GEOMETRIC MORPHOMETRIC ANALYSES OF CTENA ORBICULATA (LUCINIDAE:BIVALVIA) FROM MARINE LAKES OF SAN SALVADOR ISLAND, THE BAHAMAS, AND SURROUNDING COASTAL ENVIRONMENTS

Island ecosystems have significantly contributed to our understanding of evolution at both local and regional scales. On San Salvador Island in The Bahamas, numerous marine lakes act as evolutionary “islands” for marine communities. Analyzing potential intraspecific variation of taxa that occupy different lakes may reveal information about whether variation among lake populations is prominent on a regional scale. The goal of this study was to assess intraspecific morphological variation among live populations and co-occurring death assemblages of Ctena orbiculata (Lucinidae:Bivalvia). Specimens were sampled from two marine lakes on San Salvador, the mouth of a seagrass lagoon on the southeast corner of the island, and a lagoon in the Florida Keys. Geometric morphometrics was used to assess shape variation of shell interiors based on the positions of anterior and posterior adductor scars. Results demonstrate that mean shape of live-collected and dead-collected shells from the same locality were similar, but mean shape of live-dead pooled assemblages differed among all localities. A canonical variate analysis of shell shape indicated that lake and coastal assemblages were strongly separated based on morphological shortening of the anterior adductor muscle. Furthermore, separation between each lake was stronger than between the two coastal assemblages. Subsequent analyses demonstrated that morphological variation among assemblages was not due to allometry. More marine lakes on San Salvador, and coastal localities within and beyond The Bahamas, need to be investigated to understand the observed C. orbiculata morphological differences among localities. In addition, C. orbiculata has been hypothesized to represent a complex of morphologically-similar species. Thus, further morphometric, as well as molecular, analyses are needed to verify taxonomic classification in this and past studies.