Wnt genes are major developmental genes highly conserved across all animals. Yet, our understanding of the Wnt gene repertoire and their functions is still largely incomplete. In Lepidoptera, Wnt genes have been implicated in wing pattern development. For example, WntA has been shown as a driver of wing pattern diversification in nymphalid butterflies. In this study, we characterize the Wnt gene repertoire in Zerene cesonia (Family: Pieridae), which diverged from nymphalids ∼51 million years ago, to determine if Wnt genes may have a conserved role in wing development across distant butterfly lineages. We first show that Wnt gene content is highly conserved across butterflies, but that there is strikingly different expression across the eight Wnt genes during wing development of Z. cesonia and nymphalid butterflies. Surprisingly, while four Wnt genes (Wnt1, 6, 7, and 11) are expressed during wing development in Z. cesonia, the renown nymphalid wing patterning gene WntA was undetected. However, despite the differences in Wnt gene expression, Heparin injections yielded a similar disruption in wing color pattern development in both Z. cesonia and nymphalid butterflies. Interestingly, these assays also resulted in the loss of structurally based ultraviolet (UV) wing patterns in Z. cesonia. Collectively, the study shows that pierids maintained the highly conserved nature of Wnt gene content in Lepidoptera, but might deploy these genes very differently from nymphalid butterflies during wing pattern development.

Comparisons of high-quality, reference butterfly, and moth genomes have been instrumental to advancing our understanding of how hybridization, and natural selection drive genomic change during the origin of new species and novel traits. Here, we present a genome assembly of the Southern Dogface butterfly, Zerene cesonia (Pieridae) whose brilliant wing colorations have been implicated in developmental plasticity, hybridization, sexual selection, and speciation. We assembled 266,407,278 bp of the Z. cesonia genome, which accounts for 98.3% of the estimated 271 Mb genome size. Using a hybrid approach involving Chicago libraries with Hi-Rise assembly and a diploid Meraculous assembly, the final haploid genome was assembled. In the final assembly, nearly all autosomes and the Z chromosome were assembled into single scaffolds. The largest 29 scaffolds accounted for 91.4% of the genome assembly, with the remaining ∼8% distributed among another 247 scaffolds and overall N50 of 9.2 Mb. Tissue-specific RNA-seq informed annotations identified 16,442 protein-coding genes, which included 93.2% of the arthropod Benchmarking Universal Single-Copy Orthologs (BUSCO). The Z. cesonia genome assembly had ∼9% identified as repetitive elements, with a transposable element landscape rich in helitrons. Similar to other Lepidoptera genomes, Z. cesonia showed a high conservation of chromosomal synteny. The Z. cesonia assembly provides a high-quality reference for studies of chromosomal arrangements in the Pierid family, as well as for population, phylo, and functional genomic studies of adaptation and speciation.

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