4.3 No genetic change in invasive triploid populations
Triploids are considered an evolutionary ‘dead end’ because they lack
meiotic recombination and thus accumulate deleterious mutations (Butlin,
2002). Such ‘disadvantage’ in triploids may become an advantage in terms
of avoiding inbreeding and thus being better colonizers than diploids
(Avise, 2008). In the present study, the lack of change of
genetic diversity and structure
in invasive triploid populations is to be expected, given the
pattern of asexual gynogenesis
which produces clonal offspring from mothers (Wang et al., 2022).
This reproductive mode may make
triploid C. auratus a more powerful invader in novel environments
compared with the sexual diploid form. Firstly, parthenogenesis enables
triploids to avoid negative impacts of bottlenecks and inbreeding on
genetic diversity during invasion (Avise, 2008; Roman & Darling, 2007).
Secondly, eggs of triploids can be activated by the sperm of both
conspecific and non-conspecific fishes, providing more chances for
reproduction. Concerning adaptability, the pros and cons of invaders
being triploid are less clear-cut. On one hand, triploids possess
slightly higher genetic diversity and frequency of heterozygous loci
(Liu et al., 2017b; Luo et al., 2014) which would be an advantage in the
case of overdominance. On the other hand, the lack of meiosis and sexual
reproduction precludes reshuffling of allelic variation at loci
influencing polygenic traits, hence precluding adaptive responses. As a
whole, experiences from different organisms do suggest stronger
invasiveness of asexual forms as compared to sexual forms (Donne et al.,
2020; Pandit et al., 2011).