach will come from sampling non-coding, selectively neutral intron DNA at 25 nuclear loci. This goal is feasible because of the recent development of general PCR primers for many mammalian nuclear loci. Thus, we have an analytical method to test what the long term level of diversity has been within a lineage, and the genetic tools exist to collect the appropriate data in these two marine mammal species showing dramatically different responses to severe population bottlenecks.

Expected Results:

The level of heterozygosity in ancestral populations can, in principle, inforxn us about the susceptibility to inbreeding depression within a lineage. Using this genetic analysis we will begin to address whether inbreeding depression is a likely factor causing a slow recovery of right whale populations, and develop a general procedure to test for the vulnerability to inbreeding depression in natural populations, In certain cases the ability to reject inbreeding depression as a strong force affecting endangered species in the wild will redirect efforts toward ameliorating environmental sources of mortality and habitat degradation.

Publications and Presentations:

Publications have been submitted on this project: View all 2 publications for this project

Supplemental Keywords:

marine biology, sensitive populations, polymorphism, restoration, conservation biology., RFA, Health, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, exploratory research environmental biology, Genetics, Ecosystem/Assessment/Indicators, Ecosystem Protection, Aquatic Ecosystem, Susceptibility/Sensitive Population/Genetic Susceptibility, Habitat, genetic susceptability, Ecology and Ecosystems, Biology, Ecological Indicators, ecological effects, sensitive populations, demographic bottleneck, endangered species, adaption mechanisms, environmental sources of mortality, animal responses, marine biology, seals, genetic vulnerability, aquatic ecosystems, environmental stress, conservation biology, biological indicators, inbreeding depression, toxics, whales

Progress and Final Reports:

2000 Progress Report