The good side of filial cannibalism

When you make a chocolate egg or bunny this weekend, think about this: rabbits often eat their own cubs and chickens have their own eggs.

In fact, the consumption or abandonment of offspring has been documented in various species of mammals and birds, as well as in fish, insects and spiders. Hunger and quality control are among the many reasons given by this counter-intuitive survivor of natural selection.

Researchers from the University of Tennessee and Oxford University now suggest that in some cases, filial cannibalism and the abandonment of offspring could even be considered forms of parental protection. Posted in Borders in ecology and evolution, their mathematical model shows that, when overcrowding threatens the survival of offspring – which is often due to the spread of infection or competition for resources – sacrificing some so that most can live becomes the ultimate form of hard love.

Put all your eggs in one basket

To understand the role of overpopulation or "offspring density" in the benefit of cannibals for survival, the researchers focused on species that lay eggs.

"Spawning in common is common in various fish, insects, reptiles and amphibians," says Dr. Hope Klug, senior author, associate professor at the University of Tennessee, in Chattanooga. "This facilitates the protection, cleaning, incubation and feeding of eggs, but can also increase the transmission of disease and competition for food and oxygen."

The density of the offspring has been found to affect egg survival and, in some cases, abandonment or cannibalism in many of these species.

"For example, in young damsels of Beaugregory, fathers were more likely to eat eggs under conditions of lack of oxygen," Klug notes. "Such cases have led to the hypothesis that eating or giving up offspring could be an adaptation to improve the overall survival of the offspring by reducing their density."

Model parents eat their offspring

Klug and his colleagues created a mathematical model to test this hypothesis.

"The model has introduced an imaginary individual with a mutation of filial cannibalism or abandonment of offspring in a generic population of laying hens," says lead author, Dr. Mackenzie Davenport, also of the US. University of Tennessee.

As in previous models of the group, the gene of cannibalism spread in the population if it gave the parents extra calories.

But for the first time in this model, they found that when offspring mortality increases with spawning density, filial cannibalism and abandonment of offspring result in improved fitness.

"Under these conditions, the mutants have been able to compete and replace the generic population," reports Davenport.

This was the case even when the cannibal parents received little or no energy from the surplus food – or that it was assumed that their abandoned offspring were dying.

"Our results suggest that, surprisingly, filial cannibalism and abandonment of offspring can function as forms of parental protection, increasing total survival of the offspring."

Live fast, die young, be ready to abort

"The benefit of abandoning offspring and filial cannibalism in terms of fitness also increases with the increase in adult mortality rates, particularly in the case of filial cannibalism." ", adds the co-author, Professor Michael Bonsall of the University of Oxford.

In other words: if you are less likely to reproduce, you must be ruthless in protecting your brood. But if offspring mortality depends on density, why produce so many eggs in the first place?

"It's not always possible for parents to predict the environment in which their offspring will end up," says Bonsall. "Factors such as food availability, oxygen availability, disease and predation may be unpredictable, and in many fish and other animals females lay their eggs in nests or on male territories as additional females could then add eggs to the nest. "

"It is now up to the empiricists to test these models on various species," the authors conclude.