Appendix: detailed methods of group manipulation and data analysis
Collection & Laboratory Maintenance
Social spiders of genus Stegodyphus live together in a colony containing 1-2000 closely related
individuals [1]. Like all social spiders, colony members cooperate in shared web maintenance,
prey capture, and alloparental care [2]. Their webs are composed of two structures: a twodimensional capture web and a dense three-dimensional retreat composed of a series of silken
tunnels. Spiders reside within their retreat for the majority of the day, and only emerge in
response to prey or at night in order to repair their capture web.
Fifteen colonies of S. dumicola were collected along fences in the Kalahari Desert
between Groblerschloop and Uppington in the Northern Cape, South Africa. Colonies were hand
collected, placed in a cloth pillowcase for transport, and transported to our laboratory at the
University of Pittsburgh, Pittsburgh, PA (Collection/Export Permit: FAUNA 189/2013— #0056
AAA041-00016, Research Permit: FAUNA 1060/2012— #16634). Colonies were sorted by hand
in laboratory and their group sizes were determined by counting the number of females therein
(25-691 individuals). Six of the largest colonies were selected for use in our experiment. We
haphazardly selected 84 females for inclusion in our studies from each of these colonies.
Assignment of females to different treatment groups was determined randomly using a random
number generator in Excel (Microsoft). Prior to assignment to a given treatment, females were
housed individually in translucent 2oz deli cups that contained a ball of poultry wiring to permit
web construction. We maintained spiders in isolation for six weeks prior to the start of the
experiments. Isolated spiders were maintained on an ad libitum diet of size-matched two-weekold crickets.
Group manipulation
Assignment of females to different treatment groups was determined randomly using a random
number generator in Excel (Microsoft). Prior to assignment to a given treatment, females were
housed individually in translucent 2oz deli cups that contained a ball of poultry wiring to permit
web construction. We maintained spiders in isolation for six weeks prior to the start of the
experiments. Isolated spiders were maintained on an ad libitum diet of size-matched two-weekold crickets.
Altogether, the group identity experiment ran for eight weeks, and colonies were
disturbed after either one, two, three, four, five, six, or seven weeks. So, for example, colonies
that experienced a social disturbance after one week were then left undisturbed for seven weeks
and would have more repeated interactions with each other than colonies that were disturbed after
five weeks, and so on. Our social disturbance involved all of the members being removed from
the colony and then being placed into a new container with all the same individuals (control
treatment) or with a completely new and unfamiliar set of individuals (mixed treatment). Colonies
in the mixed treatment were reassembled using individuals taken from the same source colony
but that had not interacted. Therefore, individuals in the control and mixed colonies both
experienced the same disturbance (i.e., their old web being destroyed and a new web being
constructed), but the identity of the individuals in the mixed colonies was altered. Thus, any
differences between the control and mixed colonies could be attributed to the effects of repeated
interactions among the same members and not the effect of the social disturbance per se.
We used a split design where each of our six source colonies was used to establish one
replicate of each of our fourteen treatment combinations (mixed and control colonies at one, two,
three, four, five, six, or seven weeks since social disturbance). Our design also ensured that all
source colonies equally contributed to all treatment groups and that relatedness among
individuals was at naturally-occurring levels, which is known to influence social spider behaviour
[3, 4]. Therefore, if relatedness among individuals was more influential on behaviour than group
identity, we would expect to see no differences between the control and mixed colonies at any
treatment. All experimental colonies were housed in 1.5L clear plastic deli cups that contained a
dome of poultry wiring for web construction. Lids were covered with a 1 × 1 mm screen, which
allowed ample airflow and low humidity levels, consistent with conditions in the Kalahari.
Colonies were kept on a maintenance diet of ad libitum six-week-old crickets once weekly. To
ensure successful prey capture, crickets were immobilized prior to being placed in colonies’
capture webs. After the social disturbance, all individuals were re-housed within a new 1.5L
container with chicken wire. All colonies resumed normal feeding behaviour within 3 days of the
social disturbance. At the end of our eight-week experiment, all colonies were disassembled,
individuals were isolated back into 2 oz deli cups and their personality (i.e., boldness) was
repeatedly assayed daily for the next 5 days.
Boldness Assay
This assay was designed to measure how quickly an individual recovered from a potential
predator attack. Five boldness assays (one per day) were completed on each spider beginning 24
h after the end of the group identity treatments. Boldness assays were initiated by placing a single
individual within a rectangular enclosure (13.5×13×3.5 cm). Spiders were acclimated for 60s
before applying two jets of air to the dorsal, anterior part of the animal using an ear-cleaning
bulb. This universally elicited a huddle response from S. dumicola. As our measure of boldness,
we recorded the individual's latency to resume movement following the huddle response.
References
1.
Seibt U., Wickler W. 1988 Bionomics and social structure of'Family Spiders' of the genus
Stegodyphus, with special reference to the African species S. dumicola and S. mimosarum
(Araneida, Eresidae). Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg 30, 255304.
2.
Lubin Y., Bilde T. 2007 The evolution of sociality in spiders. Advances in the study of
Behavior 37, 83-145.
3.
Ruch J., Heinrich L., Bilde T., Schneider J.M. 2009 Relatedness facilitates cooperation in
the subsocial spider, Stegodyphus tentoriicola. BMC Evolutionary Biology 9(1), 257.
4.
Schneider J.M., Bilde T. 2008 Benefits of cooperation with genetic kin in a subsocial
spider. Proceedings of the National Academy of Sciences 105(31), 10843-10846.