Discussion
Here we used simultaneous assessment of nuclear and mtDNA along with CHC data to disentangle the species limits in a morphologically conserved insect taxon with an intricate evolutionary history. Morphological and genetic (mainly mt) evidence gathered in previous studies suggested the probable existence of four distinct evolutionary lineages within theE. ruidum complex (Aguilar-Velasco et al. 2016; Meza-Lázaro et al. 2018). However, those studies were inconclusive due to the presence of mt heteroplasmy in individuals of some populations from Oaxaca, which led to the reconstruction of clades with considerably long branches due to the preferential sequencing of the mt haplotype with the faster substitution rate over the alternative haplotype from the same specimen. Moreover, the mt markers recovered highly genetically structured populations, which is frequent in social hymenopterans due to extreme female philopatry (Johnstone et al. 2012; Hakala et al. 2019), whereas the nuclear markers had almost no variation. Below we discuss our results from two different nuclear genomic sequence data, which, together with the mt and CHC information, overcome limitations of the previous works, providing a robust framework of species delimitation that can be employed for further taxonomic and evolutionary studies in the group.