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

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

# Is adaptation to climate change really constrained in niche specialists?

Authors: Belinda van Heerwaarden and Carla M Sgrò

Published in: Proceedings of the Royal Society B, volume 281, number 1790 (September 2014)

## Abstract

Species with restricted distributions make up the vast majority of biodiversity.

Recent evidence suggests that Drosophila species with restricted tropical distributions lack genetic variation in the key trait of desiccation resistance. It has therefore been predicted that tropically restricted species will be limited in their evolutionary response to future climatic changes and will face higher risks of extinction. However, these assessments have been made using extreme levels of desiccation stress (less than 10% relative humidity (RH)) that extend well beyond the changes projected for the wet tropics under climate change scenarios over the next 30 years.

Here, we show that significant evolutionary responses to less extreme (35% RH) but more ecologically realistic levels of climatic change and desiccation stress are in fact possible in two species of rainforest restricted Drosophila. Evolution may indeed be an important means by which sensitive rainforest-restricted species are able to mitigate the effects of climate change.

## Citation

van Heerwaarden, B Sgrò CM (2014) Is adaptation to climate change really constrained in niche specialists? Proceedings of the Royal Society B

# Evolutionary capacity of upper thermal limits: beyond single trait assessments

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

Published in: Journal of Experimental Biology, volume 217, number 11 (June 2014)

## Abstract

Thermal tolerance is an important factor influencing the distribution of ectotherms, but we still have limited understanding of the ability of species to evolve different thermal limits.

Recent studies suggest that species may have limited capacity to evolve higher thermal limits in response to slower, more ecologically relevant rates of warming. However, these conclusions are based on univariate estimates of adaptive capacity.

To test these findings within an explicitly multivariate context, we used a paternal half-sibling breeding design to estimate the multivariate evolutionary potential for upper thermal limits in Drosophila melanogaster. We assessed heat tolerance using static (basal and hardened) and ramping assays.

Additive genetic variances were significantly different from zero only for the static measures of heat tolerance. Our G matrix analysis revealed that any response to selection for increased heat tolerance will largely be driven by static basal and hardened heat tolerance, with minimal contribution from ramping heat tolerance.

These results suggest that the capacity to evolve upper thermal limits in nature may depend on the type of thermal stress experienced.

## Citation

Blackburn S, van Heerwaarden B, Kellermann V, Sgrò CM (2014) Evolutionary capacity of upper thermal limits: beyond single trait assessments. Journal of Experimental Biology
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