When an invasive species shows up in a new area, one question that quickly comes to scientists mind is where will this be able to spread? For plants, environmental conditions are often key to determining the range over which the invasive will be able to spread. A plant that requires 15 weeks of freezing cold before the seed will germinate is probably not going to survive in Hawaii, even if a few plants get brought over. But, what if the invasive species has the ability to adapt to new conditions? Ragweed has recently been shown to do just that.
|By: Meneerke bloem on Wikipedia Creative Commons|
Most of us are familiar with ragweed because a great deal of us humans happen to be allergic to its pollen. If you live in the United States, well this guy is part of your normal flora so stock up on the allergy meds and suffer. If you live in Europe, oh so sorry this is an invasive species that has not only spread but has a tight grip that will not be released on your flora, so stock up on allergy meds and suffer while blaming America.
Germination, when a seed sprouts to become a seedling, is an important fitness trait for plants and is controlled by environmental conditions. For the first time, as far as I am aware, a paper was published comparing germination rates between a native population and its invasive counterpart. (Leiblein‑Wild, M., et al., 2014. Germination and seedling frost tolerance differ between the native and invasive range in common ragweed. Oecologia 174(3):739-50).
They looked at germination and seedling frost tolerance from 10 different American populations and 17 Europe populations by collecting seeds and then planting them under varying temperatures in the lab. What they found was that European (the invasive) populations had a broader range of temperatures at which they could germinate and increased seedlings frost tolerance. This would allow the invasive population to spread rapidly and beyond the range originally predicted for ragweed to occupy in Europe. This also suggests that ragweed is adapting to the new habitats and could, potentially, continue to adapt and spread.
This study was the first to look at something incredibly important, comparing the native populations environmental requirements with the invasive populations environmental requirements. While they might be the same, there are many factors that could allow an invasive population to adapt and thrive in conditions that the native population could not. Ragweed is the first, of probably many, example of invasive species showing germination adaptation. Hopefully, more research will be done in this area.