Abstract
Tradeoffs affect resource allocation during development and result in fitness consequences that drive the evolution of life history strategies. Yet despite their importance, we know little about the mechanisms underlying life history tradeoffs. Many species of Colias butterflies exhibit an alternative life history strategy (ALHS) where females divert resources from wing pigment synthesis to reproductive and somatic development. Due to this reallocation, a wing color polymorphism is associated with the ALHS: either yellow/orange or white. Here we map the locus associated with this ALHS in Colias crocea to a transposable element insertion located downstream of the Colias homolog of BarH-1, a homeobox transcription factor. Using CRISPR/Cas9 gene editing, antibody staining, and electron microscopy we find white-specific expression of BarH-1 suppresses the formation of pigment granules in wing scales and gives rise to white wing color. Lipid and transcriptome analyses reveal physiological differences associated with the ALHS. Together, these findings characterize a mechanism for a female-limited ALHS.
Highlights
Tradeoffs affect resource allocation during development and result in fitness consequences that drive the evolution of life history strategies
Using a de novo reference genome for C. crocea that we generated via Illumina and PacBio sequencing, and three rounds of bulk segregant analyses (BSA) using whole-genome sequencing from a female and two male informative crosses for Alba, we mapped the Alba locus to an ~3.7 Mbp region
We determined that the transposable element (TE) insertion was unique to the Alba morph in C. crocea by quantifying differences in read depth between morphs within and flanking the insertion (Supplementary Fig. 1) and assembling orange and Alba haplotypes for this region (Supplementary Fig. 2)
Summary
Tradeoffs affect resource allocation during development and result in fitness consequences that drive the evolution of life history strategies. Many species of Colias butterflies exhibit an alternative life history strategy (ALHS) where females divert resources from wing pigment synthesis to reproductive and somatic development. Due to this reallocation, a wing color polymorphism is associated with the ALHS: either yellow/orange or white. The wing color polymorphism arises because during pupal development the white morph, known as Alba, reallocates larval derived resources from the synthesis of energetically expensive colored pigments to reproductive and somatic development[9] This tradeoff has been well characterized in Colias crocea, the Old World species that we focus upon in this work, via radio-labelled metabolite tracking in pupae[10], as well as in the New World species Colias eurytheme (Pieridae, Lepidoptera) (Boisduval, 1852) using ultraviolet spectrophotometry[9]. This fact, along with ancestral state reconstruction[7], has led to the assumption that the
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