Sub-Antarctic Freshwater Invertebrate Thermal Tolerances: An Assessment of Critical Thermal Limits and Behavioral Responses.

Javier Rendoll-Cárcamo,Tamara Contador,Peter Convey,James Kennedy

doi:10.3390/insects11020102

Abstract

Physiological thermal limits of organisms are linked to their geographic distribution. The assessment of such limits can provide valuable insights when monitoring for environmental thermal alterations. Using the dynamic critical thermal method (CTM), we assessed the upper (CTmax) and lower (CTmin) thermal limits of three freshwater macroinvertebrate taxa with restricted low elevation distribution (20 m a.s.l.) and three taxa restricted to upper elevations (480 and 700 m a.s.l.) in the Magellanic sub-Antarctic ecoregion of southern Chile. In general terms, macroinvertebrates restricted to lower altitudinal ranges possess a broader thermal tolerance than those restricted to higher elevations. Upper and lower thermal limits are significantly different between taxa throughout the altitudinal gradient. Data presented here suggest that freshwater macroinvertebrates restricted to upper altitudinal ranges may be useful indicators of thermal alteration in their habitats, due to their relatively low tolerance to increasing temperatures and the ease with which behavioral responses can be detected.

Highlights

Understanding the mechanisms by which species distributions change along geographical gradients has been a key tool in biogeography, ecology, and evolution [1], and in the development of macroecological theories
The main objectives of the current study were to (i) assess the critical thermal maximum (CTmax) and CTmin of selected representative Magellanic sub-Antarctic freshwater macroinvertebrates whose altitudinal distributions are restricted to specific elevation ranges, (ii) compare their thermal tolerance ranges and habitat thermal breadths, and (iii) assess their behavioral responses to warming in order to identify their sensitivity and suitability as sentinel organisms for monitoring environmental thermal changes
The results obtained here showed significant differences between the critical thermal limits (CTmax and CTmin ) of different macroinvertebrate taxa inhabiting the same watershed at different elevations

Summary

Introduction

Understanding the mechanisms by which species distributions change along geographical gradients has been a key tool in biogeography, ecology, and evolution [1], and in the development of macroecological theories. Latitudinal and altitudinal gradients generally encompass several environmentally associated variables and can be considered ecological and evolutionary equivalents in terms of their influences on species adaptations [2]. The variations in and expression of species physiological traits are a direct response to the environment [2,3]. High latitude environments are often characterized by broad thermal variation while low latitude or tropical. Insects 2020, 11, 102 environments have a narrow thermal regime. Organisms inhabiting high latitudes are expected to express broader physiological thermal tolerances, especially to withstand cold temperatures [9,10]

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