Sperm motility analysis of Cobitis hankugensis, Iksookimia longicorpa (Teleostei, Cypriniformes, Cobitidae) and their unisexual natural hybrids

Hybrid sterility is an inevitable phenomenon in the speciation process to avoid indiscriminate increases in species, but it is not always unconditional. We used computer assisted sperm analysis (CASA) to analyze sperm motility of Cobitis hankugensis, Iksookimia longicorpa, and their unisexual natural hybrids. In parental species, the sperm concentrations of C. hankugensis and I. longicorpa were 11.6 ± 4.8 × 109 and 16.5 ± 6.8 × 109, respectively. For sperm motility, the total motility was higher in the parental species (C. hankugensis, 91.3%; I. longicorpa, 87.5%) than other hybrids. After 1 min, the motility duration was reduced to 14% in C. hankugensis and 3.3% in I. longicorpa. This result could indicate that the duration of sperm motility of C. hankugensis is longer than that of I. longicorpa up to 1 min after spermatozoa activation. All of the hybrids had a low concentration and it was distinct from their parent species. Total motility and other velocity parameters also showed significantly lower values except for the HHL (one from the C. hankugensis genome with two from the I. longicorpa genome) type motility measurement (13.6%). These results suggest that the hybrids derived from C. hankugensis and I. longicorpa, are not completely infertile, contrary to histological observations. Cobitis hankugensis–Iksookimia longicorpa hybrids and its parental species (left panel). Upper right panel: computer‐assisted sperm analysis (CASA) analysis snapshot of parental species and hybrid species. Lower right panel: total motility (A) and average path velocity (B) of Cobitis hankugensis—Iksookimia longicorpa hybrid and their parental species for 60 s after activation. Research Highlights The total motility was higher in the parental species than hybrids and was maintained for 1 min. Only HHL hybrid showed exceptionally high motility values, suggesting that hybrids may not be completely infertile.