Abstract
Deep sympatric intraspecific divergence in mtDNA may reflect cryptic species or formerly distinct lineages in the process of remerging. Preliminary results from DNA barcoding of Scandinavian butterflies and moths showed high intraspecific sequence variation in the autumnal moth, Epirrita autumnata. In this study, specimens from different localities in Norway and some samples from Finland and Scotland, with two congeneric species as outgroups, were sequenced with mitochondrial and nuclear markers to resolve the discrepancy found between mtDNA divergence and present species-level taxonomy. We found five COI sub-clades within the E. autumnata complex, most of which were sympatric and with little geographic structure. Nuclear markers (ITS2 and Wingless) showed little variation and gave no indications that E. autumnata comprises more than one species. The samples were screened with primers for Wolbachia outer surface gene (wsp) and 12% of the samples tested positive. Two Wolbachia strains were associated with different mtDNA sub-clades within E. autumnata, which may indicate indirect selection/selective sweeps on haplotypes. Our results demonstrate that deep mtDNA divergences are not synonymous with cryptic speciation and this has important implications for the use of mtDNA in species delimitation, like in DNA barcoding.
Highlights
Species are often regarded as basic units of evolution and correct species delimitation serves as a backbone in most biological studies (Mayr 1982; Roe and Sperling 2007)
Neighbor-joining analysis of the COI data set showed high intraspecific variation within E. autumnata, with 21 haplotypes divided into five distinct haplogroups with varying degree of support at each node, ranging from 63% to 99% (Fig. 2a, only bootstrap values higher than 85% are shown)
Standard estimates of nucleotide polymorphism were higher within E. autumnata than within E. christiy and E. dilutata (Table 1)
Summary
Species are often regarded as basic units of evolution and correct species delimitation serves as a backbone in most biological studies (Mayr 1982; Roe and Sperling 2007). A universal system for rapid, inexpensive species identification applicable for any life stage, DNA barcoding, has been proposed by Hebert et al (2003). The ambition behind DNA barcoding is identification by sequencing of short standardized gene regions in order to assign unknown individuals to species and to enhance the discovery of new species. There are several possible explanations for high intraspecific variation. This pattern may reflect the presence of cryptic species. The exploration of cryptic species within the Skipper butterfly, Astraptes fulgerator, performed by Hebert et al (2004) is a well-known example. By combining DNA barcoding with information about ecology and morphology of A. fulgerator, at least 10, largely sympatric cryptic species were revealed (but see Brower 2006).
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