Allopatric mosaics in the Indo-West Pacific crab subfamily Chlorodiellinae reveal correlated patterns of sympatry, genetic divergence, and genitalic disparity

[Display omitted] •The most comprehensive phylogeny of the crab subfamily Chlorodiellinae is presented.•Scanning electron microscopy, and new geographic range and sequence data of 892 specimens, uncovered undescribed diversity.•Several nominal species are composed of allopatric mosaics—divergent COI lineages with distinct geographic distributions.•Relationships between genetic distance (time), secondary sympatry, and the divergence of genitalia are well supported.•Our data suggest that evolution of genitalia plays an important role in completing the process of speciation in these crabs. Molecular studies have revealed that many species once thought to be wide-ranging in the Indo-West Pacific contain allopatric mosaics of endemic lineages. These lineages provide compelling evidence that substantial time is needed to evolve isolating mechanisms sufficient to permit successful secondary sympatry, and that divergence is initiated in allopatry. In this context, questions arise regarding the nature, timing, and origin of isolating mechanisms that permit secondary sympatry. We present a phylogeny of the crab subfamily Chlorodiellinae which displays allopatric mosaics within species. These allopatric lineages typically do not have divergent male genitalia, while older sympatric lineages do. We tested the relationship between genetic distance (proxy for time), sympatry, and the divergence of male genitalic morphology. Our results suggest that male genitalic divergence is not involved in the initiation of speciation in chlorodielline crabs, having likely occurred only after isolation began in allopatry. However, morphological evolution of genitalia seemingly does play an important role in completing the process of speciation in these crabs.