Maria Abou Chakra works in the Evolutionary Theory Department at the Max Planck Institute for Evolutionary Biology. In collaboration with Christian Hilbe, now at Harvard University, and Arne Traulsen, she developed mathematical models to test the mafia hypothesis. The underlying principle in their minimalistic model was that each parasite lays no more than one egg in another bird's nest, which the host may accept or eject. A more complex model allowed the parasites to lay several eggs, each of which could be destroyed or accepted individually.
"Biologists prefer the complex model, because it is closer to reality. But we came to the same conclusion with both models: the dynamics of the interaction between host and parasite is cyclical." An equilibrium is never established; instead, there are regular cycles in terms of the frequency of mafia and non-mafia parasites and hosts that accept an egg immediately or only after they have suffered retaliation. If the number of non-mafia brood parasites is high, the advantage lies with conditional accepters, hosts that leave the parasite's egg in their nest only after their nest has been destroyed. After all, there is little chance the parasite is a retaliator. This behaviour therefore increases among host birds. And this, in turn, improves the survival rate of the mafia-like brood parasites. As soon as the latter are in the majority, it makes sense for the hosts to accept unconditionally, which, in turn, renders the mafia-like behaviour unnecessary. The cycle begins anew.
Evolutionary biologist Amotz Zahavi postulated the mafia hypothesis back in 1979. It has been contentious ever since. Critics argue that the retaliation gives the parasites no advantage, carrying high costs instead. However, the future nestlings benefit from the hot-headed behaviour if the host parents do indeed keep a
|Contact: Dr. Maria Abou Chakra|