IN-SITU HYBRIDIZATION; FRESH-WATER FISH; UNISEXUAL SALAMANDERS; MOLECULAR EVOLUTION; LOACHES COBITIS; GENUS AMBYSTOMA; SEQUENCE DATA; LIKELIHOOD; POLYPLOIDY; IDENTIFICATION

Interspecific hybridization, polyploidization and transitions from sexuality to asexuality considerablyaffect organismal genomes. Especially the last mentioned process has beenassumed to play a significant role in the initiation of chromosomal rearrangements, causingincreased rates of karyotype evolution. We used cytogenetic analysis and molecular datingof cladogenetic events to compare the rate of changes of chromosome morphology and karyotypein asexually and sexually reproducing counterparts in European spined loach fish(Cobitis). We studied metaphases of three sexually reproducing species and their diploidand polyploid hybrid clones of different age of origin. The material includes artificial F1hybrid strains, representatives of lineage originated in Holocene epoch, and also individualsof an oldest known age to date (roughly 0.37 MYA). Thereafter we applied GISH techniqueas a marker to differentiate parental chromosomal sets in hybrids. Although the sexualspecies accumulated remarkable chromosomal rearrangements after their speciation, weobserved no differences in chromosome numbers and/or morphology among karyotypesof asexual hybrids. These hybrids possess chromosome sets originating from respectiveparental species with no cytogenetically detectable recombinations, suggesting theirintegrity even in a long term. The switch to asexual reproduction thus did not provoke anysignificant acceleration of the rate of chromosomal evolution in Cobitis. Asexual animalsdescribed in other case studies reproduce ameiotically, while Cobitis hybrids describedhere produce eggs likely through modified meiosis. Therefore, our findings indicate that theeffect of asexuality on the rate of chromosomal change may be context-dependent ratherthan universal and related to particular type of asexual reproduction.