The natural history of a monogamous coral-reef fish, Valenciennea strigata (Gobiidae): 2. behavior, mate fidelity and reproductive success

This study examined the behavior and reproduction of a monogamous coral-reef fish, Valenciennea strigata, to determine mate fidelity and the proximate causes of monogamy. Most fish were found in monogamous pairs that remained together over several rounds of reproduction. Pairs stayed within close proximity to each other and their burrows. Females fed at a higher rate than their mates, while males spent more time maintaining burrows. Females spawned every 13 days; males guarded eggs in the burrow for 2–3 days. Although females limited the RS of males, males did not mate polygynously under natural conditions. Reproductive success (RS) was affected primarily by survival, and secondarily by size. Both sexes enforced monogamy by guarding their mates. Three factors facilitated mate guarding: (1) all males were able to hold a nest site, (2) both sexes showed strong site fidelity, and (3) residents had an advantage in contests over mates. Thus, mates were economically defensible. Additionally, females formed a crescent of dark pigments on their abdomen that resembled a gravid condition; these marks may enhance continuation of the pair bond. Both sexes preferred large mates, and pairs were positively assorted by size. Males benefited from guarding large females because fecundity increased with size. Females may benefit from the burrowing of males, and larger males should be better burrowers.