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. A RNA-seq analysis with various appendages of Bicyclus anynana butterfly larvae indicated that the proleg transcriptome resembles the head-horn transcriptome, a novel trait in the lepidoptera, but not a thoracic leg. Under a partial segment abdominal-A ( abd-A ) knockout, both thoracic leg homologs (pleuropodia) and prolegs developed in the same segment, arguing that both traits are not serial homologs. Further, three of the four coxal marker genes, Sp5 , Sp6-9 , and araucan , were absent from prolegs, but two endite marker genes, gooseberry and Distal-less , were expressed in prolegs, suggesting that prolegs may be using a modular endite gene-regulatory network (GRN) for their development. We propose that larval prolegs are novel traits derived from the activation of a pre-existing modular endite GRN in the abdomen using abd-A , the same Hox gene that still represses legs in more lateral positions.

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.…”