To eat or not to eat: egg-based assessment of paternity triggers fine-tuned decisions about filial cannibalism

Abstract

Filial cannibalism occurs in many animal species ranging from insects to mammals, and is especially well described in teleost fishes. Numerous causes may lead to this behaviour, e.g. certainty of paternity. However, the cues males use to assess their paternity often remain unknown. One possible way to differentiate between own and foreign offspring is by using egg cues. Nevertheless, in egg-laying species, evidence for this is still scarce. In this study, male three-spined sticklebacks (Gasterosteus aculeatus), a fish with paternal care in which sneaking as well as filial cannibalism is common, were allowed to care for manipulated nests that contained different percentages of own fertilized eggs. After 7 days, embryo survival was determined. Furthermore, brood-caring as well as aggressive behaviour was measured daily. Clutches containing a higher proportion of foreign eggs were more likely to be completely cannibalized than clutches containing a lower proportion of foreign eggs, particularly when the clutch was laid early in the breeding season. However, the behavioural observations revealed no influence of paternity. The results show that paternity triggers filial cannibalism in sticklebacks and that males are able to evaluate their paternity using egg cues alone.

Figure 1.

Observed proportion of total filial cannibalism in relation to the proportion of a male's own eggs in the nest. The line gives the overall proportion of total cannibalism. The occurrence of total filial cannibalism differed between the treatments, with males having a lower percentage of own eggs having a higher chance of total cannibalism.

Figure 2.

Estimated probability of total filial cannibalism in relation to paternity (percentage of own eggs) and day during the course of the breeding season. Different probability values are coded by different colours, clarified by the panel on the right (blue equates to low cannibalism rate; red equates to high cannibalism rate). The probabilities were estimated by the ‘GLMM’ presented in table 1, which also included non-significant quadratic terms of both breeding season and paternity and all possible interactions.