Effects of mating order and male size on embryo survival in a pipefish

Abstract

In species that provide parental care, individuals should invest adaptively in their offspring in relation to the pre- and post-zygotic care provided by their partners. In the broad-nosed pipefish, Syngnathus typhleL., females transfer large, nutrient-rich eggs into the male brood pouch during mating. The male broods and nourishes the embryos for several weeks before independent juveniles emerge at parturition. Given a choice, females clearly prefer large partners. Yet, females provide protein-richer eggs when the same individual mates with a smaller than a larger male. In the present study, we allowed each female to mate with one small and one large male, in alternated order. We found a strong effect of female mating order, with larger clutches and higher embryo mortality in first- than second-laid broods, which may suggest that eggs over-ripen in the ovaries or reflect the negative effects of high embryo density in the brood pouch. In either case, this effect should put constraints on the possibility of a female being selective in mate choice. We also found that small and large males produced embryos of similar size and survival, consistent with the reproductive compensation hypothesis, suggesting that, in this species, larger males provide better nourishment to the embryos than smaller males.