Abstract
In Europe, two bisexual fish species, Cobitis taenia (TT) and Cobitis elongatoides (EE), hybridized, producing diploid and polyploid clonal lineages. This study compared, for the first time, embryonic development, hatching success, sex ratio, body size and as well as reproductive ability based on the gonad histology of F1 reciprocal diploid hybrids (TE, ET) of both species. Hybrid F1 progeny showed the same proper pattern of embryonic and larval development. Among TE and ET offspring, slightly more females and males, respectively, occurred, but sex parity among 18-month-old hybrids was observed. Two- and three-year-old F1 hybrid females were mature, possessing all stages of oogenesis in their ovaries. Females (TE) back-crossed with C. taenia males had properly developing progeny. In testes of two- and three-year-old F1 hybrids, only early stages of spermatogenesis and pyknotic cells indicating the degeneration process were observed, but they exhibited an external feature (lamina circularis) of maturation. The results were confirmed by the structure of gonads that two sexual species, C. taenia and C. elongatoides, hybridize, producing F1 progeny of sterile males and fertile females. Hybrid females may participate in subsequent steps of speciation via hybridization and polyploidy or, on the contrary, represent an element of new species isolation.
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