Post-eclosion temperature effects on insect cuticular hydrocarbon profiles

Abstract

The insect cuticle is the interface between internal homeostasis and the often harsh external environment. Cuticular hydrocarbons (CHCs) are key constituents of this hard cuticle and are associated with a variety of functions including stress response and communication. CHC production and deposition on the insect cuticle vary among natural populations and are affected by developmental temperature; however, little is known about CHC plasticity in response to the environment experienced following eclosion, during which time the insect cuticle undergoes several crucial changes. We targeted this crucial to important phase and studied post-eclosion temperature effects on CHC profiles in two natural populations of Drosophila melanogaster. A forty-eight hour post-eclosion exposure to three different temperatures (18, 25, and 30°C) significantly affected CHCs in both ancestral African and more recently derived North American populations of D. melanogaster. A clear shift from shorter to longer CHCs chain length was observed with increasing temperature, and the effects of post-eclosion temperature varied across populations and between sexes. The quantitative differences in CHCs were associated with variation in desiccation tolerance among populations. Surprisingly, we did not detect any significant differences in water loss rate between African and North American populations. Overall, our results demonstrate strong genetic and plasticity effects in CHC profiles in response to environmental temperatures experienced at the adult stage as well as associations with desiccation tolerance, which is crucial in understanding holometabolan responses to stress.

Keywords: Drosophila melanogaster; cuticular hydrocarbons; desiccation tolerance; eclosion; natural populations; phenotypic plasticity; water loss rate.

Figure 1

Schematic representation of overall experimental design and hydrocarbon collection process from Drosophila melanogaster adults exposed to three different temperatures (18, 25, and 30°C) for 48 hr. Drosophila melanogaster developmental stages and a fly emerging from its pupal case is also shown

Figure 2

Representative GC chromatograms showing cuticular hydrocarbons (CHCs) of males and females from two continents (Africa and North America) and exposed post‐eclosion to tree different temperatures (18, 25, and 30°C) for 48 hr. The peak numbers indicated correspond to CHCs identifications listed in Table 1

Figure 3

Relative patterns of CHCs in females from Africa and American D. melanogaster held at three different post‐eclosion temperatures. (a & d) Projection of PCA factor scores. (b & e). Variable correlations with the first two PCA factors. Variables in bold were retrieved as among the most correlated with the CCA model using temperature as a categorical predictor in the PCA analysis; those in red are over‐represented in 18°C populations, those in blue are characteristic of 25°C and 30°C populations. (c & f) Heat map depicting the relative proportions of the 37 analyzed CHCs in the three groups. Numbering of CHCs corresponds to that in Table 1

Figure 4

Relative patterns of CHCs in males from African and American D. melanogaster populations held at three different post‐eclosion temperatures. (a & d) Projection of PCA factor scores. (b & e) Variable correlations with the first two PCA factors. Variables in bold were retrieved as among the most correlated with the CCA model using temperature as a categorical predictor in the PCA analysis; those in red are over‐represented in 18°C populations, those in blue are characteristic of 25°C and 30°C populations. (c & f) Heat map depicting the relative proportions of the 36 analyzed CHCs in the three groups. Numbering of CHCs corresponds to that in Table 1

Figure 5

Comparison of quantitative patterns of CHCs between males (a, b) and between females (c, d) from African and American populations, held at 18°C. Numbering of CHCs corresponds to that in Table 1. (a & c) Projection of PCA factor scores. (b & d) Variable correlations with the first two PCA factors. Variables in bold were retrieved as among the most correlated with the CCA model using temperature as a categorical predictor in the PCA analysis (red = American population, gray = African population)

Figure 6

Desiccation tolerance survival curves for males (a) and females (b) for two natural populations of D. melanogaster collected from Africa and North America. The assays were run immediately after exposure to three different temperature (18, 25, and 30°C) conditions post‐eclosion for 48 hr. Overall African populations performed better than North American populations under desiccating conditions