Egg cannibalism by sticklebacks: spite or selfishness?

Summary Although it is generally agreed that humans can be spiteful, there are few if any, unambiguous examples of spite by non-human animals. Data are presented suggesting that female threespine sticklebacks show spiteful behaviour. In the field, they seek out conspecific eggs to attack while largely ignoring those of a closely-related sympatric species, the blackspotted stickleback. This occurs despite the fact that the latter's nests are more abundant and less well protected. In the laboratory, female threespine sticklebacks attack the eggs of conspecifics more than those of blackspotted sticklebacks, those of sympatric conspecific females more than those of allopatric females, and older eggs more than younger ones. Because there was no evidence of greater energetic or nutritional advantages from eating conspecific rather than heterospecific eggs, or older eggs rather than younger ones, threespine sticklebacks may be spiteful. Alternative proximate and evolutionary hypotheses to explain this discriminant egg-eating are discussed.