Pregnant pipefish with a simple brooding surface loose less weight when carrying heavier eggs: evidence of compensation for low oocyte quality?

Abstract

The evolutionary radiation of syngnathids has been accompanied by a diversification of structures involved in parental care, from a hypothetical ancestral presenting a simple brooding structure. The architectural simplicity of Nerophis male brooding structures led to the hypothesis that the relationship between father and developing embryos was feeble, unlike that observed in syngnathids with brood pouches. Here, we show that males loose considerable weight during pregnancy, especially so when egg weight is low. These results highlight the possibility of a compensatory mechanism and help justify why males in the wild tend to select large and colourful females, which are more fecund and able to produce larger eggs. Together with available information on the mating system, we also discuss some of the interplaying reasons behind the observed sex role reversal and high sexual dimorphism in the worm pipefish.