Life history strategies and production of caddisflies in a perennial headwater stream in Patagonia

Abstract

Synchrony, one of the main traits of population life histories, refers to the degree to which individuals complete a certain stage of the life cycle at the same time. It can be governed by temperature, variations in temperature, photoperiodic cues, detritus inputs, or discharge regimes. We investigated life cycles and secondary production of five caddisfly species in a second order stream in the Patagonian Mountains. In addition, we analyzed what environmental variables were implied in the caddisfly assemblage variation. Mastigoptila sp. (Glossosomatidae) and Eosericostoma aequispina (Helicophidae), Myotrichia murina (Sericostomatidae), Brachysetodes quadrifidus (Leptoceridae), and Neoatopsyche brevispina (Hydrobiosidae) showed univoltine life cycles, with an extended recruitment with no overlapping cohorts and a relatively well-synchronized imaginal emergence taking place during spring summer seasons. However, Myotrichia murina (Sericostomatidae) displayed a complex life cycle with mixed populations taking 10-12 months to develop, and pupae being collected almost continuously. The annual secondary production per species varied from 11.06 (E. aequispina) to 310.5 mg m-2 year-1 (M. murina), being overall caddisfly production (0.5 g m-2 year-1) similar to that reported for cold springs in other regions. The highest growth rates (K) were observed during late winter and spring (mostly September) and ranged from 0.70 to 3.70% day-1 in M. longicornuta and N. brevispina, respectively. Redundancy analysis indicated that seasonally dynamic variables, water temperature, discharge, and detritus biomass were the main predictors of caddisfly assemblage variation; consequently at this cold stream (mean annual 5.9°C), with a regular availability of food supply, these parameters ruled Trichoptera life histories and secondary production. As documented for other mountainous temperate areas, synchrony would be a dominant trait on life histories of Trichoptera species inhabiting Patagonian streams.