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.

Figure 1

Sampling locations for Lymantria specimens used in this study. Red symbols represent sampling locations for L. dispar subspecies (1–9), blue symbol is for L. umbrosa (10) and green symbol is for the specimen from Iran (11). For full location names, see Table 1. Background map is a cropped version of the one available at: https://commons.wikimedia.org/wiki/Maps_of_the_world#/media/File:BlankMap-World-v2.png (for information about license, follow the same link).

Figure 2

Circular map of mitochondrial genome of L. dispar dispar (Ldd_NJ). The tRNA genes are indicated using the single letter IUPAC-IUB abbreviation, corresponding to their amino acid. COI, II and III: cytochrome oxidase subunits; Cyt b: Cytochrome b; ND: NADH dehydrogenase; rrnL and rrnS rRNA correspond to ribosomal RNAs. Gypsy moth caterpillar photo credit: Catherine Béliveau^©.

Figure 3

Graphical representation of a nucleotide alignment of the 11 mitochondrial genomes sequenced in the present study. Black vertical bars represent substitutions in the nucleotide sequence relative to the Ldd_NJ genome (top). Annotations: green boxes, PCGs; red boxes, rRNA subunit genes; grey box, A + T-rich region; pink arrows, tRNAs.

Figure 4

Comparative analysis of amino acid substitutions among the 13 PCGs of the 11 mitochondrial genomes sequenced in the present study. Unsubstituted amino acids at a given position are shaded in blue; substitutions are shaded in different colors according to their conservativeness (see legend). To identify substitutions and assess their level of conservativeness, amino acid sequences were aligned in MAFFT, using the ClustalW output format.

Figure 5

Phylogenetic relationships among the nine L. dispar populations sampled here, plus a population from Iran (L?_IR) and L. umbrosa, based on all 37 mitochondrial genes, plus the A + T-rich region. (a) Bayesian inference (BI), MCMC consensus tree (10,000,000) with posterior probabilities shown on each branch. (b) Maximum Likelihood (non-partitioned data) with 1000 bootstrap replicates. L. umbrosa was used as outgroup.