Abstract

Simple Summary Perumytilus purpuratus is a mussel species that is broadly distributed along the latitudinal gradient from the Southern Pacific to the Atlantic Ocean. Along its distribution, P. purpuratus has been historically considered as one species. However, in the last decade, evidence has supported the hypothesis of two geographically divergent lineages. Within this context, we explore the evolutionary history of this inter-oceanic mussel, linking both sperm acrosome variability and molecular analyses of males at the geographic macroscale. In general, our results were in agreement with the genetic divergence that was previously reported, and showing two north and south lineage. Furthermore, our comprehensive sampling effort enabled us to precisely determine both the latitudinal positions of morpho-genetic break, which was identified at 37 degrees S on the Pacific coast, and a probable hybridization zone at 38 degrees S. In addition, we found new southern sperm variants, longer than previously reported. Overall, our results support the hypothesis of historical events and postglacial recolonization as causal phenomena for the observed divergences. Finally, we consider that, despite uncertainties in the taxonomy of P. purpuratus, the morpho-genetic divergence between the north and south P. purpuratus lineages indicates that they do not constitute the same Evolutionary Significant Unit and, therefore, they should be considered as separate entities.Abstract In recent years, advances in analyses of the sperm morphology and genetics of Perumytilus purpuratus have allowed to two evolutionary scenarios for this mussel to be suggested: (1) the scenario of cryptic species and (2) the scenario of incipient or in progress speciation. For a better understanding of the evolutionary history of P. purpuratus, we performed extensive sampling along a latitudinal gradient of ca. 7180 km of coastline-from the Southern Pacific Ocean to the Atlantic Ocean-and we delved deeper into the sperm morphology of P. purpuratus, exploring its association with the phylogeny and population genetics to determine whether the variability in sperm traits between the northern and southern regions was a signal of cryptic or incipient species. Overall, our results showed that sperm sizes were strongly correlated with the genetic structure in males of P. purpuratus. We identified at 37 degrees S on the Pacific coast a coincident break of both sperm size and genetic disruption that can be explained by historical events and postglacial recolonization as causal phenomena for the observed divergences. Furthermore, evidence of genetic admixture between lineages was found at 38 degrees S, suggesting the presence of an introgressive hybridization zone and incomplete reproductive isolation in an in fraganti or incipient speciation process.