DOI: 10.5061/dryad.n8pk0p31d
title: Data from: Predator response to the coloured eyespots and defensive posture of Colombian four-eyed frogs

description: Deimatic displays, where sudden changes in prey appearance elicit aversive
 predator reactions, have been suggested to occur in many taxa. These
 (often only putative) displays frequently involve different components
 that may also serve antipredator functions via other mechanisms (e.g.
 mimicry, warning signalling, body inflation). The Colombian four-eyed
 frog, Pleurodema brachyops, has been suggested to gain protection against
 predation through putative deimatic displays where they inflate and
 elevate the posterior part of their body revealing eye-like colour
 markings. We exposed stationary artificial frogs to wild predators to test
 whether the two components (eyespot/colour markings, defensive posture) of
 their putative deimatic display, and their combination, provide protection
 from predation without the sudden change in appearance. We did not detect
 any obvious additive effect of defensive posture and eyespots/colour
 markings on predation risk but found a marginally-significant trend for
 model frogs in the resting posture to be less attacked when displaying
 eyespots/colour markings than when they were not, suggesting that the
 presence of colour markings/eyespots may provide some protection on its
 own. Additionally, we found that models in a resting posture were overall
 more frequently attacked on the head than models in a defensive posture,
 indicating that a defensive posture alone could help redirect predator
 attacks to non-vital parts of the body. The trends found in our study
 suggest that the different components of P. brachyops’ coloration may
 serve different functions during a deimatic display, but further research
 is needed to elucidate the role of each component when accompanied by
 sudden prey movement.
description: We tested the effect of the
 defensive posture and eyespots/colour markings present in the putative
 deimatic display of <em>P. brachyops</em> by exposing 1000
 frog models, divided equally in four treatments, to natural predators in
 four different study areas. Two treatments included the eyespot/colour
 markings in the posterior dorsal region. These characteristic markings in
 <em>P. brachyops</em> consist of two rounded lumbar glands in
 a black colour accompanied by a pair of orange spots. Four different types
 of models were thus used: defensive posture with visible eyespots/colour
 markings; defensive posture without eyespots/colour markings; resting
 posture with visible eyespots/colour markings; and resting posture without
 eyespots/colour markings. 250 models of each type were placed
 semi-randomly (no two models of the same type were placed consecutively),
 distributed in equal numbers in each of the four locations. The model
 sequence was determined using an Excel-based random numbers
 generator.  In each study site, we distributed the models
 sequentially with an inter-model distance of 5 m in all directions. The
 models remained in the field for three days, with visits every 24 hours to
 check for predation attempts on them. Models found with attack marks
 during the first (24h) or second day (48h) after deployment were removed
 and replaced with a new model (i.e., models that were found with attack
 marks during the last session [third day] were not replaced). Missing
 models were also replaced to keep the number of models within each
 category constant. Replacement models were treated as new replicates and
 their time to exposure to predation was counted from the moment at which
 they were deployed. All missing models were excluded from the data because
 we were unable to reliably attribute their absence to predation events.
 Models were exposed to predation for 24–72 hours. Bird attacks were
 identifiable by V or U -shaped and stab-like marks, whereas mammal attacks
 were identified by the bite marks, as reported in similar studies. Other
 attack marks, such as multiple small holes or scratches, were also recorded, but not included
 in our analyses. We also recorded the area of the body where the model was
 attacked (head or rest of the body), as attacks in the head could be an
 additional indication that the predators do recognise them as prey.
 Alternatively, attacks in the ‘rest of the body’, particularly in models
 displaying the eyespot/colour markings, could be an indication that these
 markings might redirect predator attacks away from vital body
 parts. Differences among the morphs in attack risk over
 time were analysed via a survival analysis (Cox Regression) using the
 probability of bird/mammal attack as a binary response variable, and the
 eyespots/colour markings (with/without), posture (resting/defensive), and
 their interaction as fixed factors. To account for the non-independence of
 models within a study plot we included location as a random factor. We
 also took the subset of attacked models and tested the effect of
 eyespots/colour markings and posture (fixed factors) on the probability of
 attacks in the head using a Generalised Linear Mixed Model (GLMM) with
 binomial distribution and logit link function, and including location as a
 random effect. In all cases, we ran separate models for attacks by mammals
 and birds. All analyses were conducted in R, using the RStudio platform,
 and the package <em>coxme</em>.
description: Excel and R.