Quantification of whole brain arginine vasotocin for two Syngnathus pipefishes: elevated concentrations correlated with paternal brooding.

Arginine vasotocin (AVT) regulates many aspects of fish physiology and behavior including courtship and reproduction. This study begins to address whether paternal functions for AVT have independently evolved in species in which paternal behavior has evolved. We quantified AVT in the brains of Syngnathus fuscus and Syngnathus floridae which, like other pipefishes and seahorses of the family Syngnathidae, brood embryos within specialized structures of the male. For both species, we measured AVT concentrations seventeenfold higher for some males during brooding compared to post-brooding males. Comparable whole brain AVT concentrations between gravid females and males with broods at some embryonic development stages suggest physiological similarities that we hypothesize is related to nutrient provisioning but should be elucidated with further studies including a detailed anatomical analysis of AVT production. Earlier studies have identified differences in the brooding structures of these species. Here we documented interspecific differences in the variability and mean AVT concentration for non-brooding males, the brood stage showing a return to post-brooding concentrations, and the variability of AVT concentrations for brooding males with embryos in some development stages. Future investigations should use these data to investigate the potential for divergent AVT function between species, sexes, and brooding males with embryos of different developmental stages.