Meeting Abstract

27.1  Jan. 5  Do Tetragnatha spider jaws scale like genitalia or like armaments? BRANDT, Y*; ANDRADE, MCB; University of Toronto at Scarborough; University of Toronto at Scarborough ybrandt@utsc.utoronto.ca

In many animal taxa, copulatory appendages show negative allometry (relative appendage size decreases as body size increases) whereas appendages used in fighting and threat display are positively allometric (relative appendage size increases as body size increases). The chelicerae (jaws) of adult spiders in the genus Tetragnatha are conspicuously elongated, often exceeding the carapace (cephalothorax) in length. Spider chelicerae are used to subdue prey and to combat conspecifics, but in male and female Tetragnatha chelicerae also function to clasp and secure the partner in copulation. Male and female Tetragnatha copulate frequently throughout their adult lifespan, with last male sperm priority. Herein we describe scaling patterns of Tetragnatha chelicerae, as a step toward elucidating the selective pressures and constraints that shape chelicerae length. Carapace lengths of males do not differ from females, yet in all species, the chelicerae of males are longer than female chelicerae. Among species, carapace and chelicerae length is correlated, and male carapace length is correlated to female carapace length. After removing the effects of carapace length, male and female chelicerae length remain significantly correlated. Among species, both male and female chelicerae are positively allometric, and the allometric values do not differ between the sexes. Yet within species, females exhibit greater allometric values than do males. These scaling patterns are inconsistent with the scaling patterns of either genitalia or armaments. We discuss the potential of size-assortative mating and patterns of intra-specific body size variation to account for patterns of Tetragnathid jaw elongation.