Inter- and intraspecific functional variability of aquatic fungal decomposers and freshwater ecosystem processes.

Although considerable intraspecific trait variation is common, research dedicated to ecosystem functioning has focused mainly on species diversity. Organic matter breakdown, a key ecosystem-level process in woodland streams is mainly driven by aquatic hyphomycetes. These aquatic fungal decomposers constitute a critical link between plant litter and invertebrate detritivores in detritus-based food webs in streams. In this study, we evaluated the functional variability across a set of ten isolates each belonging to five widespread aquatic hyphomycete species, namely Articulospora tetracladia, Anguillospora crassa, Lemonniera terrestris, Neonectria lugdunensis and Tetracladium marchalianum. All the isolates originated from undisturbed streams. We estimated inter- and intraspecific variability on growth rates, litter decomposition and sporulation rates of the isolates. In addition, we also assessed the invertebrate consumption rates on leaves colonized by different isolates. Significant differences were observed within the fungal species in growth rates (A. crassa, L. terrestris, N. lugdunensis and T. marchalianum), leaf litter decomposition (A. tetracladia, L. terrestris and N. lugdunensis) and sporulation rates (A. crassa, A. tetracladia, L. terrestris and N. lugdunensis). The relative consumption rates of the shredder Schizopelex festiva significantly differed when fed with leaves colonized by isolates of L. terrestris and N. lugdunensis, however differences were not seen when fed with leaves conditioned by different species. Overall, results indicate substantial intraspecific functional variability among the isolates of aquatic hyphomycetes. Besides, our study also provides a novel insight that intraspecific functional variability is a natural phenomenon exhibited by isolates not only from polluted but also from undisturbed streams. Here the isolates demonstrated marked inter- and intraspecific functional variability, calling for a greater understanding of the functional role of aquatic hyphomycetes and its ability to influence higher trophic levels.

Exotic Eucalyptus leaves are preferred over tougher native species but affect the growth and survival of shredders in an Atlantic Forest stream (Brazil).

We evaluated the effect of leaves of native and exotic tree species on the feeding activity and performance of the larvae of Triplectides gracilis, a typical caddisfly shredder in Atlantic Forest streams. Leaves of four native species that differ in chemistry and toughness (Hoffmannia dusenii, Miconia chartacea, Myrcia lineata and Styrax pohlii) and the exotic Eucalyptus globulus were used to determine food preferences and rates of consumption, production of fine particulate organic matter (FPOM), growth and survival of shredders. We hypothesized that the consumption rates of leaves of Eucalyptus and their effects on the growth and survival of shredders could be predicted by leaf chemistry and toughness. The larvae preferred to feed on soft leaves (H. dusenii and M. chartacea) independently of the content of nutrients (N and P) and secondary compounds (total phenolics). When such leaves were absent, they preferred E. globulus and did not consume the tough leaves (M. lineata and S. pohlii). In monodietary experiments, leaf consumption and FPOM production differed among the studied leaves, and the values observed for the E. globulus treatments were intermediate between the soft and tough leaves. The larvae that fed on H. dusenii and M. chartacea grew constantly over five weeks, while those that fed on E. globulus lost biomass. Larval survival was higher on leaves of H. dusenii, M. chartacea and S. pohlii than on E. globulus and M. lineata leaves. Although E. globulus was preferred over tougher leaves, long-term consumption of leaves of the exotic species may affect the abundance of T. gracilis in the studied stream. Additionally, our results suggest that leaf toughness can be a determining factor for the behavior of shredders where low-quality leaves are abundant, as in several tropical streams.

Influence of Trichodactylus fluviatilis on Leaf Breakdown in Streams: Understanding the Role of Freshwater Crabs in Detritus-based Food Webs.

Larissa Costa, Walace Kiffer Jr., Cinthia Casotti, Juliana Rangel, and Marcelo Moretti (2016) Freshwater crabs can affect leaf breakdown by consuming leaves or invertebrate shredders. The aims of this study were to analyze the gut content of Trichodactylus fluviatilis and evaluate the influence of this macroconsumer on leaf breakdown. For this, we (i) performed gut analyses of 55 individuals of T. fluviatilis and (ii) determined leaf decay rates and FPOM production in laboratory trials containing crabs and the caddisfly shredder Triplectides sp., alone and together, and leaves differing in quality. We hypothesized that T. fluviatilis feeds both on leaves and Triplectides sp. and, consequently, leaf decay rates would be lower when these organisms were together. The main food categories in T. fluviatilis guts were algae and FPOM, while CPOM and animal tissue were rare. Leaf decay rates and FPOM production did not differ across shredder treatments or leaf species. However, the survival of Triplectides sp. was higher when alone. The results support the potential for participation of T. fluviatilis in leaf breakdown and demonstrated that, in spite of the high abundances of algae and FPOM in the gut content, adults of this species have the potential to feed both on leaf litter and larvae of Triplectides sp. However, the hypothesis of this study was only partially corroborated because decay rates did not change across treatments.