HOW THE HOUSE SPARROW CAME TO BE
House sparrows are closely associated with humans and are found across the world. However, the origins of this association are poorly understood. By investigating the DNA of sparrows from Europe and the Middle East, biologists are learning more about how this species has become so familiar to us.
Researchers at the Centre for Ecological and Evolutionary Synthesis (CEES) at the University of Oslo (UiO) have been trying to answer this question by sequencing the DNA of populations of house sparrows from across Europe and the Middle East. Teaming up with colleagues from Iran and Kazakhstan, they also investigated the Bactrianus sparrow, a subspecies found only in these regions. The Bactrianus sparrow looks like a house sparrow but is wild, avoids human contact and feeds on a very different diet. By comparing the DNA of the two sparrows, the team hoped to gain some insight into why one evolved to be closely associated with people while the other did not.
“Our findings suggest the house and Bactrianus sparrows probably split from each other about 11,000 years ago, around the time that humans were developing agriculture in the Middle East.” says researcher, Mark Ravinet. “We also found evidence that the number of house sparrows greatly increased around 6000 years ago” adds Ravinet, speaking about a new paper from the team, published this week in the Proceedings of the Royal Society of London B. This ties in well with previous suggestions that the spread of house sparrows was closely associated with the spread of early agriculture.A close association with humans has had a profound effect on house sparrows. Earlier work by the team has shown that hybridization between the house sparrow and Spanish sparrow (Passer hispaniolensis) gave rise to the Italian sparrow (Passer italiae) in the Mediterranean. This likely occurred when house sparrows moved into Europe alongside early agriculturalists. But now the team have also identified evidence that suggests house sparrows have evolved specific adaptations to life alongside humans.
“We found several genes which seem to have been under strong recent natural selection in the house sparrow, but not in its wild close relative.” says Ravinet. These include two genes which occur right next to each other, one involved in the formation of the skull and the other involved in digesting starch. “The skull gene is interesting because we know that house and Bactrianus sparrow skulls differ in shape” Ravinet explains, “but we were really excited to see the digestion gene there too”. Interestingly, this gene is part of a family of genes which help both humans and dogs digest starch and which are closely linked with a transition to an agricultural-based diet.
It seems then that just as the house sparrow has had an influence on our culture, we have played a role in shaping its biology. “We still have some way to go to investigate this further” says Ravinet, “but it is exciting to think that the evolution of a species so familiar to us is tightly linked to a major event in the development of modern human civilization”.
Ravinet, M, Elgvin, T.O, Trier, C, Aliabadian, M, Gavrilov, A & Sætre, G.P (2018) ‘Signatures of human commensalism in the house sparrow genome’, Proceedings of the Royal Society of London, B, 20181246.
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