Comparative analysis of mitochondrial genomes of geographic variants of the gypsy moth, Lymantria dispar, reveals a previously undescribed genotypic entity

Abstract

The gypsy moth, Lymantria dispar L., is one of the most destructive forest pests in the world. While the subspecies established in North America is the European gypsy moth (L. dispar dispar), whose females are flightless, the two Asian subspecies, L. dispar asiatica and L. dispar japonica, have flight-capable females, enhancing their invasiveness and warranting precautionary measures to prevent their permanent establishment in North America. Various molecular tools have been developed to help distinguish European from Asian subspecies, several of which are based on the mitochondrial barcode region. In an effort to identify additional informative markers, we undertook the sequencing and analysis of the mitogenomes of 10 geographic variants of L. dispar, including two or more variants of each subspecies, plus the closely related L. umbrosa as outgroup. Several regions of the gypsy moth mitogenomes displayed nucleotide substitutions with potential usefulness for the identification of subspecies and/or geographic origins. Interestingly, the mitogenome of one geographic variant displayed significant divergence relative to the remaining variants, raising questions about its taxonomic status. Phylogenetic analyses placed this population from northern Iran as basal to the L. dispar clades. The present findings will help improve diagnostic tests aimed at limiting risks of AGM invasions.

Reassessment of the status of Lymantria albescens and Lymantria postalba (Lepidoptera: Erebidae: Lymantriinae) as distinct ‘Asian gypsy moth’ species, using both mitochondrial and nuclear sequence data

“…Whereas the partial mitogenomes successfully resolved members of the L. dispar + L. umbrosa clade (Fig. A), revealing a tree topology identical to that reported earlier for these taxa, based on full mitogenomes (Djoumad et al ., ), the four nuclear markers used here failed to recover this topology, providing resolution only for L. umbrosa (Fig. B).…”

“…Moths were obtained either as specimens preserved at −80 ∘ C, or as archival, dry adults. Species/subspecies identification was verified by CFIA taxonomists on the basis of morphological characters (Pogue & (Djoumad et al, 2017). Schaefer, 2007), and subsequently confirmed by us on the basis of the COI barcoding sequence, except for L. albescens and L. postalba, which could not be distinguished using this barcoding approach alone (Stewart et al, 2016).…”

“…Tissue obtained from frozen and archival specimens (one or two legs in most cases) was ground in liquid nitrogen before DNA extraction. Total genomic DNA (nuclear and mt) was extracted using the Qiagen Blood & Cell Culture DNA midi kit or the Qiagen DNeasy Blood & Tissue Mini Kit (Qiagen, Hilden, Germany), following the manufacturer's instructions, with minor modifications (see Djoumad et al, 2017). After spectrophotometric quantification (NanoDrop ND-1000; Thermo Fischer Scientific Inc., Waltham, MA, U.S.A.), purified DNA was used for PCR amplification and sequencing, either directly or diluted.…”

“…With respect to L. mathura, a draft mitogenome sequence was first assembled from PacBio sequences generated in the context of an independent nuclear genome sequencing project (M. Cusson, unpublished data), using the Celera assembler (Myers et al, 2000). This sequence was then subjected to quality control through targeted amplifications and complementary Sanger sequencing, as previously described (Djoumad et al, 2017).…”

“…In an effort to bring closure to the taxonomic conundrum described above, we undertook the sequencing of a large portion of the mt genome [ten protein-coding genes (PCGs) and 12 transfer RNA (tRNA) genes] in representative specimens of L. albescens and L. postalba, plus those of L. monacha (L.), L. xylina Swinhoe and L. mathura Moore, for comparative purposes. Our analyses also included the corresponding mt sequences obtained earlier for L. umbrosa and geographic variants of L. dispar (Djoumad et al, 2017). Finally, we also sequenced four nuclear marker genes from the same specimens used for mt sequence analysis.…”