Warming increases the cost of growth

Diego Barneche is a lecturer in marine ecology at the University of Exeter (UK). You can find him on twitter, googlescholar, GitHub and his website. In this Insight, he talks about his new paper Warming increases the cost of growth in a model vertebrate, now published in Functional Ecology


About the research


How did you come up with the idea for your paper?

The cost of growth is a fundamental quantity in ecology because it is a determinant of the efficiency of energy transfer between trophic levels. Surprisingly, however, this quantity has been largely neglected in the literature. A recent meta-analysis on the mass and temperature dependence of the cost of growth in fishes suggested that this quantity systematically increases with temperature. Prof Frank Seebacher at The University of Sydney, my postdoc supervisor at the time, suggested that such a temperature-dependent cost of growth might be attributable to mitochondrial inefficiency – that is to say, the capacity of mitochondria to produce ATP per molecule of oxygen goes down at warmer temperatures. However, experiments to directly test this hypothesis were still lacking. Under the umbrella of one of Prof Seebacher’s Australian Research Council projects, we then planned an experiment to test these two hypotheses: first, we wanted to directly measure whether the cost of growth was systematically changing with temperature and body size in properly acclimated individuals; second, we wanted to verify whether these putative dependencies could be reconciled after accounting for mitochondrial inefficiency.

What are the key messages of your article?

Plot: Relationship between cost of growth and efficiency of energy transfer for an active young adult following the theory in Barneche & Allen (2018).
Plot: Relationship between cost of growth and efficiency of energy transfer for an active young adult following the theory in Barneche & Allen (2018).

That the cost of growth increased at higher temperatures, and decreased in individuals with larger body sizes. These results were maintained even after accounting for mitochondrial inefficiency. It is important to highlight though that both the cost of growth and mitochondrial inefficiency varied substantially among individuals within the same temperature, so further research exploring the mechanistic underpinning of these quantities is necessary.

What is the broader impact of your paper?

I hope that this study will appeal to physiologists and ecologists / environmental scientists in general. We still need to understand the mechanisms and ecological factors that explain variation in the cost of growth. One of the most important messages from our study is that the productivity of individuals and their contribution to the carbon cycle will be different at higher temperatures if they need to respire more oxygen to produce a fixed amount of body mass. Similar patterns have been reported for plants and microbes, whereby the carbon-use efficiency (CUE) decreases with temperature. It is still too early to say whether an increase in the cost of growth is a general response to warming in ectothermic organisms. However, this existing evidence suggests that warming may have profound, under-appreciated implications to how we model and predict the contribution of living organisms to the global carbon cycle under a warming scenario. From a practical perspective for instance, this might imply more inefficient wild fisheries productivity as the oceans warm up (see also Audzijonyte et al. 2019, GEB, doi: 1111/geb.12847; Barneche et al. 2018, Science, doi: 10.1126/science.aao6868.


About the author

I will dare to say that ecology is the best field to combine mathematics, fieldwork, lab experiments, and data analysis.

Diego hiking in New Zealand (holding a chunk of snow after seeing snow for the first time!)
Diego hiking in New Zealand (holding a chunk of snow after seeing snow for the first time!)

How did you get involved in ecology?

I did my undergraduate degree in Biological Sciences at Universidade Federal de Santa Catarina (Brazil), and during my third year as an undergrad I watched a lecture about reef-fish ecology. I was hooked from the very first slide. Everything about them was fascinating, from their bewildering morphological diversity to the ecological processes one could study using reef fishes as a model system. My very first research project then entailed understanding large-scale variation in feeding ecology of damselfishes (Barneche et al. 2009, Mar Biol, doi: 1007/s00227-008-1083-z). From that first experience, it became very clear to me that body size and environmental temperature were fundamental drivers of ecological processes. I then pursued a Masters degree in Ecology in the same institution supervised by Prof Sergio Floeter. I studied the roles of body size, area, and temperature on reef-fish species richness gradients across spatial scales (Barneche et al. 2019, GEB, doi: 10.1111/geb.12851). I finally pursued a PhD degree in theoretical ecology at Macquarie University (Australia), focused primarily on understanding how body size and temperature allow us to link ecological processes from individuals to ecosystems (Barneche et al. 2014, Ecol Lett, doi: 10.1111/ele.12309; Barneche et al. 2016, Proc B, doi: 10.1098/rspb.2015.2186; Barneche & Allen 2015, PNAS, doi: 10.1073/pnas.1506305112; Barneche & Allen 2018, Ecol Lett, doi: 10.1111/ele.12947). These experiences have broadened my professional interests, and opened an ever-stimulating research avenue that focuses on a variety of groups of organisms (not just fishes) and questions related to unifying ecology across scales of biological organisation.

What’s your current position?

I am a Lecturer in Marine Ecology at the beautiful Cornwall campus of the University of Exeter (UK). I am a member of the College of Life and Environmental Sciences, and part of the Centre for Ecology and Conservation, as well as Exeter Marine.


What is the best thing about being an ecologist?

It is hard to pinpoint the “best”. There are many great aspects about being an ecologist in my opinion. To be able to further our understanding of the functioning of the natural world is extremely rewarding – it not only offers a great sense of professional achievement, but also makes me appreciate that we (ecologists) are helping to build something much larger than one’s single career. Also, deriving and testing hypotheses from theory and observations in nature is extremely fun. I will dare to say that ecology is the best field to combine mathematics, fieldwork, lab experiments, and data analysis. In fact, I believe this is the perfect time to further the development of theory in ecology by directly testing it using fieldwork and experiments. We live in a time with access to equipment which can generate experimental data in a high-throughput manner; the first ones that come to mind are respirometers, baited remote underwater video system (BRUVs), satellite imagery, GPS tagging, and drone aerial surveys. But there are way more out there. Moreover, we now have the capacity to compile enormous ecological datasets and crunch them using advanced computational and statistical methods.

What is the worst thing about being an ecologist?

It is incredibly hard to find sites to conduct natural experiments in the absence of human impacts. Unfortunately, human impacts such as overharvesting, pollution, habitat destruction, and species introductions are pervasive globally. Compounded to that are the generally-negative effects of climate change on ecological interactions and processes. Marine ecologists who seek near-pristine sites have to either resort to travelling very long distances to get to remote locations, or embrace the limitations and work with the least-impacted nearby field sites.


What do you do in your spare time?

I love being outdoors and exercising. When at home, I love baking my own sourdough and watching Netflix.

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