Effect of temperature on egg development in the Australian stonefly genus, Austrocercella Illies (Plecoptera : Notonemouridae)

Abstract

Eggs of four species of the endemic Australian stonefly genus Austrocercella-A. alpina, A. hynesi, A. illiesi and A. tillyardi-were incubated in the laboratory at constant temperatures at 5�C intervals between 5 and 25�C. For all species, there was a significant relationship between water temperature (T, �C) and length of egg incubation (Y, days), expressed by the logarithmic equation Y = aT-b, where a and b are constants. However, a linear plot, Y = a - bT, was a better fit for A. illiesi. All species displayed high hatching success between 5 and 15�C. At 20�C, successful hatching took place in A. hynesi and A. tillyardi, but in A. alpina virtually no eggs hatched. In A. illiesi, about 50% of the eggs hatched at 20�C, but the incubation period was prolonged. Interspecific differences in egg development within the genus Austrocercella reflect life-cycle timing and the temperatures likely to be experienced by the egg stage. The few intraspecific differences were also related to temperature during the egg stage. Austrocercella shows egg developmental relationships similar to those found in many northern hemisphere stonefly species, including the Nemouridae.