Mechanisms of Color Production in a Highly Variable Shield-Back Stinkbug, Tectocoris diopthalmus (Heteroptera: Scutelleridae), and Why It Matters

Abstract

Theory suggests that aposematism, specifically the learned avoidance of unprofitable prey via memorable color patterns, should result in selection for pattern uniformity. However, many examples to the contrary are seen in nature. Conversely, honest sexual signals are likely to exhibit greater variation because they reflect underlying variation in mate quality. Here we aim to characterize and quantify the mechanistic causes of color in Tectocoris diopthalmus to shed light on the costs of color production, and thus the potential information content of its color signals. We use Tectocoris diopthalmus because it is a weakly-defended stinkbug, and presents elements that have classically been studied in the context of aposematism (red coloring), and sexual selection (sexual dichromatism and iridescent coloring). Pigment analysis reveals that variation in orange coloration is due to the amount of erythropterin pigment, stored in intracellular granules. This pigment is common in Heteroptera, and as an endogenously produced excretory byproduct is unlikely to reflect mate quality or variation in unprofitability of the bug. Electron microscopy reveals the iridescent patches are caused by an epicuticular multilayer reflector, and the hue and patch size are directly related to the layer widths and extent of coverage of this layering. Furthermore, we identified melanin as an essential component of the multilayer reflector system; therefore, the quality of the iridescent patches may be affected by aspects of rearing environment and immunocompetence. We posit that T. diopthalmus has co-opted the melanic patches of a ‘typical’ red and black aposematic signal, transforming it into a complex and variable iridescent signal that may enhance its capacity to display individual quality.

Condition‐dependence, pleiotropy and the handicap principle of sexual selection in melanin‐based colouration

“…From a proximate view, the cost of producing an immaculate cheek could be explained by feather damage (Ferns & Hinsley, 2004). Alternatively, correctly assembling melanin pigments, coordinating the expression of a given gene in multiple cells located in the same or in different body regions, as well as avoiding stochastic variation (or noise) in gene expression, may also be costly (Eldar & Elowitz, 2010;Less et al, 2011;Wang & Zhang, 2011;Fabricant et al, 2013).…”

The interplay between multiple predators and prey colour divergence

“…For this reason, the maintenance of warning signal polymorphisms and the geographic divergence in warning signals as observed in butterflies, true bugs, moths, and frogs are intriguing topics of current research (e.g. Chamberlain et al ., ; Fabricant et al ., ; Willink et al ., ; Nokelainen et al ., ). In this study, we investigate the roles of multiple predators and spatially variable predation on the geographic divergence of protective coloration.…”

Does it Pay to Care?: Exploring the Costs and Benefits of Parental Care in the Hibiscus Harlequin BugTectocoris diophthalmus(Heteroptera: Scutelleridae)

“…) and aposematic (Fabricant et al. ), which renders them unpalatable to avian predators (Fabricant & Smith ), which may reduce the potential predation risk associated with guarding. Furthermore, it is unusual to see unguarded egg clutches in the field at any time of year (R. Giffney, pers.…”