1. ¹Department of Ecology and Genetics, Århus University, Ny Munkegade, Building 540, DK 8000 Århus C, Denmark
2. ²Division of General Human Genetics, Institute of Human Genetics, University of Tübingen, Wilhelmstrasse 27, D-72074 Tübingen, Germany

Correspondence: ED Parker Jr, Department of Ecology and Genetics, Århus University, Ny Munkegade, Building 540, DK 8000 Århus C, Denmark. E-mail: dave.parker@biology.au.dk

Received 3 July 2003; Accepted 17 March 2004; Published online 19 May 2004.

Abstract

The deterministic maintenance of clonal diversity in thelytokous taxa can be seen as a model for understanding how environmental heterogeneity both can stabilize genetic diversity and can allow coexistence of competing species. We here analyze the temporal fluctuations in clonal diversity in the thelytokous Lonchopterid fly, Dipsa bifurcata (Fallén, 1810), at four localities in Sweden over an 8-year period. Estimated fitness values for clones are cyclical, synchronous among populations and correlated with seasonal changes in the environment. Differential winter viability and emergence from overwintering along with differential reproductive rate during the summer appear to be the selective mechanisms by which long-term clonal diversity is maintained. In a companion paper (Tomiuk et al, 2004), we present a model for the maintenance of clonal diversity through the mechanism of differential diapause among clones, utilizing fitness values estimated from the data presented here. In general, our results imply that fluctuating seasonal fitnesses can maintain stable genetic polymorphism within populations, as well as coexistence between closely related competitors, when coupled with differences in diapause phenology.