Genetic Color Polymorphism of the Whitelined Sphinx Moth larva (Lepidoptera: Sphingidae)

Abstract

For a trait to be considered polymorphic, it must fulfill both genetic and ecological criteria. Genetically, a polymorphic trait must have multiple heritable variants, potentially from the same female, in high-enough frequency as to not be due to mutation. Ecologically, in a single wild population, these variants must co-occur, and be capable of interbreeding. Polymorphism is frequently considered in the context of either geographical cause or genetic consequence. However, the incorporation of both in a single study can facilitate our understanding of the role that polymorphism may play in speciation. Here, we ask if the two color morphs (green and yellow) exhibited by larvae of the whitelined sphinx moth, Hyles lineata (Fabricius), co-occur in wild populations, in what frequencies, and whether they are genetically determined. Upon confirmation from field surveys that the two color morphs do co-occur in wild populations, we determined heritability. We conducted a series of outcrosses, intercrosses and backcrosses using individuals that had exhibited yellow or green as laboratory-reared larvae. Ratios of yellow:green color distribution from each familial cross were then compared with ratios one would expect from a single gene, yellow-recessive model using a two-sided binomial exact test. The offspring from several crosses indicate that the yellow and green coloration is a genetic polymorphism, primarily controlled by one gene in a single-locus, two-allele Mendelian-inheritance pattern. Results further suggest that while one gene primarily controls color, there may be several modifier genes interacting with it.

A high-quality, long-read genome assembly of the whitelined sphinx moth (Lepidoptera: Sphingidae: Hyles lineata) shows highly conserved melanin synthesis pathway genes

“…Pigmentation in the cuticle and wings of insects is largely determined by the highly conserved melanogenesis metabolic pathway, including “core” melanin synthesis genes that encode the necessary enzymes ( Sugumaran and Barek 2016 ). However, while cuticular color and pattern are, in part, inherited through allelic variation, the degree of melanin pigmentation is determined by environmental variables including temperature, photoperiod, and crowding ( Francois and Davidowtiz 2020 ; Britton and Davidowitz in review ). Purifying selection drives gene sequence conservation and phenotype variation is driven largely by gene regulation, rather than allelic differences ( Kuwalekar et al .…”