Meeting Abstract

99.2  Saturday, Jan. 7  The black widow's hourglass: a covert aposematic signal? BRANDLEY, N. C.*; JOHNSEN, S.; Duke University

While culturally iconic, the hourglass of the American black widows (Latrodectus hesperus, L. mactans, and L. variolus) is scientifically unstudied. The hourglass’ color and orientation suggest that it is an aposematic signal to avian predators. However it appears that the American widow species have been under selection for reduced coloration; adult females of L. hesperus, L. mactans, and L. variolus lack the yellow and white patterning found in their younger morphs and other Latrodectus species. Here we examine the hourglass of the black widow in two ways. First, to test the aposematic hypothesis, we used 3-D printing to create model black widows that were either all black or possessed a typical red hourglass. These models were then presented to wild songbirds in a series of feeder experiments, where preliminary data indicates that songbirds are about 3 times more likely to peck a widow that lacks an hourglass. Secondly, we also model how the loss of coloration may benefit the widow by functioning as a covert signal. While a red hourglass is conspicuous to humans and avian predators, a typical insect prey -- which lacks the LWS photoreceptors used in red vision -- has an achromatic contrast of the hourglass that is about 40% lower. This may help black widows balance the differing selective pressures of being both aposematic and a sit-and-wait predator.