Intraspecific variability in egg maturation patterns and associated life‐history trade‐offs in a polyembryonic parasitoid wasp

Abstract

1. Life‐history theory predicts a trade‐off between the resources allocated to reproduction and those allocated to survival. Early maturation of eggs (pro‐ovigeny) is correlated with small body size and low adult longevity in interspecific comparisons among parasitoids, demonstrating this trade‐off. The handful of studies that have tested for similar correlations within species produced conflicting results.2. Egg maturation patterns and related life‐history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro‐ovigenic, mean egg loads of host‐deprived females almost doubled within their first 6 days of adulthood.3. The initial egg‐loads of newly emerged females were determined and age‐specific realised fecundity curves were constructed for their clone‐mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity.4. The variation in initial egg loads was lowest among clone‐mates, intermediate among non‐clone sisters and highest among non‐sister females. The within‐clone variability indicates environmental influences on egg maturation, while the between‐clone variation may be genetically based.5. Ovaries of host‐deprived females contained fewer eggs at death (at ∼29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition.6. It is concluded that adult fecundity and longevity were not traded off with pre‐adult egg maturation.

Phenotypic plasticity of pre-adult egg maturation in a parasitoid: Effects of host-starvation and brood size

“…Energy constraints for females in our experiment may have been alleviated because we allowed them unlimited access to honey. This assumption is supported by the lack of correlation between initial egg loads and adult survival in other experiments that provided adult parasitoids with food [ 12 , 39 ]. Moreover, all females in our study were host-deprived and thus none of them became egg-limited.…”

“…Having a smaller body size, females from the starvation treatment that would reach egg-limitation might encounter greater difficulty producing and laying more eggs, and possibly pay a price through reduced life span. This possibility is supported by the finding that host-deprived females have a significantly longer life span than their host-exposed twin sisters [ 12 ]. Thus, the energetic costs of maturing and laying numerous eggs seem to reduce survival.…”

“…The species has been proposed to be pro-ovigenic [ 17 ] (the females’ full egg complement is mature at adult emergence and no additional eggs are produced during the adult stage), but a recent study showed that C . koehleri Females mature only about 30% of their eggs before adult emergence [ 12 ]. The longevity of honey-fed adults is about 30 days under lab conditions [ 18 ] and the wasps do not host-feed (personal observation).…”

“…As this species is strictly pro-ovigenic, this indicates a genetic component to pre-adult egg maturation. Finally, in the polyembryonic gregarious parasitoid Copidosoma koehleri , the focus of the present study, variation in initial egg loads among individuals decreased with genetic relatedness [ 12 ].…”

“…Nevertheless, most of the variation in the timing of reproductive investment of parasitoids is not explained by genetic background [ 10 , 12 ]. An additional potential source of variation is pre-maturation phenotypic plasticity, namely adjustment of egg maturation rates to the environmental conditions experienced by developing larvae.…”