Cis-regulatory evolution of Wnt family genes contributes to a morphological difference between silkworm species

"Closely related species often exhibit distinct morphologies that can contribute to
species-specific adaptations and reproductive isolation. One example is Lepidopteran
caterpillar appendages, such as the “caudal horn” of Bombycoidea moths, which
have evolved substantial morphological diversity among species in this group. Using
interspecific crosses, we identify the genetic basis of the caudal horn size difference
between Bombyx mori and its closest relative Bombyx mandarina. The three largest
of eight QTL account for one third the mean horn length difference between the
species. The largest of these, on chromosome 4, encompasses a conserved Wnt
family gene cluster, key upstream regulators that are well-known for their roles in
morphological diversification in animals. Using allele-specific expression analysis
and CRISPR/Cas9 knockouts, we show that tissue-specific cis-regulatory changes to
Wnt1 and Wnt6 contribute to the species difference in caudal horn size. This kind of
modularity enables highly pleiotropic genes, including key upstream growth regulators,
to contribute to the evolution of morphological traits without causing widespread
deleterious effects."