When a male fish is uncertain that he is the father of a clutch of eggs, he is likely to eat those eggs, according to a study in The American Naturalist. This filial cannibalism (the eating of one’s own offspring) increases proportionately with increased levels of cuckoldry.

In field observations of Telmatherina sarasinorum, a small fish endemic to Sulawesi, Indonesia, males increased filial cannibalism behavior threefold in the presence of one cuckolder and nearly sixfold in the presence of two or more cuckolders. The researchers Suzanne Gray, Lawrence Dill and Jeffrey McKinnon suggest that “males may use detection of cuckolders as an indication that the paternity of current offspring has been compromised”.

The evolution of filial cannibalism is thought to be driven by an energetic trade-off between caring for the current brood and investing in future reproductive success by eating offspring. In species with male parental care, a male’s assessment of the value of the current brood can incorporate information on his own energy reserves, the quality and availability of mates, prey availability and his perceived certainty of paternity. If a male perceives that the value of his current brood is low, then eating it may improve his future reproductive success.

Most work, and all theory, on the evolution of filial cannibalism has previously focused on understanding the energetic trade-off in fishes that provide parental care, mostly by males. Parental care requires an investment in both time and energy spent rearing or guarding offspring, whereas in the absence of parental care, there is no energetic cost beyond mating. In both cases, eating offspring is expected to add to future reproductive success through an energy gain; however, parental caregivers could also benefit by relieving themselves of low-value offspring.

Perceived certainty of paternity based on visual detection of cuckolders by a male could immediately indicate the value of potential offspring by providing information on expected relatedness. Filial cannibalism could be a tactic to recoup energy lost to mating efforts (e.g., through aggressive male-male interactions over mates) and hence increase energy for the next mating bout. The cost to a male of mistakenly consuming some of his own eggs may be high with respect to his reproductive fitness. However, this cost may be outweighed by the benefit of securing more energy to find another mating opportunity where his certainty of paternity is higher.

Journal reference: American Naturalist 2007. Vol. 169, pp. 258-263.

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