DOI: 10.5061/dryad.x3ffbg7g6
title: Data from: The complexity of social complexity: a quantitative multidimensional approach for studies on social organisation

description: The rapid increase in “big data” of the post-genomic era makes it crucial
 to appropriately measure the level of social complexity in comparative
 studies. We argue that commonly-used qualitative classifications lump
 together species showing a broad range of social complexity, and falsely
 imply that social evolution always progresses along a single linear
 stepwise trajectory that can be deduced from comparing extant species. To
 illustrate this point, we compared widely-used social complexity measures
 in "primitively eusocial" bumble bees with “advanced eusocial”
 stingless bees, honey bees, and attine ants. We find that a single species
 can have both higher and lower levels of complexity compared to other
 taxa, depending on the social trait measured. We propose that measuring
 the complexity of individual social traits switches focus from semantic
 discussions and offers several directions for progress. Firstly,
 quantitative social traits can be correlated with molecular,
 developmental, and physiological processes within and across lineages of
 social animals. This approach is particularly promising for identifying
 processes that influence or have been affected by social evolution.
 Secondly, key social complexity traits can be combined into
 multidimensional lineage-specific quantitative indices enabling fine scale
 comparison across species that are currently bundled within the same level
 of social complexity.
description: (Copied
 from Methods in ms) To quantify
 bumble bee queen-worker size differentiation, we used data from Cumber
 (1949) and new data. In Cumber’s publication, wing lengths of females (n =
 944) present in nine nests of six species were provided without
 distinguishing between workers and queens. However, all colonies were
 stated to contain queens and the size distribution was clearly bimodal in
 each colony, which we assumed to represent worker and queen modes. In the
 pollen-storing species (<i>B. lapidarius, B. lucorum, B. terrestris,
 B. pratorum</i>), there was clear separation of worker and queen
 distributions. For the pocket-making species (<i>B. agrorum, B.
 hortorum</i>), where queen-worker size distinction is less obvious,
 the size measurement with the minimum amount of records between the worker
 and queen modes (a clear trough in all three colonies) was assumed to
 consist of workers and queens equally, with all values smaller and larger
 than this assumed to be workers and queens, respectively. Additional size
 data using thorax width, was taken from all emerging workers (n = 434) and
 gynes (n = 26) in five <i>B. terrestris</i> colonies kept
 enclosed in standard laboratory conditions, from incipient colonies to
 queen death (de Medici & Bloch, unpublished data). A <i>B.
 terrestris</i> value was calculated from both studies using a mean
 weighted by sample size.  Queen worker size ratio, queen mean size / worker mean
 size, was calculated for comparison with stingless bee data from
 Toth et al. (Toth et al., 2004), and attine ant data from Fergusson-Gow et
 al (Ferguson-Gow et al., 2014). Additionally, a value for <i>Apis
 mellifera</i> was calculated using thorax size, and taking a mean
 from European and African strains (DeGrandi-Hoffman et al., 2004). To
 statistically compare bumble bees to stingless bees and (separately) to
 attine ants, we used species-level Wilcoxon Rank Sum tests (given the
 non-normality of the data). For comparing bumble bees and <i>Apis
 mellifera</i> (single value only), a Wilcoxon Rank Sum test does not
 provide sufficient power to allow such comparisons, thus we assumed a
 normal distribution and equal variances in a t test. To quantify
 bumble bee among-worker size differentiation, we used the following:
 <i>B. terrestris</i> data obtained from i) wing marginal cell
 length of all workers (n = 1832) produced by nine freely-foraging colonies
 over the majority of colony growth (Holland et al., 2020 preprint); ii)
 thorax width of all workers (n = 4492) found in 28 freely-foraging
 colonies around the peak of colony growth<sup> </sup>(Goulson
 et al., 2002), iii) wing length of workers (n = 139) found in wild
 colonies (Cumber, 1949). <i>B. impatiens</i> data obtained
 from thorax width of all workers (n = 1133) produced by 12 enclosed
 colonies over the later stages of colony growth (Couvillon et al., 2010;
 J. Jandt, personal communication). Other <i>Bombus</i> spp.
 data obtained from wing lengths of workers (n = 570) found in seven wild
 colonies of five species (Cumber, 1949). For the data from Cumber’s (1949)
 study, workers were determined as described above. The coefficient of
 variation, 100 x (worker head width standard deviation / worker head width
 mean), was calculated for comparison with attine ant data from Fergusson
 Gow et al. (2014) meta-study. In addition, stingless bee data from
 Waddington et al. (1986) and Gruter et al. (2017) were also used to
 calculate coefficients of variation (there was no overlap in the species
 covered by each study). A value for Apis mellifera was obtained from
 Roulston & Cane (2000). Although size in bumble bees was measured
 as thorax width or wing marginal cell length, we assume this to be
 comparable to head width (which was used for ants and stingless bees),
 because both of these measures are strongly correlated with head width
 across the full size range of <i>Bombus terrestris</i> workers
 (Pearson correlation, thorax width-head width, rho = 0.92,
 R<sup>2</sup> = 0.85;  wing cell length-head width, rho =
 0.95, R<sup>2</sup> = 0.90; n = 69, Holland unpublished data).
 To statistically compare bumble bee species to stingless bees and
 (separately) to attine ants, we used species-level Wilcoxon Rank Sum tests
 (given the non-normality of the data). As with the Queen-Worker
 comparison, for comparing bumble bees and Apis mellifera (single value
 only), a Wilcoxon Rank Sum test does not provide sufficient power to allow
 such comparisons, thus we assumed a normal distribution and equal
 variances in a t test. We produced a
 genus-level phylogenetic tree for graphical comparison using relationships
 from the following studies: within Attini, Fergusson-Gow et al. 2014;
 within Meliponini, Rasmussen & Cameron 2009; between Meliponini,
 Bombini and Apini, Cardinal & Danforth 2011; between Apidae and
 Formicidae, numerous studies, e.g. Johnson et al. 2013. The trees were
 produced, without differences in branch length, using
 TreeGraph2. As an example
 of comparing social complexity between species, we chose six species
 (<i>Apis mellifera, Atta sexdens, Bombus terrestris, Euglossa
 viridissima, Melipona fasciata,</i> and<i> Trachymyrmex
 septentrionalis</i>) for which quantitative data were available in
 five social traits. The traits were quantified as follows: 1) Worker size
 variation = log10 coefficient of variation in worker head-width
 (<i>A. mellifera</i> = Roulston & Cane 2000;
 <i>A. sexdens, T. septentrionalis</i> = Fergusson-Gow et al.
 2014; <i>B. terrestris</i> = see above; <i>M.
 fasciata</i> = Waddington et al. 1986; <i>E.
 viridissima</i> = variation among females, Eltz et al 2011); 2)
 Queen-worker body size dimorphism = mean queen size / mean worker size
 (<i>A. mellifera</i> = deGrandi-Hoffman et al 2004, see above;
 <i>A. sexdens, T. septentrionalis</i> = Fergusson-Gow et al.
 2014; <i>B. terrestris</i> = see above; <i>E.
 viridissima</i> = equal size assumed since all females can mate and
 disperse; <i>M. fasciata</i> = Toth et al. 2004); 3)
 Reproductive skew = the proportion of adult males which are queen-produced
 rather than worker-produced in queenright colonies (<i>A. mellifera,
 B. terrestris, Trachymyrmex spp.</i> = Wenseleers & Ratneiks
 2006; <i>A. sexdens </i>= 1 implied given no viable
 worker-laid eggs in Dijkstra et al. 2005; <i>E.
 viridissima</i> = the mean proportion of eggs laid by dominant
 mother, Cocom Pech 2008; <i>M. fasciata</i> = Toth et al.
 2004); 4) Colony size = log10 number of workers at peak colony size
 (<i>A. mellifera</i> = approximated at 10,000 workers;
 <i>A. sexdens, T. septentrionalis</i> = Fergusson-Gow et al.
 2014; <i>B. terrestris</i> = approximated at 200 workers;
 <i>E. viridissima</i> = Cocom Pech 2008; <i>M.
 fasciata</i> = Toth et al. 2004); 5) Colony longevity = best
 estimate of lifespan in colonies surviving foundation (<i>A.
 mellifera</i> = mean of feral colonies, Seeley 1978; <i>A.
 sexdens</i> = Keller 1998; <i>B. terrestris</i> =
 approximated at 0.5 years;  <i>E. viridissima</i> = longevity
 of adults, Skov & Wiley 2005; <i>M. fasciata</i> =
 Roubik 1983; <i>T. septentrionalis</i> = approximated at 2
 years, based on comments in Beshers & Traniello 1996 and Weber
 1966). For plotting, traits were rescaled across species, so that the minimum was set to 0 and the
 maximum was set to 1. This rescaling was performed both for all
 species together (presented in Figure 4A) and for ants and bees separately
 (Figure 4B, C). To produce the combined indices (Figure 4B, C), unweighted
 means of the 6 scaled trait values were then calculated. This is not an
 exclusive list of traits that could be quantified as components of social
 complexity, and several of these traits could be quantified by alternative
 or complementary methods. These comparisons are obviously limited by the
 amount of comparable data available.
description: (Copied from readme file): Data for Holland
 & Bloch 2020; The complexity of social complexity: a quantitative
 multidimensional approach for studies on social organisation (American
 Naturalist) Readme file
 <b>WWdata</b> Worker size variation data. Further details in ms. HeadWidth.mean, ThoraxWidth.mean, Mcell.mean, WingLength.mean = Mean sizes (mm) of workers taken for either head width, thorax width, wing marginal cell length, or wing length. NAs indicate unmeasured indicies, or values not given. CV = coefficient of variation for the size index measured (100 x (sd/mean)). Source = source of data. Gruter2017 = doi: 10.1038/s41467-016-0012-y; Waddington1986 = Waddington KD, Herbst LH, Roubik DW, 1986. Relationship between Recruitment Systems of Stingless Bees and Within-Nest Worker Size Variation. Journal of the Kansas Entomological Society 59:95-102; FergusonGow2014 = doi: 10.1098/rspb.2014.1411; Couvillon1949 = data from Jenny Jandt, relating to study in doi: 10.1111/j.1365-2311.2010.01198.x; Cumber1949 = doi: 10.1111/j.1365-2311.1949.tb01420.x.; Goulson2002 = doi: 10.1006/anbe.2002.3041; Holland2020 = doi: 10.1101/2020.05.06.079525; combination = taking a mean value from the three Bombus terrestris studies, weighted by sample size (Cumber, n = 139, Goulson, n = 4494, Holland, n = 1832); Roulston2000 = Roulston TaH, Cane JH, 2000. The Effect of Diet Breadth and Nesting Ecology on Body Size Variation in Bees (Apiformes). Journal of the Kansas Entomological Society 73:129-142. <b>QWdata</b> Worker-worker size difference data. Further details in ms. QWratio = queen mean size / worker mean size. Source = FergusonGow2014 = doi: 10.1098/rspb.2014.1411; Cumber1949 = doi: 10.1111/j.1365-2311.1949.tb01420.x.; MediciBloch = Igor Medici De Mattos & Guy Bloch, unpublished data; combination = taking a mean value from the two Bombus terrestris studies, weighted by sample size (MediciBloch = 460, Cumber, n = 178); Toth2004 = doi: 10.1007/s00040-003-0707-z; DeGrandiHoffman2004 = 10.1603/0013-8746(2004)097[1299:doaiba]2.0.co;2.   <b>quantData</b> Data from five social traits in six species. Further details, and data sources, in ms. value = value of metric specified in metric column metric = Qwsize, queen mean size / worker mean size (i.e. QWratio); PcntMales, the proportion of adult males which are queen-produced rather than worker-produced in queenright colonies (i.e. reproductive skew); wCoV, coefficient of variation in worker size; ColSize, number of workers at peak colony size; Longevity, best estimate of lifespan in colonies surviving foundation. scaledValue = value of the metric when rescaled across values for that metric from all six species, such that lowest value is 0 and highest value is 1. AntScaledValue = value of the metric when rescaled across values for that metric from both ant species, such that lowest value is 0 and highest value is 1. Used to calculate combined index for ants. BeeScaledValue = value of the metric when rescaled across values for that metric from all four bee species, such that lowest value is 0 and highest value is 1. Used to calculate combined index for bees. <b>Cumber female sizes</b> Data entered from Cumber 1949 (doi: 10.1111/j.1365-2311.1949.tb01420.x.;). Added here for convenience, since data in the original publication was presented in printed tables only. Further details in ms.