Should you eat your offspring before someone else does? Effect of an egg predator on filial cannibalism in the sand goby

Costs and benefits of parental care are expected to affect filial cannibalism. One factor that increases the costs and decreases the benefits of care is the presence of egg predators. In general, the effect of egg predators on filial cannibalism is unknown. Here, we examine the effect of an egg predator on filial cannibalism in the sand goby. Males caring for eggs were exposed to three treatments: no egg predator, visual cues from an egg predator, and chemical and visual cues from an egg predator. We hypothesized that the perceived benefits of providing care in the presence of an egg predator would be relatively low, and we expected filial cannibalism to increase in the presence of the egg predator, especially when both chemical and visual predator cues were present, as this might represent a greater threat. When both visual and chemical predator cues were present, whole-clutch cannibalism increased. In addition, larger males and males in poorer condition showed less whole-clutch cannibalism than smaller males or males in better condition. There was no effect of egg predator on partial-clutch cannibalism. However, males that engaged in partial-clutch cannibalism ate more of their eggs when the eggs were spawned by a female in relatively good condition, but a smaller proportion and number of eggs when only a single female spawned. In general, our findings suggest that male sand gobies are sensitive to the costs and benefits of care and are more likely to terminate care when the expected benefits are relatively low.