The diversity of colour patterns and its importance in interactions with the environment make colouration in animals an intriguing research focus. Aposematic colouration is positively correlated with body size in certain groups of animals, suggesting that warning colours are more effective or that crypsis is harder to achieve in larger animals. Surprisingly, this relationship has not been recovered in studies investigating insects, which may have been confounded by a focus on aposematic taxa that are also gregarious. Millipede assassin bugs (Hemiptera: Reduviidae: Ectrichodiinae) comprise species with cryptic and aposematic colour patterns across a range of body sizes, are typically solitary as adults, and are thus an excellent model for investigating a possible association between colouration and body size. Here, we use a comprehensive phylogeny for Ectrichodiinae, ancestral state reconstruction of colouration, and phylogenetic comparative methods to test for a colouration-body size association. The ancestor of Ectrichodiinae is reconstructed as cryptically coloured, with multiple subsequent transitions between aposematic and cryptic colouration. Aposematic colouration is positively associated with male body length and supports the hypothesis that selection on Ectrichodiinae body size may influence evolutionary transitions between aposematic and cryptic colouration or alternatively that selection for aposematic colouration influences body size evolution.
Supporting information 1.
Species of Ectrichodiinae that were assigned to colouration categories (i.e., cryptic, aposematic, uniform metallic, or aposematic and metallic) by five independent observers. Those without an (*) were based on at least one voucher specimen. (*) indicates live images additionally available. Species in bold are those in which a majority opinion was not achieved by the independent observers, with ties broken by the senior author’s assignment that was made prior to surveying the observers.
S1.docx
Supporting information 2.
Character matrix for colour characters and male body length in nexus format for ASRs
S2.nex
Supporting information 3.
Parsimony ancestral state reconstruction of colour character 1 on the ML phylogram (tree converted to cladogram for visual). Terminal taxa coded as cryptic (black) or either aposematic, metallic, or aposematic and metallic (blue).
S3.pdf
Supporting information 4.
BayesTraits MultiState ML and MCMC ancestral state reconstruction output for colour character 1 on ML phylogram and ultrametric trees. The grey panel lists internal node IDs and subtending terminal taxa. The blue panel are results from ML ancestral state reconstruction. The yellow panel are results from MCMC ancestral state reconstruction. Abbreviations: Ultra 0, ultrametric tree generated with penalty = 0; Ultra 10, ultrametric tree generated with penalty = 10; Ultra 10000, ultrametric tree generated with penalty = 10000.
S4.xlsx
Supporting information 5.
Parsimony ancestral state reconstruction of colour character 2 on the ML phylogram (tree converted to cladogram for visual). Terminal taxa coded as cryptic or metallic (black) or aposematic or aposematic and metallic (blue).
S5.pdf
Supporting information 6.
BayesTraits MultiState ML ancestral state reconstruction of colour character 2 on the ML phylogram (tree converted to cladogram for visual). Terminal taxa coded as cryptic or uniform metallic (black) or aposematic or aposematic and metallic (blue). Pie charts at select nodes show probability values from the ML reconstruc- tions; branches are coloured to reflect the highest probability of a colour state at that branch.
S6.pdf
Supporting information 7.
BayesTraits MultiState ML and MCMC ancestral state reconstruction output for colour character 2 on ML phylogram and ultrametric trees. The grey panel lists internal node IDs and subtending terminal taxa. The blue panel are results from ML ancestral state reconstruction. The yellow panel are results from MCMC ancestral state reconstruction. Abbreviations: Ultra 0, ultrametric tree generated with penalty = 0; Ultra 10, ultrametric tree generated with penalty = 10; Ultra 10000, ultrametric tree generated with penalty = 10000.
S7.xlsx
Supporting information 8.
Phylogenetic logistic regression parameter estimates for the effects of log-transformed male body length on colouration (colour character 2) in 132 Ectrichodiinae species. Parameters are phylogenetic signal (a), intercept (b0), and the regression coefficient (b1), and P < 0.05 are indicated in bold. Abbreviations: Ultra0, ultrametric tree generated with penalty = 0; Ultra10, ultrametric tree generated with penalty = 10; Ultra10000, ultrametric tree generated with penalty = 10000; Par, parameter; SE, standard error; BS, bootstrap; C, converged; NC, non-converged.
S8.docx