Phylogeographic and demographic history of convergence events in Neotropical adaptive radiation

Understanding the mechanisms and forces that promote and maintain adaptive phenotypic variation in nature is a fundamental question in evolutionary biology. In recent years a major breakthrough has been made in the discovery of genes that control the formation of adaptive morphological diversity [1-6], but little is known about the genetic architecture and geographic and phylogenetic distribution of adaptive alleles they segregate into wild populations [7]. Moreover, some of these populations may evolve similar traits when faced with the same selection pressure, known as phenotypic convergence [8,9].
Convergent evolution can arise at the genetic level as a product of any of the following processes: (i) independent evolution of mutations that produce the same trait in different populations or species, (ii) ancestral polymorphism differentially distributed among descendant lineages, and (iii) by introgression. There are more than 100 examples that illustrate how the three processes contribute to convergent evolution [8,10], however, few studies have evaluated the frequency (number of times) with which such adaptations arise at the population level and the demography and phylogeography of these, particularly in animals. Moreover, few studies have tested whether convergent evolution is the result of only one of these processes or, on the contrary, may result from the combination of several of them [11].

The butterflies of the genus Heliconius are a classic example of convergent evolution, where species living in sympatry share the same coloration pattern to alert predators about their toxicity [12,13]. In these butterflies, convergence between distantly related species such as H. melpomene and H. erato results from the emergence of independent mutations in the same genomic region, but for closely related species such as H. melpomene and H. timareta, mimetic convergence is the result of adaptive introgression [12-14]. There are at least 7 geographical cases where forms of H. timareta mimic H. melpomene and H. erato (Figure 1) and, although this mimesis is known to be the product of introgression of coloration genes from H. melpomene to H. timareta, it is not yet known whether this mimic convergence is due to H. melpomene and H. erato (Figure 1): (i) multiple local introgression events of a single causal allele, (ii) multiple introgression events of different causal alleles, or (iii) a single introgression event with subsequent dispersion of the introgressed allele.

Within H. melpomene, the 'postman' phenotype (red band in the anterior wing and yellow bar in the posterior wing) is found in at least 7 geographic breeds with disjunct distribution throughout Central and South America (Figure 1), while the alternate 'dennis-ray' phenotype (orange patch in the anterior wing and rays in the posterior wing) is distributed continuously in the Amazon region with at least 9 breeds converging to this phenotype (Figure 1).
Geographical distribution of the convergent radiations of H. erato, H. melpomene and H. timareta. The distribution of the main phenotypes is indicated: red band (fuchsia), dennis-ray (yellow), postman (aquamarine), yellow and red band (red), yellow band (yellow), rays (skin). The distribution of the subspecies (or breeds) of each mimetic ring, detailed in the lower part of the figure, is also indicated. This figure was modified from [14].
Phylogeographic studies of the optix gene (responsible for controlling reddish wing colorations [15]) show that the 'dennis-ray' phenotype is derived from the 'postman' phenotype [16]. However, to date the evolutionary history of other high-effect coloration loci such as the Yb locus (responsible for the yellow bar in the posterior wing [17]) has not been studied and therefore it is not known whether the current geographic distribution of the 'postman' races represents 7 independent convergence cases or, on the contrary, it is a single phenotype whose continuous distribution was disintegrated thanks to the appearance of the successful mimetic phenotype 'dennis- ray'.

Taking advantage of the knowledge on the genetics of coloration in H. melpomene [12-14], the availability of an exceptional sampling of the radiation of the H. melpomene/H. cydno/H. timareta clade, and the availability of a reference genome for this clade [18], in this project: (i) it will be studied whether the phenotypic convergence between all the mimetic pairs of H. melpomene and H. timareta is due to several independent introgression events of the same alleles in three coloration pattern loci or, conversely, it is a single introgression event involving the same allele in each of those loci; and (ii) it will be established whether the convergence in coloration patterns within the H. timareta breeds is due to several independent introgression events of the same alleles in three coloration pattern loci or, conversely, it is a single introgression event involving the same allele in each of those loci; and (ii) it will be established whether the convergence in coloration patterns within the H. melpomene and H. timareta breeds is due to several independent introgression events of the same alleles in three coloration pattern loci or, conversely, it is a single introgression event involving the same allele in each of those loci. melpomene is a product of the same allelic variants for the two phenotypes 'postman' and 'dennis-ray'.

Expected products of new scientific or technological knowledge
At least 2 publications in international journals are expected to be generated.






It is expected to attend and present the results of the present project in at least 1 international and 1 national scientific congress.






Presentations made at national scientific congresses are expected to be published as abstracts in the proceedings of the events.






4. It is expected to generate a scientific-divulgative note in the bulletin of the Colombian network of biology.
COLEVOL or any other science informative medium.




Expected training products
1.Linking of one (1) postdoc. This person will be selected by resume, according to their ability to contribute to the development of the project (i.e. knowledge and/or skills in computer science). This is a great opportunity for talented people to gain more experience in their careers and at the same time contribute to the analysis of results from state-of-the-art techniques and methodologies in genomics, which will lead to high-impact publications.




2.Linking of one (1) doctoral student. This person will be linked to the Doctorate in Biomedical and Biological Sciences, hoping that it can be financed with a Colciencias scholarship or through the assignment of a graduate assistance.




Direction of one (1) master's thesis, ideally of the future Master's Degree in Natural Sciences of the Universidad del Rosario, but in its defect, of a master's program of another University.




4. Linking of one (1) young researcher who wants to acquire or refine knowledge in the area of genomics and evolutionary biology.