Repeatability of the speciation process in butterflies: natural replicates in a suture zone system – SPECREP

For eight species in the suture zone, we will:
(1) quantify divergence for ecologically important traits (wing colour pattern, sexual pheromones, microhabitat, hostplants) and measure the contribution of these traits to reproductive isolation, using experimental approaches;
(2) quantify genome-wide patterns of divergence and the genetic architecture of reproductive isolation, based on genomic scans;
(3) identify the genetic bases of trait variation, using genetic mapping (crosses and association mapping) and genome-wide gene annotation on two de novo assembled reference genomes;
(4) analyse the relationships between divergence and reproductive isolation in a comparative framework and compare our findings with those obtained in other Lepidoptera, particularly mimetic butterflies

1- We completed field collection of specimens, except those for karyotypic analyses.
2- Our mate choice experiments (completed) for 4 species show a lot of heterogeneity, with almost absolute assortative mating in 2 species, strong assortative mating in 1 species and no assortative mating in 1 species.
3- Chemical analyses of sexual pheromones (in progress) reveal a wide range of differentiation between subspecies.
4- Quantitative analyses of colour patterns (in progress) reveal a range of phenotypical differentiation in 4 species, sme of which are nearly undistinguishable by butterflies and their predators.
5- Analyses of population structure using RADseq (in progress) show a weak but significant differentiation between subspecies of 1 species.
6- We have started assembling a reference genome for one species (in progress), and we are comparing various strategies, some of which are suited for highly heterozygous genomes.
7- We have started gene differential expression analyses in targeted tissues (in progress), in association with phenotypic differentiation.
8- Karyotype analyses (in progress) in 4 species reveal a high variability i chromosome numbers. A large amount of rearrangements impairs meiosis, and represent a postzygotic barrier to gene flow.
9- Phylogenetic patterns of speciation (in progress) in 2 Ithomiini clades shows the importance of abiotic factors in relation with the geological history of the region, but on going analyses also suggest a role for ecological characters, such as wing colour pattern.

We will carry on:
- Acquiring data (pheromons, wing colour patterns, Karyotypes, RADseq, RNAseq for more tissues, 2nd reference genome)
- Analyzing those data, and previous data (1st reference genome, 1st RADseq libraries)

Articles in peer-reviewed journals
1. Chazot N et al. 2016. Into the Andes: multiple independent colonizations drive montane diversity in the Neotropical clearwing butterflies Godyridina. Molecular Ecology. 25(22):5765–5784
2. de-Silva DL et al. 2017. Northern Andean origin and diversification of the largest ithomiine butterfly genus. Scientific Reports. 7:45966

Oral communications in conferences
1. McClure, M., Monllor, M., Venne, K., Furtos, A., Elias, M. (2017). Does divergent selection predict sexual selection in the adaptive radiation of the tropical butterfly genus Melinaea? Poster presentation at the GRC Speciation meeting, Italy, February 2017
2. McClure, M., Houssin, C., Mahrouche, L., Furtos, A., Elias, M. (2017). Does divergent selection predict sexual selection in the adaptive radiation of the tropical butterfly genus Melinaea? Oral presentation at the International Society of Chemical Ecology meeting, Japan, August 2017
3. Elias M.(2017) The far-reaching implications of mimicry in butterflies. 20th congress of Lepidpterology, Croatia, April 2017

How predictable is evolution? Do species respond in the same way to similar environmental pressures? The question of repeatability is crucial in evolutionary biology because it can inform on the mechanisms generating and shaping diversity and can shed light on how organisms might react in the face of future changes. We propose to investigate the repeatability of the genomic and phenotypic bases of speciation, the ultimate process underlying biodiversity. To this end, we take advantage of the exceptional potential for natural replication offered by a ‘suture zone’, a narrow region where multiple racial hybrid zones of butterfly species coincide at a strong environmental gradient between the Amazon and the Andes. For eight of these species, we will:
(1) quantify divergence for ecologically important traits (wing colour pattern, sexual pheromones, microhabitat, hostplants) and measure the contribution of these traits to reproductive isolation, using experimental approaches;
(2) quantify genome-wide patterns of divergence and the genetic architecture of reproductive isolation, based on genomic scans;
(3) identify the genetic bases of trait variation, using genetic mapping (crosses and association mapping) and genome-wide gene annotation on two de novo assembled reference genomes;
(4) analyse the relationships between divergence and reproductive isolation in a comparative framework and compare our findings with those obtained in other Lepidoptera, particularly mimetic butterflies
Our unique combination of cutting-edge methods in a comparative framework will provide important advances in our understanding of speciation by revealing general patterns and singularities in the speciation process. The project will also provide a large-scale test of existing models of speciation and will contribute to identifying the genomic regions underlying key phenotypic traits.