Abstract
AbstractAimMany pinniped species have experienced drastic demographic changes due to their interaction with humans. Most studies, however, have failed to detect recent bottlenecks in otariids from genetic data. The South American Sea Lion Otaria flavescens have a long history of population changes associated with interglacial expansion and hunting to almost extinction. This study aimed at investigating these different demographic fluctuations integrating population genetics and phylogeographic approaches.LocationPacific coast of South America.MethodsEighty‐five samples from the Chilean coast were collected. Eight microsatellite loci were genotyped, and D‐Loop mitochondrial DNA (mtDNA) sequenced. Genetic diversity was assessed, and tests of recent genetic bottlenecks were performed. Past demographic changes were inferred based on neutrality tests, adjustment of a sudden expansion model and Bayesian skyline plots. The magnitude and timing of the different population size changes were further investigated through approximate Bayesian computation (ABC) of coalescent inferences.ResultsThe mtDNA shows relatively high diversity (h = 0.98 and π = 0.01) compared to most otariids, corroborates the divergence between Pacific and Atlantic populations, around 80,000 years ago (ya), and revealed a secondary contact zone in the Magellan strait. Microsatellite data support a second genetic discontinuity at 40°S, associated with post‐glacial colonization of Patagonia. ABC analyses confirmed that glaciation affected the effective population size (Ne) all along the Pacific Coast, between ~50,000 and 15,000 ya. A strong reduction of Ne was also inferred for the hunting period (73–66 ya from sampling).Main conclusionsO. flavescens shows clear signatures of susceptibility to climatic and anthropogenic disturbances and a spatial genetic structure that should be taken into account in the context of management and conservation policies. Yet, despite a recent history of demographic bottlenecks, the genetic diversity remains high, likely a consequence of the demographic dynamics in otariids, characterized by large and connected metapopulations.
Highlights
Populations of large-size mammals have been affected by the conjunction of anthropogenic and climatic factors since the advent of Homo sapiens, driving many species to extinction (Koch & Barnosky, 2006; Mondanaro et al, 2019; Sandom et al, 2014)
Pinnipeds are known to have suffered drastic population reductions associated with indiscriminate hunting and oceanographic fluctuations (Alastair et al, 2015; Crespo et al, 2012; Hoffman et al, 2016; Sielfeld, 1999; Sielfeld & Guzmán, 2002; Southward et al, 2005; Soto et al, 2006; Páez-Rosas et al, 2021), with anthropogenic effects being the principal driver of drastic demographic declines (Baylis et al, 2015; Crespo et al, 2012; Hoffman et al, 2016; Páez-Rosas et al, 2021; Sielfeld, 1999; Sielfeld & Guzmán, 2002; Soto et al, 2006; Southward et al, 2005)
In order to investigate the genetic effects of recent events, the joint effects of ancient and recent demographic changes must be taken into account in order to better understand the demographic history of species
Summary
Populations of large-size mammals have been affected by the conjunction of anthropogenic and climatic factors since the advent of Homo sapiens, driving many species to extinction (Koch & Barnosky, 2006; Mondanaro et al, 2019; Sandom et al, 2014). To understand the implication of these patterns in terms of connectivity restrictions, we must consider that spatial genetic structure can emerge because of the effect of strong genetic drift, such as expected during strong demographic bottlenecks or founder events. In this context, the actual magnitude of connectivity and its effect on the persistence of genetic diversity, even under well- known demographic bottlenecks, is far from being understood.
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