Abstract:
Understanding evolutionary and ecological processes in centers is of particular interest to biogeographers, evolutionary biologists and ecologists because they provide opportunities to examine the role of geographical, historical and ecological processes in speciation. Here, we investigated the species diversity, phylogenetic relationships and phylogeographic patterns of giant clams in the Western Indian Ocean (WIO) and the Red Sea to explore scenarios of marine speciation in this under-studied region. From the ten genetically distinct clades recovered from the analyses of 253 sequenced specimens, five distinct Tridacna lineages were sampled, three of which were endemics of the WIO and the Red Sea. Our data confirm the validity of the species T. rosewateri, a WIO endemic genetically indistinguishable from T. lorenzi, which should be considered a junior synonym. The phylogenetic placement of the newly resurrected T. elongatissima provides insights into the probable origin of T. squamosina, which split from its sister species no later than 2 Ma, likely during Middle Pleistocene glacial periods. Two scenarios are discussed. Our results also suggest that T. maxima invaded the Red Sea more recently and that contemporary gene flow between Red Sea and WIO T. maxima is highly restricted. The deep Red Sea partition observed in T. squamosa suggests a much older divergence and raises the question of a possible cryptic lineage.