Individual state controls temperature dependence in a butterfly (Lasiommata maera)

In ectotherms there is typically a strong and positive correlation between growth rate and ambient temperature when food is not limiting. However, the exact relationship between growth rate and temperature varies among popula tions in many species. As a consequence, it has been suggested that selecti on for a rapid increase in growth rate with temperature should be stronger in populations experiencing a high degree of time-stress, compared with pop ulations experiencing little time-stress. In the present study we take this adaptive hypothesis further and investigate if variation in time-stress am ong individuals of a single population may affect the relationship between growth rate and ambient temperature. Time-stress was manipulated by rearing larvae of the butterfly Lasiommata maera in different day-length regimes. The results show that individuals experiencing a higher degree of time-stre ss increase their growth rates more in higher temperatures compared with in dividuals under less time-stress. Hence, the adaptive hypothesis was suppor ted and the relationship between growth rate and temperature was highly sta te dependent. These findings may be of general importance for understanding the evolution of life histories in seasonal environments.