DOI: 10.5061/dryad.7h44j0zwz
title: Social learning data in a foraging setting for Heliconius erato

description: Insects may acquire social information by active communication and through
 inadvertent social cues. In a foraging setting, the latter may indicate
 the presence and quality of resources. Although social learning in
 foraging contexts is prevalent in eusocial species, this behaviour has
 been hypothesised to also exist between conspecifics in non-social species
 with sophisticated behaviours, including Heliconius butterflies.
 Heliconius are the only butterfly genus with active pollen feeding, a
 dietary innovation associated with a specialised, spatially faithful
 foraging behaviour known as trap-lining. Long-standing hypotheses suggest
 that Heliconius may acquire trap-line information by following experienced
 individuals. Indeed, Heliconius often aggregate in social roosts, which
 could act as ‘information centres’, and present conspecific following
 behaviour, enhancing opportunities for social learning. Here, we provide a
 direct test of social learning ability in Heliconius using an associative
 learning task in which naïve individuals completed a colour preference
 test in the presence of demonstrators trained to feed randomly or with a
 strong colour preference. We found no evidence that Heliconius erato,
 which roost socially, used social information in this task. Combined with
 existing field studies our results add to data which contradict the
 hypothesised role of social learning in Heliconius foraging behaviour.
description: Experimental subjects and
 arena Experimental subjects originated from
 first-generation insectary-reared stock populations of
 <em>Heliconius</em>
 <em>erato</em> <em>phyllis</em>, descended from multiple wild-caught females collected in Mata do Jiqui, Natal, Brazil
 (5°55'39"S, 35°10'59"W). We maintained stock
 populations in large outdoor cages (3 x 3 x 2.5 m) in which free-flying butterflies were able to
 engage in natural social and flight behaviours, including chasing, mating
 and following. At night, individuals were also observed to form roosts of
 2-22 individuals. Stock
 butterflies had access to hostplants (<em>Passiflora</em>
 <em>misera</em> and <em>P</em>.
 <em>galbana</em>) and rewarding artificial white flowers. All
 butterflies were individually labelled with unique IDs. The test
 arena was composed of purple and yellow artificial flowers. These colours were chosen
 given that they are, on average, both relatively
 unpreferred.
 Rewarding flowers
 contained a ~20% sugar
 solution mixed with bee-pollen supplement while unrewarding flowers were empty. Twelve flowers of
 each colour were placed on a grid of 24, with randomised
 positions (Supplementary
 Information Figure S1). Selection of
 demonstrators Butterflies were randomly assigned to one of two
 demonstrator groups, each collectively subjected to four days of training
 (Supplementary Information Figure S2). For one group, only purple flowers
 were positively reinforced to strengthen preference for purple. For the
 other, to minimise long-term colour preference, the colour of the
 rewarding flower was randomly determined for each trial. Training was run
 between 08:00–16:00. On the following day, a final 5-minute test was
 conducted to determine demonstrators' colour preferences. Preference
 was calculated as the proportion of landings on purple and yellow flowers
 out of 20 landing events. Demonstrators with a ≤ 60% purple preference were assigned to the control group, whereas
 demonstrators with a ≥ 80%
 purple preference were
 assigned to the knowledgeable group, creating two demonstrator groups with
 unbiased and biased preferences respectively (Figure
 1). Social learning
 experiment The social learning experiment consisted of two
 phases (Figure S3). (1) During pre-training, naïve butterflies, hereafter ‘observers’, fed on
 artificial
 white
 flowers
 between 08:00–16:00 to get accustomed to artificial
 flowers. (2) In the trialling phase, which lasted for four days,
 butterflies were randomly
 assigned to either the control or the knowledgeable
 demonstrator
 groups. Observers
 were released in pairs along with 10 demonstrators to
 ensure that
 most individual-level feeding attempts
 were by the demonstrators. During trials, we scored the number of feeding
 attempts made by each observer on purple rewarding flowers and yellow
 unrewarding flowers for 15 minutes. A choice was scored when the butterfly
 landed on a flower. Statistical analysis
 Data were analysed using
 generalised linear mixed models in R using the lme4 package. First, we
 asked whether demonstrators from different groups preferred the rewarding
 colour, using a binomial GLMM with the response variable 'preference
 for rewarding colour' (proportion of landings on purple flowers) and
 fixed factor 'group' (control and knowledgeable). Then, for
 observers, we examined whether there were intergroup differences in
 preference for rewarding colour over time, using a binomial GLMM with
 response variable 'preference for rewarding colour' and fixed
 factors 'group' (control and knowledgeable) and 'trial
 day' (1 to 4). In the latter, identity was set as a random effect due
 to repeated measures. Finally, we analysed whether observers
 preferred flowers occupied
 by demonstrators using a
 binomial GLMM with response variable 'local preference' (0 = no; 1 = yes) and fixed factors
 'group' (control and knowledgeable) and 'trial day' (1
 to 4).
description: RStudio.