The impact of life stage and pigment source on the evolution of novel warning signal traits

Abstract

Our understanding of how novel color traits evolve in aposematic taxa is based largely on studies of reproductive stages and organisms with endogenously produced pigmentation. In these systems, genetic drift is often required for novel alleles to overcome strong purifying selection stemming from frequency-dependent predation and positive assortative mating. Here we show that the importance of these mechanisms can differ if selective processes are considered in larval stage instead. By integrating population genomic data, predation experiments and phenotypic measurements of larvae and their host plants, we show that novel white alleles in Neodiprion lecontei (pine sawfly) larvae spread via selection rather than drift. The cost of being rare was not offset by an enhanced aposematic display or immune function. Instead, bottom-up selection via host plants may drive divergence among populations as white larvae were disproportionately abundant on a pine species with a reduced carotenoid content relative to other pine hosts.

Support for the adaptive decoupling hypothesis from whole‐transcriptome profiles of a hypermetamorphic and sexually dimorphic insect, Neodiprion lecontei

“…The cryptic morph is lightly pigmented, ingests only the exterior of pine needles and retreats to the base of the needle when predators are near. By contrast, the aposematic morph is heavily pigmented and ingests the entire needle to sequester the toxic pine resins for use in antipredator defensive displays (Lindstedt et al, 2020). A more striking transition occurs when the aposematic morph moults into a “dispersing” final instar (hereafter, “major transition”).…”

Body size as a magic trait in two plant-feeding insect species

“…Similarly, cryptic Cephalelus uncinatus leafhoppers avoid avian predation by resting on host plants with stems that match their body size: larger individuals are always found on plants with thicker stems, while smaller individuals are found on plants with thinner stems (Augustyn et al 2017). By contrast, in aposematic species such as N. lecontei and N. pinetum (Lindstedt et al 2022), having a larger visual signal (either via larger bodies or larger groups) may enhance predator avoidance learning (Mappes and Alatalo 1997; Gamberale and Tullberg 1998; Forsman and Merilaita 1999; Riipi et al 2001). However, group or individual size may be limited by physical properties of the host.…”

Faster‐haplodiploid evolution under divergence‐with‐gene‐flow: Simulations and empirical data from pine‐feeding hymenopterans

“…lecontei tends to avoid this host. Differences between their hosts probably generate divergent selection on many different larval and adult traits (Bendall et al, 2017; Codella & Raffa, 2002; Coppel & Benjamin, 1965; Lindstedt et al, 2022). For example, differences in needle chemistry and thickness between the preferred hosts of N .…”