Life in Crumbling Clay: The Biology of Axarus Species (Diptera: Chironomidae) in the Connecticut River

Populations of a Connecticut River midge structured by geological history and downstream gene flow

“…This would be an improbable event, but population densities get very high (Werle et al 2004b) and thus some larvae should succeed in this every generation. Upstream gene £ow is unlikely in this system.…”

“…Upstream gene £ow is unlikely in this system. The adults are short-lived, and mating swarms form by the emergence of adults over about a two week period (Werle et al 2004b). Since the populations are often isolated by many kilometers of river with no habitat between them, £ies that had a tendency to make long upstream £ights would have a low probability of ¢nding mates.…”

“…Collections were made at various times of year (Table 1) from submerged clay deposits by sifting the clay through a 0.5-mm grid sieve and extracting live larvae. In some instances larvae were collected from rotting wood, but wood-dwelling larvae can only be found near clay exposures (Werle et al 2004b). At least 50 larvae were collected per population.…”

“…These are lakes formed in front of receding icesheets, and fed by runo¡ from the melting ice. Two of these lakes, Lake Hitchcock and Lake Co˛s, were situated in the middle to northern Connecticut River valley (Ridge & Larsen 1990, Ridge et al 1999) and left behind sediments called varved clays that now occur in patches along the river bottom of the modern Connecticut River (Werle et al 2004b). These sediment exposures resemble a string of beads running along the length of the river, separated by stretches of river where no clay can be found.…”

“…co˛s. The two lakes' sediments contain signi¢cantly di¡erent proportions of the two Axarus species (Werle et al 2004b). A. sp.…”