Genetic and endocrine related variability of sea otters, Enhydra lutris

Sea otters (Enhydra lutris) once ranged throughout the coastal regions of the north Pacific. They were extirpated over much of their range due to extensive hunting associated with the fur trade of the 18th and 19th centuries. The widespread population reduction and subdivision suggested that sea otters may have lost genetic diversity associated with fur trade exploitation. To test this hypothesis, I examined genetic variation within microsatellite loci and the mitochondrial DNA (mtDNA) control region within five contemporary sea otter populations and compared them to the levels in one pre-fur trade population. While mtDNA sequence variability was low within both modern and extinct populations, analysis of microsatellite allelic data revealed the pre-fur trade population had significantly more variation than all the extant sea otter populations. Populations that experience severe population reduction and associated inbreeding may also suffer from a general reduction in fitness termed inbreeding depression. Inbreeding depression may be measured by determining relative reproductive fertility within females and males and by relative physiological stress levels. The hypothesis is that the sea otter populations with the lowest genetic diversity will have the lowest sex steroid levels and the highest stress steroid levels, while the populations with the highest level of diversity will have the highest sex steroid levels and the lowest stress steroid levels. I found no significant differences between the female sex steroids (estrogens and progesterone) within pregnant vs. non-pregnant captive females and thus was not able to determine relative numbers of pregnant females within wild populations based on single blood samples. Consequently, the inbreeding indicies I measured were the male sex steroid, testosterone, and the adrenal steroids, cortisol and corticosterone. There was no significant correlation between genetic diversity and testosterone, but there was a significant negative correlation between diversity and corticosterone. While a significant correlation between these variables does not prove sea otter populations are experiencing inbreeding depression, this result does suggest inbreeding depression may be a concern within sea otter populations with the lowest genetic variability. Future monitoring of inbreeding indices may be needed to determine long term sea otter population viability.