Residual vitellus and energetic state of wolf spiderlings Pardosa saltans after emergence from egg-sac until first predation

Abstract

The aim of this study was to evaluate energetic source used by juveniles of a terrestrial oviparous invertebrate during the earliest periods of their life. Growth, behavioural activities and energy contents of Pardosa saltans spiderlings’ residual vitellus were monitored during 8 days after their emergence from their egg-sac until they disperse autonomously. The life-cycle of juvenile after emergence can be divided into three periods: a gregarious while juveniles are aggregated on their mother, dismounting off their mother’s back and dispersion. We present the first biochemical study of residual vitellus and energy expenditure during these three periods. At emergence, the mean weight of juveniles was 0.59 mg and energy stock from residual vitellus averaged 51 cal/g wet mass. During gregarious period, the weight of the juveniles aggregated on their mother did not vary significantly and juveniles utilized only 1 cal/day from their residual vitellus. During the period from dismounting until their first exogenous feed, juveniles lost weight and used 30% of their residual vitellus stock. Proteins from the residual vitellus contributed principally to their energy expenditure during this period: 1.5 µg protein/day. Juveniles’ first exogenous feeding was observed 7–8 days after emergence, when 70% of residual vitellus energy had been utilized. Juveniles dispersed after eating, reconstituting an energy stock comparable to that observed at emergence from egg-sac (50 cal/g wet mass). This new energy stock contains mainly lipids unlike the energy stock from the residual vitellus.