Meeting Abstract
Seven species of yo-yo clams ( Divariscintilla spp.) are burrow commensals of the mantis shrimp Lysiosquilla scabricauda in the Indian River Lagoon in Southeast Florida. This high-fidelity co-occurrence presents an ecological paradox given that closely related commensal galeommatoidean species typically associate with different hosts. I am interested in testing for latent niche differentiation among these co-occurring congeners, and am addressing this question using four different approaches: phylogenetic, ecological, behavioral, and dietary. A molecular phylogeny is being constructed to reveal sister relationships among the seven taxa. Extensive field surveys of host burrows have been taken to document ecological patterns of co-occurrence. One third of host burrows had commensals; one commensal species dominated often occurring by itself in high numbers, and up to four species were found together in mixed assemblages. Artificial burrow experiments are being used to infer possible microhabitat use among species, while behavioral experiments are being used to characterize commensal responses to host presence (chemotaxes) as well as other environmental cues (phototaxes, geotaxes, and thigmotaxes). Isotopic analyses of commensals and their environment (burrow water, burrow sediment and host) are being conducted to test for differential resource use among species (suspended organic matter, deposited organic matter, and host waste). At the time of writing, these lines of research are all in progress but there is evidence for clear niche differentiation in one sister taxon pair: an ectocommensal attaches directly to the host body while its sister species attaches to the host burrow walls. This micro-niche separation is associated with the evolution of morphological and behavioral differences, but it is not yet known whether it extends to dietary differentiation.
