GENETIC DIFFERENTIATION OF FITNESS-ASSOCIATED TRAITS AMONG RAPIDLY EVOLVING POPULATIONS OF THE SOAPBERRY BUG

In this study we used reciprocal rearing experiments to test the hypot hesis that there is a genetic basis for the adaptive differences in ho st-use traits among host-associated soapberry bug populations (describ ed in Carroll and Boyd 1992). These experiments were conducted on two host races from Florida, in which differences in beak length and devel opment were found between natural populations on a native host plant s pecies and those on a recently introduced plant species (colonized mai nly post-1950). Performance was generally superior on the host species from which each lab population originated (i.e., on the ''Home'' host species): in analysis of variance, there was significant population-b y-host interaction for size, development time, and growth rate. These results indicate that the population differences in nature are evolved rather than host induced. Increased performance on the introduced hos t was accompanied by reduced performance on the native host, a pattern that could theoretically promote further differentiation between the host rates.