DOI: 10.7302/bn0a-3g61
title: Convergence and divergence in anti-predator displays: A novel approach to quantitative behavioural comparison in snakes [Dataset]

description: Animals in nature use diverse strategies to evade or deter their predators, including many vivid behavioural displays only qualitatively described from field encounters with natural predators or humans. Within venomous snake mimicry, stereotyped anti-predator displays are suggested to be a critical component of the warning signal given by toxic models and thus under strong selection for independent convergence in mimetic species. However, no studies have systematically quantified variation in snake anti-predator displays across taxonomically broad clades to test how these behaviours evolve across species within a phylogenetic comparative methods framework. Here we describe a new, high-throughput approach for collecting and scoring snake anti-predator displays in the field that demonstrates both low observer bias and infinite extension across any species. Then, we show our method's utility in quantitatively comparing the behaviour of 20 highly-divergent snake species from the Amazonian lowlands of Peru. We found that a simple experimental setup varying simulated predator cues was very successful in eliciting anti-predator displays across species and that high-speed videography captured a greater diversity of behavioural responses than described in the literature. We also found that although different display components evolve at different rates with complicated patterns of covariance, there is clear evidence of evolutionary convergence in anti-predator displays among distantly related elapid coral snakes and their colubrid mimics. We conclude that our approach significantly advances opportunity for future analyses of snake behaviour, kinematics, and the evolution of anti-predator signals more generally, especially macroevolutionary analyses across clades with similarly intractable behavioural diversity.


description: (For detailed methodology, please see the published paper)
All field methods were approved by the University of Michigan Institutional Animal Care and Use Committee and the Servicio Nacional Forestal y de Fauna Silvestre (SERFOR) in Peru. We measured the anti-predator response of field-captured snakes across four field stations in the Amazonian lowlands of eastern Peru between October 2016 and December 2018: Villa Carmen Biological Station, Los Amigos Biological Station, Santa Cruz Biological Station, and Madre Selva Biological Station. We collected snakes through a combination of standardised drift-fence lines with both pitfall and funnel traps and hand-foraging during both the day and night.

As soon as each snake was safely captured or removed from a trap, we placed it into a bucket and recorded behaviour for up to one minute. After capture, we kept snakes in cloth bags in a quiet, low disturbance part of the laboratory for between 12-24 hours and handled them as a little as possible between capture and experiments. We placed snakes into a runway arena and used GoPro cameras to film multiple views.

We scheduled trials to reflect natural activity patterns by species, with diurnal snakes tested between 11am and 5pm and nocturnal snakes from 5pm to 11pm. Each snake was then exposed to a standardised set of predator cues designed to simulate different information types snakes might use to assess predation risk: "looming" cues consisting of a shadow and pressure wave created by swooping a t-shirt above the snake
description: "vibration" cues using a smartphone and wooden plank underneath the arena
description: and "tactile" cues created by tapping the snake's tail and body. We randomised the order of cue presentation across individuals and recorded the snake’s response to each of these cues for one minute trials with one minute of rest in between trials.