Remarkably Duplicate Genes as Sources for Rapid Adaptive Evolution of Sperm under Environmental Pollution in Tree Sparrow

Environmental pollution can result in poor sperm quality either directly or indirectly. However, adaptive and compensatory sperm morphology change and motility improvement rapidly evolved in tree sparrow (Passer montanus) inhabited the polluted area within the past 65 years. To identify the genetic underpinnings of the rapidly evolved sperm phenotype, both the population genomic and transcriptomic methods were used in our study. We identified a gene encoding serine/threonine protein kinase PIM1 which may drive the rapid phenotypic evolution of sperm. An unprecedent and remarkably expansion of PIM gene family caused by tandem and segmental duplication of PIM1 was subsequently noticed in tree sparrow genome. Most of the PIM1 duplicates showed a testis-specific expression pattern, suggesting their functions related to male reproduction. Furthermore, the elevated expression level of PIM1 was consistent with our earlier findings of longer and faster swimming sperm in polluted site, indicating an important role of duplicated PIM1 in facilitating rapid evolution of sperm. Our results suggested that the duplicated PIM1 provide sources of genetic variation that enable rapid evolution of sperm under environmental heavy metal pollution. The findings in this study verified the duplicated genes can be targets of selection and predominant sources for rapid adaptation to environmental change and shed lights on the sperm evolution under environmental stress.