Understanding the mechanisms and processes driving biological diversification and adaptation is still a major question in evolutionary biology that requires interdisciplinary research that addresses the role of biotic (i.e., genetic background, ecological interactions) and abiotic factors (i.e., climate). In this dissertation I studied biogeographic, chromosomic, and chemical aspects that contribute to the diversification of the Neotropical butterflies of the genus Heliconius, especially species in the sara/sapho clade. Although Heliconius is one of the best studied groups in the context of evolutionary biology and ecology, the clade sara/sapho has been largely unstudied despite having unique features. For example, some of its species show high diversification rates and a higher number of chromosomes compared to other Heliconius, and also, species in the clade seem unable to synthesise cyanogens leading to reliance on toxins sequestered from larval host plants. In Chapter I, I used 54,392 georeferenced records for 46 species and 1,012 georeferenced records for 38 interspecific hybrids of Heliconius to investigate the role of the environment in shaping their distribution and richness, as well as their geographic patterns of phylogenetic diversity and phylogenetic endemism. I also evaluated whether niche similarity promotes hybridization. I found that Heliconius displays five general distribution patterns mostly explained by precipitation and isothermality, and to a lesser extent, by altitude. Interestingly, altitude plays a major role as a predictor of species richness and phylogenetic diversity, while precipitation explains patterns of phylogenetic endemism. I did not find evidence supporting the role of the environment in facilitating hybridization because hybridizing species do not necessarily share the same climatic niche despite some of them having largely overlapping geographic distributions. Overall, I confirmed that, as in other organisms, high annual temperature, a constant supply of water, and spatial- topographic complexity are the main predictors of diversity in Heliconius. In Chapter II, I generated whole genome resequencing data for 114 individuals from seven species in the sara/sapho clade to investigate: (i) genome-wide phylogenetic relationships, (ii) the degree of genomic differentiation between species and subspecies, and (iii) the impact of chromosomal rearrangements in the evolution of the clade. The inclusion of multiple species and subspecies of this clade allowed me to redefine some of the relations previously reported, and to identify the effect of geography in shaping their diversity. Interestingly, I also found evidence for sex- autosome fusions involving autosomes 4, 9, and 14. All of these fusions seem to be associated with speciation events in this clade, with the sex-autosome 4 fusion being the oldest one. Although I do not yet understand the role or evolutionary consequences of these fusions, my study shows that chromosomal rearrangements can evolve rapidly within a clade and generate chromosomal diversity. In Chapter III, I investigated how cyanogens (chemical defences of adult Heliconius) vary both in composition and concentration across nine mimicry rings and six Neotropical ecoregions. I found that variation in the cyanogenic profile of Heliconius is not explained by the mimicry ring that a species belongs to or its locality. Instead, cyanogenic variation is the result of phylogenetic closeness and, likely, ecological factors such as host plant specialization, diversity and abundance of local hostplants locally available, availability of precursors for biosynthesis of cyanogenic compounds in pollen-source plants, as well as the local predator community. My results agree with recent modelling and meta-analyses that showed that increased toxicity of preys does not translate into increased predator learning or generation of mimetic diversity.
