Correlated evolution of physiological and life history traits in phytochemical‐tolerant <i>Drosophila</i>

Abstract We investigated the correlated evolution of fitness‐related traits in cactophilic species Drosophila buzzatii Patterson &amp; Wheeler and D. koepferae Fontdevila &amp; Wasserman (Drosophilidae, Drosophilini) as an indirect response to adaptation to high concentrations of phytochemicals in their host plant ( Trichocereus terscheckii Briton &amp; Rose). Specifically, we examined whether the experimental evolution of phytochemical tolerance influenced metabolic rate, fecundity, longevity, and starvation resistance. Our findings reveal that adaptation to phytochemical defenses led to correlated responses in both species, likely driven by genetic correlations and energy allocation strategies. Notably, sexual dimorphism was evident, underscoring the significance of sex‐specific effects in the adaptive process. The tolerant phenotypes of each species emerged from distinct pleiotropic backgrounds, with D. buzzatii exhibiting more correlated responses than D. koepferae , suggesting a deeper genetic perturbation or response during the experimental evolution. This study demonstrates how exploiting a marginally used host can impose costs on crucial fitness‐related traits, such as adult lifespan and reproductive output. Moreover, ignoring variation in tolerance to phytotoxins would overlook the diversity of responses across species. This variation is essential for understanding how different species manage to exploit toxic plants. Neglecting this aspect would result in a simplified view of insect–plant interactions, failing to account for the nuanced ways in which insects evolve strategies to detoxify or avoid harmful substances.