Phenology and life-cycle regulation of the fishing spider Dolomedes triton Walckenaer (Araneae, Pisauridae) in central Alberta

Abstract

Dolomedes triton Walckenaer, a widespread and common fishing spider in North America, has a semivoltine life cycle in central Alberta, Canada. Juvenile spiders hibernate twice. According to evidence from laboratory rearings and patterns in field collections, the main overwintering stages are instars 3-5 and 9-11. After the second overwintering period, large juveniles moult once or twice to reach the reproductive adult stage. Juveniles grow rapidly between May and August but during overwintering between September and April, virtually no growth (measured as maximum carapace width of individuals) was observed in field populations. Dolomedes triton has a variable number of juvenile stages, ranging from 10 to 15 in males and from 9 to 15 in females. Both overwintering phases are facultative even though most individuals overwinter twice in central Alberta: at high temperatures (24-25°C) and under long-day conditions (either 18 h light : 6 h dark or 19 h light : 5 h dark) juveniles can develop directly to adults. Short-day photoperiods did not prolong stage durations, but warm periods, when experienced late in development only, were associated with extra moults, and may thus delay maturation until the following spring. Although the second overwintering period is a quiescence regulated strictly by temperature, regulation of the first overwintering period is more complex, including probable preconditioning through interaction of temperature and photoperiod.