Rapid adaptation to high temperatures in Chironomus riparius.

Quentin Foucault,Andreas Wieser,Ann-Marie Waldvogel,Barbara Feldmeyer,Markus Pfenninger

doi:10.1002/ece3.4706

Abstract

Effects of seasonal or daily temperature variation on fitness and physiology of ectothermic organisms and their ways to cope with such variations have been widely studied. However, the way multivoltines organisms cope with temperature variations from one generation to the next is still not well understood. The aim of this study was to investigate whether the multivoltine midge Chironomus riparius Meigen (1803) responds mainly via acclimation as predicted by current theories or whether rapid genetic adaptation is involved. To investigate this issue, a common garden approach has been applied. A mix of larvae from five European populations was raised in the laboratory at three different pre‐exposure temperatures (PET): 14, 20, and 26°C. After three and five generations, respectively, larvae were exposed to three treatment temperatures (TT): 14, 20, and 26°C. Mortality was monitored for the first 48 hr and after emergence. After three generations, significant mortality rate differences depended on an interaction of PET and TT. This finding supports the hypothesis that chironomids respond rapidly to climatic variation via adaptive mechanisms and to a lesser extent via phenotypic plasticity. The result of the experiment indicates that three generations were sufficient to adapt to warm temperature, decreasing the mortality rate, highlighting the potential for chironomids to rapidly respond to seasonally changing conditions.

Highlights

Ambient temperature variation is a major factor affecting the fit‐ ness of organisms by regulating the speed of metabolic processes, and everything from development to reproduction (Atkinson, 1994)
This experiment was performed on an admixed C. riparius culture composed of individuals from five different populations originating from Metz (NMF) and Lyon (MF) in France, Hasselroth in Germany (MG), Collobiano in Italy (SI), and Las Vegas in Spain (SS) (Oppold et al, 2016) (Figure 1)
Populations were raised at these tempera‐ tures for three and five generations to simulate the possible seasonal exposure range; this phase will hereafter be referred to as “Pre‐Exposure Temperature” (PET)

Summary

Introduction

Ambient temperature variation is a major factor affecting the fit‐ ness of organisms by regulating the speed of metabolic processes, and everything from development to reproduction (Atkinson, 1994). Ectothermic organisms are affected, due to their dependence of body temperature from ambient temperature (Clarke & Fraser, 2004; Deutsch et al, 2008). Metabolic rates show a more or less linear temperature response over a large tem‐ perature range; below and above a species‐specific thresh‐ old, physiological performance rapidly drops. The mortality curve takes on a U shape, skewed toward higher tem‐ peratures with a maximal fitness at certain, optimal temperature (Topt). The edges of this curve are characterized by a steep drop of survival at a certain low and high temperature (Tcrit) (Regniere, Powell, Bentz, & Nealis, 2012) that usually coincides with the drop in physiological performance.

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Conclusion