A comprehensive assessment of geographic variation in heat tolerance and hardening capacity in populations of Drosophila melanogaster from eastern Australia

Authors

  • C. M. SGRÒ,

    1. School of Biological Sciences and Centre for Environmental Stress & Adaptation Research, Monash University, Clayton, Melbourne, Australia
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  • J. OVERGAARD,

    1. Department of Biological Sciences, Aarhus University, Ny Munkegade Aarhus C, Denmark
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  • T. N. KRISTENSEN,

    1. Department of Biological Sciences, Aarhus University, Ny Munkegade Aarhus C, Denmark
    2. Department of Genetics and Biotechnology, Aarhus University, Blichers Allé, Tjele, Denmark
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  • K. A. MITCHELL,

    1. Department of Genetics, and Centre for Environmental Stress & Adaptation Research, The University of Melbourne, Parkville, Melbourne, Australia
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  • F. E. COCKERELL,

    1. School of Biological Sciences and Centre for Environmental Stress & Adaptation Research, Monash University, Clayton, Melbourne, Australia
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  • A. A. HOFFMANN

    1. Department of Genetics, and Centre for Environmental Stress & Adaptation Research, The University of Melbourne, Parkville, Melbourne, Australia
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Carla M. Sgrò, School of Biological Sciences and Centre for Environmental Stress & Adaptation Research, Monash University, Clayton, Melbourne 3800, Australia.
Tel.: ++61 3 9902 0332; fax: ++61 3 9905 5613; e-mail: carla.sgro@monash.edu

Abstract

We examined latitudinal variation in adult and larval heat tolerance in Drosophila melanogaster from eastern Australia. Adults were assessed using static and ramping assays. Basal and hardened static heat knockdown time showed significant linear clines; heat tolerance increased towards the tropics, particularly for hardened flies, suggesting that tropical populations have a greater hardening response. A similar pattern was evident for ramping heat knockdown time at 0.06 °C min−1 increase. There was no cline for ramping heat knockdown temperature (CTmax) at 0.1 °C min−1 increase. Acute (static) heat knockdown temperature increased towards temperate latitudes, probably reflecting a greater capacity of temperate flies to withstand sudden temperature increases during summer in temperate Australia. Larval viability showed a quadratic association with latitude under heat stress. Thus, patterns of heat resistance depend on assay methods. Genetic correlations in thermotolerance across life stages and evolutionary potential for critical thermal limits should be the focus of future studies.

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