PhD from the University of New Mexico Candidate Ethan Gyllenhaal has been involved in a series of research projects that use genomic analyzes to explain the complex evolutionary processes that take place within and between populations of island birds. He is conducting this research in collaboration with researchers at the UNM Andersen Lab and the University of Kansas Moyle Lab.
One of his recent projects, described in an article published in Molecular ecology, explains the existence of an unexpected genetic discovery in Australian Spectacled Monarch birds.
Most of us think animals fit neatly into a separate, static category called species, but the reality of classifying animals is much more complex. Sometimes a species can split into two when groups of animals are geographically separated and allowed to adapt to different environments.
This phenomenon, called allopatric speciation, is responsible for much of the biodiversity around us, such as the stark difference, for example, between the squirrels on either side of the Grand Canyon. Other times, species may blend into each other to form a continuum, as observed by Mallet, Beltrán, Neukirchen, and Linares in the Heliconius kind of butterflies that are found in all the Americas.
Gyllenhaal’s work focuses on how these types of speciation processes occur in bird populations living on and around islands. One of his recent projects used genomic analysis to uncover the history of crossbreeds between the Spectacled Monarch birds of Australia and the Spotted-winged Monarch birds of neighboring New Guinea.
Analysis of specimens of Spectacled Monarchs had shown a curious genetic discovery: the mitochondrial DNA (the specialized DNA used by the energy-generating mitochondria of a cell) of some specimens of Spectacled Monarchs did not match nuclear DNA used by whole cells. These specimens of Spectacled Monarchs appeared to contain mitochondrial DNA from spotted-winged monarchs, raising questions about a possible crossbreeding history between the two species.
To explain how this genetic scarcity happened, the Andersen Lab team needed to create a consensus reference assembly for the targeted genomic regions – a DNA sequence code that can be used to represent anyone’s DNA. members of a population – for the Spectacled Monarch and related. species. This type of reference requires an incredible amount of compute memory to assemble, which is why Gyllenhaal and his colleagues used the Xena high memory nodes from the Center for Advanced Research Computing to perform their calculations.
While it is almost impossible to conclude with certainty that natural selection played no role in the development of genetic mismatch in spectacle monarchs, the findings of the Andersen group are consistent with the conclusion that a cross had long ago, between the Australian Spectacled Monarch and the new Guinea Spotted-winged Monarch.
Gyllenhaal explains, “I think the Australia-New Guinea division was somewhere in the realm of, I believe, 2-3 million years ago. [ago]… And the mitochondrial DNA seemed to have been, as we call it, “captured” from the population of New Guinea to the population of Australia somewhere in the order of… 200 to 400,000 years ago.
In other words, around 200 to 400,000 years ago, the geography of the region allowed New Guinea birds to interbreed with Australian birds, leaving some Spectacled Monarchs with winged monarch mitochondrial DNA. spotted which persists in the population today. This was due to the lower sea level during the Pleistocene ice cycles, which exposed a vast expanse of land connecting the two land masses, known as the Sahul Plateau.
Since the publication of this article, Gyllenhaal has continued his study of island birds with four different projects. His ongoing research examines distinctions between bird species in the Solomon Islands, variation in bird plumage in Fiji, and island biogeographic factors that affect evolutionary changes in birds.
Gyllenhaal summarizes the findings of his research to date, reporting: “[One of] the two main takeaways from published and ongoing work are that on the islands you get a lot of stuff that seems to be [discrete] species, but when they have this ability to reconnect, they will easily swap genes to the point of merging populations. The other is just … the porous[ness of the] boundaries between those species that live on different islands and have never essentially had their species boundaries tested.
Gyllenhaal’s work was funded by the University of New Mexico and the National Science Foundation.