Diet is a primary driver of the composition of gut microbiota and is considered one of the main routes of microbial colonization. Prey identification is fundamental for correlating the diet with the presence of particular microbial groups. The present study examined how diet influenced the composition and function of the gut microbiota of the Pacific harbor seal ( Phoca vitulina richardii ) in order to better understand the role of prey consumption in shaping its microbiota. This species is a good indicator of the quality of the local environment due to both its foraging and haul-out site fidelity. DNA was extracted from 20 fecal samples collected from five harbor seal colonies located in Baja California, Mexico. The V4 region of 16S rRNA gene was amplified and sequenced using the Illumina technology. Results showed that the gut microbiota of the harbor seals was dominated by the phyla Firmicutes (37%), Bacteroidetes (26%) and Fusobacteria (26%) and revealed significant differences in its composition among the colonies. Funtional analysis using the PICRUSt software suggests a high number of pathways involved in the basal metabolism, such as those for carbohydrates (22%) and amino acids (20%), and those related to the degradation of persistent environmental pollutants. In addition, a DNA metabarcoding analysis of the same samples, via the amplification and sequencing of the mtRNA 16S and rRNA 18S genes, was used to identify the prey consumed by harbor seals revealing the consumption of prey with mainly demersal habits. Functional redundancy in the seal gut microbiota was observed, irrespective of diet or location. Our results indicate that the frequency of occurrence of specific prey in the harbor seal diet plays an important role in shaping the composition of the gut microbiota of harbor seals by influencing the relative abundance of specific groups of gut microorganisms. A significant relationship was found among diet, gut microbiota composition and OTUs assigned to a particular metabolic pathway.

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The genetic consequences of species-wide declines are rarely quantified because the timing and extent of the decline varies across the species' range. The sea otter (Enhydra lutris) is a unique model in this regard. Their dramatic decline from thousands to fewer than 100 individuals per population occurred range-wide and nearly simultaneously due to the 18th-19th century fur trade. Consequently, each sea otter population represents an independent natural experiment of recovery after extreme population decline. We designed sequence capture probes for 50 Mb of sea otter exonic and neutral genomic regions. We sequenced 107 sea otters from five populations that span the species range to high coverage (18-76×) and three historical Californian samples from ~1500 and ~200 years ago to low coverage (1.5-3.5×). We observe distinct population structure and find that sea otters in California are the last survivors of a divergent lineage isolated for thousands of years and therefore warrant special conservation concern. We detect signals of extreme population decline

Pupping and molting of Phoca vitulina are processes that occur each year with high precision, although their timing varies according to location. Knowledge about the timing of these events allows us to determine when the highest numbers of individuals are hauled out, which is important to achieve a good abundance estimation. In this study we determined the timing of pupping and molting of P. v. richardii at Punta Banda Estuary, Baja California (Mexico), previously unknown at this site or along its entire distribution in Mexico. Observations were carried out during the 2011 and 2012 pupping seasons, as well as the 2012 molting season. We determined that the pupping season starts in mid-February and ends in mid-April, and that the maximum number of pups occurs in mid-March. The late premolt stage was observed from the end of March to the beginning of July, with the peak proportion of individuals in this stage at the beginning of May. The molting period extends from the end of April to mid-July, with the peak proportion of individuals molting at the beginning of June. The reverse molt pattern (starting on the torso and ending on the head and flippers) was the most common. The highest number of adult and subadult individuals on land was observed during the molting season; therefore, the best time to carry out counts to estimate seal abundance in this area is from the beginning of May to the beginning of June.