Genetic and morphometric differentiation between island and mainland southern elephant seal populations.

We compare genetic (both nuclear and mitochondrial) and morphometric measures between two putative populations of southern elephant seal (Mirounga leonina), and interpret the results in the context of data from mark-recapture and satellite-telemetric studies. One population is on the Argentine mainland, while the other is 2,400 km away on South Georgia island. We found pronounced differentiation at the mitochondrial DNA (mtDNA) control region that was distinct from the pattern of variation seen among island rookeries. Some morphometric characters and seven out of ten nuclear-DNA markers also showed differentiation between the island and mainland sites. Diversity at nuclear markers was high in both populations but mtDNA diversity was low in the mainland population, suggesting a founder event and little subsequent immigration of females. Morphological differences may suggest different selective environments at the two sites.

Seasonal variation in vitamin D metabolites in southern elephant seal (Mirounga leonina) females at south Georgia.

Southern elephant seals spend two periods on land each year, during breeding and moult, exposed to intensive UV radiation. The time between periods on land are spent at sea, with little exposure to the sun. A study of serum 25-OH-D3 and 1,25(OH)2-D3 on southern elephant seals was carried out at South Georgia. Samples were collected on four different occasions: early and late breeding, and early and late moult. The levels of 25-OH-D3 increased when seals were on land, and decreased when at sea. Two annual peaks of 25-OH-D3 were found, both of which immediately followed periods of intensive exposure of UV radiation. 1,25(OH)2-D3 levels showed a seasonal variation, but no significant changes while being on land were detected. The diving behaviour at sea for southern elephant seals and no detectable change in 25-OH-D3 indicates that the seals feed on prey containing vitamin D.

Elephant seal genetic variation and the use of simulation models to investigate historical population bottlenecks.

Because the northern elephant seal (Mirounga angustirostrus) was heavily exploited during the 19th century, it experienced an extreme population bottleneck. Since then, under legislative protection in the United States and Mexico, northern elephant seals have recovered dramatically in number, although their genomic diversity was greatly reduced, apparently as a consequence of the bottleneck. In this study we investigated DNA sequence diversity in two mtDNA regions (the control region and 16S RNA) and found low genetic variation in the northern elephant seal: there were only two control region haplotypes (sequence difference = 1%), which was consistent with an extreme founder event in the recent history of the northern species. We also reaffirmed the lack of allozyme diversity in this species. In contrast, the southern elephant seal (M. leonina), which though similarly exploited never fell below 1,000 animals, had 23 control region mtDNA haplotypes (average sequence difference = 2.3%). To investigate the extent of the founder event in the northern elephant seal we devised a simulation model based on extensive demographic data. This allowed a statistical analysis of the likely outcome of bottlenecks of different size and duration. Given these historical data, our results indicate (within 95% confidence) a bottleneck of less than 30 seals and 20-year duration, or, if hunting was the primary pressure on the population, a single-year bottleneck of less than 20 seals.

Use of a tiletamine-zolazepam mixture to immobilise wild grey seals and southern elephant seals.

A mixture of tiletamine and zolazepam at a combined dose of 1 mg/kg was a reliable and safe agent for immobilising wild grey seals (Halichoerus grypus) and southern elephant seals (Mirouga leonina). The agent had a number of advantages over all the other agents used previously.