The Role of Sexual Dimorphism and Tissue Selection in Ecotoxicological Studies Using the Riparian Spider Tetragnatha elongata.

Tetragnathid spiders (Tetragnatha spp.) found in riparian habitats have recently been used as bioindicators of sediment contamination and insect-mediated contaminant flux. We investigated whether sexual dimorphism (size and behavior) influenced the female:male ratio in composite samples, stable isotope ratios (carbon [δ13C], nitrogen [δ15N]), and Hg concentrations in the southern United States. Additionally, we explored whether biomass for contaminant analysis could be preserved by using the legs of tetragnathids as a surrogate for whole-body δ13C and δ15N signatures. We found that female tetragnathids were significantly larger than male spiders and represented a larger proportion of spiders collected at all sites. However, despite the difference in size between sexes, no differences in growth dynamics, isotopic signatures (δ13C and δ15N), or mercury concentrations were observed. It was determined that the leg of a tetragnathid can accurately represent the stable isotope signature of an entire spider.