Bird species that breed with multiple sexual partners experience fewer harmful genetic mutations, according to a study by the Milner Center for Evolution, University of Bath. These works, published in Evolutiondemonstrate for the first time how polygamy increases the efficiency of natural selection in wild populations.
Most birds mate with only one other specimen per season, while in some species, such as swans and geese, this “pairing” lasts for the life of the animal.
In contrast, some bird species are polyamorous, having multiple partners per breeding season; however, we do not know why they developed this different way of doing things.
A team of researchers have analyzed the genomes of 150 species of birds, found across all major families and in various locations across the planet, including 6 species that have been sequenced for the first time.
By counting the differences between the genes inherited from the father and the mother, the scientists were able to estimate the level of genetic diversity across each species.
The researchers were also interested in the frequency of genetic mutations in each species, and if these modified the sequence of the proteins for which they carry instructions, or if they were “silent”. The former are usually harmful, while the silent mutations are usually harmless.
Contrary to expectations, the researchers found that polyamorous species as a whole were no more diverse than monogamous species, although the small number of species with polyamorous females had more genetic diversity.
According to Kees Wanders, PhD student at the University of Bath and lead author of the study, “species evolve according to natural selection, where harmful mutations disappear from the population, in the long run, because individuals who are affected do not survive long enough to have the opportunity to reproduce, or individuals with beneficial adaptations survive longer”.
“However, individuals also evolve using sexual selection, where evolution is affected by individuals competing for access to mates, so that only the most desirable characteristics are then passed on to offspring. »
As in fruit flies
“This study suggests that sexual selection is consistent with natural selection in birds, and that harmful mutations are more effectively removed from the gene pool in polyamorous populations, where sexual selection is particularly strong,” says Wanders. “.
“We still don’t know why some species of birds are polyamorous, while most choose a mate for a season, or even for life. There are several theories aimed at explaining the evolution of polyamory in these species, but we have found evidence that it increases the efficiency of natural selection by removing harmful mutations and avoiding the effects of incest.” mentioned the researcher.
“This has previously been observed in the laboratory, with fruit flies, but this is the first time this has been seen in wild bird populations. »
Another author of the study, Dr. Araxi Urrutia, indicates “having the hypothesis according to which, in polyamorous species, when individuals struggle to find a partner and must travel farther to do so, this would mean that they there would be more genetic diversity in these species.
“However, we were surprised to see that there was no evidence for this – instead we found that these individuals had fewer harmful mutations. »
“Despite this apparent evolutionary advantage, most birds tend to stay in groups and raise their children in this way, since it offers a better chance of survival for these offspring. »
