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Temporal ecological niche partitioning is an underappreciated driver of speciation. While insects have long been models for circadian biology, the genes and circuits that allow adaptive changes in diel-niches remain poorly understood. We compared gene expression in closely related day- and night-active non-model wild silk moths, with otherwise similar ecologies. Using an ortholog-based pipeline to compare RNA-Seq patterns across two moth species, we find over 25 pairs of gene orthologs showing differential expression. Notably, the genedisco,involved in circadian control, optic lobe and clock neuron development inDrosophila, shows robust adult circadian mRNA cycling in moth heads.Discois highly conserved in moths and has additional zinc-finger domains with specific nocturnal and diurnal mutations. We proposediscoas a candidate gene for the diversification of temporal diel-niche in moths. 

Abstract Ambulycini are a cosmopolitan tribe of the moth family Sphingidae, comprised of 10 genera, 3 of which are found in tropical Asia, 4 in the Neotropics, 1 in Africa, 1 in the Middle East, and 1 restricted to the islands of New Caledonia. Recent phylogenetic analyses of the tribe have yielded conflicting results, and some have suggested a close relationship of the monobasic New Caledonian genus CompsulyxHolloway, 1979 to the Neotropical ones, despite being found on opposite sides of the Pacific Ocean. Here, we investigate relationships within the tribe using full mitochondrial genomes, mainly derived from dry-pinned museum collections material. Mitogenomic data were obtained for 19 species representing nine of the 10 Ambulycini genera. Phylogenetic trees are in agreement with a tropical Asian origin for the tribe. Furthermore, results indicate that the Neotropical genus Adhemarius Oiticica Filho, 1939 is paraphyletic and support the notion that OrectaRothschild & Jordan 1903 and TrogolegnumRothschild & Jordan, 1903 may need to be synonymized. Finally, in our analysis the Neotropical genera do not collectively form a monophyletic group, due to a clade comprising the New Caledonian genus Compsulyx and the African genus BatocnemaRothschild & Jordan, 1903 being placed as sister to the Neotropical genus ProtambulyxRothschild & Jordan, 1903. This finding implies a complex biogeographic history and suggests the evolution of the tribe involved at least two long-distance dispersal events.