4.2 Genetic changes in invasive diploid populations
The loss of genetic diversity within invasive populations resulting from
genetic bottlenecks can be prevented or even reversed by multiple
introductions from the same or distinct sources, which have been
reported in many animals and plants, such as Pseudorasbora parva ,Coptotermes formosanus , Aedes albopictus , Ambrosia
artemisiifolia and Rosa rugosa (Baltazar-Soares et al., 2020;
Blumenfeld et al., 2021; Kelager et al., 2013; Sherpa et al., 2019; van
Boheemen et al., 2017). The invasive C. auratus in Tibet was
introduced from different sources, which was also evidenced by
phylogenetic analysis of diploid mitogenomes in this study, showing that
invasive individuals were clustered into two regionally defined lineages
of native individuals (i.e., the mid Yangzte River, the lower Yangzte
River and Huai River). The two lineages showed a low but significant
genetic differentiation (F ST: 0.0449) estimated
based on genomic SNPs. In general, recent hybrid populations from
diverse intraspecific source populations should possess higher genetic
diversity than that of individual source populations (Baltazar-Soares et
al., 2020; Simon et al., 2011; Smith et al., 2020). However, the genetic
diversity of invasive diploid population of C. auratus was only
slightly (9.0%) higher than that of source populations. Interestingly,
at the individual level, the genome-wide observed heterozygosity of
invasive individuals was significantly (21.4%) lower than that of
source individuals (Figure 5a). The discordance between genetic
diversity at the population and individual levels suggests that the
total invasive population derives from genetically distinct sources,
which may mask loss of variation at the population level during
invasion. Nevertheless, the observed low levels of inbreeding suggest
that founder events have still not had a significant biological impact.
In that sense, the results provide an illustration of factors that may
cause biological invasions to be associated with lower loss of genetic
variation than expected (Blumenfeld et al., 2021; Facon et al., 2006).
On a longer time scale, triploid C. auratus now dominate the
market (Liu, 2010), and the LL wetland is padlocked since becoming a
natural reserve zone since 1999 (Chen et al. 2018). Therefore, the
diploid invasive population is expected to receive very low supplements
of new invaders recently and in the future, which could accelerate loss
of genetic diversity.