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Free keywords:
scorpaeniformes; postzygotic isolation; reference genome; hybrid speciation; hybrid zone
Abstract:
Cottus rhenanus and Cottus perifretum have formed hybrid lineages and narrow hybrid zones that can be best explained
through the action of natural selection. However, the underlying selective forces as well as their genomic targets are not well
understood. This study identifies genomic regions in the parental species that cause hybrid incompatibilities and tests whether
these manifest in a sex-specific manner to learn about processes that affect natural hybridization in Cottus. Interspecific
F2 crosses were analyzed for 255 markers for genetic mapping and to detect transmission distortion as a sign for genetic
incompatibilities. The Cottus map consists of 24 linkage groups with a total length of 1575.4 cM. A male heterogametic (XY)
sex determination region was found on different linkage groups in the two parental species. Genetic incompatibilities were
incomplete, varied among individuals and populations and were not associated with the heterogametic sex. The variance
between populations and individuals makes it unlikely that there are species-specific incompatibility loci that could affect
the gene pool of natural hybrids in a simple and predictable way. Conserved synteny with sequenced fish genomes permits to
genetically study the Cottus genome through the transfer of genomic information from the model fish species. Homology
relationships of candidate genomic regions in Cottus indicate that sex determination is not based on the same genomic regions
found in other fish species. This suggests a fast evolutionary turnover of the genetic basis of sex determination that, together
with the small size of the heterogametic regions, may contribute to the absence of fitness effects related to the Haldane’s rule
