Hierarchical Genetic Differentiation and Population Structure in the Semiterrestrial Crab Armases Rubripes (Brachyura, Sesarmidae)

Abstract

Estuaries play a crucial role in maintaining marine biodiversity and providing key ecosystem services, but they are increasingly impacted by local anthropization and global climate change. Developing effective management strategies requires a deep understanding of the genetic structure and diversity of marine species, including how their populations are connected across their distributional range. Here, we used cytochrome oxidase 1 (COI) data to test the hypothesis of significant genetic structuring in the semiterrestrial crab Armases rubripes along its distribution, from the Caribbean to the Western South Atlantic coastline. Patterns of genetic diversity, population structure, and demographic history were assessed, and phylogenetic analysis was performed. Our results support this hypothesis, revealing a potential cryptic species complex, with species‐level divergence between the Caribbean and Brazilian regions. These two regions exhibit exclusive haplotypes, with up to 16 mutational steps between them, and were recovered as well‐supported clades in our phylogenetic reconstructions and high genetic distances that are consistent with interspecific differentiation. We also uncovered unexpected genetic structure within the Brazilian coast, revealing distinct South and North groups among our sampling sites. The analysis of historical demography suggests that Caribbean clade remained stable over time, while Brazilian South group showed signs of recent demographic expansion. Overall, our results suggest that A. rubripes is likely a species complex, with Caribbean and Brazil representing separate evolving lineages.

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