Meeting Abstract
Many marine organisms have an biphasic life cycle. The early phase is the predominant dispersal mechanism in otherwise immotile organisms, resembling therein functionally terrestrial plant seeds. The evolution of these larvae and propagules, especially the diverse larval forms of marine invertebrates, has long interested marine biologists, who focused their efforts on taxa with highly labile larval life history. In the present study, we highlight the adaptive potential of larval development of throracican barnacles, which are presumably phylogenetically conserved in their life history. To infer their extent of phylogenetic conservatism and adaptive potential, we tested for phylogenetic signal, assessed the fit of assumptions and predictions of two adaptive hypotheses, and compared the fit of multiple models of trait evolution. We identified a strong phylogenetic signal for all larval traits, which traces a well-known broad separation between taxa with planktonic-feeding larvae and aplanktonic larvae. This is, however, unlikely to represent evolutionary constraints, as trait shifts are also present in each taxon. It is also unlikely to be a result of neutral evolution, as the traits did not evolve under a model of Brownian Motion, evident by multiple model comparisons. Moreover, larval developmental mode and egg size exhibit adaptive potential: they match the predictions of both adaptive hypotheses if we allow certain modifications that were shaped by mismatches between assumptions and data. We conclude that the larval development of thoracican barnacles is phylogenetically conserved, but was likely also shaped by selective pressures, which leave adaptive signatures in the current distribution of barnacle larvae.
