A new paper recently published in Scientific Advances explores the genetic history of a rare color morph of Colias butterflies. Read the abstract below, or read the full paper here.

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Title: Evidence for a single, ancient origin of a genus-wide alternative life history strategy

Abstract: Understanding the evolutionary origins and factors maintaining alternative life history strategies (ALHS) within species is a major goal of evolutionary research. While alternative alleles causing discrete ALHS are expected to purge or fix over time, one-third of the ~90 species of Colias butterflies are polymorphic for a female-limited ALHS called Alba. Whether Alba arose once, evolved in parallel, or has been exchanged among taxa is currently unknown. Using comparative genome-wide association study (GWAS) and population genomic analyses, we placed the genetic basis of Alba in time-calibrated phylogenomic framework, revealing that Alba evolved once near the base of the genus and has been subsequently maintained via introgression and balancing selection. CRISPR-Cas9 mutagenesis was then used to verify a putative cis-regulatory region of Alba, which we identified using phylogenetic foot printing. We hypothesize that this cis-regulatory region acts as a modular enhancer for the induction of the Alba ALHS, which has likely facilitated its long evolutionary persistence.

Fig. 1. The Alba phenotypes of representative Colias species, the evolutionary relationships among major Colias lineages in light of their Alba phenotypes and regional distribution, and evidence for historical introgression.

(A) Representative Colias species from both sides of the Atlantic, illustrating the female-limited Alba phenotype along with a table of life history differences between the female morphs. (B) A densitree plot of chromosome-level trees (one tree per chromosome), generated using gene trees based on a single exon per single-copy gene (on average 129 genes per chromosome; n = 4011 BUSCO genes). (C) Each specimen’s wing color is indicated with colored boxes on branch tips (blue = Alba, orange = colored, gray = NA). (D) ASTRAL species tree, generated using the longest exon per BUSCO gene, with branches color-coded by their sample’s regional distribution (blue = North America, orange = Holarctic, green = Eurasia and Africa, purple = South America). (E) Time-calibrated SNAPP tree generated using a subset of taxa and 1314 SNPs, with millions of years on the x axis. Blue bars at nodes represent 95% highest posterior distribution of node ages, with nodes having posterior support of <0.9 indicated with a dot and their value. (F) Distribution of minimal D-statistic of all species trios that showed significant levels of introgression (Bonferroni-Holm–corrected P < 0.05). Trios are grouped by Eurasian or North American regions and their respective combinations with the Holarctic taxa.

Read more at Scientific Advances.

This article was posted in News, Research and tagged Sean Schoville.