DOI: 10.5061/dryad.15dv41p53
title: Data for: How does viewing angle affect the perceived accuracy of Batesian mimicry in hoverflies?

description: Despite Batesian mimicry often eliciting predator avoidance, many Batesian
 mimics, such as some species of hoverfly (Syrphidae), are considered to
 have an “imperfect” resemblance to their model. One possible explanation
 for the persistence of apparently imperfect mimicry is that human
 perceptions of mimicry are different from those of natural predators.
 Natural predators of hoverflies have different visual and cognitive
 systems from humans, and they may encounter mimics differently. For
 example, whilst humans often encounter hoverflies at rest on vegetation,
 or in photographs or textbooks, where they are typically viewed from
 above, natural predators may approach hoverflies from the side or below.
 To test how viewing angle affects the perception of mimicry, images of
 mimetic hoverflies and their models (wasps and bees) were shown from
 different angles in an online survey. Participants were asked to
 distinguish between the images of models and mimics. The results show that
 the viewing angle does affect perceived mimicry in some species, although
 it does not provide a complete explanation for the persistence of
 imperfect mimicry in nature. The effect is also highly species-specific.
 This suggests that to better understand how selection has shaped mimetic
 accuracy in hoverflies and other taxa, further study is required of the
 viewing angles that predators utilize most commonly in nature.
description: Insect specimens and photography
 Insect specimens were collected between June 2020 and August 2021
 from various locations in the East Midlands (UK), using a hand net.
 Species were selected opportunistically from those that were most abundant
 at our field sites. Specimens were euthanized by freezing at -18°C for
 approximately 30 minutes. They were then pinned through the thorax and
 positioned into a natural-looking posture before drying for 6-24 hours.
 Specimens were suspended, with the anterior uppermost, on a motorized
 turntable (Syrp Genie II), positioned against a white background, and lit
 indirectly using two LED panel lights (22W, 5600K; Pixapro, Brierley Hill,
 UK). They were photographed using a DSLR camera (Canon EOS 600D) and macro
 lens (Tamron SP 90mm) with F20, 1/6s exposure, and ISO400. Each specimen
 was photographed from nine different viewing angles – three different
 vertical camera positions (vertical angle) at each of three equally spaced
 turntable orientations (rotational angle) (Figure 1).
 Photos of three specimens of each of 10 different species were
 selected for this study. We identified the three most abundant aposematic
 Hymenoptera at our field sites as the most plausible “model” species for
 hoverfly mimics: <em>Vespula vulgaris, Vespula germanica,
 </em>and <em>Apis mellifera. </em>The species were
 divided into a wasp group and a bee group. The wasp group consisted of the
 two common wasp species (<em>V. vulgaris </em>and<em> V.
 germanica</em>), three wasp mimics<em>
 </em>(<em>Epistrophe grossulariae, Helophilus pendulus,
 </em>and <em>Sericomyia silentis</em>), and a control
 non-mimetic fly (<em>Mesembrina meridiana</em>). <em>E.
 grossulariae </em>and <em>H. pendulus </em>are both
 considered accurate mimics of <em>Vespula </em>species when
 observed from a dorsal view (Dittrich <em>et al.</em>, 1993;
 Leavey <em>et al.</em>, 2021). The accuracy of <em>S.
 silentis </em>has not been assessed. The bee group consisted of the
 honeybee, <em>A. mellifera,</em> two bee mimics
 (<em>Eristalis pertinax </em>and<em> Eristalis
 tenax</em>), and a control non-mimetic fly (<em>Cheilosia
 albitarsis</em>). <em>Eristalis </em>species have been
 shown to be very inaccurate mimics of <em>Vespula </em>species
 when viewed dorsally (Dittrich <em>et al.</em>, 1993), but the
 accuracy of their mimicry of <em>Apis</em> has not been
 quantified. The choice of which control non-mimetic fly was included in
 each group was arbitrary. A different control non-mimetic fly was included
 in each group so that all species were encountered the same number of
 times by each participant (see below).
 Survey A survey was coded
 using RStudio (R Core Team, 2019) using the shiny (Chang <em>et
 al.</em>, 2022), shinyjs (Attali, 2021), shinycssloaders (Sali and
 Attali, 2020) and rdrop2 (Ram and Yochum, 2020) packages and deployed on
 the shinyapps.io server (Posit Software, 2022). Upon opening the survey,
 the user was allocated at random to the bee or wasp group and a single
 vertical angle and rotational angle combination (from the nine
 demonstrated in Figure 1). The user was given information explaining how
 to complete the survey (Figure S1), shown a “model photo” (of a specimen
 that was not included in the question set) of either <em>Apis
 mellifera </em>or <em>Vespula germanica</em> (depending
 on which group had been selected) from the selected viewing angle, and
 told which model type (“bee” or “wasp”) the photo showed.
 The user was then shown the rest of the photos in the group from
 the selected viewing angle. For the wasp group, participants were shown 18
 photos in a random order (three specimens of six species) and asked the
 question, “Is this a wasp?”. For the bee group, participants were shown 12
 photos in a random order (three specimens of four species) and asked the
 question, “Is this a bee?”. For each image, the participants were asked to
 select an answer (either “Yes” or “No”) and then were told if they were
 correct or incorrect. This allowed participants to continue to learn what
 the images showed throughout the survey. Once all images in the first
 model group had been shown, the participant was shown the model photo for
 the other group from the same viewing angle and told which model type it
 showed. Participants were then asked to classify the images of the species
 in this group in the same manner as the previous group. The participants
 were not given a time limit to answer individual questions or complete the
 survey overall. Once all 30 questions had been asked, the participant was
 thanked for taking part and shown their overall score.
 The link to this survey was sent out to various student and staff
 email lists at the University of Nottingham, as well as to members of the
 public via social media. Participants completed the survey using their own
 device, meaning that display types/resolutions and viewing distances
 varied. One hundred and forty-six responses to the survey were received.
 Due to the random allocation to each treatment, the number of participants
 allocated to each treatment varied from 9 to 20 (N for each treatment:
 high dorsal = 9, high ventral = 17, high side-on = 19, mid dorsal = 16,
 mid ventral = 20, mid side-on = 18, low dorsal = 18, low ventral = 11, low
 side-on = 18). Statistical
 analysis Statistical analysis was carried out
 using R version 4.3.1 (R Core Team, 2019). A set of nested Generalized
 Linear Mixed Effects models (GLMMs) was fitted to the entire data set
 using the glmmML function (Broström, 2022). The response variable was
 whether the image was correctly classified, and binomial errors were
 assumed. The participant ID and insect specimen were fitted as random
 effects. The species, vertical angle, rotational angle, and question
 number were fitted as fixed effects. The order in which the questions were
 asked was centered around zero, with values ranging from -14.5 to 14.5.
 Another fixed effect called group order was fitted to account for whether
 the questions were asked in the first or second species group. The
 question number and group order were included in the models to determine
 if learning occurred across the question set. All two-way interactions
 between these fixed effects were included in the maximal model.
 Preliminary inspection of the data suggested there was not a strong
 three-way interaction between species, vertical angle, and rotational
 angle. To determine the best model to describe the
 data, a model selection process was followed as in Symonds and Moussalli
 (2011) and Smolis <em>et al.</em> (2023). The dredge function
 from the MuMIn package (Barton, 2023) was used to fit models with every
 combination of the fixed effects and their two-way interactions and
 compare them using the corrected Akaike information criterion (AICc) to
 find the best model. ΔAICc (the difference in AICc between the best model
 and model <em>i</em>) and the AICc weight (ωi) were calculated
 by the dredge function. The accumulated AICc weight (acc ωi) was
 calculated and used to determine the 95 % confidence set of models. The
 evidence ratio (ER) was calculated using the equation:  ER = exp( − 1/2
 ∆AICc<sub>best</sub>) / exp(−1/2
 ∆AICc<sub>i</sub>)  (from Symonds and
 Moussalli (2011)), where is the ΔAICc value for the best model, so is
 equal to zero. The predictor weight was calculated for each predictor by
 summing the weights of the models in which they were included. In
 preliminary analysis, we encountered convergence errors for some
 statistical models, owing to the near-perfect recognition of images of the
 control (non-mimetic) species, and one of the <em>A.
 mellifera</em> specimens. To avoid this problem, these images were
 removed from the dataset before conducting the final analysis.
description: # Data for: How does viewing angle affect the perceived accuracy of
 Batesian mimicry in hoverflies?
 [https://doi.org/10.5061/dryad.15dv41p53](https://doi.org/10.5061/dryad.15dv41p53) This dataset comprises the raw data obtained from a survey that asked participants to identify wasps, bees, hoverflies, and non-mimetic flies from different viewing angles. ## Description of the data and file structure The data consists of one Excel spreadsheet.  Column A - The response number. 146 responses to the survey were obtained in total. Columns B-AF - The responses to the questions. Each participant was shown 30 photos of wasps, bees, non-mimetic flies, and hoverflies. The photos were in two groups, a wasp group and a bee group. When shown the wasp group, the participant would see 18 photos, one after the other, of wasps, wasp-mimicking hoverflies, and a control non-mimetic fly, all shown from one viewing angle. The angle the images were from was randomised for each participant. For each photo, the participant would be asked, "Is this a wasp?" and prompted to select either yes or no. When shown the bee group, the participant would see 12 photos, one after the other, of bees, wasp-mimicking bees, and a control non-mimetic fly, again shown from one randomised viewing angle (the same as was selected for the wasp group). Each participant was shown both the bee and wasp groups of photos, but the order the two groups were shown was randomised. Each participant would also see three images of each species. The data in these columns shows which answer the participant selected. Columns AG-BJ - The species of insect and the angle of the photo that the participant was shown. These correspond to the answers given in columns B-AF; for example, the response in column B was given to the species shown in column AG. The species of insects shown are labelled as follows: Amellifera = *Apis mellifera*, a honeybee Epertinax = *Eristalis pertinax,* a hoverfly Etenax = *Eristalis tenax*, a hoverfly Calbitarsis = *Cheilosia albitarsis,* a non-mimetic fly Vvulgaris = *Vespula vulgaris*, a wasp Vgermanica = *Vespula germanica*, a wasp Hpendulus = *Helophilus pendulus*, a hoverfly Ssilentis = *Sericomyia silentis*, a hoverfly Egross = *Epistrophe grossulariae,* a hoverfly Mmeridiana = *Mesembrina meridiana,* a non-mimetic fly The data in columns AG-BJ are encoded as follows: E.g., Mmeridiana3.2.front.JPG Mmeridiana = species 3 = specimen number, from 1-3 2 = vertical angle, either 1 (high), 2 (mid), or 3 (low) (see publication for more details on viewing angles) front = rotational angle, either front (ventral), back (dorsal), or side (side-on) (see publication for more details on viewing angles) So the second specimen of *Apis mellifera* viewed from a low dorsal angle would be: Amellifera2.3.back.JPG ## Sharing/Access information NA