Scientists describe the evolutionary race of nest parasites and their hosts

(ORDO NEWS) — An international team of researchers has described a gene inheritance mechanism that allows cuckoo weavers to quietly toss their eggs into the nests of several bird species at once. However, in response to nest parasitism, host birds develop new adaptations that make life increasingly difficult for cuckoo weavers.

Nest parasitism is characteristic of some fish and insects, but it is most studied in birds – for example, in cuckoos, which use the nests of other bird species to raise their own offspring.

This lifestyle has many benefits, although it comes with some challenges. For example, nest parasites need to be able to accurately imitate the color, size, and pattern of other people’s eggs so that the owners of the nest do not guess the deception.

Scientists have long wondered how the characteristics of the eggs are passed on to offspring from parents who may have grown up in the nests of various bird species. Now the staff of the University of Cambridge (UK), the University of Cape Town (South Africa) and Boston University (USA) were able to answer this question.

The authors of the article studied cuckoo weavers, a nesting parasite common in Africa, throwing their eggs at once to several species of cisticola and prinia. The scientists analyzed DNA samples from 196 weavers raised in 141 nests of host birds from four different species.

It turned out that the characteristics of the eggs of the female weavers inherit along with the mother’s W chromosome. This chromosome is specific to female birds in the same way that the Y chromosome is unique to male mammals.

Such a mechanism allows cuckoo weavers to avoid inheriting the genes that determine the appearance of eggs from fathers who may have grown in a nest of a completely different host. In addition, it was this type of inheritance that allowed different female cuckoo weavers to mimic the eggs of different host species.

However, during their existence side by side with nest parasites, host birds have developed a number of protective adaptations. For example, ghosts have developed an amazing variety of colors, shades and patterns of eggs, allowing birds to accurately distinguish between their own and other people’s eggs.

Maternal inheritance slows down the ability of cuckoo weavers to counter-adapt. They have already learned to reproduce some variations of the eggs of their owners, but this is not always possible to do this accurately enough.

For example, two lines of female weavers lay eggs that are blue and red in color, which still resemble those of certain subspecies of prairie, despite their patterns. However, scientists have not found any evidence that weavers can produce the necessary pigments to create the green eggs that some other hosts carry.

At the same time, in the adoptions themselves, the color of the eggs is inherited from two parents, and this allows them to accelerate the process of the emergence of new adaptations and achieve a greater variety of eggs.

Scientists believe that the continuation of this evolutionary race can force cuckoo weavers to switch to other hosts less adapted to their parasitism. Otherwise, weavers may become more dependent on young individuals of the host species, which have not yet studied the color patterns of their own eggs and may confuse them with others.

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