Mitochondrial genetic divergence of Chiton articulatus (Polyplacophora: Chitonida) in the Mexican Tropical Pacific

Context Chiton articulatus is a gonochoric, free-spawning mollusc with short-lived trochophore larvae inhabiting rocky shores along the fragmented and heterogeneous Mexican Tropical Pacific (MTP). Its limited dispersal in this patchy environment may lead to genetic divergence among populations. Aims Our objective was to characterise the genetic diversity and population structure of C. articulatus based on mitochondrial DNA. Methods We conducted a phylogeographic analysis using the cytochrome c oxidase subunit I (COI) gene of mitochondrial DNA collected from 100 C. articulatus organisms located across its geographic distribution. Key results The findings showed high levels of genetic diversity and a high number of private haplotypes. The structure analysis indicated six genetically distinct clusters with low connectivity. Divergence between the northern and southern populations was evident, with central mixing suggesting that gene flow adhered to the stepping-stone model. The historical demography indicated that the populations experienced sudden expansions during the late Pleistocene and early Holocene. Conclusions The northernmost and southernmost C. articulatus populations exhibit significant genetic divergence, suggesting the presence of distinct stocks in the MTP. Nevertheless, we recommend prioritising the conservation of central populations, as they serve as essential genetic reservoirs for all populations. Implications Our findings contribute to the broader understanding of how limited larval dispersal and habitat fragmentation shape population structure in marine invertebrates. The identification of distinct genetic stocks and central populations acting as genetic reservoirs underscores the importance of integrating genetic data into marine spatial planning and fisheries management. This research provides a framework for the conservation of other intertidal species with similar life histories in fragmented coastal environments.