Capturing speciation in action: Rapid population divergence in the Caribbean bioluminescent ostracod Photeros annecohenae (Myodocopida: Cypridinidae)

Abstract

Species that have complex courtship behaviors are some of the most evolutionarily diverse lineages observed in nature. Divergent, pre-mating calls are effective in both generating and/or maintaining reproductive isolation. Complex courtship displays provide numerous characters in which a small change can reinforce or lead to reproductive isolation. The multiple characters of these displays often evolve interactively, increasing potential variants of phenotypic display traits. Because many characters can be quantified and used to document variation among species, organisms that use complex courtship behaviors provide model systems for testing the influence of ecology on lineage diversification and trait evolution. Here, we quantify differences in the courtship behavior, morphology, and genetic trait change of male Photeros annecohenae over an intermediate range of geographic distances along reef habitats of the Mesoamerican barrier reef of Belize. Differences in bioluminescent ostracod behavior, morphology, and genetics have been documented across large geographic distances (500-1000 km) and at smaller geographic scales (~12km) P.annecohenae exhibits measurable population genetic structure but minimal behavioral and morphological differentiation. Our findings support the hypothesis that differences observed in behavioral, morphological, and genetic characters across isolated populations of P. annecohenae are occurring along this intermediate range at short geographic differences. The observed morphological, behavioral, and genetic isolation of male P. annecohenae offers novel insight toward our understanding of the speciation continuum.