Javiera Benavente: Scaling of metabolism and excretion along a temperature gradient

In this blog post, Dr. Javiera Benavente, who recently graduated with their PhD from the University of Auckland, discusses with their recently accepted paper, “Plasticity and evolution shape the scaling of metabolism and excretion along a geothermal temperature gradient.”

About the paper

In this paper, we investigated how phenotypic plasticity and contemporary evolutionary adaptation can shape how the size- and temperature-dependence of metabolic and excretion rates respond to warming. To do this, we common-reared mosquitofish that invaded geothermal springs that span a wide thermal gradient within the last 100 years. After common-rearing, we measured metabolic and excretion rates across different body sizes at four different rearing temperatures. Adaptation is predicted to mediate the response of organisms to environmental warming, potentially triggering novel eco-evolutionary dynamics. A major challenge to understanding, and predicting, adaptive responses and their ecological consequences is parsing the effects of phenotypic plasticity and evolutionary adaptation in organisms’ responses to warming. Physiological rates like metabolism and excretion shape the ecological role of organisms by dictating their energy demand and nutrient recycling potential. Given that physiological rates are heavily influenced by body size and temperature, the body size and temperature scaling of metabolism and associated physiological processes are fundamental parameters in many models attempting to predict the ecological outcome of environmental warming. Therefore, this spurred our interest in investigating if these scaling parameters can evolve in timescales relevant to current environmental warming.

Above: Javiera collecting mosquitofish. Below: One of the geothermal ponds from which we collected the mosquitofish for this study (Credit: Dave Fryxell)

We have been working on this system for some time. We are exploring how temperature differences can affect traits like body size, physiological rates, and behaviour, as well as the potential consequences that temperature-induced changes can have on the ecological role of these fish. Therefore, the natural progression was to investigate if differences found across temperatures in nature were the product of phenotypic plasticity or contemporary evolutionary adaptation. Our results suggest that organisms’ responses to warming depends on the interaction of evolutionary adaptation and phenotypic plasticity in different traits. Evolutionary differences across populations found in this study also highlight the importance of intraspecific variation in the scaling of physiological rates, as different populations may respond differently to changes in temperature.

Mosquitofish in a geothermal spring (Credit: Kevin Simon)

Although evolutionary adaptation has been assessed in metabolism scaling parameters at the intraspecific level before, it is not easy to parse evolutionary from plastic responses to warming. Many common-garden experiments focus on small organisms with very short generational times. In contrast, we common-reared a non-model freshwater fish species for two generations. One question that arises from our results is what are the ecological consequences of the evolutionary and plastic responses found in this study?

About the research

Understanding how organisms respond to novel environmental conditions is key to understanding how resilient species and ecosystems are to human-induced selective pressures, such as climate change. Evolutionary adaptive responses on key functional traits are likely to trigger novel eco-evolutionary dynamics that need to be considered to make accurate predictions about the future of global biodiversity. Ecological change caused by warming will probably depend on the interaction of contemporary evolution and plastic responses across multiple traits. Combining natural experiments with common-rearing experiments can help us parse the contribution of phenotypic plasticity and evolutionary change on each of these traits, improving our understanding of how species cope with rapid ecological change.

The mosquitofish from this geothermal system are from an ideal ecosystem for studying contemporary evolution and adaptation in response to warming. However, despite mosquitofish being a relatively easy fish to breed, working with live animals is always challenging. Setting up the experiment and rearing the fish took several months and constant dedication. Our research adds to the growing body of evidence of evolution happening at ecologically relevant timescales, and it proposes new mechanisms on how evolutionary and plastic responses in different traits can help organisms cope with warming. It would be interesting to assess how adaptive responses in these traits, and other traits we have been studying, can change interspecific interactions and the ecological role of these fish, potentially triggering new eco-evolutionary dynamics.

About the author

I was always interested in nature, picking up insects, playing with lizards, watching nature documentaries, and reading books about animals and dinosaurs. But I became really interested in evolutionary biology after my undergraduate thesis on the population genetics of rainbow trout in Chile. I recently finished my PhD in environmental sciences at the University of Auckland. I am currently looking for a postdoc position while I write up publications from the remaining chapters of my PhD dissertation.   

Javiera collecting mosquitofish (Credit: Dave Fryxell)

Enjoyed the blog? Read the research here.

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