Short-term exposure to predation affects body elemental composition, climbing speed and survival ability in Drosophila melanogaster

Abstract

Factors such as temperature, habitat, larval density, food availability and food quality substantially affect organismal development. In addition, risk of predation has a complex impact on the behavioural and morphological life history responses of prey. Responses to predation risk seem to be mediated by physiological stress, which is an adaptation for maintaining homeostasis and improving survivorship during life-threatening situations. We tested whether predator exposure during the larval phase of development has any influence on body elemental composition, energy reserves, body size, climbing speed and survival ability of adult Drosophila melanogaster. Fruit fly larvae were exposed to predation by jumping spiders (Phidippus apacheanus), and the percentage of carbon (C) and nitrogen (N) content, extracted lipids, escape response and survival were measured from predator-exposed and control adult flies. The results revealed predation as an important determinant of adult phenotype formation and survival ability. D. melanogaster reared together with spiders had a higher concentration of body N (but equal body C), a lower body mass and lipid reserves, a higher climbing speed and improved adult survival ability. The results suggest that the potential of predators to affect the development and the adult phenotype of D. melanogaster is high enough to use predators as a more natural stimulus in laboratory experiments when testing, for example, fruit fly memory and learning ability, or when comparing natural populations living under different predation pressures.

Keywords: Body reserves; Drosophila melanogaster; Elemental composition; Fear ecology; Negative geotaxis; Spider predation; Stress; Survival.

Figure 1. Dry body mass (A) and mass of lipids (B) of D. melanogaster flies that were exposed to spider predation in the experimental group and reared without spiders in the control group.

Data represent mean ± 95% confidence intervals. *** indicates significant main effects of sex and treatment (two-way ANOVA, P < 0.0001). X indicates significant interaction between sex and treatment (two-way ANOVA, P < 0.0001); different letters denote significant differences by Tukey’s post hoc tests (P < 0.001).

Figure 2. Elemental composition of adult D. melanogaster flies reared in different conditions.

Average carbon percentage (A), nitrogen percentage (B), and carbon and nitrogen ratio (C) of D. melanogaster flies reared with spiders in the experimental group and without spiders in the control group. Error bars represent ±95% confidence intervals. * indicates main effects of sex (two-way ANOVA, P < 0.05), *** indicates significant main effects of sex and treatment (two-way ANOVA, P < 0.0001). X indicates significant interaction between sex and treatment (two-way ANOVA, P < 0.0001); different letters denote significant differences by Tukey’s post hoc tests (P < 0.01).

Figure 3. Geotaxis responses (mean ± 95% confidence intervals) of D. melanogaster flies reared with spiders in the experimental group and without spiders in the control group.

The y-axis represents percentage of flies that have reached the 7-cm mark in 10 s. *** indicates significant main effects of sex and treatment (two-way ANOVA, P < 0.0001).

Figure 4. Survival percentage (mean ± 95% confidence intervals) of D. melanogaster adult individuals during 12-h exposure to predation by jumping spider.

The flies of the experimental group were previously exposed to predation during the larval stage, while in the control group the flies were raised without spiders. *** indicates significant main effect of treatment (two-way ANOVA, P < 0.0001).