The Evolution of Color Patterns In Heliconius Butterflies

Abstract

The evolution of color patterns in Heliconius butterflies provides a compelling example of how biodiversity and novel traits arise through natural selection. These butterflies exhibit a rich diversity of geographic color patterns, which are shaped by various evolutionary pressures. While we understand how predation and the presence of effective warning signals drive the convergence of color patterns among unpalatable species, leading to region-specific warning signals that enhance survival, how these selective pressures allow pattern diversity to flourish is less well understood. The development of these vivid color patterns in Heliconius butterflies is controlled by a handful of color pattern genes like optix. Non-coding variation in proximity of these genes is crucial for morphological divergence because changes in non-coding regions can significantly impact gene expression. Genes like optix are also involved in regulating many other genes, bringing together regulatory networks in order to bring about pigment production and pattern formation. However, the nature of these gene regulatory networks and how they are controlled by transcription factor genes like optix is not well understood. This dissertation addresses these questions through a combination of ecological and genetic approaches. Field experiments reveal how local predation pressures and frequency-dependent selection maintain balanced polymorphisms in Heliconius doris and permit pattern diversity in some regions but not others. Genomic techniques like ATAC-seq and CRISPR/Cas9 genome engineering identify conserved and pleiotropic regulatory elements associated with the optix gene, highlighting their role in adaptive morphological traits. Lastly I investigate adaptive hubs as genomic features underpinning the optix gene regulatory network which bring key, yet distant, regulatory elements into physical contact to facilitate the coordinated expression of genes involved in adaptive traits. By integrating ecological data with advanced genomic techniques, this comprehensive study enhances our understanding of the selective pressures and genetic mechanisms driving the evolution of color patterns in Heliconius butterflies. Its findings provide broader insights into the ecological, genetic and epigenetic factors contributing to biodiversity and adaptive evolution.