Acclimation effects on thermal tolerance in ameronothrid mites at sub-Antarctic Marion Island

[摘要] ENGLISH ABSTRACT:Evidence for widespread ecological impacts due to rapid climate change is on theincrease, with further warming predicted over the next century. This increase in warminghas lead to organisms adjusting their distribution range and where this is not possibleorganisms must cope with the stressful environments in a different way. One potential wayto handle environmental stress is via a mechanism known as phenotypic plasticity, whichallows an organism to express different phenotypes depending on the biotic or abioticenvironment in a way that may alter that organism's fitness. Acclimation temperatures canpotentially cause plastic (reversible and irreversible) changes in the response of individualsto stressful experimental conditions that could increase their survival. The issue of whetherthis acclimation will be beneficial to the organism or not remains contentious, with supportoffered both for and against the idea of beneficial acclimation. The aims of theinvestigation were to determine the thermal limits of five ameronothrid mite species(Halozetes marinus, H marionensis, H belgicae, H. fulvus and Podacarus auberti) fromvarying terrestrial habitats and to test whether there is beneficial acclimation on the thermaltraits. Along with the beneficial acclimation hypothesis several alternative hypotheses werealso tested. In addition, locomotor performance was determined as it has been suggestedthat locomotion performance is a reliable and practical measure of potential fitness ofanimals. The same hypotheses testing the effects of acclimation temperature on the thermallimits were tested on three performance traits; performance breadth, optimum speed andoptimum temperature. Support for beneficial acclimation was found in the performancebreadth and optimum speed traits for all species except for Halozetes marinus. For theoptimum temperature trait the prediction for the compensation hypothesis was met and thatof the beneficial acclimation hypothesis rejected, with the only exception again being thatof H marinus. In the case of the locomotor performance traits the prediction for the beneficial acclimation hypothesis in the performance breadth and optimum speed traits arethe same for that of the compensation hypothesis, therefore the overall response of themore terrestrial mite species is one of compensation. However, support for beneficialacclimation was not found in the thermal limit traits of all five species, with the higheracclimation temperatures (specifically 150 C) resulting in negative responses in LLT in H.marinus and H. belgicae, and in ULT in H. fulvus. Phenotypic flexibility varied betweenmarine and terrestrial species. The less variable marine environment showed lowerflexibility than that of terrestrial species in the performance breadth trait and optimumtemperature trait, but there was a lack of variation between the marine and terrestrialspecies in the temperature tolerance traits. These results show that the effects ofacclimation on various traits, especially fitness related traits, are complex and require moreattention if the consequences are to be fully explained. This study therefore providesinsight into the effects of acclimation on performance traits and thermal limit traits and hasimplications for the evolution of plastic responses in terrestrial arthropods.

[发布机构] Stellenbosch University