Abstract
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 PIM1duplicates 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.
Keywords: tree sparrow, rapid evolution, sperm, heavy metal
pollution, duplicate genes, PIM1