Species in the making: Genomic analyses reveal incipient speciation in the Ground Tit

Isolation in glacial refugia and the subsequent differentiation in habitat and morphology shaped the evolution of the Ground Tit.

Many bird species have adapted to life at the Qinghai-Tibet Plateau, about 4500 meters above sea level. Most of these species are endemic to this area and show no genetic structure. In technical terms, they are panmictic. A notable exception is the Ground Tit (Pseudopodoces humilis). This small passerine is comprised of two distinct populations, one in the central region of the Qinghai-Tibet Plateau and one in the east margin. A recent study in the journal Zoological Scripta reconstructed the evolutionary processes that shaped these two populations.

ground tit.jpg

A Ground Tit on the lookout in Nyingtri Prefecture, Tibet, China. © Cherry Wong | Oriental Bird Images

 

Desert or Ice Ages?

Previous genetic work on the Ground Tit uncovered two distinct lineages. But the origin of these populations was unclear. One study – using the mitochondrial control region – estimated the divergence of these lineages at ca. 1 million years ago. This would indicate that the separation was driven by the desertification of the Qaidam Basin. Another study – based on two mitochondrial genes – calculated that these populations diverged about 300,000 years ago. This date points to a glacial refugia scenario in which these populations became isolated in separate areas during the Pleistocene ice ages. To determine which scenario is more likely, a group of Chinese scientists sequenced the genomes of these birds and performed a suite of genetic and ecological analyses.

 

Demographic and Ecological Modelling

The genomic data confirmed the existence of two distinct lineages. Demographic modelling supported a scenario where these populations diverged about 100,000 years ago and subsequently continued exchanging genes. Gene flow was primarily from the edge to the platform population. This result suggests that the two populations have been isolated in separate refugia.

To validate this hypothesis, the researchers turned to ecological niche modelling. Reconstructing the range of the Ground Tit revealed that during the Last Glacial Maximum (about 20,000 years ago) both populations were smaller and resided in distinct margins of the plateau.

ground_tit2.jpg

A pair of Ground Tits near Hongyuan (Tibetan Plateau), Sichuan, China. © Ulrich Weber | Oriental Bird Images

 

Current Differentiation

A detailed look at the current populations shows that they are also differentiated in habitat and morphology. The platform population is restricted to higher altitudes and colder climates compared to the edge population. Regarding morphology, the populations differ in body weight, wing length and tail length. Putting everything together, the researchers nicely summarize their findings.

Our results based on genome‐wide data revealed an incipient speciation with unidirectional gene flow from the edge to platform populations, suggesting that both refugial isolation and the subsequent habitat differentiation and morphological
divergence have contributed and maintained the incipient speciation pattern between the platform and edge populations of the Ground Tit.

 

References

Jiang, Z.Y., Gao, B., Lei, F.M. & Qu, Y.H. (2019) Population genomics reveals that refugial isolation and habitat change lead to incipient speciation in the Ground tit. Zoologica Scripta, Early View.

Qu, Y. H. & Lei, F.M. (2009) Comparative phylogeography of two endemic birds of the Tibetan plateau, the white-rumped snow finch (Onychostruthus taczanowskii) and the Hume’s ground tit (Pseudopodoces humilis). Molecular Phylogenetics and Evolution, 51:312-326.

Yang, S.J., Yin, Z.H., Ma, X.M. & Lei, F.M. (2006) Phylogeography of ground tit (Pseudopodoces humilis) based on mtDNA: Evidence of past fragmentation on the Tibetan Plateau. Molecular Phylogenetics and Evolution, 41:257-265.

 

This paper has been added to the Paridae page.

Advertisements

One thought on “Species in the making: Genomic analyses reveal incipient speciation in the Ground Tit

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s