We firstly assembled and annotated the genome of the damselfy Ischnura elegans and for the first time identified X-linked loci within odonates. Our results revealed orthologous relationships between X-linked genes of I. elegans, which is an extant representative of an ancestral insect lineage, and (X-) chromosome regions of more derived insect lineages (manuscript under review). Secondly, we performed a genome-wide genotype (RADseq) analysis using individuals from both allopatric and sympatric populations in Spain to estimate degree of hybridization and overall introgression patterns. This showed that some I. graellsii individuals originate from an admixed population presumably subjected to introgression from I. elegans into I. graellsii (in contrast to the previously recorded introgression from I. graellsii into I. elegans). Using resequencing we are able to assess – for the first time – introgression into I. graellsii across the whole genome (in preparation). Using mating experiments we show, however, that reproductive barriers are stronger in I. graellsii than in I. elegans. Overall, premating isolation was higher than other barriers (in preparation).
Multiple sympatric zones in Spain have been sampled for subsequent genomic analyses using RADseq. These results suggest the presence of hybrids from different crosses (F1, F2 and backcrosses) in all sympatry regions. Introgression levels were detected to be low in Central Spain and relatively high in the western part of Spain. No difference was detected between autosomal and X-linked genomic windows. This data has been supplemented with a RADseq dataset of 120 extra individuals from Spain comprising extra geographical hybrid zones and allopatric I. elegans populations from Europe (in preparation). Using a RADseq dataset comprising temporal samples from the oldest hybrid zone in western Spain, we also plan to assess the introgression dynamics and temporal progression of introgression at autosomal and sex-chromosome loci (in preparation).
In parallel, a pedigree has been constructed to identify genes of sexually and naturally selected traits in a hybrid pedigree. Offspring will be genotyped for genome-wide distributed SNPs, using RADseq genotyping to perform a QTL analysis (in preparation). Ultimately, we will screen the panel of mapped candidate genes across populations of the hybrid zone (with already available RADseq genomic data), which will enable us to compare population genetic structure at these characterised genes with the genome-wide population structure. This will allow us to test the hypothesis whether “speciation genes” can be more often found on the X chromosome and determine the factors leading to heterogeneity in genomic divergence between species.
