Seasonal plasticity in two satyrine butterflies: state-dependent decision making in relation to daylength

In this study we investigate how the need for seasonal timing of diapause a nd sexual maturation have selected for plasticity in life history traits in two butterfly species, Lasiommata maera and Lopinga achine. We test the ge neral hypothesis that insects living in temperate areas should have shorter development times at progressively later dates of the growth season, and t hat they use daylength as a cue to determine the date. Both species have tw o different larval growth periods; the first in autumn and the second after termination of diapause in spring. Due to the difference in photoperiodic change in autumn and spring, we expected larvae to interpret daylengths qua litatively differently in the two growth periods. In other words, developme ntal decisions in response to daylength should depend on the seasonal state (autumn or spring) of larvae. In laboratory experiments we investigated th e reaction norms relating larval development times to daylength. In both sp ecies the slopes of these reaction norms were different in autumn and in sp ring. The results of the experiment on L. maera a supported specific predic tions both in autumn and in spring. The same was true in autumn for L. achi ne but development time in spring seemed to be insensitive to daylength. In all cases, short development times were associated with high larval growth rates rather than with small final body sizes. Growth and development in t hese species can be described as state-dependent decision processes, where information about the external and internal environment is used at several points in development.