The Highly Divergent Mitochondrial Genomes Indicate That the Booklouse, Liposcelis bostrychophila (Psocoptera: Liposcelididae) Is a Cryptic Species

An advanced approach for rapid visual identification of Liposcelis bostrychophila (Psocoptera: Liposcelididae) based on CRISPR/Cas12a combined with RPA

Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae) is a booklouse pest that is a threat to commodity storage security worldwide. Accurate and sensitive methods of L. bostrychophila on-site identification are essential prerequisites for its effective management. Evidence suggests that L. bostrychophila contains 3 intraspecific biotypes that are morphologically indistinguishable but can be discriminated at the level of mitochondrial genome organization and sequences. The traditional molecular identification methods, such as DNA barcoding and PCR-RFLP, are instrumentally demanding and time-consuming, limiting the application of the identification in the field. Therefore, this study developed a new CRISPR/Cas12a-based visual nucleic acid system based on the mitochondrial gene coding for NADH dehydrogenase subunit 2 (nad2), combined with recombinase polymerase amplification (RPA) to accurately identify L. bostrychophila from 4 other common stored-product booklice, and also differentiate 3 biotypes of this species at the same time. The entire identification process could be completed at 37 °C within 20 min with high sensitivity. The system could stably detect at least 1 ng/μl of DNA template. The green fluorescence signal produced by the trans-cleaving of the single-stranded DNA reporter could be observed by the naked eye under blue light. Additionally, the suggested system combined with the crude DNA extraction method to extract DNA rapidly, enabled identification of all developmental stages of L. bostrychophila. With crude DNA, this novel diagnostic system successfully identified an unknown booklouse by holding the reaction tubes in the hand, thus can be considered as an accurate, rapid, highly sensitive, and instrument-flexible method for on-site visual identification of L. bostrychophila.

The Genetic Diversity and the Divergence Time in Extant Primitive Mayfly, Siphluriscus chinensis Ulmer, 1920 Using the Mitochondrial Genome

In this study, the mitochondrial (mt) genomes of Siphluriscus chinensis (Ephemeroptera: Siphluriscidae) were evaluated in specimens collected from two sites in China: Niutou Mountain, Zhejiang Province (S. chinensis NTS) and Leigong Mountain, Guizhou Province (S. chinensis LGS) and were successfully sequenced. The lengths of the mt genomes of S. chinensis NTS and S. chinensis LGS were 15,904 bp (ON729390) and 15,212 bp (ON729391), respectively. However, an in-depth comparison of the two mt genomes showed significant differences between the specimens collected from the two sites. A detailed analysis of the genetic distance between S. chinensis NTS and S. chinensis LGS was undertaken to further achieve an accurate delimitation of S. chinensis. The genetic distance between S. chinensis NTS and the other three species within Siphluriscidae was a high value, above 12.2%. The two mt genomes were used to reconstruct phylogenetic relationships and estimate divergence time. The results demonstrated robust differences between S. chinensis NTS and S. chinensis LGS, which revealed that a kind of cryptic species existed. Maximum likelihood (ML) and Bayesian inference (BI) analyses produced well-supported phylogenetic trees that showed evolutionary relationships between Siphluriscidae (((S. chinensis HQ875717 + S. chinensis MF352165) + S. chinensis LGS) + S. chinensis NTS). The most recent common ancestor (MRCA) of four species within Siphluriscidae began to diversify during the Neogene [11.80 million years ago (Mya); 95% highest posterior densities (HPD) = 6.17–19.28 Mya], and S. chinensis NTS was first to diverge from the branches of S. chinensis LGS. In short, based on mitochondrial genomes, our results showed that the specimens collected from Leigong Mountain, Guizhou Province (S. chinensis LGS) belonged to S. chinensis, and the specimens collected from Niutou Mountain, Zhejiang Province (S. chinensis NTS) were a cryptic species of S. chinensis.

Extreme mitochondrial DNA divergence underlies genetic conflict over sex determination

Cytoplasmic male sterility (CMS) is a form of genetic conflict over sex determination that results from differences in modes of inheritance between genomic compartments.^1-3 Indeed, maternally transmitted (usually mitochondrial) genes sometimes enhance their transmission by suppressing the male function in a hermaphroditic organism to the detriment of biparentally inherited nuclear genes. Therefore, these hermaphrodites become functionally female and may coexist with regular hermaphrodites in so-called gynodioecious populations.³ CMS has been known in plants since Darwin's times⁴ but is previously unknown in the animal kingdom.^5-8 We relate the first observation of CMS in animals. It occurs in a freshwater snail population, where some individuals appear unable to sire offspring in controlled crosses and show anatomical, physiological, and behavioral characters consistent with a suppression of the male function. Male sterility is associated with a mitochondrial lineage that underwent a spectacular acceleration of DNA substitution rates, affecting the entire mitochondrial genome-this acceleration concerns both synonymous and non-synonymous substitutions and therefore results from increased mitogenome mutation rates. Consequently, mitochondrial haplotype divergence within the population is exceptionally high, matching that observed between snail taxa that diverged 475 million years ago. This result is reminiscent of similar accelerations in mitogenome evolution observed in plant clades where gynodioecy is frequent,^9,10 both being consistent with arms-race evolution of genome regions implicated in CMS.^11,12 Our study shows that genomic conflicts can trigger independent evolution of similar sex-determination systems in plants and animals and dramatically accelerate molecular evolution.

Fragmentation in mitochondrial genomes in relation to elevated sequence divergence and extreme rearrangements

Background

A single circular mitochondrial (mt) genome is a common feature across most metazoans. The mt-genome includes protein-coding genes involved in oxidative phosphorylation, as well as RNAs necessary for translation of mt-RNAs, whose order and number are highly conserved across animal clades, with few known exceptions of alternative mt-gene order or mt-genome architectures. One such exception consists of the fragmented mitochondrial genome, a type of genome architecture where mt-genes are split across two or more mt-chromosomes. However, the origins of mt-genome fragmentation and its effects on mt-genome evolution are unknown. Here, we investigate these origin and potential mechanisms underlying mt-genome fragmentation, focusing on a genus of booklice, Liposcelis, which exhibits elevated sequence divergence, frequent rearrangement of mt-gene order, and fragmentation of the mt genome, and compare them to other Metazoan clades.

Results

We found this genus Liposcelis exhibits very low conservation of mt-gene order across species, relative to other metazoans. Levels of gene order rearrangement were, however, unrelated to whether or not mt-genomes were fragmented or intact, suggesting mitochondrial genome fragmentation is not affecting mt-gene order directly. We further investigated possible mechanisms underpinning these patterns and revealed very high conservation of non-coding sequences at the edges of multiple recombination regions across populations of one particular Liposcelis species, supportive of a hypothesis that mt-fragmentation arises from recombination errors between mt-genome copies. We propose these errors may arise as a consequence of a heightened mutation rate in clades exhibiting mt-fragmentation. Consistent with this, we observed a striking pattern across three Metazoan phyla (Arthropoda, Nematoda, Cnidaria) characterised by members exhibiting high levels of mt-gene order rearrangement and cases of mt-fragmentation, whereby the mt-genomes of species more closely related to species with fragmented mt-genomes diverge more rapidly despite experiencing strong purifying selection.

Conclusions

We showed that contrary to expectations, mt-genome fragmentation is not correlated with the increase in mt-genome rearrangements. Furthermore, we present evidence that fragmentation of the mt-genome may be part of a general relaxation of a natural selection on the mt-genome, thus providing new insights into the origins of mt-genome fragmentation and evolution.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01218-7.

Study on Gas Chromatographic Fingerprint of Essential Oil from Stellera chamaejasme Flowers and Its Repellent Activities against Three Stored Product Insects

The objective of this study was to establish the chromatographic fingerprints of the essential oil (EO) from Stellera chamaejasme flowers collected from various natural sites by gas chromatography (GC) combined with chemometric methods. The EO was obtained by hydrodistillation, and its chemical composition was analyzed by gas chromatography-mass spectrometry (GC-MS). Most components were identified as ketones and the relatively high-content components were fitone (38.973%), n-hentriacontane (5.807%), myristic acid (4.944%) and phytol (3.988%). In addition, the repellent activities of the EO from S. chamaejasme flowers and its four main chemical compounds were evaluated against three stored product pests (Tribolium castaneum, Lasioderma serricorne, Liposcelis bostrychophila) for the first time. In this work, the EO and the four chemical compounds showed a repellent effect against three storage pests after 2 and 4 h exposure. The experimental method and repellent activity of S. chamaejasme flower EO could provide a basis for the development of botanical pesticide and the utilization of the rich plant resources of S. chamaejasme in the future.

The First Complete Mitochondrial Genomes of Two Sibling Species from Nitidulid Beetles Pests

Carpophilus dimidiatus (Fabricius, 1792) and Carpophilus pilosellus Motschulsky are two sibling species and economically important storage pests worldwide. The first complete mitochondrial (mt) genomes of both were sequenced using next-generation sequencing. The mt genomes of C. dimidiatus and C. pilosellus are circular, with total lengths of 15,717 bp and 15,686 bp, respectively. Gene order and content for both species are similar to what has been observed in ancestral insects and consist of 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and a control region. Comparing the mt genome data of C. dimidiatus and C. pilosellus, they are similar in organization, arrangement patterns, GC contents, transfer RNA (tRNA) secondary structures, and codon usage patterns. Small differences were noted with regards to the nucleotide similarity of coding regions and the control region. This is the first publication of the complete mitochondrial genomes of two sibling species. The mt genome sequences can supplement the nuclear markers of the Carpophilus genus in research species identification, system evolution, and population genetic structure, and also will be valuable molecular marker for further genetic studies.

Nuclear Orthologs Derived from Whole Genome Sequencing Indicate Cryptic Diversity in the Bemisia tabaci (Insecta: Aleyrodidae) Complex of Whiteflies

The Bemisia tabaci complex of whiteflies contains globally important pests thought to contain cryptic species corresponding to geographically structured phylogenetic clades. Although mostly morphologically indistinguishable, differences have been shown to exist among populations in behavior, plant virus vector capacity, ability to hybridize, and DNA sequence divergence. These differences allow for certain populations to become invasive and cause great economic damage in a monoculture setting. Although high mitochondrial DNA divergences have been reported between putative conspecifics of the B. tabaci species complex, there is limited data that exists across the whole genome for this group. Using data from 2184 orthologs obtained from whole genome sequencing (Illumina), a phylogenetic analysis using maximum likelihood and coalescent methodologies was completed on ten individuals of the B. tabaci complex. In addition, automatic barcode gap discovery methods were employed, and results suggest the existence of five species. Although the divergences of the mitochondrial cytochrome oxidase I gene are high among members of this complex, nuclear divergences are much lower in comparison. Single-copy orthologs from whole genome sequencing demonstrate divergent population structures among members of the B. tabaci complex and the sequences provide an important resource to aid in future genomic studies of the group.

Genetics and Genomics of an Unusual Selfish Sex Ratio Distortion in an Insect

Diverse selfish genetic elements have evolved the ability to manipulate reproduction to increase their transmission, and this can result in highly distorted sex ratios [1]. Indeed, one of the major explanations for why sex determination systems are so dynamic is because they are shaped by ongoing coevolutionary arms races between sex-ratio-distorting elements and the rest of the genome [2]. Here, we use genetic crosses and genome analysis to describe an unusual sex ratio distortion with striking consequences on genome organization in a booklouse species, Liposcelis sp. (Insecta: Psocodea), in which two types of females coexist. Distorter females never produce sons but must mate with males (the sons of nondistorting females) to reproduce [3]. Although they are diploid and express the genes inherited from their fathers in somatic tissues, distorter females only ever transmit genes inherited from their mothers. As a result, distorter females have unusual chimeric genomes, with distorter-restricted chromosomes diverging from their nondistorting counterparts and exhibiting features of a giant non-recombining sex chromosome. The distorter-restricted genome has also acquired a gene from the bacterium Wolbachia, a well-known insect reproductive manipulator; we found that this gene has independently colonized the genomes of two other insect species with unusual reproductive systems, suggesting possible roles in sex ratio distortion in this remarkable genetic system.