The results of the study indicate that evolution has calibrated the immune systems of a number of bird species over millions of years, enabling them to deal with diseases specific to the particular environment and climate in which they live.

Rapid climate change increases the risk that these tailor-made immune systems may be insufficient, and not only in birds. Emily O'Connor, one of the biologists behind the study, believes that the results could apply to certain other animals as well, as the immune system genes they examined are common to all vertebrates.

"Evolution may not be able to "keep up" with climate change. There is a risk that many animals simply will not be able to cope with changes in the number and type of pathogens that they will be exposed to," she says.

When the climate changes and, for example, northern Europe becomes warmer and wetter, diseases that previously have not existed in temperate climates could start to appear. This may present a challenge for some animals.

Emily O'Connor and her colleagues studied 37 different bird species living in different climatic regions. They investigated diversity in immune system genes in each species, which influences how effectively the immune system is able to combat diseases.

They also looked at temperature and precipitation for the different areas from 1901 to 2017. In this way, they have demonstrated that diversity of immune system genes a species has is related to the climate it lives in. Species that live their entire lives in tropical, rainfall-rich areas and do not move, have the most diverse immune system genes. This high diversity enables these species to handle more pathogens, according to the researchers.

Migratory birds that spend their winters in tropical areas and breed in temperate climates have immune systems similar to those of European resident birds. According to the researchers, this could be because they are able escape disease by moving.

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Journal Reference:

1. Emily A. O'Connor, Dennis Hasselquist, Jan-Åke Nilsson, Helena Westerdahl, Charlie K. Cornwallis. Wetter climates select for higher immune gene diversity in resident, but not migratory, songbirds. Proceedings of the Royal Society B: Biological Sciences, 2020; 287 (1919): 20192675 DOI: 10.1098/rspb.2019.2675