Geographical Parthenogenesis and Polyploidy in Daphnia pulex

Abstract

Ploidy-level variation among asexual clones of Daphnia pulex showed a clear latitudinal pattern. Only a single diploid clone was identified at the high-arctic Igloolik site, and it comprised only 2% of the individuals in the populations at that locality (clone 43 in Weider et al. 1987). Conversely, at Windsor, the temperate site, only diploids were found; and at the low-arctic locality of Churchill, both diploids and polyploids were common. The clear association between latitude and ploidy level supports the view that polyploidy is selected for in extreme environments. If representative of a general trend in animals, these results suggest that geographical patterns in the distribution of parthenogens arise from indirect rather than direct selection for shifts in the breeding system.