Plasticity of the thermal developmental reaction norms in the european peacock butterfly Inachis io (Lepidoptera, Nymphalidae)

Abstract

The goal of the study was to analyze the plasticity of the developmental thermal reaction norms in the peacock butterfly Inachis io as affected by different photoperiodic conditions and group versus individual keeping. Overwintered imagoes were collected in Stariy Peterhof (Saint-Petersburg, Russia) in May 2010 and 2012–2013. Twelve experimental regimes were used: 4 thermal (16, 18, 20 and 22°C) and 3 photoperiodic (12, 18 and 22 h of light per day). Under short-daylight conditions (12 h), the larvae were shown to develop a little faster than under long-day conditions (22 h), although the thermal developmental thresholds were invariable in both cases. The linear regression coefficient characterizing developmental thermolability was significantly higher only in males more affected during their development by the short-day photoperiod than females. Under the 18-h daylight regime, larval development was less thermolabile and characterized by a lower thermal threshold than under the shorter or longer photoperiod. The influence of the short-day photoperiod on the larval development manifested itself most distinctly in the body mass changes in emerging pupae: under all thermal regimes, the pupae were lighter under the short-than long-day photoperiod. The pupal body mass grew with the rise in temperature, contrary to the temperature–size rule. Individual keeping led to the longer duration and lower thermolability of larval and pupal development, as well as to a reduced pupal body mass. Individual keeping exerted a stronger influence on females than on males.