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Rapid evolution of foxgloves in the presence of hummingbirds

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  • Rapid evolution of foxgloves in the presence of hummingbirds

    Charles Darwin used to love to putter about in his garden pondering the mysteries of life and after studying the foxgloves growing there concluded in 1878 that only bumblebees were capable of pollinating them. I'm sure that the news of a new study showing that, after being transplanted to the tropics in America, foxgloves have apparently evolved there to accommodate hummingbirds, would have elated him.

    The researchers compared foxgloves being grown in Britain with those introduced to Costa Rica and Colombia approximately 200 years ago and have revealed how flowering plants can respond to a new environment -- as well as the presence of a new pollinator -- with some rapid physical changes.

    The study discovered that the base of the narrow cone structure of the flowers, the proximal corolla tube (which hold the flower's nectar, which, due to the shape of the tube, is only accessible to pollinators with long mouth parts) was up to over a quarter times larger in foxgloves now growing in Colombia and Costa Rica.

    The study's co-author, Maria Clara Castellanos of the University of Sussex said, "We found foxglove populations in Costa Rica and Colombia now have flowers with longer tubes at the base, when compared to native populations. There is also substantial natural selection on this floral characteristic in the naturalised populations."

    The researchers made clear that while the changes observed in foxgloves are consistent with changes that hummingbirds have imposed on the native plants they pollinate, the study does not prove that the birds directly caused the rapid changes seen in the flowers, instead they emphasized the importance of studying other plants in this context.

    As Castellanos remarked, "Plants around the world are experiencing changes in their pollinators and it is important to understand the evolutionary implications of this."

    This all reminds me in a way of how 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.


    Source: Rapid evolution in foxgloves pollinated by hummingbirds


    Researchers have found common foxgloves brought to the Americas have rapidly evolved to change flower length in the presence of a new pollinator group, hummingbirds. The findings are published in the British Ecological Society's Journal of Ecology.

    Researchers from the University of Sussex, Universidad de Los Andes (Colombia) and Universidad de Costa Rica, studying the common foxglove Digitalis purpurea, a bumblebee pollinated species native to Europe, have shown for the first time how rapid physical changes can occur in flowers following a change in environment and the presence of a new pollinator.

    The researchers compared foxgloves in the UK, which are pollinated by bumblebees, with foxgloves introduced in two independent events to Costa Rica and Colombia around 200 years ago, which are pollinated by different species of bumblebees and also hummingbirds. They found the base of the cone structure of the flowers, called the proximal corolla tube, was 13-26% larger in populations in the Americas.

    Foxgloves have long, narrow proximal corolla tubes. This part of the flower holds the nectar and by being this shape, they restrict floral visitors to those with long mouthparts such as long-tongued bumblebees.

    "We found foxglove populations in Costa Rica and Colombia now have flowers with longer tubes at the base, when compared to native populations. There is also substantial natural selection on this floral characteristic in the naturalised populations." said Dr. Maria Clara Castellanos at the University of Sussex and one of the authors of the study.

    "Long corollas are a common feature in many hummingbird-pollinated plants, likely because this improves the precision of pollen transfer during the pollination interaction. It is also possible that long corolla tubes exclude other pollinators that are less effective."

    Because foxgloves are biennial (meaning each generation takes two years) these changes have occurred in around 85 generations, indicating a rapid evolutionary change.

    In the study the researchers also confirmed that hummingbirds are effective foxglove pollinators. "We counted pollen grains deposited in flowers and found that after a single visit they can bring in more pollen than a bumblebee." said Dr. Castellanos.

    The study also confirms how invasions can be used to understand evolution of floral structures. The researchers say that scenarios like this are likely to happen often as humans influence the range of plants and pollinators.

    Dr. Castellanos said: "Our research shows how rapid evolutionary change in a new environment can be an important force behind the extraordinary diversity of flowers."

    Foxgloves are now naturalised in many areas of the world. They were introduced to Colombia and Costa Rica in the 19th Century, most likely by English architects and engineers. In these new tropical environments, foxgloves grow at high altitudes above 2,200 meters where temperatures are broadly similar to those in their native European range. Because there are no seasons, populations flower at different times of the year.

    In the study, the researchers looked at both native UK foxglove populations and populations in mountainous areas in Colombia and Costa Rica. They compared the shape of the flowers and the reproductive success of the plants. They also recorded the pollinators in each location and how effective each pollinator was at transferring pollen.

    The authors caution that although the changes they observed are consistent with natural selection hummingbirds have imposed during the evolution of native plants they pollinate, the study doesn't prove the changes to foxgloves have been directly caused by hummingbirds.

    To do this, the researchers are planning to experimentally exclude pollinators from foxgloves in the field and record the consequences for the plants. They are also studying the genetic basis of the traits both in the greenhouse and using genomic approaches.

    The researchers emphasised the importance of studying other plant groups in this context. "Plants around the world are experiencing changes in their pollinators and it is important to understand the evolutionary implications of this" said Dr. Castellanos.



    Source

    © Copyright Original Source




    The full paper, Rapid evolution of a floral trait following acquisition of novel pollinators is available at the hyperlink provided. Here is the abstract:

    Abstract:
    1. Changes in the pollinator assemblage visiting a plant can have consequences for reproductive success and floral evolution. We studied a recent plant trans‐continental range expansion to test whether the acquisition of new pollinator functional groups can lead to rapid adaptive evolution of flowers.
    2. In Digitalis purpurea, we compared flower visitors, floral traits and natural selection between native European populations and those in two Neotropical regions, naturalised after independent introductions. Bumblebees are the main pollinators in native populations while both bumblebees and hummingbirds are important visitors in the new range. We confirmed that the birds are effective pollinators and deposit more pollen grains on stigmas than bumblebees.
    3. We found convergent changes in the two new regions towards larger proximal corolla tubes, a floral trait that restricts access to nectar to visitors with long mouthparts. There was a strong positive linear selection for this trait in the introduced populations, particularly on the length of the proximal corolla tube, consistent with the addition of hummingbirds as pollinators.
    4. Synthesis. The addition of new pollinators is likely to happen often as humans influence the ranges of plants and pollinators but it is also a common feature in the long‐term evolution of the angiosperms. We show how novel selection followed by very rapid evolutionary change can be an important force behind the extraordinary diversity of flowers.

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  • #2
    Interesting!
    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 . . .

    Frank

    I do not know, therefore everything is in pencil.

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