Diet Affects Egg Laying, Biomass, and Stable Isotope Values in Tetragnathid Spiders

Riparian tetragnathid spiders are used as biosentinels of aquatic contamination because they are specialized feeders of aquatic emergent insects and are also prey items for terrestrial predators (e.g., birds). Analysis of both trophic position (e.g., stable nitrogen isotopes) and contaminant concentrations are needed to utilize tetragnathids as biosentinels, which can present challenges when collecting enough biomass to reach analytical detection limits, due to their relatively small size. The purpose of this study was to investigate the impacts of a controlled diet source on spider biomass, egg laying and stable isotope values (δ¹³C and δ¹⁵N). Diet significantly influenced the biomass and egg laying of tetragnathids, with some spiders losing up to 50% of their biomass in a single egg-laying event. δ¹³C had a faster turnover rate in the whole-body of spiders compared to legs, which is important, as spider legs are presently used as surrogates for whole-body δ¹³C values.