Does a negative genetic correlation between wing morph and early fecundityimply a functional constraint in Gryllus firmus?

We tested the hypothesis that wing muscle size and triglyceride production mediate a life-history trade-off between wing morph (or flight capability) and early fecundity. Roff et al. recently selected for lower number of eggs laid in the first week by Gryllus firmus (sand cricket) and reported a cor related increase in lone-winged (and presumably flight-capable) females, bu t did not test structural or energetic reproductive costs associated with f light capability. We used ovary weight of virgin crickets as an index of th eir early fecundity and dorsal longitudinal flight muscle (DLM) weight as a quantitative measure of flight muscle status. A preliminary experiment ind icated that DLM weight is highly correlated with other measures of DLM stat us (colour, histolysis state, size). We used a haemolymph assay for acylgly cerol concentration as an index of mobile triglyceride derivatives thought to provide energy for flight. Both DLM weight and acylglycerol concentratio n were negatively related to ovary weight of long-winged crickets, indicati ng wing muscle size and triglyceride concentrations mediate reproductive co sts. In short-winged females, only DLM weight had a negative phenotypic rel ationship with ovary weight. The heritability of DLM weight and acylglycero l concentration are unknown, so we used the direction and size of standardi zed differences between base and selected populations to test whether DLM w eight and acylglycerol concentration are negatively genetically correlated with ovary weight. Acylglycerol concentration and DLM weight increased in t he population selected for low numbers of eggs laid within both wing morphs . Large standardized differences in short-winged females provide strong cor roborative evidence of a genetic relationship between early fecundity and R ight capability. These results indicate negative genetic correlations betwe en wing morph and early fecundity reflect inherited variation in costs of e arly reproduction, related to physiological investment in flight capability (flight muscle size and triglyceride allocation), rather than being an arb itrary assumption of a life-history trade-off model.