Genetics Abstracts
|
Pending Publishing Permission
Do sea otters affect the genetic diversity of seagrass? Erin Rechsteiner, Hakai, University of Victoria Full Abstract
Predators can affect the reproductive strategies and evolution of their prey. Although predator effects are often thought of in terms of direct predation, disturbance of habitat by predators can also affect ecological communities. In this study, we asked how sea otter diets differed among areas where sea otters had been established from 1 – 30 years, and if disturbance via sea otter foraging on clams affected reproductive strategies or genetic diversity of seagrass (Zostera marina), given that this plant can reproduce both sexually and asexually. We found that sea otter diets consisted of up to 70% clams in some areas that were long-established and in areas dominated by bachelor male groups. We used line-transect surveys to determine the extent of sea otter disturbance via clam-digging in seagrass meadows (n = 3 transects in each of 15 meadows) in areas where sea otters had been present for >20 years, <10 years, and where otters were ecologically absent. We found that seagrass meadows were disturbed by sea otters most frequently where sea otters were long-established. We hypothesized that digging for clams would induce a flowering response in seagrass via disturbance of the rhizome mat, and that investment in flowering, vs. clonal reproduction would increase the genetic diversity of the seagrass meadow. We recorded the proportion of flowering seagrass shoots in each meadow, and then used microsatellites (n = 30-50 blades per meadow) to measure heterozygosity and allelic richness of each meadow. Preliminary results suggest that greater heterozygosity and allelic richness occur in seagrass meadows where sea otters were established >20 years than where sea otters have been for <10 years, or are absent. |
Pending Publishing Permission
Genetic analyses of southern sea otters inform the present and illuminate the past Roderick B. Gagne Full Abstract
Genetic indices can provide powerful insight into the health, genetic status, and demographic history of populations of conservation concern. We combined demographic information with genotype data on 38 microsatellite loci from 1,006 southern sea otters (Enhydra lutris nereis) to address fundamental questions regarding current genetic status and historic mortality events. We used multiple approaches to estimate the effective population size (Ne) and genetic diversity of the population. In the simplest sense, Ne is an estimate of the number of individuals in the population that are contributing genetically and provides a measure of the adaptive potential of the population. Ne estimates are of particular importance in southern sea otters as the subspecies is federally threatened and Ne is part of the delisting criterion. Genetic diversity was low and did not change significantly over time. Notably, the demographic effective population size was much larger than the genetic estimates when based on samples collected throughout the range of the population. However, when the spatial scale of the analysis was constrained to a portion of the range consistent with the movements of individual sea otters (based on tagging data), the demographic and genetic estimates of Ne converged. This finding, coupled with the results of spatially explicit genetic structure analyses, suggests there is subtle genetic structure in the population that was not previously detected. Following assessment of the extant population, we used genetic analyses to estimate the timing of past mortality events that would have resulted in extensive loss of genetic diversity. Our preliminary results agree with previous findings that major population declines had already greatly reduced sea otter genetic diversity prior to the near-extirpation of sea otters during the fur trade. |
Pending Publishing Permission
Investigating the relationship between genetics and disease outcome in necropsied southern sea otters (Enhydra lutris nereis) Nicole H. Carter, Wildlife Genomics and Disease Ecology Lab, University of Wyoming Full Abstract
Southern sea otter (SSO-Enhydra lutris nereis) population recovery is impacted by a variety of factors including predation, biotoxin exposure, infectious disease, oil spills, habitat degradation, and resource limitation. Factors underlying the high susceptibility of SSO to death from bacterial, protozoan and acanthocephalan infections remains poorly characterized. In addition, common pathologies such SSO death due to cardiomyopathy could have a multifactorial basis that includes a genetic component. Our core objective is to investigate the relationship between genetic attributes and disease outcome in a large sample of necropsied SSO. We hypothesize that 1) Sea otters that are more closely related are likely to share similar disease outcomes and 2) Sea otters that die due to some common processes possess lower genetic diversity, when compared to the larger SSO population. To investigate these hypotheses, we will combine 15 years of detailed SSO necropsy data with existing microsatellite genetic data for 360 individuals. In the first year of the project, we will use 37 microsatellite loci to construct a pedigree and calculate pairwise relatedness and internal relatedness among sea otters. In the second year, we will incorporate data on pathogen exposure and key case(s) of death onto the pedigree and pairwise relatedness matrices, to determine if certain etiologies are associated with specific family lines or relatedness categories. Our analyses will incorporate supplementary data on environmental, behavioral and density-dependent co-variates, to control for the confounding influences of these factors. This work is part of a larger project which will involve sequencing across the entire SSO genome to test for associations among variation in the sea otter genome, in relation to pathogen susceptibility and disease outcome. Our study will inform conservation management decisions to optimize sea otter population health and facilitate population recovery. |
|
Pending Publishing Permission
Sea otter genetics update: diversity, population structure and taxonomy Shawn Larson, The Seattle Aquarium Full Abstract
Sea otters, Enhydra lutris, were once abundant along the nearshore areas of the north Pacific Rim from northern Japan to Baja California, Mexico. Starting in 1741 the Pacific maritime fur trade eliminated sea otter populations throughout nearly all of their range and by 1910 resulted in 13 small scattered populations, totaling less than 1% of their original abundance. Previous work found lower genetic diversity in sea otters sampled in the early 1990s compared to pre-fur trade samples. Sea otter populations were re-sampled between 2008-2011 throughout much of their range and analyzed using 20 microsatellite markers. Here we report genetic diversity and population structure compared to samples collected 20 years earlier. Genetic diversity was found to increase in most sampled locations but particularly in those founded by translocations founded by more than one population and those experiencing immigration from adjacent groups. We also investigated taxonomic relationships between populations. There are currently three recognized sea otter subspecies based on skull morphology: Russian (E.l. lutris), Northern (E.l. kenyoni), and Southern (E.l. nereis). Microsatellite and the mitochondrial DNA D loop variability suggest there may be more than three taxonomically distinct populations. |