DISPERSAL OF RAMAZZOTTIUS AND OTHER TARDIGRADES IN RELATION TO TYPE OF REPRODUCTION

The relationships between the type of reproduction and sexuality and the types of substrates inhabited by semiterrestrial tardigrade populations are reported. Specimens of the genus Ramazzottius (Eutardigrada, Hypsibiidae) were collected from a limited area of hilly to mountainous zones near Modena and Reggio Emilia (Italy). The lichen substrate Xanthoria parietina, typically colonized by R. oberhaeuseri, was the main subject of study, though animals were also extracted from moss cushions. The sex ratio, correlated with the type of reproduction, clearly differed when the lichen or moss samples were collected from tree trunks or limited rocky areas, or came from extensive rocky outcrops. In the former case, the cytological characteristics of oocytes and the absence of males attest to thelytokous parthenogenesis. In the latter, some male specimens were always found, though several samples showed cytological evidence of parthenogenetic and amphimictic females. Differences in the distribution and frequency of the studied tardigrade strains which all utilize passive dispersal mechanisms, notwithstanding substrate and terrain homogeneity, are chiefly due to different modes of reproduction.