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Rapid evolution in birds in Southeast Asia

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  • Rapid evolution in birds in Southeast Asia

    Source: Rapidly diversifying birds in Southeast Asia offer new insights into evolution

    New findings from zoologists working with birds in Southeast Asia are shining fresh light on the connections between animal behaviour, geology, and evolution - underlining that species can diversify surprisingly quickly under certain conditions.

    The zoologists, from Trinity College Dublin's School of Natural Sciences, sequenced DNA and took measurements and song recordings from Sulawesi Babblers (Pellorneum celebense), shy birds that live in the undergrowth on Indonesian islands.

    Although these islands were connected by land bridges just tens of thousands of years ago, and although the babblers look so similar that they are currently all considered a single subspecies, the new study shows that their DNA, body size and song have all changed in what is a very brief period of time from an evolutionary perspective.

    The zoologists believe that this evolutionary divergence is likely facilitated by the babblers' understorey lifestyle, which limits the birds' movements even though they could easily fly between the islands if they chose to.

    In the short time these islands have been isolated, the babbler subspecies have evolved to vary genetically from each other by as much as 1/3 as they do from more distantly related bird species that separated millions of years ago.

    Fionn Ó Marcaigh, first author on the paper and a PhD Candidate in Trinity's School of Natural Sciences, said:

    "Everyone has heard of Darwin's finches evolving completely different bill shapes on the Galápagos islands. The Galápagos are isolated out in the Pacific, so the birds there have had millions of years to evolve separately. But sometimes evolution can occur on much smaller scales of time and space and can be harder to detect just by looking at the animals in question.

    "Unlike the Galápagos, the islands we looked at are just 20 km or less from the mainland. The more we study biodiversity, the more we realise is out there, as species and islands that have never been examined closely can turn out to be full of surprises.

    "And a lot of it is under threat: in our study, the islands with the most distinct populations were those made of a particular rock type. This ultramafic rock is full of minerals like nickel, which get into the soil and change which plants can grow, to which the birds have to adapt. But that same nickel is being sought by mining companies so time is running out for the islands' biodiversity before we've even captured a full picture of it or understood how it's evolved."


    © Copyright Original Source

    The entire paper Evolution in the understorey: The Sulawesi babbler Pellorneum celebense (Passeriformes: Pellorneidae) has diverged rapidly on land-bridge islands in the Wallacean biodiversity hotspot can be read by clicking on the hyperlink provided, but the abstract from it can be seen below:


    Tropical islands hold great treasures of Earth's biodiversity, but these fragile ecosystems may be lost before their diversity is fully catalogued or the evolutionary processes that birthed it are understood. We ran comparative analyses on the ND2 and ND3 mitochondrial genes of the Sulawesi babbler Pellorneum celebense, an understorey bird endemic to Sulawesi and its continental islands, along with its morphology and song. Genetic, acoustic, and morphological data agree on multiple isolated populations, likely representing independently evolving lineages. The Sulawesi babbler shows signs of rapid speciation, with populations diverging between Central and Southeast Sulawesi, and even on land-bridge islands which were connected within the last few tens of thousands of years. The genetic divergence between Sulawesi babbler populations in this time has been around 33% of their divergence from sister species which have been isolated from Sulawesi for millions of years. This is likely facilitated by the Sulawesi babbler's understorey lifestyle, which inhibits gene flow and promotes speciation. Similar patterns of endemism are seen in Sulawesi's mammals and amphibians. This work highlights the undocumented biodiversity of a threatened hotspot, wrought by complex processes of speciation which interact with ecology and geology. Subspecific taxonomy has at times been controversial, but we argue that discrete populations such as these play a key role in evolution. Lying as they do at the heart of the biodiversity hotspot of Wallacea, these islands can reveal much about the evolution of biodiversity at all of its levels, from the gene to the ecosystem.

    We've seen this sort of thing with insects before. It has long been understood that apple maggot flies evolved through sympatric speciation from flies that had only laid their eggs only on hawthorns some 200 years ago after apples were introduced to America by immigrants roughly 200 years ago. And even in birds, we've seen some rapid evolution of traits.

    For instance, non-native South American apple snails have pretty much replaced the native species in Florida causing serious problems for the already endangered snail kite, a bird that feeds on them, because they are too large for the bird's bill to crack. But within ten years the bills of the snail kites have increased in size since the invasion of the South American snail allowing it to forage on this new, larger prey.

    Now, to be clear the bills didn't magically get larger. Instead, what we saw was that those with larger beaks were able to survive while their smaller billed relatives didn't. And as they reproduced their descendants with the largest beaks were able to do better than those with smaller beaks, hence leaving more offspring. And this continued through every generation. IOW, natural selection acting upon a mutation.

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  • #2
    This is a good example of evolution being environmentally driven.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .


    I do not know, therefore everything is in pencil.


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