Brood parasitism: Scientists crack a million-year-old evolutionary puzzle about fake eggs

For example, two different lines of female cuckoo-weavers evolved to lay eggs with either a red or blue background, as an evolutionary response to similar diversity in their rump-like hosts. But there is no evidence that they can form the exact mixture of pigments needed to lay the olive green eggs that some host females can produce.

In a previous study, Professor Spottiswoode found that an increasing proportion of eggs laid by rust-legged rusts are olive green, indicating that this is an accelerated evolutionary counterattack.

As expected, the researchers found that host birds transmit the ability to lay “anti-fraud” eggs through a genetic process different from that of cuckoo weavers, that is, through inheritance from both parents.

“Cuckoo weavers are losing a powerful source of evolutionary innovation, and this may spoil them in the arms race that is going on here. The way they inherit their ability to mimic the host’s eggs is at a disadvantage because they are more likely to lose the host’s defenses. The host species is more effective and limits the ability of the parasite. on responding to it,” Spottiswood said.

Obviously, if cuckoo weavers inherited their ability to imitate eggs from both parents, they would risk that the eggs would not resemble the host’s eggs, but would likely allow them to have a wider palette for color production. . Being inherited only from the mother greatly limits their possibilities.

“We may be seeing the emergence of unique ‘egg signatures’, which can force cuckoo weavers to switch to other naive host species. Or parasitic birds may become increasingly dependent on young host individuals who have not yet learned to have their own signatures and are bad at detecting mismatched eggs. “.

The study also suggests that selection pressures for host defenses led to cuckoo weavers passing control of egg appearance to the maternal part of the genome at least two million years ago.

The international team’s study was published in Proceedings of the National Academy of Sciences† This article is based on a Cambridge University press release.