Despeciation, once thought impossible, merged separate species of Madagascan birds back into one.
The finches of the Galapagos Islands famously sparked Charles Darwin’s epiphany on his theory of evolution. But a group of birds from a different tropical island has reversed the common assumption that evolution only creates ever more complex and distinct organisms. Scientists from the Field Museum at the University of Chicago have discovered that a group of birds in Madagascar have backtracked over their evolutionary pathway in a rare instance of “despeciation,” or the fusion of separate species.
The spectacled tetraka is a small, yellow-green warbler native to the various lowland forests of Madagascar. The evidence for the bird’s uncommon evolutionary ride comes from its mitochondrial DNA (mtDNA), which is located in the mitochondria organelle instead of inside the nucleus. Because mtDNA experiences fewer mutations than nuclear DNA, it can provide a clearer picture of evolutionary relationships between different species.
SEE ALSO: Bubonic Plague Could Be Millions of Years Older Than We Thought
The mtDNA from spectacled tetrakas varies up to 7.6 percent between individuals, which is a huge amount for birds living in such close quarters. In comparison, human mtDNA only varies by 1.5 percent at most, even between populations across the world. But weirdly enough, while the birds’ mtDNA varies so much, their nuclear DNA remains highly similar from bird to bird — a necessity for interbreeding. The mtDNA variations are evidence that the ancestors of the spectacled tetraka were slightly different species which reunited as a single species, thanks to similarities in their nuclear DNA.
To strengthen their theory, the researchers also looked for despeciation in organisms that would co-evolve with the birds: their lice. Parasites usually tag along with the evolution of their host species in order to maintain as much specificity as possible in their attack strategy. Different populations of tetrakas carried different kinds of lice. Even though the separate bird lineages have since blended back into a single species, the lice never crossed back over those lines of speciation.
This complex evolutionary pathway may be a result of Madagascar’s temperamental climate. The island frequently shifts through long phases of dry and wet weather that change the birds’ access between different forests. The tetraka ancestors likely radiated into distinct species during a dry period, when pathways between forests were cut off and the birds were isolated into separate populations. When the rains came back, the birds reconvened and regained the ability to interbreed as one species.
Despeciation is incredibly rare, but the extreme environmental changes caused by human activities may make the phenomenon more common. Habitat stress can force previously divergent species to consolidate, resulting in greater biodiversity loss. Understanding how this has happened in the past can help us get a better grip on how exactly evolution works, and minimize our interference with its natural course.
Based on materials provided by The Field Museum Public Relations.
Facebook comments