Meeting Abstract
A combination of extreme morphological and functional specializations in seahorses and pipefishes (Syngnathidae) makes them a compelling system to study how complex structure-function relationships evolve and feed back into the morphological evolution of organisms. Syngnathids possess an elongated snout, which they use in a modified form of prey capture whereby rapid dorsal head rotation brings the mouth close to prey. In addition, it has been shown that they power amplify their strikes, which allows seahorses and pipefish to approach prey exceptionally quickly. In these fishes it has been previously predicted that snout length should trade off with snout cross-sectional area to minimize inertial forces during rotation. However, drag forces on the snout can also be significant during head rotation, and may be minimized as well, which would primarily effect snout width and length. We tested these predictions in a phylogenetic context using a newly constructed phylogeny in combination with a dataset of linear measurements of 50 species of syngnathids. Phylogenetic regression and model-based comparative methods were used to investigate the relationships and relative rates of snout width, depth, length and area. We find that snout cross-sectional area does trade-off with snout length even when phylogeny is taken into account, but this relationship is largely driven by constraints on snout width: snout width and not depth is correlated with snout length, and snout width has much slower (20x slower) rates of morphological diversification compared to snout depth. Our interpretation is that the joint effects of drag and inertial forces constrain snout shape diversity in syngnathids.
