Limited thermal plasticity may constrain ecosystem function in a basally heat tolerant tropical telecoprid dung beetle, Allogymnopleurus thalassinus (Klug, 1855)

Honest Machekano,Nonofo Gotcha,Chipo Zidana,Casper Nyamukondiwa

doi:10.1038/s41598-021-01478-x

Honest Machekano, Nonofo Gotcha + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-01478-x

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Abstract

Tropical organisms are more vulnerable to climate change and associated heat stress as they live close to their upper thermal limits (UTLs). UTLs do not only vary little across tropical species according to the basal versus plasticity ‘trade-off’ theory but may also be further constrained by low genetic variation. We tested this hypothesis, and its effects on ecosystem function using a diurnally active dung rolling beetle (telecoprid), Allogymnopleurus thalassinus (Klug, 1855) that inhabits arid environments. Specifically, (i) we tested basal heat tolerance (critical thermal maxima [CTmax] and heat knockdown time [HKDT]), and (ii) ecological functioning (dung removal) efficiency following dynamic chronic acclimation temperatures of variable high (VT-H) (28–45 °C) and variable low (VT-L) (28–16 °C). Results showed that A. thalassinus had extremely high basal heat tolerance (> 50 °C CTmax and high HKDT). Effects of acclimation were significant for heat tolerance, significantly increasing and reducing CTmax values for variable temperature high and variable temperature low respectively. Similarly, effects of acclimation on HKDT were significant, with variable temperature high significantly increasing HKDT, while variable temperature low reduced HKDT. Effects of acclimation on ecological traits showed that beetles acclimated to variable high temperatures were ecologically more efficient in their ecosystem function (dung removal) compared to those acclimated at variable low temperatures. Allogymnopleurus thalassinus nevertheless, had low acclimation response ratios, signifying limited scope for complete plasticity for UTLs tested here. This result supports the ‘trade-off’ theory, and that observed limited plasticity may unlikely buffer A. thalassinus against effects of climate change, and by extension, albeit with caveats to other tropical ecological service providing insect species. This work provides insights on the survival mechanisms of tropical species against heat and provides a framework for the conservation of these natural capital species that inhabit arid environments under rapidly changing environmental climate.

Highlights

Climate change is expected to increase global mean temperature by 1.5–4.5 °C by the end of the century if mitigation measures fail
Tropical organisms are especially vulnerable to heat stress because they live in habitats with temperatures close to their upper thermal limits (UTLs) and often lack the capacity to compensate adaptively through phenotypic p lasticity[28,29,30] partly due high investment in high basal heat tolerance or genetic c onstrains[31,32,33]
It follows that variation in UTLs is lower than that of lower thermal limits (LTLs) even across space and species

Summary

Introduction

Climate change is expected to increase global mean temperature by 1.5–4.5 °C by the end of the century if mitigation measures fail. Tropical organisms are especially vulnerable to heat stress because they live in habitats with temperatures close to their UTLs and often lack the capacity to compensate adaptively through phenotypic p lasticity[28,29,30] partly due high investment in high basal heat tolerance or genetic c onstrains[31,32,33] It follows that variation in UTLs is lower than that of lower thermal limits (LTLs) even across space and species (reviewed in[17]). By constantly being exposed to soil heat, dung beetles should theoretically adapt to heat and presumably have inherent high basal resistance to heat stress It remains unknown which species trade off plasticity for basal high temperature tolerance, and how that is likely to subsequently impact on its essential ecosystem function, e.g. dung removal. Previous reports suggest global warming poses a threat to these species by likely reducing their field fitness and ecological function apart from increasing their risk of e xtinction[2,24,40,46]

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