Temperature-mediated developmental plasticity in winter and summer larvae of Palaemon serratus.

In a seasonal environment, variation in larval phenotype and developmental plasticity allow crustacean larvae to maximise survival by lengthening or shortening their development. The aim of this study is to investigate the effects of temperature, laying season and their interaction on larval developmental pathways (larval instars and larval stages). We monitored the different larval stages and calculated the number of larval instars reached during the development of winter and summer larvae of Palaemon serratus incubated at 12, 16 or 20 °C. We observed a great variability in the larval development (6-13 larval instars and 6 to 11 larval stages). A higher temperature decreases the development time and the number of larval instars. At a given temperature, the development time of winter and summer larvae was not different. Two larval stages were considered supernumerary (zoea 4 and 6), as they were more frequent at low temperatures. At higher temperatures, some larvae started to develop pleopods as early as the third instar, larval stage which had never been described (named here zoea 3'). This phenomenon was more common in winter larvae than in summer larvae. These results provide new insights into the expression of developmental plasticity in decapod larvae.