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).