Introgression and species demarcation in western European Leuctra fusca (Linnaeus, 1758) and L. digitata Kempny, 1899 (Plecoptera: Leuctridae)

The compilation of a DNA barcoding library of Norwegian stonefly (Plecoptera) species revealed that Leuctra fusca (Linnaeus, 1758 Linnaeus, C. (1758), Systema naturae Per Regna Tria Naturae: Secundum Classes, Ordines, Genera, Species, Cum Characteribus, Differentiis, Synonymis, Locis. Stockholm: Laurentius Salvius. [Google Scholar]) and Leuctra digitata Kempny, 1899 (Leuctridae) share haplotypes in northernmost Scandinavia. Phylogenetic analyses of the mitochondrial (mt) DNA barcode marker COI and the nuclear marker 28S show that the shared haplotypes must result from the introgression of a L. fusca mitochondrion into a L. digitata population on at least two occasions. Although mt introgression is widespread in animals, this represents the first documented case in Plecoptera. This study also included specimens of L. cf. fusca from the Sierra Nevada massif in Spain, a population previously known as L. carpentieri Despax, 1945. Their mt haplotypes are ca. 13% different from other European L. fusca. However, their 28S alleles are compatible with their morphological identification as L. fusca. In view of the possibility of mt introgression, the taxonomic status of this population remains undecided.