Adult size of eight hunting spider species in Central Amazonia: Temporal variations and sexual dimorphisms

Abstract

We studied temporal variation in adult size and sexual size dimorphism (SSD) of seven hunting spider species, Ctenus amphora, C. crulsi, C. manauara, C. villasboasi (Ctenidae), Phoneutria fera, P. reidyi (Ctenidae), and Ancylometes rufus (Pisauridae) in a tropical rainforest, and one species from a relatively open vegetation habitat, C. minor, in central Amazonia. Size variation was great within and among field trips. Spiders were generally smaller in October (end of dry season) when compared with other months: adults of C. amphora, C. crulsi and C. manauara were significantly smaller in October 1995 when compared to February 1996; P. fera were smaller in October 1998 than in June 1998; and A. rufus were smaller in October 1998 than in August 1998. The temporal variation in size is possibly a result of low prey availability during the dry season. Six species had significant differences in prosoma length between males and females: C. amphora, C. crulsi, C. manauara and C. minor had larger males (which is considered rare in spiders), and P. reidyi and P. fera had larger females. However, considering an alternative index of size, the "rough area" (an approximate measure of the area of the spider as seen from above), the males were significantly larger for all species (up to 2.8 times in C. minor), because they have longer legs relative to their prosoma length. We suggest that selection for high mobility may be the reason for adult males with longer legs, and that the smaller species had higher degrees of sexual dimorphism in leg length because of the relative size of obstacles in the leaf litter.