Constraints on the evolution of thermal sensitivity of foraging in Trichogramma: Genetic trade-offs and plasticity in maternal selection

Negative genetic correlation between performance at different temperatures or temperature-dependent mutations may promote evolution of thermal special ization in ectotherms. The first hypothesis implies that a selective change in performance at one temperature simultaneously results in change in perf ormance at others, while the second implies a delay before observing such i ndirect responses. Comparison of the direction of evolution among Trichogra mma lines selected for improvement of parasitization capacity at low, mediu m, or high temperatures indicated that a change in performance at one tempe rature concurrently resulted in opposite changes at distant temperatures. U nexpectedly, selection at high temperatures resulted in a decrease in adult fitness components, while adult performance expressed at cold temperatures simultaneously increased. The relationship between maternal fecundity and offspring fitness components varied across the thermal range. No correlatio n between these traits was present at cold or medium temperatures, but nega tive relationships appeared at high temperatures. We show that maternal sel ection resulting from a conflict between adult and offspring fitness compon ents may have resulted in reversed evolution of the adult traits at the hig h end of the thermal range. Thus, genetic trade-offs in performance at diff erent temperatures and phenotypic plasticity in maternal selection may cons train evolution of the thermal niche in Trichogramma.