Bio 375 : Exercise 12

Cannibalism is widespread in natural populations of fishes, where the stomachs of adults frequently contain conspecific juveniles. Furthermore, field observations suggest that guardian males routinely eat offspring from their own nests. Molecular genetic analyses of embryos in the stomachs of males captured in the field show that males often do eat their own young.

A) This is not altruism, but could Hamilton’s rule apply here? Explain.

B) Molecular analysis of uneaten broods indicates that there often are some non-descendants mixed in with the brood that the male is caring for. These likely come from sneaker males siring some offspring, egg thievery by the resident male, or take-overs of nests already with eggs. One would think that if males have to eat some eggs, that they should preferentially eat eggs of the other male, not their own. Explain how thinking about mechanism (one of Tinbergen’s 4 questions) can shed light on the maladaptive function of eating descendant eggs (another of Tinbergen’s 4 questions). Hint: Think of the male as a receiver of cues from the eggs.