The Accumulation of Genetic Variation in a Parthenogenetic Snail

Abstract

Variation present in 13 populations of an apomictic freshwater prosobranch, Thiara balonnensis, was assessed electrophoretically With one exception, each population contained a single unique clone. Genetic similarities, SJ, among clones ranged from 0.98 to 0.60. A minimum length Wagner network directly linked most geographically adjacent populations and patristic distance was related to geographic distance, expressed as latitude difference. This pattern of variation was postulated to result from the evolution of new clones by mutation and the loss of alleles after geographic separation. The extent of the variation present in this species suggests that in favorable environments, apomictic species may persist and accumulate variation without recombination or segregation. In this case a favorable environment was one subject to regular restriction and recolonization. Numbers of asexual species may be limited by numbers of such environments.