Comparative studies of critical physiological limits and vulnerability to environmental extremes in small ectotherms: How much environmental control is needed?

Carla M. SGRÒ,Ary A. HOFFMANN

doi:10.1111/1749-4877.12297

Carla M. SGRÒ, Ary A. HOFFMANN

Open Access

https://doi.org/10.1111/1749-4877.12297

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Journal: Integrative zoology	Publication Date: Jul 1, 2018
Citations: 45	License type: CC BY 4.0

Affiliation: Monash University, University of Melbourne

Abstract

Researchers and practitioners are increasingly using comparative assessments of critical thermal and physiological limits to assess the relative vulnerability of ectothermic species to extreme thermal and aridity conditions occurring under climate change. In most assessments of vulnerability, critical limits are compared across taxa exposed to different environmental and developmental conditions. However, many aspects of vulnerability should ideally be compared when species are exposed to the same environmental conditions, allowing a partitioning of sources of variation such as used in quantitative genetics. This is particularly important when assessing the importance of different types of plasticity to critical limits, using phylogenetic analyses to test for evolutionary constraints, isolating genetic variants that contribute to limits, characterizing evolutionary interactions among traits limiting adaptive responses, and when assessing the role of cross generation effects. However, vulnerability assessments based on critical thermal/physiological limits also need to take place within a context that is relevant to field conditions, which is not easily provided under controlled environmental conditions where behavior, microhabitat, stress exposure rates and other factors will differ from field conditions. There are ways of reconciling these requirements, such as by taking organisms from controlled environments and then testing their performance under field conditions (or vice versa). While comparisons under controlled environments are challenging for many taxa, assessments of critical thermal limits and vulnerability will always be incomplete unless environmental effects within and across generations are considered, and where the ecological relevance of assays measuring critical limits can be established.

Highlights

Correspondence: Ary Hoffmann, School of BioSciences, Bio21Institute, The University of Melbourne, 30 Flemington Road, VIC 3010, Australia.Climate change is expected to result in a rapid increase in the frequency of extreme climatic events (IPCC2016)
Thermal limits of small ectotherms depend on the nature of the response trait being measured, the exposure period and the rate at which stress is applied
Regardless of the extent of experimental control, a challenge for all studies assessing thermal limits and their plasticity is the choice of endpoint used, and their relevance to the ecological context of the organism being studied. This means considering the relevance of all aspects of environmental control discussed above with respect to natural situations, including exposure times and speeds at which thermal conditions are experimentally changed, the conditions that are experienced prior to assessment within and across generations, and the state of the organism (Colinet et al 2015)

Summary

Introduction

Thermal limits of small ectotherms depend on the nature of the response trait being measured, the exposure period and the rate at which stress is applied Variation in upper thermal limits of mountain grasshoppers distributed across an elevation gradient largely partitions within species rather than across species (Slatyer et al 2016); the high level of variation among samples from different elevations, which may reflect local adaptation within a taxon or local plastic responses, needs to be understood when comparing the vulnerability of species.

Results

Conclusion