Islands in the Andes: Are populations of the Plumbeous Sierra-finch in Ecuador genetically distinct?

Recent study points to population expansion during the Last Glacial Maximum.

The sponge of the Andes. That is how the Páramo ecosystem is sometimes called. This collection of lakes, peat and grasslands can be found at 3500 meter above sea level and higher. These pockets of vegetation are separated by valleys and glaciers, giving rise to an ecological archipelago of Páramo islands. Birds (and other organisms) living on these “islands” might get isolated and gradually evolve into different species. A recent study in the Journal of Ornithology checked whether this is happening to the Plumbeous Sierra-finch (Geospizopsis unicolor).

Plumbeous_Sierra-finch.jpg

The Plumbeous Sierra-finch (Geospizopsis unicolor) © Allan Drewitt | Flickr

 

Haplotypes

Elisa Bonaccorso and her colleagues collected samples from 17 locations across the Ecuadorian Andes. Genetic analyses of two mitochondrial markers revealed no genetic differentiation between different Páramo islands. Indeed, the haplotype network shows that different islands (the colors) share the same haplotypes (the circles). If there was genetic differentiation, the circles would have distinct colors.

This pattern can be explained in several ways. Possibly, the finches are not isolated on their respective Páramo islands and they can travel between islands over low ridges (so-called “nudos”). This would result in gene flow between neighboring islands. Alternatively, the birds have been isolated for an insufficient amount of time to develop genetic differentiation.

finch_map_haplo.jpg

(A) Sampling locations in Ecuador and (B) the resulting haplotype network. The sharing of different haplotypes (the circles) by different islands (the colors) show that there is no genetic differentiation between the islands. From: Bonaccorso et al. (2019) Journal of Ornithology

 

Last Glacial Maximum

The second explanation (isolated for an insufficient amount of time) is supported by other analyses. The researchers used ecological niche modelling to reconstruct the range of the Plumbeous Sierra-finch during the Last Glacial Maximum (21,000 years ago) and the Middle Holocene (6,000 years ago). During these periods, the Páramo extended to lower elevations and connected the now isolated islands. This might have facilitated gene flow between different finch populations. Moreover, the genetic data indicated a population expansion between 14,000 and 28,000 years ago.

These findings support a scenario in which populations from different Páramo islands came into contact during the Last Glacial Maximum. However, the authors caution that more research with genomic data is needed to confirm this hypothesis.

 

References

Bonaccorso, E., Rodríguez-Saltos, C., Vélez-Márquez, A., & Muñoz, J. (2019). Population genetics of the Plumbeous Sierra-finch (Geospizopsis unicolor) across the Ecuadorian paramos: uncovering the footprints of the last ice age. Journal of Ornithology, 1-9.

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