The current study employed high-throughput sequencing to obtain complete mitochondrial genome sequences from 80 species of Lepidopteran moths, greatly contributing to the systematic evolutionary analysis of Lepidoptera. Typically, the genome size of these moths ranges from 300 to 1500 Mb. Each species was sequenced at approximately 15 Gb, providing coverage of the entire genome at 10 to 50×. Evaluation of mitochondrial assembly integrity showed coverage depths between 450 and 5866×, confirming the suitability of the 15 Gb data for precise extraction and circularization of the mitochondrial genome.
The gene order within insect mitochondrial genomes is typically highly conserved, with previous studies primarily focusing on tRNA rearrangements. A frequently observed rearrangement region in Lepidopteran species involves the gene cluster trnA-trnR-trnN-trnS1-trnE-trnF (Timmermans et al., 2014; Park et al., 2016), encompassing events such as trnE-trnS1 ectopy, trnR duplication, and trnE deletion (Timmermans et al., 2014; Kim et al., 2017; Zhou et al., 2020; Chen et al., 2022). In this study, the identified trnS1-trnE inversion also occurs within this gene cluster, precisely within a region with opposite transcriptional direction, suggesting it may represent a hypervariable zone of the mitochondrial genome. Furthermore, our analysis reveals that all three species of Zygaenidae (E. aedea, H. rhodope, and P. atratus) exhibit the trnS1-trnE inversion, indicating that this inversion likely predates the divergence of Zygaenidae species. Conversely, among the four species of Gelechiidae studied, only M. albilinella displays this inversion, suggesting it occurred after the divergence of Gelechiidae species.
The protein-coding genes within mitochondrial genomes are typically highly conserved. In our study, all 13 protein-coding genes across all species lacked introns, and any length variation observed primarily occurred through the insertion or deletion of triplet codons, thus avoiding frameshift mutations. Moreover, variations in the number of tandem repeats of triplet codons emerged as the primary mechanism driving length variation in these protein-coding genes. Similarly, the tandem duplication or deletion of short segments represented a common mode of length variation in non-coding regions of the mitochondrial genome, such as tRNA genes. Notably, these variations are also frequently observed in lower plants, including algae (Zhang et al., 2015).
The high-level phylogenetic analysis conducted in this study confirms the monophyly of nine superfamilies, including Yponomeutoidea, Tortricoidea, Zygaenoidea, Cossoidea, Gelechioidea, Bombycoidea, Geometroidea, and Noctuoidea, which aligns with findings from previous research (Li et al., 2010; Mitter et al., 2017; Kawahara er al., 2019). However, due to the limited number of samples, the positioning of Copromorphoidea within the tree varied depending on the construction method used. Specifically, results from both ML and BI methods suggested different relationships for Copromorphoidea: ML placed it closely related to Tortricoidea, whereas BI linked it with Gelechioidea. Given the uncertainty surrounding the taxonomic status of Copromorphoidea based on previous morphological and molecular data, further research with an expanded sample size from this superfamily is warranted to achieve a more comprehensive understanding of its phylogenetic relationships.
The findings of this study, derived from mitochondrial genome data, strongly support the proposed topological arrangement of (Bombycoidea + (Geometroidea + Noctuoidea)). However, previous analyses based on nuclear genomic data presented a different evolutionary relationship, suggesting (Geometroidea + (Noctuoidea + Bombycoidea)) (Cho et al., 2011; Regier et al., 2013). Additionally, the ML tree resulting from joint transcriptome and nuclear genome data analysis displayed the configuration: (Noctuoidea + (Geometroidea + Bombycoidea)) (Bazinet et al., 2013; Kawahara et al., 2019). A comprehensive comparison of these various research outcomes reveals discrepancies in the phylogenetic relationships among lepidopteran moths, potentially attributed to differing mutation rates across mitochondrial genes, transcriptomes, and nuclear genes. Nonetheless, the results of this study offer insights into the higher-level phylogenetic relationships among lepidopteran moths, as evidenced by mitochondrial whole-genome data analysis.
The monophyly of the superfamily Tineoidea has faced challenges in previous research (Bazinet et al., 2013; Regier et al., 2015), particularly concerning the taxonomic status of the family Gracillariidae within this superfamily. Stainton (1854) initially proposed the taxonomic classification of Gracillariidae, elevating it to superfamily status (Scoble, 1992). However, in 1996, Gracillariidae was reassigned from Microlepidoptera to Tineoidea (Nielsen & Rangsi, 1996). The current study's findings strongly support the affinity between Gracillariidae and Yponomeutoidea as sister groups (Regier et al., 2013), a conclusion corroborated by prior nuclear genome phylogenetic analyses (van Nieukerken et al., 2011; Mitter et al., 2017). The recognition of Gracillarioidea as a superfamily in prior studies lends additional support to our proposal to separate Gracillariidae from Tineoidea and reclassify it within Gracillarioidea.
There have long been divergent views on the taxonomic classification of Thyrididae. Initially proposed by Herrich-Schäffer (1845), Thyrididae was later placed within the superfamily Pyraloidea based on morphological traits (Common, 1970; Whalley, 1976). However, the taxon Thyridoidea has been used in most studies (van Nieukerken et al., 2011; Heikkilä et al., 2015; Leley, 2016; Santos et al., 2021). The findings of our current study strongly uphold the monophyly of Thyrididae, distinguishing it significantly from other groups within Pyraloidea. This aligns with previous research based on mitochondrial or nuclear genome data (Mutanen et al., 2010; Timmermans et al., 2014; Heikkilä et al., 2015). Therefore, our study advocates for separating Thyrididae from the superfamily Pyraloidea and relocating it to the superfamily Thyridoidea.
Migration plays important role in the survival and reproduction of insects, facilitating the spread of many alien species. In our study, all 80 newly identified moth species were collected within China. Remarkably, six of these species, S. chambae, C. capensis, A. munda, A. alberti, P. insulata, and C. falcata, had not previously been recorded in China. These specimens were collected in Jiangcheng County, Pu'er City, Yunnan Province, using light trapping methods. Situated in the border region between China, Vietnam, and Laos, this area serves as a potential entry point for migratory species. Thus, it is plausible that these six moth species entered China through migration, highlighting their status as potential alien species.
In summary, this study contributes to the resource of mitochondrial genome data available for moth phylogeny. However, it's important to note that the sample coverage across taxa is not uniform, with significant variation in the number of species, particularly in superfamilies such as Copromorphoidea and Tineoidea, where samples are relatively scarce. Additionally, our focus on comparative analysis at the mitochondrial genome level means that suggestions for revising the existing classification system are primarily informed by molecular data. Moving forward, the inclusion of more morphological data is anticipated. Integrating biological characteristics with whole-genome data will offer more robust evidence for understanding the evolution and phylogeny of lepidopteran moth species across different taxonomic levels.