68.1 Friday, Jan. 6 Evolutionary morphology of the caudal musculoskeletal system in syngnathid fish: from swimming to prehension ... in different ways ADRIAENS, D.*; NEUTENS, C.; CHRISTIAENS, J.; VAN LOO, D.; DE KEGEL, B.; BOISTEL, R.; VAN HOOREBEKE, L.; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium; Université de Poitiers, France; Ghent University, Belgium email@example.com
Seahorses and pipehorses possess the unique characteristic of extensive tail bending, allowing them to grasp onto the substrate. Current phylogenetic hypotheses suggest that grasping performance evolved more than once, as it seems to have arisen independently in pipehorses and seahorses. Pipehorse species with prehensile tail are nested within pipefish species (that lack this prehensile tail), hence are not sister group to the seahorses. Considering the different evolutionary strategies giving rise to a prehensile tail (starting from a rigid one), it is hypothesised that some crucial (and hence shared) structural modifications occurred at the level of (1) body armour organisation, (2) vertebra organisation, (3) interaction between plates en vertebra and (4) muscle organisation. To test these hypotheses, the caudal system in pipefish (ancestral condition), pipehorse and seahorse are compared, using histological and micro-CT data. The results confirm some hypotheses, but not all. As such, body armour organisation in pipehorse proved to be different from that of seahorses, providing both an increased capacity for flexibility between consecutive segmented plates (overall to partial plate reduction). Modifications in the musculature are also extensive, where seahorses represent a unique organisation of the muscle-tendon complexes for syngnathids (plate-like versus ancestral conical myoseptal organisation, and muscle fiber extension). This study thus confirms that within a single clade (syngnathids), at least two different evolutionary strategies have independently yielded an adaptive solution for a novel function, i.e. tail prehension.