Limited scope for plasticity to increase upper thermal limits

Authors: Belinda van Heerwaarden, Vanessa Kellermann and Carla M Sgrò

Published in: Functional Ecology (early view)

Summary

Increases in average temperature and the frequency of extreme temperature events are likely to pose a major risk to species already close to their upper physiological thermal limits. The extent to which thermal phenotypic plasticity can buffer these changes and whether plasticity is constrained by basal tolerance levels remains unknown.

We examined the effect of developmental temperature under both constant and fluctuating thermal regimes (developmental acclimation), as well as short-term heat hardening, on upper thermal limits (CTmax) in a tropical and temperate population of Drosophila melanogaster.

We found evidence for thermal plasticity in response to both developmental acclimation and hardening treatments; CTmax increased at warmer developmental temperatures and with a prior heat hardening treatment. However, hardening and acclimation responses were small, improving CTmax by a maximum of 1·01 °C. These results imply that overheating risk will only be minimally reduced by plasticity.

We observed significant associations between developmental temperature and both basal CTmax and hardening capacity (a measure of the extent of the plastic response). Basal CTmax increased, while hardening capacity decreased, with increasing developmental acclimation temperature. This indicates that increases in basal heat resistance at warmer temperatures may come at the cost of a reduced capacity to harden.

While plasticity in CTmax is evident in both populations of D. melanogaster we studied, plastic increases in upper thermal limits, particularly at warmer temperatures, may not be sufficient to keep pace with temperature increases predicted under climate change.

Citation

van Heerwaarden B, Kellerman V, Sgrò CM (2016) Limited scope for plasticity to increase upper thermal limits. Functional Ecology PDF DOI

 

What can plasticity contribute to insect responses to climate change?

Authors: Carla M Sgro, John S Terblanche and Ary A Hoffmann

Published in: Annual Reviews of Entomology (early view)

Abstract

Plastic responses figure prominently in discussions on insect adaptation to climate change.

Here we review the different types of plastic responses and whether they contribute much to adaptation.

Under climate change, plastic responses involving diapause are often critical for population persistence, but key diapause responses under dry and hot conditions remain poorly understood.

Climate variability can impose large fitness costs on insects showing diapause and other life cycle responses, threatening population persistence.

In response to stressful climatic conditions, insects also undergo ontogenetic changes including hardening and acclimation. Environmental conditions experienced across developmental stages or by prior generations can influence hardening and acclimation, although evidence for the latter remains weak. Costs and constraints influence patterns of plasticity across insect clades, but they are poorly understood within field contexts.

Plastic responses and their evolution should be considered when predicting vulnerability to climate change—but meaningful empirical data lag behind theory.

Citation

Sgrò CM, Terblanche J, Hoffmann AA (2016) What can plasticity contribute to insect respones to climate change? Annual Reviews of Entomology 61: 433–451. PDF DOI

 

Low evolutionary potential for egg-to-adult viability in Drosophila melanogaster at high temperatures

Authors: Torsten N Kristensen, Johannes Overgaard, Jan Lassen, Ary A Hoffmann and Carla Sgrò

Published in: Evolution, volume 69, issue 3 (March 2015)

Abstract

To cope with the increasing and less-predictable temperature forecasts under climate change, many terrestrial ectotherms will have to migrate or rely on adaptation through plastic or evolutionary means.

Studies suggest that some ectotherms have a limited potential to change their upper thermal limits via evolutionary shifts, but research has mostly focused on adult life stages under laboratory conditions.

Here we use replicate populations of Drosophila melanogaster and a nested half-sib/full-sib quantitative genetic design to estimate heritabilities and genetic variance components for egg-to-adult viability under both laboratory and seminatural field conditions, encompassing cold, benign, and hot temperatures in two separate populations.

The results demonstrated temperature-specific heritabilities and additive genetic variances for egg-to-adult viability. Heritabilities and genetic variances were higher under cold and benign compared to hot temperatures when tested under controlled laboratory conditions. Tendencies toward lower evolutionary potential at higher temperatures were also observed under seminatural conditions although the results were less clear in the field setting.

Overall the results suggest that ectotherms that already experience temperatures close to their upper thermal tolerance limits have a restricted capacity to adapt to higher temperatures by evolutionary means.

Citation

Kristensen TN, Overgaard J, Lassen J, Hoffmann, AA and Sgrò CM (2015). Low evolutionary potential for egg‐to‐adult viability in Drosophila melanogaster at high temperatures. Evolution 69: 803–814 PDF DOI

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

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 thermalplasticity along a latitudinal gradient in Drosophila simulans from eastern Australia. Journal of Evolutionary Biology 27:2541–2553 PDF DOI