Unisexual hybrids break through an evolutionary dead end by two-way backcrossing

Area of Science:

• Evolutionary biology
• Genetics
• Reproductive biology

Background:

• Unisexual vertebrates, produced via clonal or hemiclonal reproduction, face challenges in purging deleterious mutations, potentially limiting their evolutionary lifespan.
• Hemiclonal reproduction (hybridogenesis) involves the elimination of one parental genome during oogenesis, resulting in haploid eggs from a single parent.
• Typically, hemiclonal hybrids are backcrossed with males of the paternal species.

Purpose of the Study:

• To investigate the potential return of hemiclonal genomes to the maternal gene pool in wild populations of greenlings (Hexagrammos).
• To determine if two-way backcrossing occurs and its implications for the genetic diversity and survival of hemiclonal lineages.

Main Methods:

• Utilized a specific cytogenetic marker to distinguish hemiclonal hybrid progeny from the maternal species.
• Observed mating frequencies of Hexagrammos hybrids with both maternal and paternal ancestors in a natural setting.

Main Results:

• Hexagrammos hybrids exhibited equal mating frequencies with both maternal and paternal ancestors.
• Demonstrated that hemiclonal genomes can be reintroduced into the maternal gene pool through observed backcrossing.

Conclusions:

• Two-way backcrossing, where clonal genomes return to the gene pool for recombination, is crucial for enhancing genetic variability in hemiclonal genomes.
• This process significantly reduces the extinction risk for hybrid lineages, potentially extending their evolutionary survival beyond initial predictions.