Adaptation: an invasion mechanism adopted by an alien seaweed

Mahasweta Saha and collaborators have an interesting paper published in the last issue (July) of Journal of Ecology titled “Rapid adaptation to controlling new microbial epibionts in the invaded range promotes invasiveness of an exotic seaweed“. The lead author of this article, Mahasweta Saha, wrote a blog post below describing the context and results of her research.

Along with ocean warming and habitat and biodiversity loss, invasive species are one of the important components of global change. Rabbits are classic examples of invasive species from the terrestrial environment. According to a news article published in The Guardian in 2010, “Britain’s 40m rabbits cost more than £260m a year in damage to crops, businesses and infrastructure”. Even if we disregard the damage that they cause at national and international level, I know from my personal experience that these cute little bunnies are not welcomed at all!

My neighbours in Suchsdorf (Kiel, Germany) do not appreciate the local rabbit population as these rabbits frequently munch on their plants causing damage to their beautiful garden. In response, my neighbours installed electric wire around the garden to stop wild rabbits from entering. Initially, this appeared to be working but to our surprise, the bunnies turned out to be very smart. To cope with the new challenge of the electric wire, I observed that they simply adjusted their hop’s height and made higher hops compared to their usual ones. Thus, the smart bunnies simply adapted themselves to the new challenge that they faced in their life.

This story is very much applicable to my study published in Journal of Ecology, entitled “Rapid adaptation to controlling new microbial epibionts in the invaded range promotes invasiveness of an exotic seaweed” which involved a model seaweed Gracilaria vermiculophylla adopting a similar strategy to survive and thrive in a new invaded environment. This East Asian red algae is actually one of the top most alien seaweed species that has been introduced to Europe. It was first detected in significant amounts along the Kiel Fjord (Baltic sea) in 2005, followed by a ‘bust’ and subsequent regrowth of their population in the following years. Looking for the reasons, we analyzed the defense mechanisms of native (South Korean population) and alien Gracilaria (German and Danish population) against bacterial enemies originating from respective local habitats.


Red algae Gracilaria vermiculophylla growing attached in stones in Nordstand (North Sea)

By an elegant experimental approach, which included a crosswise testing of alien and native populations of the algal host and co-occuring bacteria, we showed that the native and alien populations of Gracilaria were equally well defended in their actual habitat, but weakly defended when confronted to potentially harmful bacterial enemies from the other habitats. This means that, within a few years, the alien population lost its defence capacities against its old foes but acquired potent defenses against the new ones.

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M. Saha with Gracilaria vermiculophylla in the climate chamber of GEOMAR

Our study is novel and exciting because it is the first study demonstrating the role of defence adaptation to new bacterial enemies in contributing to the success of an alien plant invasion. Such adaptation dynamics could be also applicable to other types of host plants, enemy interaction in general, and for cases of shifting plant and enemy interactions under climate change.

Mahasweta Saha
Department of Experimental Ecology
Helmholtz Center for Ocean Research

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