No link between nymph and adult coloration in shield bugs: weak selection by predators

Abstract

Many organisms use different antipredator strategies throughout their life, but little is known about the reasons or implications of such changes. For years, it has been suggested that selection by predators should favour uniformity in local warning signals. If this is the case, we would expect high resemblance in colour across life stages in aposematic animals where young and adults share similar morphology and habitat. In this study, we used shield bugs (Hemiptera: Pentatomoidea) to test whether colour and colour diversity evolve similarly at different life stages. Since many of these bugs are considered to be aposematic, we also combined multi-species analyses with predation experiments on the cotton harlequin bug to test whether there is evidence of selection for uniformity in colour across life stages. Overall, we show that the diversity of colours used by both life stages is comparable, but adults are more cryptic than nymphs. We also demonstrate that nymphs and adults of the same species do not tend to look alike. Experiments on our model system suggest that predators can generalise among life stages that look different, and exhibit strong neophobia. Altogether, our results show no evidence of selection favouring colour similarity between adults and nymphs in this speciose clade.

Ontogenetic change in effectiveness of chemical defence against different predators in Oxycarenus true bugs

“…In insects, defences (including chemical defences and their advertising by warning signals) may change dramatically during metamorphosis (Aldrich, 1988; Medina, Vega‐Trejo, Wallenius, Esquerré, et al, 2020; Medina, Vega‐Trejo, Wallenius, Symonds, et al, 2020). This is true both for chemical defences and for their advertising by warning signals.…”

“…For example, the efficacy of chemical defences often decreases in adults compared to larvae in Coreidae (Aldrich, 1988), whereas in some Pentatomidae, the defence efficacy increases from larvae to adults (Johansen et al, 2011; Schlee, 1986). Moreover, the presence of wings in adults is often associated with the development of new colour patterns, typically more cryptic than in larvae (such as in Pentatomidae, Medina, Vega‐Trejo, Wallenius, Esquerré, et al, 2020; Wachman et al, 2008). Causes of these ontogenetic changes may include, among others, life‐stage‐specific predation (Johansen et al, 2011, Medina, Vega‐Trejo, Wallenius, Esquerré, et al, 2020), a higher degree of integument sclerotization in adults or the trade‐off between the defensive and pheromonal function of adult scent glands (Aldrich, 1988).…”