Multi-locus DNA sequence variation in a complex of four leaf beetle species with parapatric distributions: Mitochondrial and nuclear introgressions reveal recent hybridization

Evolutionary Relationships of Omani Macrotermes subhyalinus, Macrotermitinae

A study was conducted to investigate the evolutionary relationships of Macrotermes subhyalinus from Oman, in the southeastern part of the Arabian Peninsula. Sequences of the mitochondrial COI and the nuclear large-subunit ribosomal RNA (LSU rRNA, 28S) genes were used to investigate the populations of M. subhyalinus across their distribution in Oman to determine their relationships with other Macrotermes species. Our findings indicate that M. subhyalinus in Oman is a member of an East African clade, distinct from those in West Africa. Analyses of the COI showed that there is base composition bias among the taxa (non-stationarity) that has not been considered in earlier studies. We provide the first report of pseudogene copies of 28S in M. subhyalinus that are differentially amplified.

Whole-genome sequencing reveals asymmetric introgression between two sister species of cold-resistant leaf beetles

A large number of genetic variation studies have identified cases of mitochondrial genome introgression in animals, indicating that reproductive barriers among closely related species are often permeable. Because of its sheer size, the impact of hybridization on the evolution of the nuclear genome is more difficult to apprehend. Only a few studies have explored it recently thanks to recent progress in DNA sequencing and genome assembly. Here, we analysed whole-genome sequence variation among multiple individuals of two sister species of leaf beetles inside their hybrid zone, in which asymmetric mitochondrial genome introgression had previously been established. We used a machine learning approach based on computer simulations for training to identify regions of the nuclear genome that were introgressed. We inferred asymmetric introgression of ≈2% of the genome, in the same direction that was observed for the mitochondrial genome. Because a previous study based on a reduced-representation sequencing approach was not able to detect this introgression, we conclude that whole-genome sequencing is necessary when the fraction of the introgressed genome is small. We also analysed the whole-genome sequence of a hybrid individual, demonstrating that hybrids have the capacity to backcross with the species for which virtually no introgression was observed. Our data suggest that one species has recently invaded the range of the other and/or some alleles that where transferred from the invaded into the invading species could be under positive selection and may have favoured the adaptation of the invading species to the Alpine environment.

Genome Assembly of the Cold-Tolerant Leaf Beetle Gonioctena quinquepunctata, an Important Resource for Studying Its Evolution and Reproductive Barriers between Species

Coleoptera is the most species-rich insect order, yet is currently underrepresented in genomic databases. An assembly was generated for ca. 1.7 Gb genome of the leaf beetle Gonioctena quinquepunctata by first assembling long-sequence reads (Oxford Nanopore; ± 27-fold coverage) and subsequently polishing the resulting assembly with short sequence reads (Illumina; ± 85-fold coverage). The unusually large size (most Coleoptera species are associated with a reported size below 1 Gb) was at least partially attributed to the presence of a large fraction of repeated elements (73.8%). The final assembly was characterized by an N50 length of 432 kb and a BUSCO score of 95.5%. The heterozygosity rate was ± 0.6%. Automated genome annotation informed by RNA-Seq resulted in 40,568 predicted proteins, which is much larger than the typical range 17,000–23,000 predicted for other Coleoptera. However, no evidence of a genome duplication was detected. This new reference genome will contribute to our understanding of genetic variation in the Coleoptera. Among others, it will also allow exploring reproductive barriers between species, investigating introgression in the nuclear genome, and identifying genes involved in resistance to extreme climate conditions.

Widespread co-occurrence of two distantly related mitochondrial genomes in individuals of the leaf beetle Gonioctena intermedia

Mitochondrial genome heteroplasmy-the presence of more than one genomic variant in individuals-is considered only occasional in animals, and most often involves molecules differing only by a few recent mutations. Thanks to new sequencing technologies, a large number of DNA fragments from a single individual can now be sequenced and visualized separately, allowing new insights into intra-individual mitochondrial genome variation. Here, we report evidence from both (i) massive parallel sequencing (MPS) of genomic extracts and (ii) Sanger sequencing of PCR products, for the widespread co-occurrence of two distantly related (greater than 1% nucleotide divergence, excluding the control region) mitochondrial genomes in individuals of a natural population of the leaf beetle Gonioctena intermedia Sanger sequencing of PCR products using universal primers previously failed to identify heteroplasmy in this population. Its occurrence was detected with MPS data and may have important implications for evolutionary studies. It suggests the need to re-evaluate, using MPS techniques, the proportion of animal species displaying heteroplasmy.

Glacial survival of trophically linked boreal species in northern Europe

Whether non-arctic species persisted in northern Europe during the Last Glacial Maximum (LGM) is highly debated. Until now, the debate has mostly focused on plants, with little consideration for other groups of organisms, e.g. the numerous plant-dependent insect species. Here, we study the late-Quaternary evolution of the European range of a boreo-montane leaf beetle, Gonioctena intermedia, which feeds exclusively on the boreal and temperate trees Prunus padus and Sorbus aucuparia Using species distribution models, we estimated the congruence between areas of past and present suitable climate for this beetle and its host plants. Then we derived historical hypotheses from the congruent range estimates, and evaluated their compatibility with observed DNA sequence variation at five independent loci. We investigated compatibility using computer simulations of population evolution under various coalescence models. We find strong evidence for range modifications in response to late-Quaternary climate changes, and support for the presence of populations of G. intermedia in northern Europe since the beginning of the last glaciation. The presence of a co-dependent insect in the region through the LGM provides new evidence supporting the glacial survival of cold-tolerant tree species in northern Europe.

Revision of Mandarella Duvivier from Taiwan, with a new species, new synonymies and identities of highly variable species (Insecta, Chrysomelidae, Galerucinae, Alticini)

Taiwanese species of Mandarella Duvivier are compared on the basis of morphological and molecular evidence. Only three of eleven morphospecies are considered to be valid. Mandarellauenoi (Kimoto, 1969) is transferred from the genus Luperus Geoffroy. Stenoluperustaiwanus Kimoto, 1991 and Stenoluperuskimotoi Döberl, 2001 are synonymized with Mandarellauenoi. Taiwanese records of Stenoluperustibialis Chen, 1942, Stenoluperusnipponensis Laboissière, 1913, and Stenoluperuspotanini (Weise, 1889) were based on misidentifications and represent Mandarellauenoi. The Taiwanese population previously erroneously identified as Stenoluperuspallipes Gressitt and Kimoto, 1963 is here described as a new species, Mandarellatsouisp. n., Stenoluperusesakii Kimoto, 1969, Stenoluperusmatsumurai Takizawa, 1978, and Mandarellataiwanensis Medvedev, 2012 are synonymized with Mandarellaflaviventris (Chen, 1942).

Fast Census of Moth Diversity in the Neotropics: A Comparison of Field-Assigned Morphospecies and DNA Barcoding in Tiger Moths

The morphological species delimitations (i.e. morphospecies) have long been the best way to avoid the taxonomic impediment and compare insect taxa biodiversity in highly diverse tropical and subtropical regions. The development of DNA barcoding, however, has shown great potential to replace (or at least complement) the morphospecies approach, with the advantage of relying on automated methods implemented in computer programs or even online rather than in often subjective morphological features. We sampled moths extensively for two years using light traps in a patch of the highly endangered Atlantic Forest of Brazil to produce a nearly complete census of arctiines (Noctuoidea: Erebidae), whose species richness was compared using different morphological and molecular approaches (DNA barcoding). A total of 1,075 barcode sequences of 286 morphospecies were analyzed. Based on the clustering method Barcode Index Number (BIN) we found a taxonomic bias of approximately 30% in our initial morphological assessment. However, a morphological reassessment revealed that the correspondence between morphospecies and molecular operational taxonomic units (MOTUs) can be up to 94% if differences in genitalia morphology are evaluated in individuals of different MOTUs originated from the same morphospecies (putative cases of cryptic species), and by recording if individuals of different genders in different morphospecies merge together in the same MOTU (putative cases of sexual dimorphism). The results of two other clustering methods (i.e. Automatic Barcode Gap Discovery and 2% threshold) were very similar to those of the BIN approach. Using empirical data we have shown that DNA barcoding performed substantially better than the morphospecies approach, based on superficial morphology, to delimit species of a highly diverse moth taxon, and thus should be used in species inventories.