The roles of hybridization and habitat fragmentation in the evolution of Brazil’s enigmatic longwing butterflies, Heliconius nattereri and H. hermathena

Heliconius nattereri is found in a section of the Atlantic Forest spanning portions of the states of Espírito Santo and Bahia. It is the only Heliconius species that is endangered and has pronounced sexually dimorphic patterns, with females displaying a "tiger stripe" pattern and males displaying a non-mimetic yellow and black wing pattern. Heliconius hermathena is associated with white sand habitats throughout the Brazilian Amazon. It has a patchy distribution and produces a network of described subspecies, including H. hermathena curva, which was just described in 2019. The species has a putatively non-mimetic color pattern, with some subspecies displaying subtle variations. The authors of this study aimed to assess the historical population fragmentation and genetic health of these species. They assembled genomes and re-sequenced whole genomes of eight H. nattereri and 71 H. hermathena individuals. The results showed that both species harbor little genetic diversity, skewed site frequency spectra, and high deleterious mutation loads consistent with recent bottlenecks. The study found that Heliconius hermathena consists of discrete, strongly isolated populations that likely arose from a single population that dispersed after the last glacial maximum. However, the authors found no genome-wide evidence that H. hermathena is a hybrid species. Instead, they found that H. hermathena mimicry evolved through introgression from co-mimetic Heliconius erato, of a genomic region upstream of the cortex gene. The study's results contribute to a growing body of evidence that introgression of color patterning alleles between co-mimetic species is a general feature of Heliconius evolution. The authors suggest that historical population fragmentation and historical habitat fragmentation have significantly reduced the genetic health of these rare species. The study's findings have implications for conservation efforts. The authors recommend that conservation strategies focus on preserving the remaining habitats of these species and protecting them from further habitat loss and fragmentation. They also suggest that genetic analysis can inform conservation efforts by identifying areas of high genetic diversity and providing insights into the evolutionary history of the species. The study's results also highlight the importance of understanding the evolutionary history of species and the impact of human activities on their genetic health. The authors emphasize the need for continued research into the biology and genomics of Heliconius species to inform conservation efforts and inform conservation efforts. The study's findings have implications for our understanding of the evolutionary history of Heliconius species and the impact of human activities on their genetic health. The authors suggest that conservation strategies should focus on preserving the remaining habitats of these species and protecting them from further habitat loss and fragmentation.