Fig. 1: Schematic overview of gametogenesis and reproduction of diploid and triploid hybrids within C. hankugensis-I. longicorpa complex (redrawn from refs. 38,41,44).
From: A cyclical switch of gametogenic pathways in hybrids depends on the ploidy level
After crosses of two parental sexual species, Cobitis hankugensis (HH, marked in blue) and Iksookimia longicorpa (LL, marked in orange), diploid hybrids (HL) are produced with the mitochondrial DNA (designated as ‘mt’) from one of the sexual species (L). Diploid hybrids form diploid clonal gametes with ‘L’ mtDNA. After fertilization of such eggs by sperm of one of the parental species, triploid hybrids with L mtDNA appear (HHL). In triploids, a single-copied genome (L) is eliminated during their gametogenesis, and the remaining haploid gametes (HH) produce haploid ‘H’ gametes with ‘L’ mtDNA. After fertilization of such gametes by sperm from C. hankugensis, diploid sexual species appear but with ‘L’ mtDNA. After fertilization of gametes produced by triploids by sperm from the other parental species, I. longicorpa, new diploid hybrids appear with ‘L’ mtDNA. Q1-3 indicates the gap of knowledge in studied asexual hybrid complex: Q1. The cytogenetic mechanisms underlying unreduced gametes formation by diploid hybrids; Q2. Gametogenic stage and mechanisms of putative genome elimination in triploid hybrid females; Q3. Gametogenic alteration underlying hybrid sterility in triploid hybrid males.
