Phylogenetic comparative analysis supports aposematic colouration–body size association in millipede assassins (Hemiptera: Reduviidae: Ectrichodiinae)

Abstract

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.

From cryptic to colorful: Evolutionary decoupling of larval and adult color in butterflies

“…), and in moths and millipede assassins (Hemiptera: Reduvidae) larger species are more likely to present warning coloration (Kang et al. ; Forthman and Weirauch ), suggesting this could be a general tendency in aposematic organisms. In contrast to caterpillars, we found no evidence of a link between high color contrast and size in adult butterflies, despite the correlation between caterpillar and adult size.…”

Body size in Batesian mimicry

“…Looking at honest signalling, for many taxa aposematism is more prevalent in larger species (Hagman and Forsman 2003;Forthman and Weirauch 2018), although the trend is not universal (Cheney et al 2014). Even within species, we see examples of aposematism appearing as individuals increase in size through developmental stages (Gaitonde et al 2018).…”

Herbivore‐induced defenses are not under phylogenetic constraints in the genusQuercus(oak): Phylogenetic patterns of growth, defense, and storage

“…Phylogenetic comparative methods (PCM) are statistical tools that are commonly used to address the issue of non‐independence among data points (Ackerly, 2009; Felsenstein, 1985; Forthman & Weirauch, 2018; Pennell et al., 2016). Access to phylogenetic information is a major advance in developing PCM that places an emphasis on detecting phylogenetic signal (Mounce et al., 2018; Pennell et al., 2016).…”