Abstract

The southern coastline of South America is a remarkable area to evaluate how Quaternary glacial processes impacted the demography of the near-shore marine biota. Here we present new phylogeographic analyses in the pulmonate Siphonaria lessonii across its distribution, from northern Chile in the Pacific to Uruguay in the Atlantic. Contrary to our expectations, populations from the southwestern Atlantic, an area that was less impacted by ice during glacial maxima, showed low genetic diversity and evidence of recent expansion, similar to the patterns recorded in this study across heavily ice-impacted areas in the Pacific Magellan margin. We propose that Atlantic and Pacific shallow marine hard-substrate benthic species were both affected during the Quaternary in South America, but by different processes. At higher latitudes of the southeast Pacific, ice-scouring drastically affected S. lessonii populations compared to non-glaciated areas along the Chile-Peru province where the species was resilient. In the southwest Atlantic, S. lessonii populations would have been dramatically impacted by the reduction of near-shore rocky habitat availability as a consequence of glacio-eustatic movements. The increase of gravelly and rocky shore substrates in the southwest Atlantic supports a hypothesis of glacial refugia from where the species recolonized lower latitudes across the Atlantic and Pacific margins. Our results suggest that current patterns of genetic diversity and structure in near-shore marine benthic species do not solely depend on the impact of Quaternary glacial ice expansions but also on the availability of suitable habitats and life-history traits, including developmental mode, bathymetry and the likelihood of dispersal by rafting.

Highlights

  • In southern South America, glacial periods produced major shifts in sea level, climate and landscapes, in marine near-shore environments[10]

  • Considering the geographic range and the reproductive biology of the species, S. lessonii is a suitable model to infer the impact of Quaternary glacial cycles over its distribution range, demographic inferences, recolonization pathways and its local persistence across a latitudinal gradient in areas that were differentially affected by the Quaternary glacial processes

  • A first phylogeographic genetic approach based on a fragment of the mitochondrial DNA c oxidase subunit I (COI) gene recognized the presence of two genetic clades in the species, one on the Pacific margin of South America and one on the Atlantic side, which would have diverged between 100,000 and 1,000,000 years ago[24]

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Summary

Introduction

In southern South America, glacial periods produced major shifts in sea level, climate and landscapes, in marine near-shore environments[10]. Near-shore marine species in the Atlantic Magellan margin could have persisted in situ during the last glacial period, in contrast to their conspecific populations located in the Pacific. A phylogeographic study conducted on a broadly distributed species would represent an important contribution to propose an integrated scenario of how coastal marine biota have responded to historical climate changes along temperate and cold areas of southern South America. The results of this study are congruent with a historical scenario involving Quaternary demographic and distribution contractions of S. lessonii surviving in glacial refugia in the southern portion of the southeastern Pacific, followed by recolonization of the deglaciated areas. A broader phylogeographic study of S. lessonii is required to better understand the historical biogeography of a species widely distributed across the southern Atlantic and Pacific coasts of South America

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