Male-male Competition in a Toad With Dynamic Sexual Dichromatism: Males React Similarly to Robotic Models That Vary in Color
Elaborate visual signals play a crucial role in communication between many breeding animals, often evolving through female mate choice and male-male competition. Neotropical Yellow Toads (Incilius luetkenii) exhibit a temporary elaborate visual trait during their brief annual mating events, transitioning from a drab, female-like brown coloration to a vibrant lemon-yellow. They engage in scramble competition, where males physically compete with both lone and amplectant males for access to females. Previous studies suggest that male color may serve as a sex identification signal in the toads’ large breeding aggregations, and that females do not appear to choose males based on color. In this study we investigated whether variation in male coloration functions as an intrasexual signal during male-male interactions. Using realistic robotic model toads in a two-choice arena, we addressed two questions. First, do male Yellow Toads respond differently to a lone male versus a male in amplexus with a female when both males are the same color? Secondly, do male Yellow Toads respond differently to two amplectant males varying in the brightness of their yellow coloration? Males approached the amplectant pair nearly twice as often as the lone male, although this pattern was not statistically significant. Males did not exhibit a differential reaction to bright amplectant males versus dull amplectant males. Therefore, variation in male yellow color and the presence of a female do not appear to influence male-male competitive behavior. Overall, this study contributes to our understanding of temporary color change in vibrantly colored anuran species.ABSTRACT
Comparison of live Neotropical Yellow Toads (Incilius luetkenii) and 3D printed robotic model toads. (A, B) Photographs of male Yellow Toads in amplexus with females in typical postures. (C, D) Photographs of 3D-printed robotic model toads showing similar postures to the models. (E) Photograph of four 3D printed robotic models, showcasing the difference in color between the bright (left) and dull (right) single toad models and amplectant pair models. (F) Reflectance spectra of three bright male Yellow Toads (upper three curves) and three dull male toads (lower three curves). (G) Reflectance spectra of the four bright Yellow Toad models (upper four curves) and the four dull Yellow Toad models (lower four curves).
Schematic representation of the two experiments wherein we exposed subject male Yellow Toads (Incilius luetkenii; at the top of each image) to two robotic stimuli (at the bottom of each image). (A) In the first experiment subjects were presented with a dull single male and a dull male in amplexus with a female. (B) In the second experiment subjects were presented with a bright male in amplexus with a female and a dull male in amplexus with a female. See methods for further details on arena design and video analyses of subject male behavior.
Responses of male Yellow Toads (Incilius luetkenii) to a robotic model simulating a male in amplexus with a female versus a lone male toad. (A) Subject males spent similar amounts of time interacting with both males in amplexus and single male models. (B) Subject males approached the amplectant pair first nearly twice as often as they did the single male model, yet this was only weak evidence of a differential response. (C) Subject males made a similar number of contacts with both the males in amplexus and single male models (error bars show standard error). (D) Subject males took a similar amount of time to approach both males in amplexus and single male models. In (A) and (D), boxplots depict the median (thick black bar), 1st and 3rd quartiles, and the point value of each individual.
Responses of male Yellow Toads (Incilius luetkenii) to a robotic model simulating a bright versus dull male robotic model toad, both in amplexus with a brown female. (A) Subject males spent similar amounts of time interacting with both bright and dull male models. (B) Subject males approached the bright and dull male models first at a similar frequency. (C) Subject males made a similar number of contacts with both the bright and dull male models (error bars show standard error). (D) Subject males took a similar amount of time to approach both the bright and dull male models. In (A) and (D), boxplots depict the median (thick black bar), 1st and 3rd quartiles, and the point value of each individual.
Contributor Notes
