Evidence for a single, ancient origin of a genus-wide alternative life history strategy
Kalle Tunström, Alyssa Woronik, Joseph J. Hanly, Pasi Rastas, Anton Chichvarkhin, Andrew Warren, Akito Y. Kawahara, Sean D. Schoville, Vincent Ficarrotta, Adam H. Porter, Ward B. Watt, Arnaud Martin, Christopher W. Wheat
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.