4.4 Candidate genes within genomic regions of putative sweeps
The regions with potential selective sweeps for invasive diploid
populations of C. auratus were widely detected across the genome.
The SNPs within these regions were annotated to 191
candidate genes with enriched GO
terms mainly related to
mannosidase activity and embryo
development (Table S4). The biological significance of selection in
genes related to mannosidase are not immediately obvious, although in
humans mannosidase deficiency can cause disease, such as congenital
dyserythropoietic anemia (Moremen, 2002). The selective sweeps related
to genes involved in embryo development may be attributed to an
advancement of spawning time in Tibet (Liu et al., 2015a) and subsequent
exposure of embryos to the cold waters. The water temperature during
reproduction period is about 20 °C in the native range (e.g. the mid and
lower Yangtze River) and is below 10 °C in the invasive range (Huo et
al., 2013; Zhang et al., 2016). Low temperature exposure can increase
the mortality and frequency of abnormal larvae in C. auratus(Wiegand et al., 1989), resulting in individual selection during
embryonic development.
For triploids, selection occurs at the whole individual level owing to
the asexual gynogenesis and would be expected to be low, as numbers of
mitogenome haplotypes and genetic diversity in invasive populations were
not reduced as compared to the source populations. Hence, it is doubtful
whether signals of selective sweeps found in invasive triploids were
actual targets of selection; more likely these signals would derive from
the process of establishment of triploids from diploid ancestors. It is
nevertheless interesting that one enriched GO term found in triploids is
‘development of secondary sexual characteristics’. A previous study has
shown that the ratio of males among invasive triploid C. auratusin Croatia was only 2.3% which was lower than that reported in the
native range (Gui & Zhou, 2010; Jakovlic & Gui, 2011). It would be of
interest to further investigate the ratio of males in Tibet.