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Plasticity of the thermal requirements of exotherms and adaptation to environmental conditions.

ABSTRACT:

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In exothermal organisms, temperature is an important determinant of the rate of ecophysiological processes, which monotonically increase between the minimum (t d min) and maximum (t d max) temperatures typical for each species. In insects, t d min and t d max are correlated and there is a approximately 20°C interval (thermal window W T = t d max - t d min) between them over which insects can develop. We assumed that other exotherms have similar thermal windows because the thermal kinetics of their physiological processes are similar. In this study, we determined the thermal requirements for germination in plants. Seeds of 125 species of Central European wild herbaceous and crop plants were germinated at nine constant temperatures between 5 and 37°C, and the time to germination of 50% of the seeds D and rate of germination R (=1/D) were determined for each temperature and the Lactin model used to determine t d min, t d max, and W T. The average width of the thermal windows for seeds was significantly wider (mean 24°C, 95% CI 22.7-24.2°C), varied more (between 14.5 and 37.5°C) and development occurred at lower temperatures than recorded for insects. The limiting temperatures for germination, t d min and t d max, were not coupled, so the width of the thermal window increased with both a decrease in t d min and/or increase in t d max. Variation in W T was not associated with taxonomic affiliation, adult longevity, or domestication of the different species, but tends to vary with seed size. Plants are poor at regulating their temperature and cannot move to a more suitable location and as a consequence have to cope with wider ranges in temperatures than insects and possibly do this by having wider thermal windows.

Synthesis

The study indicated specificity of W T in different exotherm taxa and/or their development stages.

SUBMITTER: Honek A

PROVIDER: S-EPMC4161183 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Plasticity of the thermal requirements of exotherms and adaptation to environmental conditions.

Honek Alois A Martinkova Zdenka Z Lukas Jan J Dixon Anthony F G AF

Ecology and evolution 20140715 15

<h4>Unlabelled</h4>In exothermal organisms, temperature is an important determinant of the rate of ecophysiological processes, which monotonically increase between the minimum (t d min) and maximum (t d max) temperatures typical for each species. In insects, t d min and t d max are correlated and there is a approximately 20°C interval (thermal window W T = t d max - t d min) between them over which insects can develop. We assumed that other exotherms have similar thermal windows because the ther ...[more]

PMID: 25247067

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Project description:The most diverse and abundant family of termites, the Termitidae, evolved in African tropical forests. They have since colonised grassy biomes such as savannas. These open environments have more extreme conditions than tropical forests, notably wider extremes of temperature and lower precipitation levels and greater temporal fluctuations (of both annual and diurnal variation). These conditions are challenging for soft-bodied ectotherms, such as termites, to survive in, let alone become as ecologically dominant as termites have. Here, we quantified termite thermal limits to test the hypothesis that these physiological limits are wider in savanna termite species to facilitate their existence in savanna environments. We sampled termites directly from mound structures, across an environmental gradient in Ghana, ranging from wet tropical forest through to savanna. At each location, we quantified both the Critical Thermal Maxima (CTmax ) and the Critical Thermal Minima (CTmin ) of all the most abundant mound-building Termitidae species in the study areas. We modelled the thermal limits in two separate mixed-effects models against canopy cover at the mound, temperature and rainfall, as fixed effects, with sampling location as a random intercept. For both CTmax and CTmin , savanna species had significantly more extreme thermal limits than forest species. Between and within environments, areas with higher amounts of canopy cover were significantly associated with lower CTmax values of the termite colonies. CTmin was significantly positively correlated with rainfall. Temperature was retained in both models; however, it did not have a significant relationship in either. Sampling location explained a large proportion of the residual variation, suggesting there are other environmental factors that could influence termite thermal limits. Our results suggest that savanna termite species have wider thermal limits than forest species. These physiological differences, in conjunction with other behavioural adaptations, are likely to have enabled termites to cope with the more extreme environmental conditions found in savanna environments and facilitated their expansion into open tropical environments.

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Plasticity of the thermal requirements of exotherms and adaptation to environmental conditions.

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Synthesis

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Plasticity of the thermal requirements of exotherms and adaptation to environmental conditions.

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