Integrating genetic, phenotypic and ecological analyses to assess the variation and clarify the distribution of the Cortes geoduck (Panopea globosa)

Abstract

The Cortes geoduck (Panopea globosa) has been considered a Gulf of California (GC) endemic but anecdotal and unpublished evidence has suggested its presence in Bahía Magdalena (BM), on the Pacific coast of southern Baja California. Establishing the identity of geoduck clams and their distribution limits is not only of clear biological significance to understand their structural and functional variation, but is also of consequence for their conservation and management, given the multi-million dollar fishery they support in north-west Mexico. We analysed Panopea clams from Mexican populations, including BM, using an integrative approach including genetics, morphometrics, and an ecological niche model. Our genetic results (restriction fragment length polymorphisms of nuclear ribosomal DNA and mtDNA cytochrome c oxidase subunit I sequences) clearly identify BM geoducks as P. globosa, implying a significant geographical range expansion outside of the GC and refuting its status as endemic to the Gulf. On the other hand, clams from BM were phenotypically different (shell significantly higher) from other Mexican P. globosa and Panopea generosa specimens, which may account for the confusion in their morphological identification. The ecological niche model for P. globosa, integrating ecological and distributional data from the GC, revealed a very low probability (<10%) that this species could successfully occupy BM. Our results and those of others suggest that the Cortes geoduck population in BM may be adapted to specific environmental conditions differing from those experienced by conspecifics inside the Gulf and is likely isolated. This is highly relevant for the management plans of Mexican geoducks.

How sea level change mediates genetic divergence in coastal species across regions with varying tectonic and sediment processes

“…Many phylogeographic studies within the Gulf have focused on rocky intertidal (Deng & Hazel, ; Hurtado, Frey, Gaube, Pfeiler, & Markow, ; Hurtado et al., ), rocky shore (Riginos, ; Riginos & Nachman, ), sandy substrate (Byrne et al., ; Hurtado et al., ; de Jesús Suárez‐Moo et al., ), reef (Lin, Sánchez‐Ortiz, & Hastings, ) and offshore pelagic (Segura, Rocha‐Olivares, Flores‐Ramírez, & Rojas‐Bracho, ) species. As with estuaries, these other habitats are discontinuously distributed along coastlines (Riginos & Nachman, ).…”