The mitochondrial (mt) genome is, to date, the most extensively studied genomic system in insects, outnumbering nuclear genomes tenfold and representing all orders versus very few. Phylogenomic ...analysis methods have been tested extensively, identifying compositional bias and rate variation, both within and between lineages, as the principal issues confronting accurate analyses. Major studies at both inter- and intraordinal levels have contributed to our understanding of phylogenetic relationships within many groups. Genome rearrangements are an additional data type for defining relationships, with rearrangement synapomorphies identified across multiple orders and at many different taxonomic levels. Hymenoptera and Psocodea have greatly elevated rates of rearrangement offering both opportunities and pitfalls for identifying rearrangement synapomorphies in each group. Finally, insects are model systems for studying aberrant mt genomes, including truncated tRNAs and multichromosomal genomes. Greater integration of nuclear and mt genomic studies is necessary to further our understanding of insect genomic evolution.
Force reactive functional groups, or mechanophores, have emerged as the basis of a potential strategy for sensing and countering stress-induced material failure. The general utility of this strategy ...is limited, however, because the levels of mechanophore activation in the bulk are typically low and observed only under large, typically irreversible strains. Strategies that enhance activation are therefore quite useful. Molecular-level design principles by which to engineer enhanced mechanophore activity are reviewed, with an emphasis on quantitative structure-activity studies determined for a family of
gem
-dihalocyclopropane mechanophores.
Molecular-level design principles by which to engineer enhanced mechanophore activity are reviewed, with an emphasis on quantitative structure-activity studies determined for a family of
gem
-dihalocyclopropane mechanophores.
Termites have colonized many habitats and are among the most abundant animals in tropical ecosystems, which they modify considerably through their actions. The timing of their rise in abundance and ...of the dispersal events that gave rise to modern termite lineages is not well understood. To shed light on termite origins and diversification, we sequenced the mitochondrial genome of 48 termite species and combined them with 18 previously sequenced termite mitochondrial genomes for phylogenetic and molecular clock analyses using multiple fossil calibrations. The 66 genomes represent most major clades of termites. Unlike previous phylogenetic studies based on fewer molecular data, our phylogenetic tree is fully resolved for the lower termites. The phylogenetic positions of Macrotermitinae and Apicotermitinae are also resolved as the basal groups in the higher termites, but in the crown termitid groups, including Termitinae + Syntermitinae + Nasutitermitinae + Cubitermitinae, the position of some nodes remains uncertain. Our molecular clock tree indicates that the lineages leading to termites and Cryptocercus roaches diverged 170 Ma (153-196 Ma 95% confidence interval CI), that modern Termitidae arose 54 Ma (46-66 Ma 95% CI), and that the crown termitid group arose 40 Ma (35-49 Ma 95% CI). This indicates that the distribution of basal termite clades was influenced by the final stages of the breakup of Pangaea. Our inference of ancestral geographic ranges shows that the Termitidae, which includes more than 75% of extant termite species, most likely originated in Africa or Asia, and acquired their pantropical distribution after a series of dispersal and subsequent diversification events.
The evolutionary success of beetles and numerous other terrestrial insects is generally attributed to co-radiation with flowering plants but most studies have focused on herbivorous or pollinating ...insects. Non-herbivores represent a significant proportion of beetle diversity yet potential factors that influence their diversification have been largely unexamined. In the present study, we examine the factors driving diversification within the Scarabaeidae, a speciose beetle family with a range of both herbivorous and non-herbivorous ecologies. In particular, it has been long debated whether the key event in the evolution of dung beetles (Scarabaeidae: Scarabaeinae) was an adaptation to feeding on dinosaur or mammalian dung. Here we present molecular evidence to show that the origin of dung beetles occurred in the middle of the Cretaceous, likely in association with dinosaur dung, but more surprisingly the timing is consistent with the rise of the angiosperms. We hypothesize that the switch in dinosaur diet to incorporate more nutritious and less fibrous angiosperm foliage provided a palatable dung source that ultimately created a new niche for diversification. Given the well-accepted mass extinction of non-avian dinosaurs at the Cretaceous-Paleogene boundary, we examine a potential co-extinction of dung beetles due to the loss of an important evolutionary resource, i.e., dinosaur dung. The biogeography of dung beetles is also examined to explore the previously proposed "out of Africa" hypothesis. Given the inferred age of Scarabaeinae as originating in the Lower Cretaceous, the major radiation of dung feeders prior to the Cenomanian, and the early divergence of both African and Gondwanan lineages, we hypothesise that that faunal exchange between Africa and Gondwanaland occurred during the earliest evolution of the Scarabaeinae. Therefore we propose that both Gondwanan vicariance and dispersal of African lineages is responsible for present day distribution of scarabaeine dung beetles and provide examples.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The entire mitochondrial genome of the tobacco hornworm,
Manduca sexta (Lepidoptera: Spinghidae) was sequenced — a circular molecular 15516 bp in size. The arrangement of the protein coding genes ...(PCGs) was the same as that found in the ancestral insect, however
Manduca possessed the derived tRNA arrangement of CR-M-I-Q which has been found in all Lepidoptera sequenced to date. Additionally,
Manduca, like all lepidopteran mt genomes, has numerous large intergenic spacer regions and microsatellite-like repeat regions. Nucleotide composition is highly A+T biased, and the lepidopterans have the second most biased nucleotide composition of the insect orders after Hymenoptera. Secondary structural features of the PCGs identified in other Lepidoptera were present but highly modified by the presence of microsatellite-like repeat regions which may significantly alter their function in the post-transcriptional modification of pre-mRNAs. Secondary structure models of the ribosomal RNA genes of
Manduca are presented and are similar to those proposed for other insect orders. Conserved regions were identified within non-translated spacer regions which correspond to sites for the origin and termination of replication and transcription. Comparisons of gene variability across the order suggest that the mitochondrial genes most frequently used in phylogenetic analysis of the Lepidoptera,
cox1 and
cox2, are amongst the least variable genes in the genome and phylogenetic resolution could be improved by using alternative, higher variability genes such as
nad2,
nad3,
nad4 and
nad5.
Larval feeding by the moth genus Ogmograptis (Bucculatricidae: Lepidoptera) creates one of the most iconic features of the Australian bush—the ‘scribbles’ found on smooth‐barked Eucalyptus. The ...taxonomic history of Ogmograptis has been challenging, with members of the genus being initially described in four different genera representing three different superfamilies. While prior phylogenetic analysis has placed Ogmograptis within the Bucculatricidae, these findings were not strongly supported and there was poor resolution of the early diverging, non‐Apoditrysia superfamilies that Ogmograptis has been assigned to by different authors. As a consequence, the unique larval biology of scribbly moths cannot yet be interpreted in an evolutionary context. Phylogenomic analysis of whole mitochondrial (mt) genome data for Ogmograptis, related non‐Apoditrysia and taxa representing the superfamily‐level diversity of the order strongly supports its placement within the Bucculatricidae, a monophyletic Gracillarioidea and a clade of Gracillarioidea + Yponomeutoidea that was sister to the Apoditrysia. The hypermetamorphic larval development in Ogmograptis can thus be interpreted as an elaboration of the ancestral pattern of the clade Gracillarioidea + Yponomeutoidea that has specialised for phellogen/callus feeding within the bark. The utility of mt genomes for deep‐level phylogenetic study of the Lepidoptera is reviewed against prior multi‐locus and nuclear phylogenomic datasets. Mt phylogenomic analyses are sensitive to analytical methods and the inclusion versus exclusion of high‐variability data partitions for deep‐level relationships, already shown to be uncertain by multi‐locus or nuclear phylogenomic analyses, in particular relationships between apoditrysian and obtectomeran superfamilies. While mt genomes are ideal for examining the relationships of rare, physically small or difficult to collect taxa such as Ogmograptis, due to the low technical hurdles to collecting whole genomes, continued attention to the analytical sensitivities of phylogenies that use this data source is needed to reliably advance our understanding of deep lepidopteran evolution.
Thickening of the integument as a mechanism of resistance to insecticides is a well recognised phenomenon in the insect world and, in recent times, has been found in insects exhibiting ...pyrethroid-resistance. Resistance to pyrethroid insecticides in the common bed bug, Cimex lectularius L., is widespread and has been frequently inferred as a reason for the pest's resurgence. Overexpression of cuticle depositing proteins has been demonstrated in pyrethroid-resistant bed bugs although, to date, no morphological analysis of the cuticle has been undertaken in order to confirm a phenotypic link. This paper describes examination of the cuticle thickness of a highly pyrethroid-resistant field strain collected in Sydney, Australia, in response to time-to-knockdown upon forced exposure to a pyrethroid insecticide. Mean cuticle thickness was positively correlated to time-to-knockdown, with significant differences observed between bugs knocked-down at 2 hours, 4 hours, and those still unaffected at 24 hours. Further analysis also demonstrated that the 24 hours survivors possessed a statistically significantly thicker cuticle when compared to a pyrethroid-susceptible strain of C. lectularius. This study demonstrates that cuticle thickening is present within a pyrethroid-resistant strain of C. lectularius and that, even within a stable resistant strain, cuticle thickness will vary according to time-to-knockdown upon exposure to an insecticide. This response should thus be considered in future studies on the cuticle of insecticide-resistant bed bugs and, potentially, other insects.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Woodward and Hoffman once jested that a very powerful Maxwell demon could seize a molecule of cyclobutene at its methylene groups and tear it open in a disrotatory fashion to obtain butadiene ...(Woodward, R. B.; Hoffmann, R. The Conservation of Orbital Symmetry. Angew. Chem., Int. Ed. 1969, 8, 781–853). Nearly 40 years later, that demon was discovered, and the field of covalent polymer mechanochemistry was born. In the decade since our demon was befriended, many fundamental investigations have been undertaken to build up our understanding of force-modified pathways for electrocyclic ring-opening reactions. Here, we seek to extend that fundamental understanding by exploring substituent effects in allowed and forbidden ring-opening reactions of cyclobutene (CBE) and benzocyclobutene (BCB) using a combination of single-molecule force spectroscopy (SMFS) and computation. We show that, while the forbidden ring-opening of cis-BCB occurs at a lower force than the allowed ring-opening of trans-BCB on the time scale of the SMFS experiment, the opposite is true for cis- and trans-CBE. Such a reactivity flip is explained through computational analysis and discussion of the so-called allowed/forbidden gap.
A traditionally controversial taxon, the Tipulomorpha has been frequently discussed with respect to both its familial composition and relationships with other Nematocera. The interpretation of ...internal relationships within the Tipuloidea, which include the Tipulidae sensu stricto, Cylindrotomidae, Pediciidae and Limoniidae, is also problematic. We sequenced the first complete mitochondrial (mt) genome of Symplecta hybrida (Meigen, 1804), which belongs to the subfamily Chioneinae of family Limoniidae, and another five nearly complete mt genomes from the Tipuloidea. We did a comparative analysis of these mt genomics and used them, along with some other representatives of the Nematocera to construct phylogenetic trees. Trees inferred by Bayesian methods strongly support a sister-group relationship between Trichoceridae and Tipuloidea. Tipulomorpha are not supported as the earliest branch of the Diptera. Furthermore, phylogenetic trees indicate that the family Limoniidae is a paraphyletic group.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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