DOI: 10.5061/dryad.s1rn8pkff
title: Selection for evasive mimicry imposed by an arthropod predator

description: It has long been hypothesized that a species that is relatively easy to
 catch by predators may face selection to resemble a species that is harder
 to catch.  Several experiments using avian predators have since
 supported this “evasive mimicry” hypothesis.  However, the sudden
 movement of artificial evasive prey in each of the above experiments may
 have startled the predators, generating an avoidance response unrelated to
 difficulty of capture. Additionally, in the above experiments, the
 catchability of prey was all or nothing, while in nature predators may
 occasionally catch evasive prey or fail to catch slower species, which
 might inhibit learning. Here, using mantids as predators, we conducted an
 experimental test of the evasive mimicry hypothesis that circumvents these
 limitations, using live painted calyptrate flies with modified evasive
 capabilities as prey. We found that mantids readily learned to avoid
 pursuing the more evasive prey types. Warning signals based on evasiveness
 and their associated mimicry may be widespread phenomena in
 nature.  These findings not only further support its plausibility
 but demonstrate that even arthropod predators can select for it.
description: Training phase The training phase of our
 experiment involved repeatedly presenting two similar-sized flies, one
 with thorax painted black and one with thorax painted white, to individual
 mantids (<em>Tenodera sinensis</em>). The presentations (seven
 in total) were made every second day over a period of two weeks. The two
 presented flies were clipped and painted as part of a 2 (Black B or White
 W) x 2 (Clipped C or Not Clipped N) treatment design i.e. only the white
 fly was clipped (BN/WC; treatment 1), only the black fly was clipped
 (BC/WN; treatment 2), both flies were clipped (BC/WC; treatment 3),
 neither fly was clipped (BN/WN; treatment 4). Each mantid only experienced
 a single training treatment and there were 20 mantids per
 treatment.  Presentations of flies to mantids took
 place in sequential order based on treatment, so that flies were first
 given to a mantid in treatment 1, then a mantid in treatment 2, then 3 and
 4.  After setup, the flies and mantids were checked every 20 minutes over
 a three-hour duration. Once a mantid had caught one fly, the remaining fly
 was removed. If no flies were caught after three hours both were removed.
 Since it takes mantids of the size (L3-L4) used in this experiment more
 than 20 minutes to consume a fly, the mantids were never able to consume
 both flies between consecutive checks. Note that failed capture attempts
 (or the precise timing of successful captures) were not recorded in the
 training phase, only the fly type that was successfully caught. 
 Test phase The test phase was conducted once
 for each mantid and involved presenting unclipped (BN/WN)  yet tethered
 flies and observing which colour of fly, if any, was first attacked. The
 mantids were tested following the same sequential order of treatment as
 above and monitored in the same manner as in the training phase.
description: # Selection for evasive mimicry imposed by an arthropod predator
 This paper describes an
 experiment conducted to test whether mantids can learn to use a signal
 (black or white) to discriminate between flies that are hard to catch
 (wings not clipped) from flies that are easy to catch (wings clipped). ##
 Description of the data and file structure We have two data sets and
 associated code. The first data set represents the training data over
 seven presentations of pairs of flies (one black and one white) to mantids
 (80 in total, split evenly over four training treatments). The second data
 set represents the test data in which mantids were presented with a black
 and a white fly with unclipped wings. ### Training data set The training
 data set provided in MS Excel format comprises 80 rows (20 mantids for
 each of 4 treatments) and 9 columns, comprising the following variables:
 Individual : a unique ID for the individual mantid (1-80) Treatment : 1-4
 (1 = BN/WC, 2 = BC/WN, 3 = BC/WC, 4 = BN/WN) D1-D7 : type of fly (if any)
 attacked on given training day D1-D7 (0 = No fly attacked; 1 = White fly
 attacked; 2 = Black fly attacked) ### Test data set The test data set
 provided in MS Excel format comprises 80 rows (20 mantids for each of 4
 treatments) and 3 columns, comprising the following variables: Individual
 : a unique ID for the individual mantid (1-80) Training teatment : 1-4 (1
 = BN/WC, 2 = BC/WN, 3 = BC/WC, 4 = BN/WN) WBN120 : whether white (= 1),
 black (= 2) or no fly (= 0) was attacked ## Sharing/Access information The
 experiments were run by KLH and the data were analyzed by TNS. Further
 details of the experiment are available as Supplementary Methods
 associated with the main paper. ## Code/Software All visualization and
 analysis of the above data was conducted in R. ### R Training code: ####
 Data preparation and visualization We first read the above data file, then
 convert it from wide to long format and define some variables based on
 transformations of the existing variables. We then sum the number of
 outcomes (no fly attacked, white fly attacked, black fly attacked) over
 all mantids within each treatment over each training day and plot these
 distributions out in a stacked bar chart. For ease of interpretation, we
 have used white bars to represent the number of white flies attacked,
 black bars to represent the total number of black flies attacked and grey
 bars to represent the total number of times no fly was attacked. ####
 Statistics Our analysis of the training data was limited to testing
 whether more white or black flies were consumed by mantids over the seven
 days of presentations within any given treatment, using a simple Wilcoxon
 Signed rank test (with the mantid as the pairing variable). To do so, we
 first subsetted the data by treatment, then calculated the frequency of
 black and white (and no) flies caught by each mantid over the course of
 their training. Sign tests use less information but here we show that they
 result in identical qualitative conclusions. ### R Test code: #### Data
 preparation and visualization The data are already in long format, so we
 simply sum the number of times a white fly, black fly or no fly was
 attacked for each of the 4 treatments and plot the results as a stacked
 barchart. #### Statistics For ease of interpretation, we have focused on
 instances in which one of the two flies (black or white) were attacked
 (90% of cases). We then fitted two binary logistic models (intercept only
 and a model in which treatment affected the log odds of being attacked)
 and compared them using a log likelihood ratio test (LRT). Following
 evidence for an overall effect of training treatment on the log odds of
 attacking a black (as opposed to white) fly, we compared among treatments
 with a post-hoc Tukey HSD implemented using the glht function of the
 multcomp package. Finally, to test the null hypothesis that attack on the
 two types of fly were equally likely we compare the total number of white
 and black flies attacked by each mantid using a separate sign test for
 each of the four treatments.