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-of’ theory but may also be further constrained by low
genetic variation. We tested this hypothesis, and its efects on ecosystem function using a diurnally
active dung rolling beetle (telecoprid), Allogymnopleurus thalassinus (Klug, 1855) that inhabits arid
environments. Specifcally, (i) we tested basal heat tolerance (critical thermal maxima [CTmax] and
heat knockdown time [HKDT]), and (ii) ecological functioning (dung removal) efciency 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). Efects of acclimation were signifcant for heat tolerance, signifcantly increasing
and reducing CTmax values for variable temperature high and variable temperature low respectively.
Similarly, efects of acclimation on HKDT were signifcant, with variable temperature high signifcantly
increasing HKDT, while variable temperature low reduced HKDT. Efects of acclimation on ecological
traits showed that beetles acclimated to variable high temperatures were ecologically more efcient 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-of’ theory, and
that observed limited plasticity may unlikely bufer A. thalassinus against efects 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.
