ABSTRACT
Although intraspecific trait variation is increasingly recognized as affecting ecosystem processes, few studies have examined the ecological significance of among-population variation in behavioral traits in natural ecosystems. In freshwater habitats, crayfish are consumers that can influence ecosystem structure (e.g., macroinvertebrate communities) and function (e.g., leaf litter breakdown). To test whether crayfish behavioral traits (activity, boldness, and foraging voracity) are major contributors of leaf litter breakdown rates in the field, we collected rusty crayfish (Faxonius rusticus) from eight streams across the midwestern USA and measured behaviors using laboratory assays. At the same streams, we measured breakdown rates of leaf packs that were accessible or inaccessible to crayfish. Our results provide evidence that among-population variation in crayfish boldness and foraging voracity was a strong predictor of leaf litter breakdown rates, even after accounting for commonly appreciated environmental drivers (water temperature and human land use). Our results suggest that less bold rusty populations (i.e., emerged from shelter more slowly) had greater direct impacts on leaf litter breakdown than bold populations (P = 0.001, r2 = 0.85), potentially because leaf packs can be both a shelter and food resource to crayfish. Additionally, we found that foraging voracity was negatively related to breakdown rates in leaf packs that were inaccessible to crayfish (P = 0.025, r2 = 0.60), potentially due to a trophic cascade from crayfish preying on other invertebrates that consume leaf litter. Overall, our results add to the growing evidence that trait variation in animals may be important for understanding freshwater ecosystem functioning.
ABSTRACT
Crayfishes are among the most widely introduced freshwater taxa and can have extensive ecological impacts. Knowledge of the parasites crayfish harbor is limited, yet co-invasion of parasites is a significant risk associated with invasions. In this study, we describe a novel microsporidium, Cambaraspora faxoni n. sp. (Glugeida: Tuzetiidae), from two crayfish hosts in the Midwest USA, Faxonius virilis and Faxonius rusticus. We also expand the known host range of Cambaraspora floridanus to include Procambarus spiculifer. Cambaraspora faxoni infects muscle and heart tissue of F. rusticus and develops within a sporophorous vesicle. The mature spore measures 3.22 ± 0.14 µm in length and 1.45 ± 0.13 µm in width, with 8-9 turns of the polar filament. SSU sequencing indicates the isolates from F. virilis and F. rusticus were identical (100%) and 93.49% similar to C. floridanus, supporting the erection of a new species within the Cambaraspora genus. The novel parasite was discovered within the native range of F. rusticus (Ohio, USA) and within a native congeneric (F. virilis) in the invasive range of F. rusticus (Wisconsin, USA). Faxonius virilis is invasive in other regions. This new parasite could have been introduced to Wisconsin with F. rusticus or it may be a generalist species with a broad distribution. In either case, this parasite infects two crayfish species that have been widely introduced to new drainages throughout North America and could have future effects on invasion dynamics or impacts.
