Limnephilus spp.

Salokannel, Juha, Lee, Kyung Min, Rinne, Aki & Mutanen, Marko, 2021, ddRAD Sequencing Sheds Light on Low Interspecific and High Intraspecific mtDNA Divergences in Two Groups of Caddisflies, Insect Systematics and Diversity (AIFB) 5 (5), pp. 1-10 : 8

Limnephilus spp.

The three studied Limnephilus species seem to make an exception within the Finnish caddisfly fauna with distinct polymorphism in their DNA barcodes, with minimum Kimura-2 parameter divergences between the clusters varying from 6.8 to 10.1%. However, no clear morphological differences nor division of ddRAD sequences were detected in this study. A likely explanation for the genetic polymorphism in their mtDNA is historical admixture between closely related species, resulting in mitochondrial introgression and subsequent co-occurrence of two distinct lineages of COI within a species. Alternatively, this pattern could have resulted from retained historical genetic polymorphism. The former explanation would get indirect support if one of the clusters was observed being genetically closer to any other related species than to the other cluster. We explored this possibility in our own data, but also using all data accessible to us in the BOLD database.

One of the two mtCOI clusters of L. flavicornis is both genetically and phylogenetically closer to its morphological sister species marmoratus than the other intraspecific mtCOI cluster. This observation suggests introgression of mtCOI from L. marmoratus to L. flavicornis in the past, although the evidence for this scenario cannot be considered as compelling. The supposedly introgressed, yet then diverged COI haplotype is now widespread in L. flavicornis populations, as among our material (n = 18) both haplotypes seem common.

One of two mtCOI clusters of L. sericeus is almost identical (divergence <0.5%) with that of the public barcodes available ( Zhou et al. 2016) for L. abbreviatus Banks, 1908 (Supp Table 2 [online only]), which is one of the Nearctic species of L. sericeus group ( Ruiter 1995). This suggests a relatively recent introgression of mtCOI from L. abbreviatus to L. sericeus . However, it is surprising that the haplotype would have spread all the way from North America through Siberia to Finland. Such a spread could potentially have been promoted by endosymbiotic bacteria, Wolbachia in particular ( Hurst and Jiggins 2005, Smith et al. 2012), but we do not have evidence that being happened as we did not screen Wolbachia .

Neither of the mtCOI clusters of L. centralis is closely associated with other taxa with public DNA barcodes available ( Zhou et al. 2016) or other data accessible to us in BOLD. The closest match (about 4%) of the second cluster is Central European L. italicus McLachlan, 1884 (Supp Table 2 [online only]), which is originally described as a variety of L. centralis ( McLachlan 1884) . The second mtCOI cluster may suggest introgression from L. italicus to L. centralis long in the past or an introgression from an unknown species to L. centralis . So far, the second mtCOI cluster specimens were found only from the continent of Finland, while the first cluster sequences appear widely in Europe (Supp Table 2 [online only]), including South West Finland.