Lepidopteran prolegs are novel traits, not leg homologs

Abstract

Lepidopteran larvae have both thoracic legs and abdominal prolegs, yet it is unclear whether these are serial homologs. We examined the role of three Hox genes in proleg development in Bicyclus anynana butterflies using CRISPR-Cas9 and discovered that under a partial segment abdominal-A (abd-A) knockout, both types of appendages can develop in the same segment, arguing for prolegs being a novel trait, not a leg serial homolog. We also discover that specificity protein (sp) genes do not co-localize with Distal-less (Dll) in prolegs, as they do in legs, and that the proleg gene-regulatory network (GRN) mostly resembles the head-horn GRN, another novel trait in the lepidoptera. We propose that larval prolegs evolved from the co- option of a partial limb GRN into novel embryonic coordinates in the abdomen.

Larvae of grassland caterpillar endemic to Qinghai–Tibet Plateau (Lepidoptera: Lymantriinae: Gynaephora): identification, distribution, and ultramorphology

“…5, S3). The strong thoracic legs of herbivorous insects can support the entire body during feeding, and they also function as the center of movement when the larvae are resting on the plant's surface 29 . Moreover, the unsegmented prolegs of the last instar larvae feature 17-25 crochets, while the rst instar larvae only have four crochets (Figs.…”

Cis-regulatory modes of Ultrabithorax inactivation in butterfly forewings

“…The ectopic activation of Ubx into the pupal forewing results in the gain of hindwing features, suggesting Ubx is sufficient to drive T3-like identity when expressed in T2 ( Lewis et al, 1999 ; Tong et al, 2014 ). Besides its roles in adult wing differentiation, Ubx is also known to repress thoracic leg identity in transient embryonic appendages of the first abdominal segment, called pleuropods ( Zheng et al, 1999 ; Masumoto et al, 2009 ; Tong et al, 2017 ; Tendolkar et al, 2021 ; Matsuoka et al, 2022 ). The general organization of Hox gene clusters has been well described in Lepidoptera, but their regulation has been seldom studied.…”

Cis-regulatory modes ofUltrabithoraxinactivation in butterfly forewings

“…The ectopic activation of Ubx into the pupal forewing results in the gain of hindwing features, suggesting Ubx is sufficient to drive T3-like identity when expressed in T2 (Lewis et al 1999; Tong et al 2014). Besides its roles in adult wing differentiation, Ubx is also known to repress thoracic leg identity in transient embryonic appendages of the first abdominal segment, called pleuropods (Zheng et al 1999; Masumoto et al 2009; Tong et al 2017; Tendolkar et al 2021; Matsuoka et al 2022).…”