According to a study by the Milner Center for Evolution, University of Bath, bird species that breed with multiple sexual partners suffer fewer harmful genetic mutations. This work, published in Evolution, shows 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 ‘mating’ lasts for life.
In contrast, some bird species are polyamorous, having multiple mates per breeding season. However, we do not know why they developed this different approach.
A team of researchers has analyzed the genomes of 150 bird species found in all major families and in various locations around the world, including 6 species that have been sequenced for the first time.
By counting the differences between the genes inherited from the father and mother, the scientists were able to estimate the level of genetic diversity for each species.
The researchers were also interested in the frequency of genetic mutations in each species and whether these altered the sequence of the proteins they carry instructions for or whether they were ‘silent’. The former are usually harmful, while the silent mutations are usually harmless.
Contrary to expectations, the researchers found that polyamorous species were not more diverse overall than monogamous species, although the small number of species with polyamorous females showed greater genetic diversity.
According to Kees Wanders, a PhD student at the University of Bath and the study’s lead author, “Species evolve through natural selection, in which harmful mutations disappear from the population over the long term because affected individuals, or individuals, do not survive long enough to have the opportunity to reproduce with beneficial adaptations survive longer”.
“However, individuals also evolve through sexual selection, in which evolution is influenced by individuals competing for access to mates, so that only the most desirable traits are then passed on to offspring. »
Like fruit flies
“This study suggests that sexual selection is consistent with natural selection in birds and that deleterious 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 bird species are polyamorous, while most choose a mate for a season or even for life. There are several theories that aim to explain the evolution of polyamory in these species, but we found evidence that it increases the efficiency of natural selection by eliminating harmful mutations and avoiding the effects of incest,” he said researcher.
“This has previously been observed in the laboratory in fruit flies, but this is the first time it has been observed in wild bird populations. »
Another author of the study, Dr. Araxi Urrutia, points out “that the hypothesis is that in polyamorous species, if individuals have difficulty finding a mate and they have to travel further to do so, it would mean that they would have greater genetic diversity there in these.” Species.
“However, we were surprised to see that there was no evidence of this – instead, we found that these individuals had less harmful mutations. »
“Despite this obvious evolutionary advantage, most birds tend to stay in groups and raise their young that way, as it offers a better chance of survival for those offspring.” »