SEX-RATIO, OVIPOSITION AND EARLY DEVELOPMENT OF THE ANTARCTIC ORIBATID MITE ALASKOZETES-ANTARCTICUS (ACARI, CRYPTOSTIGMATA) WITH OBSERVATIONS ON OTHER ORIBATIDS

Data are presented on oviposition rates of individual female Alaskozet es antarcticus (Acari: Cryptostigmata) over the course of a four month laboratory study at a constant temperature of 7-degrees-C. Although m ost females carried mature eggs, only a minority (6/24) laid them, at a rate of 0.021 female-1 d-1 (approximately one egg every seven weeks) . The presence of other females or males did not alter this rate signi ficantly. Individual females laid eggs singly or in batches deposited over a short period; several females could also contribute to one batc h. Each female probably matures a single batch of eggs in its lifetime . Development rates were rapid, suggesting that eggs laid early in the short Antarctic summer could reach the protonymph stage by the end of that season. Field observations of egg content in A. antareticus and Halozetes belgicae suggested differences between the two species. A. a ntarcticus maintained a high egg content (c. 6 female-1, maximum 14) o verwinter, with oviposition commencing early in the subsequent spring, while H. belgicae showed a peak monthly mean of c. 2 eggs female-1 (m aximum 4) in late summer followed by a burst of oviposition. A. antarc ticus samples gave female-biased, and H. belgicae male-biased, sex rat ios for much of the year. This is discussed in the context of differin g strategies of energy use and survival. The data are compared with th e egg contents of oribatid mite samples from other maritime and sub-An tarctic sites, and data on temperate species from the literature. Ther e was no evidence for the occurrence of parthenogenesis in any of the Antarctic species studied.