Meeting Abstract
Marine to freshwater transitions play an important role in accounting for tropical freshwater fish biodiversity. Fishes which have historically invaded freshwater habitats from marine ones (marine-derived lineages or MDLs) may experience ecological opportunity, and are apt systems for examining how habitat transitions lead to ecomorphological diversification. We examined how such an ecological transition has affected the body-shape diversity of tropical needlefish and halfbeaks (Beloniformes). Body-shape and size correlate with many aspects of ecology and life history: foraging through locomotion and feeding morphology, reproduction by predicting offspring size and number, and more generally, larger fishes generally occupy higher trophic niches. Using micro-computed tomographic (µCT) scanning, geometric morphometrics, and phylogenetic comparative methods we examined body-shape evolution in 30 species of needlefishes from the Zenarchopteridae and Belonidae families. Using a multi-locus, published molecular phylogenetic tree, we examined patterns and tempo of evolution body-shape evolution in Asian and South American beloniform clades. We found that freshwater belonids have greater diversity in body shape than their marine relatives. The primary axis of body shape variation is elongation, driven by lengthening of either the rostral or trunk regions, and with miniaturization and ‘halfbeak’ morphologies prevalent among freshwater species. While body shape diversity is greater in freshwater over marine needlefishes, access to new prey may also have influenced the evolution of freshwater taxa. In particular, we find that insect-feeding is also commensurate with many of the notable changes in body shape among freshwater beloniforms, moving the needlefish bauplan beyond ancestral piscivory.
