Plasticity for desiccation tolerance across Drosophila species is affected by phylogeny and climate in complex ways

Abstract

Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extremes, yet responses to aridity may be equally important. Here we focus on plasticity in desiccation resistance, a key trait shaping distributions of Drosophila species and other small ectotherms. We examined the extent to which 32 Drosophila species, varying in their distribution, could increase their desiccation resistance via phenotypic plasticity involving hardening, linking these responses to environment, phylogeny and basal resistance. We found no evidence to support the seasonality hypothesis; species with higher hardening plasticity did not occupy environments with higher and more seasonal precipitation. As basal resistance increased, the capacity of species to respond via phenotypic plasticity decreased, suggesting plastic responses involving hardening may be constrained by basal resistance. Trade-offs between basal desiccation resistance and plasticity were not universal across the phylogeny and tended to occur within specific clades. Phylogeny, environment and trade-offs all helped to explain variation in plasticity for desiccation resistance but in complex ways. These findings suggest some species have the ability to counter dry periods through plastic responses, whereas others do not; and this ability will depend to some extent on a species' placement within a phylogeny, along with its basal level of resistance.

Keywords: climate change; desiccation; phenotypic plasticity; seasonality; trade-off.

Figure 1.

Relationship between basal resistance, plasticity and environment. General linear model showing the relationship between basal desiccation resistance and desiccation hardening (HC-3.5 and ARR) for the two environmental variables explaining the largest amount of variation in plasticity. (a) Basal desiccation resistance and P_ANN and T_MAX, (b) basal desiccation resistance and P_WARM and T_MAX, (c) hardening capacity at 3.5 (HC-3.5) and T_MAX and P_WARM and (d) acclimation response ratio (ARR) and P_ANN and P_WARM.

Figure 2.

Evidence for trade-offs between basal resistance and plasticity. (a) The relationship between mean basal desiccation resistance (white circles) and (b) hardening capacity (HC-3.5) (solid circles) for precipitation of the warmest quarter (P_WARM).

Figure 3.

Patterns in basal desiccation resistance and plasticity across the phylogeny. Phylogenetic hypothesis for the 32 Drosophila species examined in this study, branch lengths reflect standardized time. Values next to the branches and the colours represent the ancestral state and the confidence intervals in hours for (a) basal desiccation resistance and (b) hardening capacity.

Figure 4.

Evidence for phylogenetically structured trade-offs in the Drosophila phylogeny. Stochastic character mapping for HC-3.5 for species displaying characteristics in line or divergent with the trade-off hypothesis. Pie graphs represent the posterior probabilities of a character state for each node calculated by re-sampling 100 character histories.