Sperm can evolve in a few generations in response to environmental stress, but we know little about the molecular mechanisms that allow such rapid adaptation. Tree sparrows (Passer montanus) in the heavy-metal-polluted city of Baiyin in western China show longer and faster sperm than sparrows from unpolluted, nearby Liujiaxia, suggesting sperm adaptation to heavy pollution. Writing in Molecular Ecology, Wang et al. use comparative genomics to study sperm evolution in sparrows from these two locations. Combining analysis of signatures of selection based on genome sequences with gene-expression analysis, the authors identify PIM1 (a gene that encodes a serine/threonine protein kinase) as a candidate for being involved in sperm evolution. Looking at other avian genomes, the authors show a large-scale expansion of the PIM gene family in several lineages — as well as of seven other gene families adjacent to PIM — caused by the duplication of PIM1. Analysis of gene-expression levels of PIM1 duplicates in different tissues in birds from the two sites showed that PIM1 is expressed only in testes. Expression levels of PIM1 were higher in sparrows from polluted Baiyin than in those from unpolluted Liujiaxia. However, the authors did not find changes in sperm traits or PIM1 expression levels when they experimentally inhibited PIM1 in tree sparrows from Liujiaxia. These results suggest that PIM1 expansion might have facilitated sperm adaptation to pollution in Baiyin sparrows, but more work is necessary to unravel the molecular mechanism that regulates PIM1 expression levels.
Original reference: Mol. Ecol., https://onlinelibrary.wiley.com/doi/10.1111/mec.16833 (2022)
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