Project Description
The current management of Steller sea lions in Alaska is based on studies conducted by scientists at Texas A&M university and at NMML. Those studies demonstrated the existence of at least two stocks or distinct population segments (DPS) in Alaska. Recent data using additional samples from Alaska and Russia suggests that a third stock may exist in Russia with a dividing line west of the Commander Islands (Baker et al. 2005). In addition another recently published paper (O'Correy-Crow et al. 2006) argues for a smaller resolution break in the Eastern Aleutian Islands. This work will build on those studies to further investigate stock delineation and to examine measures of genetic migration of individuals within and among stocks to help clarify the potential for population recovery and the need for protection. In addition, a finer resolution examination of rookeries will help us understand the dynamics that govern gene flow in localized areas. A study of the major histocompatibility complex within Stellers will use existing samples to investigate the vulnerability of specific regions to unknown threats and ultimately the susceptibility to population stress.
Issues & Justification
Conractors working with the NMML have sequenced mitochondrial DNA (mtDNA) nucleotide sequences for over 2300 animals. The majority (about 1,600) of the data are from pups taken at their natal rookery. In 2008 we will continue to build the database by sequencing control region and cytochrome b pups from Alaskan western stock rookeries. These data will be used in our continuing efforts to understand gene flow patterns, evolutionary history, and stock structure throughout the range of the species. We will focus on 1) rookeries and regions for which data are scarce, 2) rookeries and regions in which previous years sampling offers the opportunity to look at trends through time, and 3) areas critical to understanding stock structure. Issue number 3 is particularly important because separation of the western and Asian stocks is based upon somewhat lower divergence than is the separation of eastern and western stocks. Part of this work will emphasize samples from Medney Island and the nearby regions in the Aleutian Islands and the Kamchatka Peninsula. Steller sea lion pup work in fy 08 is scheduled to include the capture and handling of pups at rookeries in the Central Gulf of Alaska. The collection of tissue samples from these areas will be used to examine genetic variability in comparison to previous collections.
The use of Y-markers will allow us to examine male-mediated gene flow. The contrast of male-female movements may help explain the differences in genetic variability seen between nuclear and mitochondrial analyses. Studies of the Major Histocompatability Complex (MHC) will yield insight as to the diversity and ultimate vulnerability of particular areas to perturbation. This is based on the hypothesis that the MHC is a region in which low diversity represents a low arsenal of defense against potential threats to the health of the individual. If a difference in the variability of this region exists across the population, it could signal areas of proportionally greater vulnerability to extinction.
Goals
- Capture and tissue sample sea lion pups in Alaska and Russia.
- Assess stock delineation, rookery structure, and diversity across the range using genome analysis from amplified mtDNA.
Methods
Steller sea lion pups will be captured by hand during the annual pup branding work that occurs each June-July. Tissue samples collected from the rear flipper of each pup will be contributed by NMML scientists as well as collaborators with the Alaska Dept. of Fish & Game and the Alaska Sea Life Center. Samples will be collected from pups in the Gulf of Alaska, Eastern Aleutian Islands and Russia. Tissue samples will be preserved in ethanol and separated for archiving and for use by contractors. DNA extraction , PCR amplification and mDNA sequencing will follow published methods. Control region sequences will be examined from as many of the pups from critical rookeries as possible for stock assessment studies. The cytochrome b gene will be sequenced for a subset of these in order to build up the existing database for evolutionary studies. Nuclear DNA currently being analyzed will be compared to this data for finer scale studies of movement and gene flow.