All-Female Hybrid Fish Switch Male Partners For Variety

By switching mating species, an all-female hybrid fish species has sustained its survival through thousands of years.

AsianScientist (Oct. 24, 2016) – A hybrid species of all-female fish in the north Pacific Ocean may have survived for an uncharacteristically long period of time by switching mating species, researchers in Japan have found. Their work was published in Ecology and Evolution.

Some animal species are comprised of female-only members, giving themselves a competitive advantage over species that produce both male and female offspring. Since the females are capable of bearing offspring, they can quickly outnumber other species in which half the population—the males—do not. However, these all-female species are disadvantaged due to a lack of variety in their gene composition. This affects their ability to develop genetic adaptations to environmental changes and parasitic attacks—and thus their long-term survival as a species.

One all-female species of fish has found a way to get the best of worlds. Researchers from Hokkaido University have found that a hybrid strain of north Pacific Ocean greenling fish belonging to the genus Hexagrammos boosts its long-term survival by switching from males in one species to another in the same genus.

The team led by Dr. Hiroyuki Munehara analyzed the genes of two naturally-occurring hybrid greenling strains: Hexagrammos octogrammus/H. agrammus (Hoc/Hag) and H. octogrammus/H. otakii (Hoc/Hot). They also looked at the genes of the fish that provided these hybrids with their original maternal genetic material, H. octogrammus (Hoc).

The hybrids produce all-female offspring, but they mate with males whose sperm activate the egg to start development. Both the male and female genetic material play roles in the newly-developing embryo, but only the female genome is inherited by the subsequent generation because the male material is excluded when the offspring form their own eggs.

By comparing the genes of the three species, the researchers were able to form a genealogical tree that showed that the species Hot and Hag, which provide the hybrid species with the male genetic material, diverged from their common ancestor around 1.5 million years ago.

Their analysis revealed that Hoc/Hot hybrids did not originate as a result of breeding between Hoc and Hot. Rather, hybrid Hoc/Hag females switched from breeding with Hag males to breeding with the larger Hot males that would better protect their eggs. This ‘host switch’ is thought to have first occurred approximately 2,000 to 20,000 years ago and is likely a reason that these hybrids have managed to survive for so long.

The article can be found at: Munehara et al. (2016) Origins of Two Hemiclonal Hybrids among Three Hexagrammos Species (Teleostei: Hexagrammidae): Genetic Diversification through Host Switching.


Source: Hokkaido University; Photo: Nagaaki Sato.
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