A potential role for overdominance in the maintenance of colour variation in the Neotropical tortoise beetle, Chelymorpha alternans

Biotic factors as key determinants for ovarian and oothecal developmental plasticity of a tortoise beetle

Ovarian development in r-selected species is a highly dynamic process widely studied in various insect groups. An array of biotic and abiotic factors may influence it. So, the present investigation was to evaluate the impact of a female's age and mating status on the ovarian development, ootheca formation, body colour polymorphism, and fat content of the tortoise beetle, Aspidomorpha miliaris (Fabricius). Females of a certain age and mating status were dissected to demonstrate changes in their ovarioles, lateral oviduct, accessory gland, elytral colour, fat body content, and body size. It was predicted that age or mating status would not affect the ovarian parameters like length and width of ovarioles, lateral oviducts, accessory glands, body size, fat body content, and elytral colour. However, the ootheca-forming modifications would be initiated by ageing and mating. The current study demonstrated the substantial effect of age and mating status on the growth of the accessory glands and ovarioles. On the other hand, fat body contents declined comparatively in multiply-mated females. Besides this, the beetle exhibits elytral colour polymorphism till sexual maturity. An accessory gland was exclusively detected in multiply-mated females. This discovery opens opportunities for further investigation into the precise function of the gland, which is likely involved in the formation of ootheca.

Heterozygote advantage and pleiotropy contribute to intraspecific color trait variability

The persistence of intrapopulation phenotypic variation typically requires some form of balancing selection because drift and directional selection eventually erode genetic variation. Heterozygote advantage remains a classic explanation for the maintenance of genetic variation in the face of selection. However, examples of heterozygote advantage, other than those associated with disease resistance, are rather uncommon. Across most of its distribution, males of the aposematic moth Arctia plantaginis have two hindwing phenotypes determined by a heritable one locus-two allele polymorphism (genotypes: WW/Wy = white morph, yy = yellow morph). Using genotyped moths, we show that the presence of one or two copies of the yellow allele affects several life-history traits. Reproductive output of both males and females and female mating success are negatively affected by two copies of the yellow allele. Females carrying one yellow allele (i.e., Wy) have higher fertility, hatching success, and offspring survival than either homozygote, thus leading to strong heterozygote advantage. Our results indicate strong female contribution especially at the postcopulatory stage in maintaining the color polymorphism. The interplay between heterozygote advantage, yellow allele pleiotropic effect, and morph-specific predation pressure may exert balancing selection on the color locus, suggesting that color polymorphism may be maintained through complex interactions between natural and sexual selection.