Interspecific and geographic variation of diapause intensity and seasonal adaptation in the Drosophila auraria species complex (Diptera: Drosophilidae)

Species of the Drosophila auraria complex entered reproductive diapause in autumn in response to short daylengths. Their diapause ended even at short daylengths without special stimuli. For D. auraria Peng, D. triauraria Bock & Wheeler and D. subauraria Kimura, duration of diapause was longer at a shorter daylength but such a relationship was not clear in D. biauraria Bock & Wheeler. High temperature or continuous illumination broke diapause but chilling had a small or no effect in terminating diapause. In outdoor cultures of D. auraria and D. triauraria, diapause was almost terminated by spring in individuals which had eclosed in early autumn, but not in most individuals which had eclosed in mid-or late autumn. Excluding D. biauraria (below), for sympatric populations D. subauraria had the deepest diapause, D. auraria had the shallowest one and D. triauraria had the intermediate one. It was proposed that the deeper diapause of D. subauraria or D. triauraria was an adaptation to the earlier start of its diapause in autumn. Also in these three species, diapause was deeper in northern populations. This variation may occur because northern populations enter diapause earlier and experience relatively longer daylengths which are less effective in maintaining diapause. D. biauraria had rather deep diapause compared with the other three species and this species did not show clinal variation in the diapause intensity.