Ancient female philopatry, asymmetric male gene flow, and synchronous population expansion support the influence of climatic oscillations on the evolution of South American sea lion (Otaria flavescens)

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.

Genetic connectivity of the South American fur seal (Arctocephalus australis) across Atlantic and Pacific oceans revealed by mitochondrial genes

“…This is supported by low F ST values among them, and a lack of current genetic structure, with several haplotypes being shared between populations across both oceans, indicating one single southern Pacific-Atlantic population, similar to the Australian and Cape fur seals (Arctocephalus pusillus), where the Australian population is the result of a single, recent historical founder from the South African Cape fur seal (Lento, Haddon, Chambers, & Baker, 1997). The phylogenetic pattern found in the present study is in contrast with other studies of the South American sea lions (Otaria flavescens), which have almost the same geographic range as South American fur seals (King, 1983), and where populations from the Pacific and from the Atlantic presented a clear genetic structure and significant genetic diversity between oceans, suggesting the separation of both populations into different evolutionarily significant units (Oliveira et al, 2016;Túnez et al, 2007).…”

Contrasting phylogeographic pattern among Eudyptes penguins around the Southern Ocean

“…Demographic expansion was also found for E. chrysocome at the Falkland Islands/Islas Malvinas around 7,000 ya, although there is little evidence for strong glaciation in this area 10 . However, other factors such as changes in marine productivity associated with glacial periods probably occurred and could have affected demographic patterns, as suggested for sea lions ( Otaria flavescens ) 91 , even if the area was not covered by ice during the LMG. Finally, demographic expansion of E. moseleyi at Amsterdam (~15,000 ya) and to a lesser extent at Nightingale (~7,000 ya) could also be related to the period where present day temperatures were reached after the glacial period (~10,000 years ago) 90 .…”

The northernmost haulout site of South American sea lions and fur seals in the western South Atlantic

“…comm.) and genetic studies 18,19 have confirmed that South American fur seals and South American sea lions from Argentine and Uruguayan colonies disperse northwards to Brazil.…”