Abstract
Larvae of parasitoid wasps develop on a single arthropod host, and often face resource limitation that induces a tradeoff between egg maturation and somatic growth. Part of the variation in the growth-reproduction allocation was shown to be heritable, but how the larval developmental environment affects this allocation is not well-known. Detection of life history tradeoffs is often facilitated under stress conditions. We therefore exposed developing female larvae of the polyembryonic parasitoid Copidosoma koehleri (Hymenoptera: Encyrtidae) to laboratory manipulations aimed to restrict host resources (either host-starvation or high larval density). We compared the females’ body sizes and egg loads shortly after adult emergence (<24 h) to those of closely related control females, which developed at a lower larval density within non-starved hosts. Host-starvation reduced the females’ body sizes but not their initial egg loads. Females that experienced high larval density produced more eggs but were similar in body size to the low-density controls. Thus, the relative allocation to reproduction increased in response to both manipulations of host condition. Developmental duration and longevity were similar in all treatments. The negative correlation between body size and reproductive allocation, observed in the host-starvation treatment, is compatible with previous evidence from other parasitoids. In the high larval density treatment, however, reproductive allocation increased while body size was maintained, suggesting that the higher density increased rather than limited host resources per developing parasitoid female. The additional host resources that were diverted into egg production possibly resulted from increased feeding and body mass gain by hosts parasitized by large broods of wasps. Our results demonstrate phenotypic plasticity in resource allocation between growth and reproduction in a developing parasitoid. This plasticity may contribute to an adaptive balance between longevity and mobility vs. fecundity during the adult stage.
Highlights
Animals trade off somatic growth and maintenance with reproductive investment under resource limitations
Tradeoffs due to resource constraints often apply to larvae of parasitoid wasps that consume a single host individual during their development
The fraction of the egg complement that is mature at adult emergence is termed the Ovigeny Index (OI) and provides a measure of early-life investment in reproduction
Summary
Animals trade off somatic growth and maintenance with reproductive investment under resource limitations. Phenotypic plasticity of pre-adult egg maturation in a parasitoid life-history traits such as fecundity and longevity [1]. Some of the tradeoffs are evolved and heritable, resulting from selection for one life-history trait at the expense of another [2]. An individual’s resource allocation to survival vs reproduction varies with environmental conditions, indicating phenotypic plasticity in balancing the tradeoff [3]. Tradeoffs due to resource constraints often apply to larvae of parasitoid wasps that consume a single host individual during their development. Egg development starts during the larval phase and continues in the adult. The fraction of the egg complement that is mature at adult emergence is termed the Ovigeny Index (OI) and provides a measure of early-life investment in reproduction. An OI of 1 (strict pro-ovigeny) indicates that the female emerges with all of her oocytes mature and ready for oviposition; whereas an OI of 0 (extreme syn-ovigeny) denotes that the female emerges with no mature oocytes [5]
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