Title: The evolution of reproductive mode in the Carassius auratus complex
Abstract:
Freshwater fish of the genus Carassius are widely spread in Asia, Europe, and Australia. This includes the Carassius auratus complex, a phylogenetically diverse species complex with uncertain taxonomy. The C. auratus complex is native to Asia but has been introduced to non-native habitats throughout the world. It includes sexually reproducing, diploid as well as polyploidy individuals, which predominately reproduce asexually through gynogenesis. The evolutionary relationship between the different reproductive modes as well as the invasion history of different lineages are poorly understood. A phylogenetic approach using mitochondrial DNA Cyt b sequence in combination with six microsatellites markers was used to investigate the invasion history of different lineages and reproductive modes and to understand the evolutionary relationship between different reproductive modes. The Cyt b analysis was based on sequences from 10 native populations from China and 35 invasive populations from Europe and Australia. Furthermore, 1427 individuals representing 93 populations from China, Europe and Australia were genotyped at six microsatellite loci to determine their level of ploidy and reproductive mode. Furthermore, phylogenies of three nuclear genes were used to test two different hypotheses of the origin of triploid lineages, allopolyploidy and autopolyploidy.
We suggest that the invasion of C. auratus complex in Europe went through two routes, was could have been driven by both historical and anthropogenic events. The microsatellite analysis revealed 67.19% of individual’s triploids and 33.8% diploids were discovered among 1427 individuals. Interestingly, most of the native populations consisted of a mixed of diploids and triploids but were dominated by triploid individuals. While invasive populations showed a considerable variety in reproductive mode ranging from purely diploid to purely triploid and mixed populations. Additionally, diploids are dominant in older Eastern European populations whereas triploids are dominant in more recently established in Central European populations. Using both mtDNA and Microsatellite’s markers revealed the absence of separation on the ploidy level. Alleles shared by both diploid and triploid individuals while sympatric diploids and triploids share mtDNA haplotypes in the seven highly diverged lineages and sublineages. Moreover, high genetic diversity in triploid forms can be through propagule vectors, which compensate genetic bottleneck effects in successfully invasive species. The origin of gynogens could not be resolved by nuclear DNA using Rag1 and S7 genes, as Rag1 analysis showed that are originated from allopolyploid while S7 shows that it is the result of autopolyploid. The C. auratus complex provides an ideal model for studying the reproductive traits of polyploids triploids, which is of great value in animal genetics and reproductive biology.
