Meeting Abstract

134.3  Monday, Jan. 7  Reduction of an aposematic signal: the role of microhabitat in North American black widows (Latrodectus) BRANDLEY, NC*; JOHNSON, MG; JOHNSEN, S; Duke University ncb9@duke.edu

An aposematic signal may warn a predator of the signaler’s dangerous capabilities. While much work has focused on the evolution and form of aposematic signals, few studies have examines why they may be lost or reduced. Ancestral trait reconstruction suggests that two species of North American black widows (Latrodectus mactans and L. hesperus) exhibit a reduction of aposematic coloration. While these species still possess the black widow’s iconic ventral red hourglass, they usually lack the dorsal coloration seen in congeners. To examine why L. mactans may have reduced its coloration, we present microhabitat comparisons between it and a sympatric black widow, L. variolus, that has retained its dorsal coloration. We found that the dorsally all-black L. mactans (N=21) tends to prefer lower microhabitats than that the dorsally colored L. variolus (N=27, p<.05). We suggest that when considering microhabitats, the differences in coloration between the species may represent a cost-benefit tradeoff between signaling to predators and avoiding presenting a queue to eavesdroppers. Because L. mactans is found close to the ground with its hourglass pointed upwards, it is less likely that a predator will view its dorsal side than for L. variolus. However many prey still approach from below, and reducing dorsal coloration may improve L. mactans’ foraging ability.