Siberian jays, Perisoreus infaustus, display quite a bit of nepotism when it comes to foraging in northern Scandinavia and on the taigas of Siberia. It makes evolutionary sense to share a large carcass with family (however extended) rather than with random birds. And according to new findings published in Molecular Ecology, these birds have evolved the ability to identify distant and unfamiliar relatives – gradually increasing their aggression with decreasing levels of relatedness.
Kinship drives a lot of the cooperation we see between animals. By helping out closely related individuals, they propagate their own genes. It’s called inclusive fitness, and it explains why some mammal, bird, and fish species can recognize siblings they may have never met before. But what about distantly related individuals they’ve never met?
To see if genetic relatedness influences aggressive interactions, a team led by University of Zurich’s Michael Griesser observed dozens of groups of Siberian jays foraging at feeders baited with pig fat near Arvidsjaur, Sweden, during non-breeding season in 1999, 2008, and 2009. The researchers fitted them all with a metal ring and a couple of plastic colored ones for identification. They also took a small 50-microliter blood sample from each to determine sex and genetic relatedness.
These crow relatives live in family groups of up to seven members who share a territory, but only the breeding pair is reproductively active. The non-breeders are either offspring that stayed behind or birds that immigrated early on in their lives. Dominant juveniles typically expel their subordinate siblings, forcing them to join groups that are at least four territories away. Parents protect their chicks from predators and share food with them, sometimes for years after they’ve become fully fledged. But the breeding pair behave aggressively towards non-breeding immigrants – displacing them or chasing them away from their food (pictured above and below). While immigrants are potential future mates, they could also reduce nestling condition.
This is a male non-breeder approaching a breeding pair. UZH
Breeding pairs, the team discovered, are especially aggressive toward the most distantly related group members. "Siberian jays are able to recognize fine-scale differences in their kinship to other individuals, even to individuals that are unfamiliar to the breeders before they settle in their group," Griesser says in a statement.
Yet, when the researchers switched their nestlings, the parents tolerated these swapped chicks just as well as their own. They must have different mechanisms for recognizing socially unfamiliar birds and their own offspring. So, how the jays are able to assess degree of kinship is still a bit of a mystery. Griesser suspects that it’s visual, he tells IFLScience, though they don’t have proof of that right now.
Siberian jays likely evolved this ability because of their cooperative behavior. Several groups can gather at the carcasses of large herbivores – like moose or reindeer killed by wolves, bears, or cars – so tolerating unfamiliar relatives is an evolutionary advantage. And knowing who’s closely related and who’s not also helps avoid inbreeding.
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