Theoretical models predict that increased mate availability accelerates filial cannibalism by the parental male, but we do not yet fully understand how the various aspects of mate availability contribute to this effect. We examined the effects of two elements of mate availability—female fecundity and sex ratio—on filial cannibalism by the lizard goby, Rhinogobius flumineus, which is a paternal nest brooding fish. We used three types of females (stimulus-females): a single female with slim belly (not ready to spawn), a single gravid female (ready to spawn), and two gravid females. Stimulus-females were housed in a transparent cage and shown to subject males just before and after spawning with a separate female, after which males cared for the brood. A single gravid stimulus-female accelerated filial cannibalism, compared with a control-stimulus consisting of an empty cage, but only during the early care period. In contrast, a single slim-bellied stimulus-female did not accelerate cannibalism. A stimulus of two gravid females accelerated cannibalism to the same degree as a single gravid female stimulus. Our results suggest that in lizard gobies, filial cannibalism by parental males is accelerated by female quality (fecundity) in the early care period, but not by a higher number of available females (sex ratio).
