2.1.2 Sympatric populations
During fieldwork in the years 2014-2018 in north-central and north-west Spain, we conducted a revision of the distribution data of both species along the Iberian Peninsula from 2011 (reviewed in Boudot et al., 2009). From two hybrid regions, north-central Spain (Arreo, Cañas, Mateo, Perdiguero, Valbornedo, Valpierre, and Villar) and north-west Spain (Doniños, Laxe, Louro and Xuño) we included populations in which: 1) I. elegans was the dominant species; 2) I. graellsiiwas the dominant species, and 3) both species were present at different proportions. Additionally, available information of presence/absence from previous years (1987-2003) was also included. Populations were visited between June and July during sunny days, and sampling was done with entomological nets. Immature and mature males were included when estimating the number of individuals in each species (species proportion). Additionally, we included one population from north-east Spain (Menorca, in the Balearic Islands) to test the replacement ofI. graellsii by I. elegans in the Balearic Islands (results are given in supplementary Figure S4).
For the genomic work, a minimum of 20 adult males were collected during the flight season between 2008-2015 using hand nets and stored in 100% ethanol until DNA extraction. Because phenotypic hybrid assignment is only possible through detailed morphological analyses of male caudal appendages and prothoracic tubercle (see Monetti et al., 2002), all individuals in this study (of which a majority were females) werea priori morphologically assigned to either I. elegans orI. graellsii based on their thorax colour and prothoracic tubercle morphology. For populations with both species (I. elegans and I. graellsii ), we included samples of both species and aimed to keep the species proportion observed in the field at each site (Table 1). Previous data and our results allow us to discuss the present results in a time- and space-frame context.