Taxonomy of hybridizing Colias croceus (Geoffroy, 1785) and Colias erate (Esper, 1805) (Lepidoptera, Pieridae) in light of mitochondrial and nuclear DNA, with occurrence and effects of Wolbachia infection

The lack of reliable characters and the wide color variation make it difficult to distinguish between Colias species. The sequences of mtDNA are often not reliably distinguishing between species of Colias. On the other hand, the genetic divergences within some species are so large that cryptic speciation appears likely to have taken place. Wolbachia are the most widespread endosymbiotic bacteria manipulating the reproduction of their hosts. The screening for the presence of Wolbachia in the sister species Colias croceus and Colias erate showed an infection rate of 100% in the Slovak population. Most specimens of these two species that frequently hybridize are infected by the Wolbachia strain ST141. The role of introgression as the likely reason for DNA barcode sharing is suggested by mitochondrial markers of COI and Control region as well as nuclear genes of CAD, EF1 alpha, GAPDH, IDH, MDH, RPS5 and Wingless. Our findings suggest that the high vertical transmission of Wolbachia infection, fitness advantage and strong cytoplasmic incompatibility have accelerated the spread of Wolbachia and moreover is related to the spread of introgressed mtDNA in the new species after hybridization. Occurrence of many hybrids with intermediate morphological features suggest hybridization to frequently occur between the two species.

Automated summary

The lack of reliable characters and color variation make it difficult to distinguish between Colias species. mtDNA sequences are not always reliable in distinguishing between Colias species. However, genetic differences within some species suggest the possibility of cryptic speciation. Wolbachia is a common endosymbiotic bacteria that affects host reproduction. Research on Colias croceus and Colias erate showed a high infection rate of Wolbachia and its potential role in introgression of mtDNA.