Genetic and karyotype divergence between parents affect clonality and sterility in hybrids

Abstract

Asexual reproduction can be triggered by interspecific hybridization, but its emergence is supposedly rare, relying on exceptional combinations of suitable genomes. To examine how genomic and karyotype divergence between parental lineages affect the incidence of asexual gametogenesis, we experimentally hybridized fishes (Cobitidae) across a broad phylogenetic spectrum, assessed by whole exome data. Gametogenic pathways generally followed a continuum from sexual reproduction in hybrids between closely related evolutionary lineages to sterile or inviable crosses between distant lineages. However, most crosses resulted in a combination of sterile males and asexually-reproducing females. Their gametes usually experienced problems in chromosome pairing, but females also produced a certain proportion of oocytes with premeiotically duplicated genomes, enabling their development into clonal eggs. Interspecific hybridization may thus commonly affect cell cycles in a specific way, allowing the formation of unreduced oocytes. The emergence of asexual gametogenesis appears tightly linked to hybrid sterility and constitutes an inherent part of the extended speciation continuum.

Sperm specificity and potential paternal effects in gynogenesis in the Amazon Molly (Poecilia formosa)

“…In another gynogenetic complex, asexual reproduction may be a strategy to overcome hybrid sterility as demonstrated by gynogenetic Cobitis elongatoides and C. taenia hybrids ( Dedukh et al, 2020 ). As genetic divergence in the parental species increases, the karyotype of the hybrid gynogenetic species has greater heterozygosity providing greater hybrid vigor ( Marta et al, 2023 ). However, viable hybrid species, such as P. formosa , suggest that interspecies reproduction may not always be highly specific.…”