DOI: 10.7302/bksb-t580
title: A kinematic analysis of Micrurus coral snakes reveals unexpected variation in stereotyped anti-predator displays within a mimicry system [dataset]

description: Warning signals in chemically defended organisms are critical components of predator-prey interactions, often requiring multiple coordinated display components for a signal to be effective. When threatened by a predator, venomous coral snakes (genus Micrurus) display a vigorous, non-locomotory thrashing behaviour that has been only qualitatively described. Given the high-contrast and often colourful banding patterns of these snakes, this thrashing display is hypothesized to be a key component of a complex aposematic signal under strong stabilizing selection across species in a mimicry system. 
By experimentally testing snake response across simulated predator cues, we analysed variation in the presence and expression of a thrashing display across five species of South American coral snakes. 
Although the major features of the thrash display were conserved across species, we found significant variation in the propensity to perform a display at all, the duration of thrashing, and the curvature of snake bodies that was mediated by predator cue type, snake body size, and species identity. We also found an interaction between curve magnitude and body location that clearly shows which parts of the display vary most across individuals and species. 
Our results suggest that contrary to the assumption in the literature that all species and individuals perform the same display, a high degree of variation persists in thrashing behaviour exhibited by Micrurus coral snakes despite presumably strong selection to converge on a common signal. This quantitative behavioural characterization presents a new framework for analysing the non-locomotory motions displayed by snakes in a broader ecological context, especially for signalling systems with complex interaction across multiple modalities.
description: All animal-related procedures have been approved by the University of Michigan Institutional Animal Care and Use Committee (Protocols #PRO00006234 and #PRO00008306) and the Peruvian government SERFOR (Servicio Nacional Forestal y de Fauna Silvestre
description: permit numbers: 029-2016-SERFOR-DGGSPFFS, 405-2016-SERFOR-DGGSPFFS, 116-2017-SERFOR-DGGSPFFS). We collected data during five field expeditions in the Amazonian lowlands of Peru from March 2016 to December 2018, at Villa Carmen, Los Amigos, Madre Selva, and Santa Cruz Biological Stations (Fig. 1A).

We recorded anti-predator behavior in a pop-up behavioral arena constructed of corrugated plastic (Fig. 1B) illuminated by a string of led lights attached to the inner surface at the top edge of the arena walls. We placed snakes into the arena, one at a time, and immediately began recording their behaviour. Between each snake we cleaned the arena with unscented soap and water. We covered the inner surface of the arena with an adhesive transparent plastic film (Con-Tact, Rubbermaid) to facilitate thorough and rapid cleansing and preserve the visual fiducial markings. We recorded snake behavior using either two or three GoPro (San Mateo, California) Hero 4+ Black or three Hero 5+ Black cameras filming from overhead and lateral views (see Figure 1B for camera positions) at 30, 60, or 120 frames per second, depending on the lighting conditions.

We used three different stimuli to elicit anti-predator behaviors: overhead looming, pulsed vibration, and a tactile stimulus through physical contact. To simulate avian predation threat, we quickly moved a piece of cloth across the top of the arena to create the visual looming and pressure wave stimuli produced by a swooping bird. To simulate a large mammal predator, we used the vibration produced by a cellular phone and placed it in contact with the arena. To test for response after contact with a predator, we used a 1m snake hook to tap the snake’s tail. We randomized all treatments across individuals, and we recorded snake behaviors for up to two minutes, allowing one minute of time to rest between the trials.