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Thermal physiology of entomopathogenic nematodes (EPN) is a critical aspect of field performance and fitness. Thermal limits for survival and activity, and the ability of these limits to adjust (i.e. show phenotypic flexibility) depending on recent thermal history, are generally poorly established, especially for non-model nematode species. Here we report the acute thermal limits for survival, and the thermal acclimation-related plasticity thereof for two key endemic South African EPN species, Steinernema yirgalemense and Heterorhabditis zealandica. Results including LT50 indicate S. yirgalemense (LT50 = 40.8±0.3°C) has greater high temperature tolerance than H. zealandica (LT50 = 36.7±0.2°C), but S. yirgalemense (LT50 = -2.4±0°C) has poorer low temperature tolerance in comparison to H. zealandica (LT50 = -9.7±0.3°C), suggesting these two EPN species occupy divergent thermal niches to one another.
Acclimation had both negative and positive effects on temperature stress survival of both species, although the overall variation meant that many of these effects were non-significant. There was no indication of a consistent loss of plasticity with improved basal thermal tolerance for either species at upper lethal temperatures. At lower temperatures measured for H. zealandica, the 5°C acclimation lowered survival until below -12.5°C, where after it increased survival. Such results indicate that the thermal niche breadth of EPN species can differ significantly depending on recent thermal conditions, and should be characterized across a broad range of species to understand the evolution of thermal limits to performance and survival in this group.
This submission has been accepted at PeerJ.
Acclimation and lethal thermal tolerances for two species of entomopathogenic nematodes, Heterorhabditis zealandica and Steinernema yirgalemense
Error bars reflect ±1 standard error. Data represents the cohorts seperately: red indicates the first batch of experiments scored by MPH, blue indicates the second cohort of experiments scored by EL.
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