Weaponry, color, and contest success in the jumping spider Lyssomanes viridis

Abstract

a b s t r a c tWeaponry and color badges are commonly theorized to function as visual signals of aggressiveness or fighting ability. However, few studies have supported a signaling function of weaponry, and the role of color in invertebrate competitive interactions remains virtually unexplored. Jumping spiders (Salticidae) make excellent invertebrate models for studying weaponry and color because males of many species are colorful and possess exaggerated chelicerae, which are used as weapons in escalated contests. To determine whether color or weaponry might function as visual signals in male-male competitions, we investigated relationships between contest success, cheliceral length, and red coloration in Lyssomanes viridis. Males having longer chelicerae than their opponents were significantly more likely to win (p = 0.0008). Males who won, despite being smaller than their opponents, had significantly less red chelicerae than their opponents (p = 0.01). Male and female cheliceral length, as well as foreleg length, correlated tightly with body size. Cheliceral and foreleg length showed significantly stronger positive allometry in males than in females. We conclude that male chelicerae and forelegs are under strong positive selection for their use in physical fights and/or as visual signals of fighting ability.

“Reverse” sexual dichromatism in a Neotropical frog

“…We created calibration curves for each frog or leaf photograph for each color channel by fitting the relationship between the RGB values of the gray standards and their measured percentage reflectance with an exponential trend line (following Johnsen, ; Tedore & Johnsen, ). The equation for this trend line was used to convert the RGB values from the frog and leaf locations to percentage reflectance in each color channel.…”

How to measure color using spectrometers and calibrated photographs

“…It is possible to create a highly controlled lighting environment and to develop a repeatable photographing procedure, allowing one to calibrate everything ahead of time (see Troscianko and Stevens, 2015), but a safer solution is to place a calibration standard within each image so that it can never be lost (Tedore and Johnsen, 2012), much like geologists place a hammer or a coin for scale. For example, the calibration standard can be a set of gray regions that vary from dark to light gray (Fig.…”

Pheromones exert top-down effects on visual recognition in the jumping spiderLyssomanes viridis

“…Stereotypic threat displays are also characterized by raised forelegs, but the legs, rather than being flicked, simply alternate between being fully extended and partially bent at the joint connecting the femur to the patella, and the pedipalps are lowered in a neutral position (Tedore and Johnsen, 2012). For the purposes of this experiment, a display was classified as a courtship if at least one pedipalp and both forelegs were extended above the head, and as a threat if one or both forelegs were raised and held immobile above the head for at least 3s (Fig.1).…”

“…The female forehead spot becomes redder and more clearly defined upon maturation (C.T., unpublished), and is arguably the most distinctive feature of the female's color pattern. This raises the question of what the spot is for, as male L. viridis' striking color pattern, exaggerated chelicerae, and courtship and agonistic behaviors suggest that sexual selection has acted primarily on the male phenotype, not the female's (Tedore and Johnsen, 2012). Still, it is possible that the red spot is assessed by males as a signal of quality, and that males prefer females with spots having particular spectral characteristics.…”

“…The legs and abdomen of a mature male are covered with black stripes (Table1, first image). Males also have red hairs on the dorsal and dorsofrontal region of the cephalothorax, and exaggerated reddish-brown chelicerae, which scale positively allometrically with body size (Tedore and Johnsen, 2012). Mature females, in contrast, have a crown of red hairs against a background of white hairs on the dorsal and dorsofrontal regions of the cephalothorax (Table1, second image).…”