The foraging behaviour of the salt-marsh parasitoid, Anagrus delicatus (Hymenoptera: Mymaridae), is distinguished by few eggs laid per patch of hosts and frequent dispersal among patches. We investigated the within-population genetic variability in six quantitative traits associated with this unusual behavior: fecundity (lifetime number of eggs), time on a patch, number of ovipositions per patch, oviposition rate, ovipositor length, and tibia length (a measure of body size). Forty-one wasp isolines were initiated from single parthenogenetic females from 3 isolated salt marshes, and were maintained for up to 8 generations in the greenhouse. We estimated the genetic variance and broad-sense heritability (h2) of these traits and tested trait means for differences among isolines (genetic variation) and sites (geographic variation).
We found significant genetic variability among isolines for all traits except oviposition rate. Both the behavioural and morphological traits had similar levels of genetic variance, indicating that the evolvability (ability to respond to selection) of the traits is similarly high. However, the behavioural traits had higher residual variances, resulting in lower heritabilities. Only two traits had significant heritabilities. Fecundity, which is likely a good proxy for fitness, ceteris paribus, varied from on average 26 to 40 eggs per isoline and had the highest h2, 0.47 +/- 0.16 (mean +/- 1SE). Ovipositor length had an h2 of 0.36 +/- 0.17. These results suggest that that the traits comprising the foraging strategy of A. delicatus should be amenable to selection (e.g., isolines could be selected that lay more eggs per host patch and consequently visit fewer patches).
Genetic correlations among traits were numerous and positive. One important prediction from these data is that selection for larger wasps will result in large offspring with greater egg loads and higher oviposition rates. Wasps with this combination of attributes are likely to be more efficient natural enemies for use in biological control. In addition, there was no significant divergence (genetic or otherwise) in wasp morphology or behaviour among the three sites, even though they were separated by 8 km or more.