Fig. 1: Chrosomus eos-neogaeus fish complex.

Hybridization events between C. eos (EE) and C. neogaeus (NN) resulted in diploid hybrids (EN) that reproduce asexually by gynogenesis: unreduced eggs requiring sperm from males of a close species, such as C. eos, to initiate development⁶⁶. The sperm haplome (E’) may or may not be incorporated into the embryo (paternal leakage), resulting in either triploid individuals (E’EN) or diploid clones identical to their mother (EN)^66,67,68. The first generation triploids reproduce asexually: they reject the sperm haplome (E’) before meiosis and produce eggs with the hybrid genome (EN), in a process called ameiotic hybridogenesis ^27,28. Again, the sperm haplome (E*) may or may not be incorporated into the embryo, leading to triploid (E*EN) or diploid individuals. These second-generation triploids reproduce sexually: they reject the C. neogaeus haplome (N) before meiosis and produce reduced C. eos haploid eggs in a process called meiotic hybridogenesis ^27,28. Fertilization by a C. eos sperm results in the production of C. eos individuals. See²⁸ for a more extensive description of the complex and²⁷ for a more detailed description of the gametogeneses employed by the members of this complex. Legend: Solid lines indicate the fusion of the paternal genome with the maternal genome in the embryo; dashed lines indicate the exclusion of the paternal genome from the embryo. Figure adapted from²⁸.