Cryptic genetic variation revealed by diet uncovers a trade-off between growth and telomere length

Evolutionary theory predicts that variation in longevity persists due to trade-offs between early-life fitness traits (e.g., growth or fecundity) and long-term somatic maintenance. However, such trade-offs can be difficult to detect and may often become apparent only under certain conditions. For instance, developing in novel or atypical environments may alter the genetic architecture of traits, revealing trade-offs that are otherwise hidden under normal conditions. To test this, we compared full-sibling families of the Mexican spadefoot (Spea multiplicata) reared across two larval diets: a typical detritus diet and an atypical live shrimp diet, which they are competitively excluded from in nature. The shrimp diet significantly increased broad-sense genetic variance and heritability for larval growth rate, whereas heritability for post-metamorphic telomere length - a known longevity correlate - remained similar across diets. Moreover, only on the shrimp diet did families with faster growth exhibit shorter telomeres, consistent with a diet-dependent trade-off between growth and somatic maintenance. Overall, our study shows that developing under atypical dietary conditions exposes previously cryptic genetic variation in growth, thereby revealing a trade-off with somatic maintenance. These findings have implications for understanding how environmental change, such as rapid dietary shifts, can shape aging processes and vulnerability to age-related disease.