Tag Archives: thermotolerance

Increases in the evolutionary potential of upper thermal limits under warmer temperatures in two rainforest Drosophila species

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Authors: Belinda van Heerwaarden, Michelle Malmberg and Carla M Sgrò

Published in: Evolution (early view)

Abstract

Tropical and subtropical species represent the majority of biodiversity. These species are predicted to lack the capacity to evolve higher thermal limits in response to selection imposed by climatic change. However, these assessments have relied on indirect estimates of adaptive capacity, using conditions that do not reflect environmental changes projected under climate change.

Using a paternal half-sib full-sib breeding design, we estimated the additive genetic variance and narrow-sense heritability for adult upper thermal limits in two rainforest-restricted species of Drosophila reared under two thermal regimes, reflecting increases in seasonal temperature projected for the wet tropics of Australia and under standard laboratory conditions (constant 25‌°C).

Estimates of additive genetic variation and narrow-sense heritability for adult heat tolerance were significantly different from zero in both species under projected summer, but not winter or constant, thermal regimes. In contrast, significant broad-sense genetic variation was apparent in all thermal regimes for egg-to-adult viability.

Environment-dependent changes in the expression of genetic variation for adult upper thermal limits suggest that predicting adaptive responses to climate change will be difficult.

Estimating adaptive capacity under conditions that do not reflect future environmental conditions may provide limited insight into evolutionary responses to climate change.

Citation

van Heerwaarden B, Malmburg M, Sgrò CM (2016) Increases in the evolutionary potential of upper thermal limits under warmer temperatures in two rainforest Drosophila species. Evolution PDF DOI

Spatial analysis of gene regulation reveals new insights into the molecular basis of upper thermal limits

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Authors: Marina Telonis-Scott, Allannah S Clemson, Travis K Johnson and Carla M Sgrò

Published in: Molecular Ecology, volume 23, issue 24 (December 2014)

Abstract

The cellular stress response has long been the primary model for studying the molecular basis of thermal adaptation, yet the link between gene expression, RNA metabolism and physiological responses to thermal stress remains largely unexplored.

We address this by comparing the transcriptional and physiological responses of three geographically distinct populations of Drosophila melanogaster from eastern Australia in response to, and recovery from, a severe heat stress with and without a prestress hardening treatment.

We focus on starvin (stv), recently identified as an important thermally responsive gene. Intriguingly, stv encodes seven transcripts from alternative transcription sites and alternative splicing, yet appears to be rapidly heat inducible.

First, we show genetic differences in upper thermal limits of the populations tested. We then demonstrate that the stv locus does not ubiquitously respond to thermal stress but is expressed as three distinct thermal and temporal RNA phenotypes (isoforms). The shorter transcript isoforms are rapidly upregulated under stress in all populations and show similar molecular signatures to heat-shock proteins. Multiple stress exposures seem to generate a reserve of pre-mRNAs, effectively ‘priming’ the cells for subsequent stress.

Remarkably, we demonstrate a bypass in the splicing blockade in these isoforms, suggesting an essential role for these transcripts under heat stress. Temporal profiles for the weakly heat responsive stv isoform subset show opposing patterns in the two most divergent populations. Innate and induced transcriptome responses to hyperthermia are complex, and warrant moving beyond gene-level analyses.

Citation

Telonis-Scott, M, Clemson AS, Johnson TK, Sgrò, CM (2014) Spatial analysis of gene regulation reveals new insights into the molecular basis of upper thermal limits,
Molecular Ecology PDF DOI

No patterns in thermal plasticity along a latitudinal gradient in Drosophila simulates from eastern Australia

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Authors: Belinda van Heerwaarden, Richard Foo Heng Lee, Johannes Overgaard and Carla M Sgrò

Published in: Journal of Evolutionary Biology, volume 27, issue 11 (November 2014)

Abstract

Phenotypic plasticity may be an important initial mechanism to counter environmental change, yet we know relatively little about the evolution of plasticity in nature.

Species with widespread distributions are expected to have evolved higher levels of plasticity compared with those with more restricted, tropical distributions.

At the intraspecific level, temperate populations are expected to have evolved higher levels of plasticity than their tropical counterparts. However, empirical support for these expectations is limited. In addition, no studies have comprehensively examined the evolution of thermal plasticity across life stages.

Using populations of Drosophila simulans collected from a latitudinal cline spanning the entire east coast of Australia, we assessed thermal plasticity, measured as hardening capacity (the difference between basal and hardened thermal tolerance) for multiple measures of heat and cold tolerance across both adult and larval stages of development. This allowed us to explicitly ask whether the evolution of thermal plasticity is favoured in more variable, temperate environments.

We found no relationship between thermal plasticity and latitude, providing little support for the hypothesis that temperate populations have evolved higher levels of thermal plasticity than their tropical counterparts.

With the exception of adult heat survival, we also found no association between plas- ticity and ten climatic variables, indicating that the evolution of thermal plasticity is not easily predicted by the type of environment that a particular population occupies. We discuss these results in the context of the role of plasticity in a warming climate.

Citation

van Heerwaarden B, Lee RFH, Overgaard J, Sgrò CM (2014) No patterns in thermal plasticity along a latitudinal gradient in Drosophila simulans from eastern Australia. Journal of Evolutionary Biology PDF DOI