Trine Bilde: Responses to thermal stress in a social spider

Trine Bilde, Professor of Evolutionary Biology in the Department of Biology at Aarhus University, discusses with us her recently accepted paper, “Behavioural and physiological responses to thermal stress in a social spider”.

About the paper

The social spider Stegodyphus sarasinorum in communal attack of prey. Photo: Virginia Settepani.
The social spider Stegodyphus sarasinorum in communal attack of prey. Photo: Virginia Settepani.
  • What’s your paper about?

The study investigates behavioural and physiological adaptations to temperature stress in a desert living social spider, specifically behavioural changes in microhabitat use, and whether the wax layer which is an important part of the the exoskeleton of the spiders, and which protects the animal against water loss by evaporation changes in response to temperature change. We are particularly keen to investigate whether these responses are plastic, or might be shaped by local adaptation (genetics).

  • What is the background behind your paper?

These spiders live in areas that experience extreme and high temperatures; they build communal nests in which the temperature can reach more than 55°C. This temperature is lethal to most arthropods, so we are interested in understanding which adaptations and responses the spiders employ to cope with high temperatures.

  • How did you come up with the idea for it?

We have observed that spiders move to the area beneath the nest during the heat of the day. Because this area constitutes a presumably windy and cooler microhabitat, it was hypothesized that this behaviour is an adaptive response to prevent heat stress. In addition, we wondered whether the cuticle layer is ‘fixed’, or can be adjusted according to temperature, which would provide an additional and complementary heat stress response.

  • What are the key messages of your article?

Our study provides evidence of both local adaptation and phenotypic plasticity in physiological and behavioural traits relating to temperature tolerance. Population differences in trait expression suggests local adaptation to different thermal environments, and individuals plastically adjust cuticle wax composition and cooling behaviour in response to temperature changes.  

  • How is your paper new or different from other work in this area?

We performed experiments that are key for disentangling associations, which can be difficult to interpret, to actually testing predictions of expected causal relationships. This provides us with improved understanding of which factors are driving changes in trait expression.

  • Does this article raise any new research questions?

It is particularly interesting that cuticle wax composition can be changed over relatively short time scales, in response to temperature changes. This raises the question of what the costs of implementing these changes are, and of understanding other physiological functions of the cuticle wax layer.

  • Who should read your paper (people that work in a particular field, policy makers, etc.)?

 People that are interested in evolutionary ecology, how organisms adapt to the environment, in desert arthropods, and in species distribution patterns.

About the research

Photo: A nest of the African social spider Stegodyphus dumicola in Namibia. The nest consists of thick silk layers with multiple entry holes underneath the nest, facing the ground. A large capture web extends from the nest, and a few spiders can be seen active on the web. The spiders are predominantly inactive during the day and remain inside the nest, unless they attack prey intercepted in the web. The spiders move to the area immediate below the nest to cool down at peak summer temperatures. They are active in web maintenance activities at dusk and dawn. (Photo Trine Bilde).
Photo: A nest of the African social spider Stegodyphus dumicola in Namibia. The nest consists of thick silk layers with multiple entry holes underneath the nest, facing the ground. A large capture web extends from the nest, and a few spiders can be seen active on the web. The spiders are predominantly inactive during the day and remain inside the nest, unless they attack prey intercepted in the web. The spiders move to the area immediate below the nest to cool down at peak summer temperatures. They are active in web maintenance activities at dusk and dawn. (Photo Trine Bilde).
  • What is the broader impact of your paper (outside of your specific species/study system).

It is important to understand how organisms are able to occupy wide and variable temperature conditions, particularly in the face of rapid global change. By generating new insights into the mechanisms that mediate adaptive responses, we are better able to predict how organisms will respond to environmental change, and whether they are able to cope with rapid changes.

  • Why is it important?

Ultimately, it informs us about extinction and colonisation patterns, and on current and future species distribution patterns.

  • Did you have any problems setting up the experiment/gathering your data?

It is always very challenging to perform ecologically relevant experiments on African social spiders, from collecting them in the field to developing the methods for performing experiments in the lab. But these spiders are super cool and fun to work with!

  • Where you surprised by anything when working on it?

We are always surprised how high temperatures, almost 50°C, that these spiders can tolerate.

  • What does your work contribute to the field?

It helps us in understanding how evolution shapes diversity and the occupation of even the most extreme environments.

  • What are the big questions still to answer?

One very interesting question is whether and how plasticity in temperature responses is sufficient to buffer against rapid environmental change, which may occur faster than what can be tracked by evolutionary (genetic) responses.

  • What is the next step in this field going to be?

Employing more integrative and interdisciplinary studies in understanding the mechanisms underlying adaptive responses.

  • What would you like to do next?

We would like to go to Africa and perform field experiments and field collections, to follow up on this work, but currently the pandemic makes it impossible.

About The Author

  • How did you get involved in ecology?

I got involved in the foraging ecology of arthropods in agro-ecosystems during my PhD, and then became particularly interested in evolutionary ecology.

  • What are you currently working on?

I work on wild animal populations to understand what shapes their distribution, what their adaptive potential is, and to understand the type of adaptations and plastic responses that they employ.

  • What’s your current position?

I am a professor in Evolutionary Biology at Aarhus University, Department of Biology.

  • What project/article are you most proud of?

I am very excited about this study in Functional Ecology, because of its interdisciplinary approach.

  • What is the best thing about being an ecologist?

To study cool animals in their natural ecological settings.

  • What is the worst thing about being an ecologist?

The challenges of obtaining permits, organising the logistics of fieldwork, and having to deal with huge variation of unpredictable field conditions….

  • What do you do in your spare time?

I hike in remote mountains and play bridge (the card game).

  • One piece of advice for someone in your field…  

“Nothing in Biology Makes Sense Except in the Light of Evolution” (by the evolutionary biologist Theodosius Dobzhansky).

Read the paper in full here

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