Spiders have long been noted as classic examples of extreme sexual dimorphism and adaptations to the lifestyle of a sit-and-wait predator. We examined sex-based differences in the metabolic rate of two species of wolf spider that differ in their degree of sexual dimorphism and predatory strategy. Pardosa milvina (Hentz 1877) is a small active wolf spider that does not exhibit a large degree of sexual dimorphism in body size. Hogna helluo (Walckenaer 1837) is a large, strongly sexually dimorphic wolf spider with large, sedentary females and smaller, active males. We found that P. milvina had a higher mass-specific metabolic rate than H. helluo. Also, P. milvina males had a higher metabolic rate than P. milvina females but there was no difference in mass-specific metabolic rate between H. helluo males and females. Our data demonstrate that an actively foraging species, P. milvina, exhibits a higher metabolic rate than species with a sit-and-wait strategy, H. helluo. This suggests that activity levels may be correlated with metabolic rates. In addition, we hypothesize that sexual selection and selection for specific reproductive roles may have resulted in species differences in sexual dimorphism for metabolic rate.
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