Genome assembly and methylome analysis of the white wax scale insect
provides insight into sexual differentiation of metamorphosis in hexapod
Abstract
Scale insects are hemimetabolous, showing “incomplete” metamorphosis
and no true pupal stage. Ericerus pela, commonly known as the white wax
scale insect (hereafter, WWS), is a wax-producing insect found in Asia
and Europe. WWS displays dramatic sexual dimorphism, with notably
different metamorphic fates in males and females. Males develop into
winged adults, while females are neotenic and maintain a nymph-like
appearance, which are flightless and remain stationary. Here we report
the de novo assembly and analysis of the WWS genome. From these data, we
constructed a robust phylogenetic analysis of 24,923 gene families from
16 representative insect genomes, which indicates that holometabola
evolved from hemimetabolous insects in the Late Carboniferous, about 50
million years earlier than previously thought. To study the distinct
development of males and females, we analyzed the methylome landscape in
either sex. Surprisingly, WWS displayed high levels of methylation
(4.42%) when compared to other insects. We observed differential
methylation patterns for genes involved in steroid and sesquiterpenoids
production as well as related fatty acid metabolism pathways. We show
here that both males and females produce distinct profiles of ecdysone
(the principal insect steroid hormone) and juvenile hormone (a
sesquiterpenoid), consistent with their different development fates. Our
results provide a comprehensive genomic and epigenomic resource of scale
insects that provide new insights into the evolution of metamorphosis
and sexual dimorphism in insects.