The developmental cycles of two co-occurring sponge mites Unionicola crassipes (Müller) and Unionicola minor (Soar) (Acari, Hydrachnellae)

Abstract

A description is given of the annual cycles of the common sponge mites Unionicola crassipes and Unionicola minor, two very closely related species. In the Netherlands, both species have two cycles. The cycles were identified by collecting samples in the field and by breeding the different stages from sponge material.Hibernating females of U. crassipes are active earlier in the spring than those of U. minor. Consequently the first generation peak of U. crassipes occurs about two weeks earlier than that of U. minor. The second generations of both species, following about two months later, roughly coincide. Niche overlap is prevented by the gap between the first generations of both species and possibly also by differences in prey selection. U. crassipes is larger than U. minor and able to select larger prey specimens (copepods) than U. minor.

Variability in the life history of Unionicola crassipes, a sponge-associated water mite (Acari: Unionicolidae)

“…The pattern of sex-ratio change over the seasons is also consistent with several previous studies (Bottger 1972b;Meyer and Schwoerbel 198 1 ;Riessen 1982;Davids et al 1985). The evolutionary and ecological significance of early male emergence and female-biased sex ratio in U .…”

“…crassipes at Bradshaw's Pond is different from any other yet reported for this mite. Despite intensive sampling programs that included examination of sponges, neither Bottger (1972b) nor Davids et al ( 1985) found eggs, deutonymphs, tritonymphs, and adults together in early spring.…”

“…Bottger ( 1972 b) described a univoltine life cycle for U. crassipes in Germany, as did Riessen (1982) for mites in Quebec, Conroy (1974) for a population in British Columbia, and Crowell and Davids (1979b) for mites in New York and Ontario. However, Riessen (1982) and Davids et al (1985) found the overwintering stage to be ovigerous (egg bearing) adult females, Crowell and Davids (1979b) found that deutonymphs overwintered, and Bottger (1972b) found both adult females and deutonymphs overwintering. No environmental factor that determines voltinism o r overwintering stages has been identified.…”

“…Although thefe is sometimes little morphological difference between U. crassipes-type mites in different localities (Conroy 1984), there are major differences in life histories. In the Netherlands, Davids et al (1985) reported two generations per year, with the 'present address: Department of Zoology, Erindale College, University of Toronto, Mississauga, Ont., Canada L5L 1C6. fertilized females overwintering.…”

Competitive Exclusion, Harem Behaviour and Host Specificity of the Water Mite Unionicola ypsilophora (Hydrachnellae, Acari) Inhabiting Anodonta cygnea (Unionidae)

“…Some species are associated with a host throughout their entire post-larval life; others utilize a mollusc or sponge only to undergo metamorphosis (MITCHELL and PITCHFORD 1953, BOTTGER 1972, HEVERS 1980DAVIDS et al 1985). Those species which are permanently associated with a molluscan host presumably feed on host tissue (BAKER 1977) or on materials entering the mussel's mantle cavity.…”