Emigration propensity and flight performance are decoupled in a butterfly

Dispersal, defined as any movements potentially leading to gene flow, is a major process driving a species' capacity to cope with human-induced environmental modifications. However, the dispersal process is multi-causal, which currently hinders predictions regarding a species' resilience to global change. We used a multifaceted approach to disentangle the relative importance of a suite of dispersal-related factors in the butterfly Lycaena tityrus, including condition- (morphology and behavior) and context- (environmental) dependent factors. Experiments were conducted at an experimental platform dedicated to study dispersal, the Metatron, to record emigration propensity in two-patch experimental metapopulations under different environmental conditions. The butterflies' individual condition was subsequently assessed in the laboratory. Individual condition did not generally influence emigration propensity. We detected a significant sex bias in emigration propensity, being generally higher in females than in males, but in a context-dependent manner. The environmental context affected emigration propensity, which was higher when habitat quality was poor. Our results show that emigration is not random in L. tityrus, but is rather an active process triggered by sex and habitat quality. Our main finding was that individual condition, and particularly flight ability measured by a performance test, was not related to emigration propensity in experimental metapopulations. Our results may have important implications for forecasting future species distributions, as deteriorating environmental contexts are likely to increase emigration whatever the individual condition is.