Abstract
The South American sea lion (Otaria flavescens) is widely distributed along the southern Atlantic and Pacific coasts of South America with a history of significant commercial exploitation. We aimed to evaluate the population genetic structure and the evolutionary history of South American sea lion along its distribution by analyses of mitochondrial DNA (mtDNA) and 10 nuclear microsatellites loci. We analyzed 147 sequences of mtDNA control region and genotyped 111 individuals of South American sea lion for 10 microsatellite loci, representing six populations (Peru, Northern Chile, Southern Chile, Uruguay (Brazil), Argentina and Falkland (Malvinas) Islands) and covering the entire distribution of the species. The mtDNA phylogeny shows that haplotypes from the two oceans comprise two very divergent clades as observed in previous studies, suggesting a long period (>1 million years) of low inter-oceanic female gene flow. Bayesian analysis of bi-parental genetic diversity supports significant (but less pronounced than mitochondrial) genetic structure between Pacific and Atlantic populations, although also suggested some inter-oceanic gene flow mediated by males. Higher male migration rates were found in the intra-oceanic population comparisons, supporting very high female philopatry in the species. Demographic analyses showed that populations from both oceans went through a large population expansion ~10,000 years ago, suggesting a very similar influence of historical environmental factors, such as the last glacial cycle, on both regions. Our results support the proposition that the Pacific and Atlantic populations of the South American sea lion should be considered distinct evolutionarily significant units, with at least two managements units in each ocean.
Highlights
In the marine environment, there is considerable potential for connectivity and dispersion, and barriers to dispersal can be difficult to recognize
Results of STRUCTURE analysis of the microsatellite variation suggest the species is mainly structured in an Atlantic and a Pacific group (K = 2, Ln = -3598.96 by Evanno’s method) (Fig 5A, S1 Fig), individuals from the Falkland/Malvinas Islands, and in lesser extent, Argentina have a reasonable proportion of membership in the cluster associated with the Pacific
The test for migrants or hybrids between the two ocean basins performed in STRUCTURE suggested that only six individuals presented a proportion lower than 90% of the genetic component associated with their ocean of sampling (S2 Fig)
Summary
There is considerable potential for connectivity and dispersion, and barriers to dispersal can be difficult to recognize This is especially true for highly mobile species such as marine mammals and pelagic fish. While some of these species do appear to show panmixia across vast oceanographic scales (e.g. the European eel, Anguilla Anguilla [1]; the blue hake, Antimora rostrata [2]; and the common dolphin, Delphinus delphis in the North Atlantic [3]), it is more common for population subdivision to be found. We consider the biogeographic mechanisms that may define population structure in another coastal marine mammal species, distributed around the southern end of South America
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