Abnormality in the fissioning control of a strain of asexual Dugesia dorotocephala found near Fort Collins, Colorado

Abstract

Asexual Dugesia dorotocephala, collected from a new site several miles northwest of Fort Collins, Colorado, appeared similar, at the time of collection, to ones collected from other sites in the same general locale . However, these exhibited marked differences in the more crowded conditions of laboratory culture : abnormally long, 30-50 mm specimens, seemingly unable to fission, developed . Since previous studies of asexual D. dorotocephala had revealed an inhibitory effect of cohorts on fissioning (Best et al., 1969(Best et al., , 1975Pigon et al., 1974), experiments were conducted with this new strain to ascertain the effect of population density (group size) on fissioning incidence . Results are described which show that this inhibitory effect of cohorts on fissioning is exaggerated in this new strain .