Meeting Abstract

P2.100  Saturday, Jan. 5  Morphological and behavioral sexual dimorphism in scorpions as compensation for locomotor costs of reproduction CARLSON, BE*; MCGINLEY, S; ROWE, MP; The Pennsylvania State University; The Pennsylvania State University; Sam Houston State University bec169@psu.edu

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation are poorly understood. We evaluated an enigmatic morphological sexual dimorphism in the metasoma (‘tail’) of striped bark scorpions, which we propose is a compensatory coadaptation to increase the efficacy of escalatory defensive behavior (stinging) in females. Sex differences in evasive locomotor performance due to costs of reproduction would favor greater aggression in females and the development of structures to support this defensive tactic. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards perceived threats. Female scorpions stung at a higher rate than males, and greater body mass (which often occurs in females) was associated with higher sting rates. While females were more aggressive overall, we found no evidence that the shape of the metasoma supports stinging performance, though the males’ heavier metasomas curiously appeared to enhance locomotion. Males sprinted faster than females, partly explained by the fact that lighter bodies and heavier metasomas increased sprint speed. Although sexual dimorphism in these scorpions may be best explained by other undocumented differences in niche or behavior or by sexual selection, these results suggest the larger metasoma of males may indeed have evolved to increase running speed as they rely on evasion to escape predation, while relatively inactive and aggressive females may conserve resources by producing smaller metasomas.