The longer the conditioning, the better the quality? The effects of leaf conditioning time on aquatic hyphomycetes and performance of shredders in a tropical stream

In this study, we aimed to evaluate the effects of leaf conditioning time on aquatic hyphomycete assemblages and the performance of invertebrate shredders. We hypothesized that post-conditioning effects, i.e., that phase in which leaf nutritional quality no longer increase or even decline, occur late in tropical streams. Consequently, leaf quality would increase monotonously with fungal colonization and leaves conditioned for longer periods would promote higher growth and survival of shredders than leaves conditioned for shorter periods. Leaves of the tree species Miconia chartacea were conditioned for different time periods (7, 15, 30, 45 and 60 days) in an Atlantic Forest stream (Southeast Brazil) and offered to larvae of the caddisfly shredder Triplectides gracilis in food preference and monodietary experiments. Leaf toughness, total phenolics and tannins decreased with conditioning time. The leaves were poorly colonized by aquatic fungi, and sporulation rates were low. The larvae consumed leaves from all conditioning periods, but those conditioned for 30 days were preferred over those conditioned during the initial periods (7 and 15 days). In the monodietary trials, larval survival was high in all treatments, and the larvae fed leaves conditioned for 7 and 15 days had high growth rates. Our results show that leaves conditioned for longer periods did not constitute a better food resource for shredders, which did not corroborate the proposed hypothesis. The influence of leaf conditioning time on detritivore-mediated decomposition may be more relevant in streams with a high diversity of aquatic hyphomycetes that may colonize the leaves more effectively.