Interactions among morphotype, nutrition, and temperature impact fitness of an invasive fly

Abstract

Invasive animals depend on finding a balanced nutritional intake to colonize, survive, and reproduce in new environments. This can be especially challenging during situations of fluctuating cold temperatures and food scarcity, but phenotypic plasticity may offer an adaptive advantage during these periods. We examined how lifespan, fecundity, pre-oviposition periods, and body nutrient contents were affected by dietary protein and carbohydrate (P:C) ratios at variable low temperatures in two morphs (winter morphs WM and summer morphs SM) of an invasive fly, Drosophila suzukii. The experimental conditions simulated early spring after overwintering and autumn, crucial periods for survival. At lower temperatures, post-overwintering WM lived longer on carbohydrate-only diets and had higher fecundity on low-protein diets, but there was no difference in lifespan or fecundity among diets for SM. As temperatures increased, low-protein diets resulted in higher fecundity without compromising lifespan, while high-protein diets reduced lifespan and fecundity for both WM and SM. Both SM and WM receiving high-protein diets had lower sugar, lipid, and glycogen (but similar protein) body contents compared to flies receiving low-protein and carbohydrate-only diets. This suggests that flies spend energy excreting excess dietary protein, thereby affecting lifespan and fecundity. Despite having to recover from nutrient depletion after an overwintering period, WM exhibited longer lifespan and higher fecundity than SM in favorable diets and temperatures. WM exposed to favorable low-protein diet had higher body sugar, lipid, and protein body contents than SM, which is possibly linked to better performance. Although protein is essential for oogenesis, WM and SM flies receiving low-protein diets did not have shorter pre-oviposition periods compared to flies on carbohydrate-only diets. Finding adequate carbohydrate sources to compensate protein intake is essential for the successful persistence of D. suzukii WM and SM populations during suboptimal temperatures.

Keywords: Drosophila suzukii; carbohydrates; fecundity; lifespan; overwintering; protein.

Figure 1

Drosophila suzukii WM and SM lifespan in variable diets and temperatures. The box represents the interquartile range, the line in the middle is the median, and whiskers represent extreme values within 1.5 times the interquartile range. Different lowercase letters represent differences between diets for each temperature (separately for WM and SM); different uppercase letters represent differences between temperatures for each diet (separately for WM and SM). The number represents sample size for each treatment. Asterisks represent diet and temperature treatments where SM and WM were significantly different

Figure 2

Drosophila suzukii WM and SM fecundity in variable diets and temperatures (total egg lay, mean ± SE). Different lowercase letters represent differences between diets for each temperature (separately for WM and SM); different uppercase letters represent differences between temperatures for each diet (separately for WM and SM). The number represents sample size for each treatment. Asterisks represent diet and temperature treatments where SM and WM were significantly different

Figure 3

Drosophila suzukii WM and SM pre‐oviposition period in variable diets and temperatures (calendar days, mean ± SE). Different lowercase letters represent differences between diets for each temperature (separately for WM and SM); different uppercase letters represent differences between temperatures for each diet (separately for WM and SM). The number represents sample size for each treatment. Asterisks represent diet and temperature treatments where SM and WM were significantly different

Figure 4

Drosophila suzukii winter (WM) and summer morph (SM) total body content of protein, sugar, lipid, and glycogen exposed to different diets (Protein:Carbohydrate 0:0, 0:1, 1:4, 1:2, 1:1; mean ± SE) for seven days at 17°C. Bars with same letters within each nutrient are not significantly different (Tukey HSD). Asterisks represent significant differences between WM and SM within each diet (t test).

Figure 5

Weekly total body content of protein, sugar, lipid, and glycogen in Drosophila suzukii WM females during five weeks of overwintering at 1°C