THE DISTRIBUTIONS OF PARTHENOGENETIC ASCID MITES (ACARI, PARASITIFORMES) DO NOT SUPPORT THE BIOTIC UNCERTAINTY HYPOTHESIS

Fifteen out of 50 species of ascid mites (30%) that we collected from four synanthropic and seven natural habitats in North America and Aust ralia existed as all-female populations. In contrast to the prediction s of the biotic uncertainty hypothesis (i.e, that parthenogenetic spec ies are rare, restricted in distribution and survive through dispersal ability), we found that parthenogentic ascid mites were present in te n out of 11 habitats sampled, but were not superior colonists. In a gl asshouse experiment, pasteurized soil in pots was colonized first by b isexual species and only later by all-female species. Furthermore, a h abitat requiring strong dispersal abilities (decaying fungal sporocarp s) lacked parthenogenetic species and a review of literature and colle ctions indicated that all-female ascid species rarely form the phoreti c associations with insects necessary to exploit patchy and ephemeral resources. The assumptions that parthenogens are reproductively superi or to but competitively inferior to sexual relatives were not supporte d by experiments comparing a bisexual and an all-female species of Las ioseius.