Parental care drives reproductive gland evolution in fishes

Background/Question/Methods

Animals are under immense pressure to find and attract mates. In addition to traditional, pre-copulatory competition, there is growing appreciation that post-copulatory sexual selection can impact male reproductive success and shapes anatomy and behaviour. Reproductive accessory glands are organs involved in reproduction but not directly in the production or release of gametes. In fish, the function of these glands has only been described in a handful of species, where they play diverse and crucial roles in reproduction. The selective factors leading to the evolution of accessory glands in fishes remain a mystery, with two leading hypotheses — they evolved in response to pressures from sperm competition and/or from parental care. We tested these hypotheses and explored the evolutionary past of accessory glands. To do so, we conducted a systematic literature survey on ray-finned fishes, documenting the presence or absence of male reproductive accessory glands, as well as information regarding parental care, spawning behaviour, and mating system, for 618 species, representing 267 families.

Results/Conclusions

We found accessory glands in 26 different families and 116 species, with most species found in three clades: the blennies, gobies, and catfishes. Using a novel Bayesian analysis of correlation, we show that the evolution of accessory glands is strongly associated with male parental care and pair spawning, supporting the hypothesis that these glands arose as a means to enhance parental care activities. This study represents the first large-scale phylogenetic comparative analysis of accessory glands across fishes and provides novel insights into the evolution this organ. These results also highlight the importance of parental care in shaping vertebrate reproductive anatomy and behaviour.