Simple inheritance of color and pattern polymorphism in the steppe grasshopper Chorthippus dorsatus

Abstract

The green–brown polymorphism of grasshoppers and bush-crickets represents one of the most penetrant polymorphisms in any group of organisms. This poses the question of why the polymorphism is shared across species and how it is maintained. There is mixed evidence for whether and in which species it is environmentally or genetically determined in Orthoptera. We report breeding experiments with the steppe grasshopper Chorthippus dorsatus, a polymorphic species for the presence and distribution of green body parts. Morph ratios did not differ between sexes, and we find no evidence that the rearing environment (crowding and habitat complexity) affected the polymorphism. However, we find strong evidence for genetic determination for the presence/absence of green and its distribution. Results are most parsimoniously explained by three autosomal loci with two alleles each and simple dominance effects: one locus influencing the ability to show green color, with a dominant allele for green; a locus with a recessive allele suppressing green on the dorsal side; and a locus with a recessive allele suppressing green on the lateral side. Our results contribute to the emerging contrast between the simple genetic inheritance of green–brown polymorphisms in the subfamily Gomphocerinae and environmental determination in other subfamilies of grasshoppers. In three out of four species of Gomphocerinae studied so far, the results suggest one or a few loci with a dominance of alleles allowing the occurrence of green. This supports the idea that brown individuals differ from green individuals by homozygosity for loss-of-function alleles preventing green pigment production or deposition.

Evidence for morph-specific substrate choice in a green-brown polymorphic grasshopper

“…Most populations, therefore, consist of a mix of three common color morphs (uniform green, lateral green, and uniform brown; Figure 1 ). There is evidence that color morphs are genetically determined in this species and other species of the Chorthippus clade ( Sansome and La Cour 1935 ; Köhler 2006 ; Winter et al 2021 ), although it is possible that some individuals represent phenocopies, i.e. developmental variants that resemble genetic variants ( West-Eberhard 2003 ).…”

Ontogeny of color development in two green–brown polymorphic grasshopper species

“…These species are paradigmatic for color polymorphic grasshoppers with genetically controlled color morphs (Schielzeth & Dieker, 2020;Winter et al, 2021). We followed individuals through their life stages to document the development of color phenotypes.…”

Plastic background colour matching in the springbok mantis

“…A notable example of intra‐specific colour variation is the widespread green–brown colour morphology of many insects (Bedford, 1978; Castner & Nickle, 1995; Eacock et al., 2017; Edmunds, 1972; Goodman, 2021; Köhler et al., 2017; Musolin & Numata, 2003; Winter et al., 2021; Yumnam et al., 2021), which likely corresponds to the dominance of various shades of green and brown in terrestrial habitats. Green–brown colour differences are typically characterised by the co‐occurrence of green morphs and brown morphs, and can be phenotypically plastic when colour differences are induced by environmental cues (Booth, 1990; Nijhout, 1999).…”

“…In intermediate morphs, coloration can vary between body regions, such that some sections of the body are more or less likely to be one colour or another (e.g. Winter et al., 2021). Such intra‐individual heterogeneity in body coloration could be favoured if it enhances crypsis, such as by disguising the body outline through disruptive coloration (Merilaita & Lind, 2005; Price et al., 2019; Stevens & Merilaita, 2009).…”

“…While much research has focused on the cryptic function of contrasting coloration, the mechanisms that produce heterogeneous colour arrangements within individuals are less well understood. A simple genetic architecture underlying the inheritance of green versus brown body segments has been inferred for the steppe grasshopper (Winter et al., 2021), suggesting that intra‐individual colour variation can be genetically determined. Plasticity could also play an important role in producing the mixed colour patterns characteristic of intermediate colour morphs if certain body regions are more sensitive to environmental cues than others.…”