Unpredictable environments may help explain the evolution of cooperative behavior, according to a decade-long study of Kalahari Desert birds. Research has shown that white-browed weaving sparrows (Ploceasser mahali) work to rear the offspring of other birds as a strategy to cope with periods of dry weather. The results are among the first to support an evolutionary theory called altruistic betting coverage, which states that traits can emerge to reduce reproductive variability, even if they do not increase the number of offspring produced overall.

“A large number of studies have highlighted the role that kinship and kinship within families can play in the evolution of cooperation,” says Andrew Young, evolutionary biologist at the University of Exeter in the Kingdom. -Uni, who led the research, Posted in Scientists progress. “But one thing we didn’t have a good grasp on was the ecological factors. “

Weavers live in family groups, with a single breeding pair and up to 10 non-breeding helpers who feed and provide food for the chicks. Rainfall is unpredictable in the Kalahari and food is scarce during times of drought.

The results showed that the groups with the most helpers significantly improved the number of chicks reared in dry conditions. The reverse was also true: the groups with the most helpers raised fewer chicks in wet weather. This effect was robust enough that aids reduced breeding success overall, suggesting that cooperative behavior evolved as it reduced variation in breeding due to weather conditions.

The hedging strategy works because the most important consideration is relative physical condition – how many offspring each group produces relative to the others. Although groups with a lot of helpers are affected in wet weather, the success of the assisted offspring of these groups during dry periods more than makes up for it. “An offspring is actually worth a lot more under bad conditions than under very good conditions,” Young says. “Because you could contribute from one to a thousand [offspring] in good conditions, but one of ten offspring that survive in your competitor pool in dry conditions.

The article offers some of the earliest empirical evidence for altruistic betting coverage, according to Patrick Kennedy, an evolutionary biologist at the University of Bristol, UK. “It’s a convincing demonstration of this effect in the wild, and it’s incredibly comprehensive,” he says.

Kennedy notes that if the researchers recorded only average reproductive success, they might assume the aids were unnecessary. “This article is really interesting,” he says, “because it disentangles how the effect of assistants is different in different environmental states.”

The evolutionary mechanism is a form of kinship selection, which explains how and why animals help related animals even when such behaviors do not directly help the individual pass on their own genes. Because assistant weavers are the older siblings of the chicks they help feed, they indirectly aid in the spread of shared genes.

The researchers tested the effects of the aids by observing 400 broods born to 68 mothers in 36 social groups in the Tswalu Kalahari reserve in the Northern Cape Province of South Africa. “They are fantastic birds,” Young says. “The name mahali means fierce and they have quite a attitude.

The results showed that only females help raise the chicks. Removal of male auxiliary birds from groups had no impact on the number of offspring produced. This is important, says Young, because it shows that the increase in the number of chicks produced by helpers in dry conditions is not simply the result of the larger group size.

Researchers aren’t sure why groups with more helpers actually produced less offspring in humid conditions. One possibility is the increase in predator visits, possibly due to additional birds at the nest attracting more attention.

The study highlights the value of long-term studies and data sets, says Dustin Rubenstein, an evolutionary ecologist at Columbia University in New York City, who first proposal the concept of cooperative breeding as a betting hedging strategy ten years ago. And the weavers made perfect subjects. “They don’t live that long,” says Rubenstein, “so you can look at lifelong reproductive success for more individuals. “

About 5% of mammals show cooperative breeding behavior, Rubenstein adds, including lions, elephants, mongooses, meerkats and wild dogs. But the longer lifespan of these animals makes long-term studies less practical. “There are huge variations among social insects,” he adds, “so it would be interesting to look at a wider range of these”.

Young and his group would then like to look at other ways the cooperation could benefit the birds, beyond breeding success. Mothers who don’t have to forage for food might be able to put more effort into improving the quality of eggs, for example. “There is evidence that it can accelerate its investment in the egg stage,” he says.