When Charles Darwin pondered how a single species could, over time, become two distinct ones, he realized that natural selection could act differently on separate populations, gradually driving them apart. This insight was so powerful that it gave rise to an entirely new scientific field: evolutionary biology.
To this day, the emergence of new species remains a central concept in evolutionary biology, and understanding the mechanisms behind it is one of the field’s key research questions. At the same time, hybridisation between populations that have evolved in isolation can influence the pace of speciation—either speeding it up, slowing it down, or even reversing it altogether.
A recent study by Ingo Müller and colleagues delved into the evolutionary history of Melidectes, a bird genus found in New Guinea that includes six species living in various mountainous regions at different elevations. Most of these species occupy separate areas, but two of them meet and hybridise in the central mountain range.
Despite this overlap, scientists had assumed that differences in plumage and adaptations to elevation would help maintain clear species boundaries. However, Müller and his team used genomic and genetic analyses to show that these visible differences do not, in fact, prevent gene flow between the two species. On the contrary, the researchers discovered that their genes are mixing extensively across most of their shared range.
This makes the bird community formed by these two species quite unusual. It follows a pattern where the most genetically distinct and least interbreeding populations are found at the geographical edges of their ranges. Remarkably, this is the case even though their maternally inherited mitochondrial genomes still sort neatly into two deeply divergent lineages, consistent with their traditional species identities.
These findings led the researchers to conclude that the two incipient species have recently begun to merge—possibly due to increased contact brought on by climate warming—resulting in nearly complete fusion into a single lineage. In other words, a speciation process that was well underway has now stalled, and the two almost-species appear to be on the path to becoming one unified species again.
Previous thoughts on the same topic:
The Dire Wolf and the Rights of Extinct Human Species
Shower Taking and Interfering Elephants
The fundamentals of conservation biology wavered
When I was in the school, if two animals can interbreed and produce an offspring, that is fertile and can produce more offspring, so the original animals belong the same species.
ReplyDeleteThat is called the biological species concept. There are also other concepts, such as the morphological species concept. In the case described in the main text, the two species fulfilled the second concept and were on their way toward the first one, but had not yet reached that level of differentiation.
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