Rising temperature reduces divergence in resource use strategies in coexisting parasitoid species

Abstract

Coexistence of species sharing the same resources is often possible if species are phylogenetically divergent in resource acquisition and allocation traits, decreasing competition between them. Developmental and life-history traits related to resource use are influenced by environmental conditions such as temperature, but thermal trait responses may differ among species. An increase in ambient temperature may, therefore, affect trait divergence within a community, and potentially species coexistence. Parasitoids are interesting models to test this hypothesis, because multiple species commonly attack the same host, and employ divergent larval and adult host use strategies. In particular, development mode (arrested or continued host growth following parasitism) has been recognized as a major organiser of parasitoid life histories. Here, we used a comparative trait-based approach to determine thermal responses of development time, body mass, egg load, metabolic rate and energy use of the coexisting Drosophila parasitoids Asobara tabida, Leptopilina heterotoma, Trichopria drosophilae and Spalangia erythromera. We compared trait values between species and development modes, and calculated trait divergence in response to temperature, using functional diversity indices. Parasitoids differed in their thermal response for dry mass, metabolic rate and lipid use throughout adult life, but only teneral lipid reserves and egg load were affected by developmental mode. Species-specific trait responses to temperature were probably determined by their adaptations in resource use (e.g. lipogenesis or ectoparasitism). Overall, trait values of parasitoid species converged at the higher temperature. Our results suggest that local effects of warming could affect host resource partitioning by reducing trait diversity in communities.

Variation in lipid synthesis, but genetic homogeneity, among Leptopilina parasitic wasp populations

“…Lipid synthesis was then found to vary intraspecifically in the parasitic wasp genus Leptopilina , but only one or few populations were ever tested simultaneously (Eijs et al., 1998; Le Lann et al., 2014; Moiroux et al., 2010; Visser et al., 2010). To gain a better understanding of intraspecific variation in lipid metabolism of parasitic wasps, a large‐scale analysis of lipid synthesis in Leptopilina was thus needed.…”

“…Another environmental factor that may affect the plastic induction of lipid synthesis is temperature, because the temperature at which experiments were performed differed between populations collected in 2013 and 2016. Only one study has so far tested the same wasp population at different temperatures (Le Lann et al., 2014): L. heterotoma females developed on the same D. melanogaster host strain at 20 and 23°C, after which adults were allowed to feed during 7 days. Body size and teneral lipid content did not differ between developmental temperatures, with the latter being ~20% (Le Lann et al., 2014).…”

“…Only one study has so far tested the same wasp population at different temperatures (Le Lann et al., 2014): L. heterotoma females developed on the same D. melanogaster host strain at 20 and 23°C, after which adults were allowed to feed during 7 days. Body size and teneral lipid content did not differ between developmental temperatures, with the latter being ~20% (Le Lann et al., 2014). Results obtained at 20°C, where an increase in lipid levels after feeding was found, were indeed similar to earlier findings (Visser et al., 2010), where the same population, host strain, and temperature were used.…”

“…An exception are species in the genus Leptopilina , which have been popular model systems for a multitude of research fields, including, but not limited to, studies on (theoretical) ecology and behavior (e.g., foraging behavior), chemical communication (e.g., host‐finding cues), life histories (e.g., time vs egg limitation), and physiology (e.g., host immunity) (Fleury, Gibert, Ris, & Allemand, 2009; Haccou, Vlas, Alphen, & Visser, 1991; Heavner et al., 2017; Janssen, van Alphen, Sabelis, & Bakker, 1995; Visser, van Alphen, & Hemerik, 1992; Wertheim, Vet, & Dicke, 2003). Initially, L. heterotoma (Figure 1) was found to lack lipid synthesis (Eijs, Ellers, & van Duinen, 1998), but data on another population later revealed active lipid synthesis (Le Lann et al., 2014; Visser et al., 2010). In a study using the closely related species Leptopilina boulardi , four populations were tested using the same host species that revealed contrasting lipogenic phenotypes: two populations synthesized lipids, while two populations did not (Moiroux et al., 2010).…”

“…Here, we started by collecting nine different L. heterotoma populations from the field in Europe in 2013 and tested these populations for the ability to synthesize lipids. Based on previous results in Leptopilina (Eijs et al., 1998; Le Lann et al., 2014; Moiroux et al., 2010; Visser et al., 2010) , we expected to find variation in the ability for lipid synthesis between populations. Intraspecific variation in ability for lipid synthesis was indeed observed between these populations, but all nine cultures perished before genetic structure could be determined.…”