Big Ideas in Macrophysiology

01 October 2018 - By: Jacinta Kong

Big Ideas in Macrophysiology

By Jacinta Kong, PhD Candidate, University of Melbourne

In July 2018, a group of experimental physiologists, ecologists and modellers congregated in Florence, Italy for the Animal Biology Satellite Meeting “The height, breadth and depth of physiological diversity: variation across latitudinal, altitudinal and depth gradients”. Held prior to the SEB Annual Meeting, the symposium was organised by Dr Simon Morley (British Antarctic Survey, UK), Professor John Spicer (Plymouth University, UK) and Professor Francisco Bozinovic (Pontifical Catholic University of Chile, Chile) with the theme of patterns of physiological diversity on a global scale – the field of macrophysiology1

UPDATING PHYSIOLOGICAL DIVERSITY AND ITS ECOLOGICAL IMPLICATIONS

The idea for an SEB satellite meeting came about after John and Simon took a research trip to Antarctica last year. During the trip, they discussed updating John’s 19992 book, how temperature and oxygen plays a role in structuring macrophysiological patterns and how testing these patterns has changed in recent years. John, Simon and Francisco saw an SEB satellite meeting as an opportunity to bring together scientists from a diverse pool of expertise to discuss the development and future of macrophysiology. Attendees travelled from a wide range of latitudes to showcase physiological diversity and its underlying mechanisms from marine to terrestrial systems around the world and be treated to Italian coffee. Here are some of the highlights of the day.

THERMAL PERFORMANCE ON THE WORLD’S STAGE


The hottest topic of the meeting was the role of temperature as a mechanism underlying spatial gradients in biodiversity. Central to this was the thermal performance curve (TPC) or how animal performance changes over a range of temperatures. “There are two reasons why TPCs are such a useful   concept for understanding responses of organisms to environmental change” explains Dr Enrico Rezende (Pontifical Catholic University of Chile, Chile), “the first –reason is that the empirical curve is very pervasive”. Dr Jennifer Sunday (McGill University, Canada) opened the meeting with a summary of how the characteristics of these TPCs, such as upper thermal tolerance CTmax, varies between marine and terrestrial systems across latitude3. “I still remember when I first plotted the data… it was just really striking” reminisces Jennifer. She showed that these differences may mean that marine and terrestrial species will shift their distribution in response to climate change differently6. She also highlighted that global scale patterns are not reflective of how an organism behaves in its environment at local scales4.

CURVE THINKING ACROSS SCALES


The second reason why TPCs are so pervasive in ecology and evolutionary biology, according to Enrico, is that “we have some idea from our understanding of thermodynamics of how it works”. Enrico developed a theoretical model of a TPC to compare TPCs found across different measurements of performance or fitness and levels of biological organisation. Enrico found that the shape of the TPC, or the thermal window, became narrower as you moved up in biological complexity. “Thermal adaptation is an emergent property”, he explains, meaning you may not see a pattern at the cellular level, but a pattern emerges when you look at the population level. “I wasn’t expecting such compelling differences between levels of organisation” says Enrico, noting that he does not have an explanation for this pattern but emphasises “the take home message there is that people are measuring traits in individuals, but you cannot extrapolate to populations. When we want to make predictions for things like climate change and assess the resilience of populations… we should measure at the level of populations not at the level of individuals”. Enrico remains optimistic that with the development of theoretical approaches, ecologists, physiologists and evolutionary biologists will be able to translate experimental work from the lab to the field and make predictions of biological responses to environmental change. Jennifer’s approach to tackling these big questions is ‘curve thinking’ in multiple dimensions; adaptation, acclimation and biotic interactions from individual to ecosystem levels are all challenges physiologists need to address in partnership with ecologists and evolutionary biologists.

COUNTERING CONSERVATISM IN CONSERVATION

One of the goals of macrophysiology is to “provide clear physiological diversity advice to conservationists so that they can prioritise their decisions” says Simon. This is a step forward from the traditional way of thinking about physiology in terms of averages. “We assume single populations are representative across their entire distribution” explains Dr Christine Cooper (Curtin University, Australia), “it’s only been more recently that we’ve started to appreciate that there is variation at the subspecies level, population level and even at the individual level”. This variation in physiological traits becomes important when translocating species to different areas.

Christine showed that subspecies of the Australian brushtail possum (Trichosurus vulpecula), which are widely distributed across much of Australia and inhabit different climatic environments, geographically varied in their energy, heat and water use7. “We would suggest that if you are moving possums to an arid habitat, that the best subspecies to use would be the west Australian subspecies that seems to be better adapted to living in a more arid environment” says Christine.

Dr Scott Bennett (IMEDEA, Spain) showed how ignoring local adaptation potentially underestimated the vulnerability of marine communities to climate warming. He identified reefs around the world that were potentially vulnerability hotspots or resilient to a warming climate under two scenarios, which did or did not incorporate local variation in physiological traits. “These hotspots or safe spots are important to recognise because they can help regional planning for potential climate refuges” says Scott,“or for focusing attention on ameliorating other stressors in very vulnerable areas”. Both Christine’s and Scott’s studies are clear examples of how understanding physiological differences on small scales can have important ecological implications which need to be emphasised in conservation and management. Scott explains “it’s important to provide context on local scales because a lot of management occurs at regional and local scales, so global studies are out of context of these users”.

HEATED DISCUSSIONS: TEMPERATURE AND OXYGEN

The day finished with a group discussion on the current and future thinking on macrophysiology including discussion on testing long-standing hypotheses of the temperature-size rule and the oxygen limitation hypothesis, as well as the measurement of CTmax. Everyone from seasoned researchers to newer PhD students got involved in the discussion, perhaps fuelled by coffee or by the comfortable atmosphere. As Simon observed “it is key to real progress in understanding, when everyone is willing to explore their own and others long, and not so long, held views”. The discussion also highlighted some less obvious points. “There was an obvious difference of opinion in the room on what Macrophysiology was for diagnosis or elucidation – and exploring that was both fruitful and illuminating” observed John, “The key thing I loved was that there was time to really chew over the issues raised”.

References:

1. Gaston, K. J. et al. Macrophysiology: a conceptual reunification. Am Nat 174, 595-612, doi:10.1086/605982 (2009).
2. Spicer, J. I. & Gaston, K. J. Physiological diversity and its ecological implications. (Malden, Mass. : Blackwell Science, 1999., 1999).
3. Sunday, J. M., Bates, A. E. & Dulvy, N. K. Global analysis of thermal tolerance and latitude in ectotherms. Proc R Soc B: Biol Sci 278, 1823-1830, doi:10.1098/rspb.2010.1295 (2011).
4. Sunday, J. M. et al. Thermal-safety margins and the necessity of thermoregulatory behavior across latitude and elevation. Proc Natl Acad Sci USA 111, 5610-5615, doi:10.1073/pnas.1316145111 (2014).
5. Sinclair, B. J. et al. Can we predict ectotherm responses to climate change using thermal performance curves and body temperatures? Ecol Lett 19, 1372-1385, doi:10.1111/ele.12686 (2016).
6. Sunday, J. M., Bates, A. E. & Dulvy, N. K. Thermal tolerance and the global redistribution of animals. Nature Clim. Change 2, 686- 690, doi: http://www.nature.com/nclimate/journal/v2/n9/abs/nclimate1539.html#supplementary-information (2012).
7. Cooper, C. E., Withers, P. C., Munns, S. L., Geiser, F. & Buttemer, W. A. Geographical variation in the standard physiology of brushtail possums (Trichosurus): implications for conservation translocations. Cons Phys 6, coy042-coy042, doi:10.1093/ conphys/coy042 (2018).


 

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Jacinta Dara Kong

Jacinta Kong

Jacinta is a PhD candidate at the University of Melbourne studying how species are adapted to climate. Jacinta is interested in the physiological mechanisms underpinning the distribution and phenology of species and is obsessed with Australian matchstick grasshoppers. You can read about matchstick grasshoppers here - https://jacintakongresearch.wordpress.com/matchstick-grasshoppers/