Are Signals of Local Environmental Adaptation Diluted by Laboratory Culture?

Abstract

Insects have the ability to readily adapt to changes in environmental conditions, however the strength of local environmental adaptation signals under divergent conditions and the occurrence of trait inertia after relaxation of selection, remains poorly understood, especially for traits of climate stress resistance (CSR) and their phenotypic plasticity. The strength of environmental adaptation signals depend on several selection pressures present in the local environment, while trait inertia often occurs when there is a weakening or removal of a source of selection. Here, using Drosophila melanogaster, we asked whether signals of adaptation in CSR traits (critical thermal limits, heat and chill survival and, desiccation and starvation resistance) persist after exposure to laboratory culture for different durations (two vs. ten generations) across four climatically distinct populations. We show that culture duration has large effects on CSR traits and can both amplify or dilute signals of local adaptation. Effects were however dependent upon interactions between the source population, acclimation (adult acclimation at either 18 °C, 23 °C or 28 °C) conditions and the sex of the flies. Trait plasticity is markedly affected by the interaction between the source population, the specific acclimation conditions employed, and the duration in the laboratory. Therefore, a complex matrix of dynamic CSR trait responses is shown in space and time. Given these strong interaction effects, 'snapshot' estimates of environmental adaptation can result in misleading conclusions about the fitness consequences of climate variability.

Keywords: Climate change; Desiccation resistance; Safety margin; Starvation resistance; Survival; Thermal tolerance; Trade-off.

Fig. 1

The effect of source population (Citrusdal, Durban, Polokwane, or Stellenbosch), time spent in culture (F2 vs F10 generation), developmental acclimation (18 °C, 23 °C or 28 °C) and sex (male or female) on CT_MAX ( °C) (left) and CT_MIN ( °C) (right) estimates in Drosophila melanogaster. Boxplot indicating median CT_MAX ( °C) and CT_MIN ( °C), upper and lower quantiles and maximum and minimum values (whiskers), with raw data overlaid (black dots).

Fig. 2

The effect of source population (Citrusdal, Durban, Polokwane, or Stellenbosch), time spent in culture (F2 vs F10 generation), developmental acclimation (18 °C, 23 °C or 28 °C) and sex (male or female) on heat (left) and chill survival (right) (%) estimates in Drosophila melanogaster. Box and whiskers indicate mean, standard error and mean ± 1.96 SE.

Fig. 3

The effect of source population (Citrusdal, Durban, Polokwane, or Stellenbosch) (represented by the rows), time spent in culture (F2 vs F10 generation), developmental acclimation (18 °C (blue), 23 °C (green) or 28 °C (red)) and sex (male or female) on desiccation (left column) and starvation (right column) resistance (time in hours) estimates in Drosophila melanogaster. Differences between acclimation treatments are indicated on each plot.