Having sex results in healthier fish

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A mini-Olympics for fish has shown scientists why asexual fish can never take over the world.

Using speed as a marker, researchers from the University of British Columbia looked at why the hybrid fish produced when red-bellied dace (Phoxinus eos) and a finescale dace (Phoxinus neogaeus) mate aren’t more successful.

These hybrids are the only asexual vertebrates in North America. They have the ability to reproduce asexually (without a mate) and are found across the continent. They need sperm from either species to stimulate egg development but not for the genetic makeup of the offspring.

So in theory, these hybrids should be extremely successful as they do not need a mate to produce offspring. In reality the asexual hybrids live alongside the sexual reproducing dace and do not manage to out-compete them.

The scientists found that using speed as a measure of overall health that the hybrids simply weren’t as healthy as the parent species. In a series of speed tests they found that hybrids performed worse than at least one of the parent species.

It is likely that at best the hybrids have no physiological advantage over the sexual species and at worst that they may actually be at a physiological disadvantage to the parent species, especially as they are often found to harbour more parasites on their fins than sexuals.

This means that any advantage to asexual reproduction is outweighed by the physical failings of the fish. So while in theory asexual fish would could out-compete any sexual fish, in practise sexual reproduction always wins, which I am sure will come as a great relief to many...

For more information see: Mee, J. A., C. J. Brauner, E. B. Taylor 2011. Repeat swimming performance and its implications for inferring the relative fitness of asexual hybrid dace (Pisces: Phoxinus) and their sexually reproducing parental species. Physiological and Biochemical Zoology.