Genetic Analyses confirm Hybridization in a Threatened Tern Species

New study finds evidence for hybridization between two tern species.

The global population of Chinese Crested Terns (Thalasseus bernsteini) comprises less than 100 individuals. All known breeding populations on mainland China and Taiwan are found within colonies of Greater Crested Terns (T. bergii). It is no surprise that mixed pairs were observed in these colonies. A new study in the ornithological journal Ibis now provides genetic evidence for hybridization.

 

terns

A Chinese Crested Tern mounting a Greater Crested Tern (picture by Lin Chen; Yang et al. 2018)

 

DNA analyses

Jia Yang and colleagues collected DNA samples from five Chinese Crested Terns, six Greater Crested Terns and three putative hybrids. The two species – which turned out the be sister species – shared little genetic variants, while the putative hybrids showed an intermediate genetic make-up. The analyses thus clearly showed that hybridization occurs. But it is not certain whether the hybrids are fertile and backcrossing occurs.

 

Curse or blessing?

Hybridization might pose another threat to the already endangered Chinese Crested Tern. Although it depends how you look at it. On the one hand, gene flow from Greater Crested Terns might introduce new genetic variation into the small gene pool of the Chinese Crested Tern. A kind of genetic rescue. On the other hand, hybridization might lead to genetic assimilation and eventually extinction.

If hybrids are sterile, hybridization will definitely be a threat. Producing sterile offspring is a waste of reproductive potential. And if there are less than 100 individuals left, you don’t want to waste anything.

 

Chinese_crested_tern_colony.jpg

A breeding Chinese Crested Tern (from http://www.wikipedia.com/)

 

Hubb’s Principle

Finally, the behavioural mechanism responsible for hybridization between these tern species is Hubb’s principle, where species with a small population size are more likely to mate with a more abundant species because members of its own species are difficult to find. When explaining this in the paper, the authors refer to my 2016 review paper where I introduce this concept in the context of goose hybridization. I really appreciate the citation (and recommend others to cite it as well…)

 

References

Yang, J., Chen, G., Yuan, L., Huang, Q., Fan, Z., Lu, Y., Liu, Y. & Chen, S. (2018) Genetic evidence of the world’s most endangered tern, the Chinese Crested Tern Thalasseus bernsteiniIbis

 

This paper had been added to the Charadriiformes page.

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