Measuring and testing genetic differentiation with ordered versus unordered alleles

Estimates and variances of diversity and differentiation measures in subdivided populations are proposed that can be applied to haplotypes (ordered alleles such as DNA sequences, which may contain a record of their own histories). Hence, two measures of differentiation can be compared for a single data set: one (GST) that makes use only of the allelic frequencies and the other (NST) for which similarities between the haplotypes are taken into account in addition. Tests are proposed to compare NST and GST with zero and with each other. The difference between NST and GST can be caused by several factors, including sampling artefacts, unequal effect of mutation rates and phylogeographic structure. The method presented is applied to a published data set where a nuclear DNA sequence had been determined from individuals of a grasshopper distributed in 24 regions of Europe. Additional insights into the genetic subdivision of these populations are obtained by progressively combining related haplotypes and reanalyzing the data each time.

Estimating Species Phylogeny from Gene-Tree Probabilities Despite Incomplete Lineage Sorting: An Example from Melanoplus Grasshoppers

Estimating phylogenetic relationships among closely related species can be extremely difficult when there is incongruence among gene trees and between the gene trees and the species tree. Here we show that incorporating a model of the stochastic loss of gene lineages by genetic drift into the phylogenetic estimation procedure can provide a robust estimate of species relationships, despite widespread incomplete sorting of ancestral polymorphism. This approach is applied to a group of montane Melanoplus grasshoppers for which genealogical discordance among loci and incomplete lineage sorting obscures any obvious phylogenetic relationships among species. Unlike traditional treatments where gene trees estimated using standard phylogenetic methods are implicitly equated with the species tree, with the coalescent-based approach the species tree is modeled probabilistically from the estimated gene trees. The estimated species phylogeny (the ESP) is calculated for the grasshoppers from multiple gene trees reconstructed for nuclear loci and a mitochondrial gene. This empirical application is coupled with a simulation study to explore the performance of the coalescent-based approach. Specifically, we test the accuracy of the ESP given the data based on analyses of simulated data matching the multilocus data collected in Melanoplus (i.e., data were simulated for each locus with the same number of base pairs and locus-specific mutational models). The results of the study show that ESPs can be computed using the coalescent-based approach long before reciprocal monophyly has been achieved, and that these statistical estimates are accurate. This contrasts with analyses of the empirical data collected in Melanoplus and simulated data based on concatenation of multiple loci, for which the incomplete lineage sorting of recently diverged species posed significant problems. The strengths and potential challenges associated with incorporating an explicit model of gene-lineage coalescence into the phylogenetic procedure to obtain an ESP, as illustrated by application to Melanoplus, versus concatenation and consensus approaches are discussed. This study represents a fundamental shift in how species relationships are estimated - the relationship between the gene trees and the species phylogeny is modeled probabilistically rather than equating gene trees with a species tree.

Postglacial expansion and genome subdivision in the European grasshopper Chorthippus parallelus

A noncoding nuclear DNA marker sequence (Cpn1-1) was used to investigate subdivision in the grasshopper Chorthippus parallelus and deduce postglacial expansion patterns across its species range in Europe. Investigation of the spatial distribution of 71 Cpn1-1 haplotypes and estimation of levels of genetic differentiation (KST values) between populations and geographic regions provided evidence for subdivision of C. parallelus into at least five major geographic regions and indicated that the French form of C. parallelus originated after range expansion from a Balkan refugium. Further evidence for subdivision of C. parallelus between Italy and northern Europe suggests that the Alps may have formed a significant barrier to gene flow in this grasshopper.

Tests of pleistocene speciation in montane grasshoppers (genus Melanoplus) from the sky islands of western North America

There has a been a resurgence of debate on whether the Pleistocene glaciations inhibited speciation. This study tests a model of Pleistocene speciation, estimating the phylogenetic relationships and divergence times of 10 species of montane grasshoppers, genus Melanoplus, using 1300 bp of the mitochondrial gene cytochrome oxidase I (COI). Based on average pairwise distances (corrected for multiple substitutions using Kimura's two-parameter model), all species appear to have originated within the Pleistocene. Sequence divergences between species are less than 4%, corresponding to divergence times less than 1.7 million years ago. Branching patterns among the species suggest that speciation was associated with more than one glacial-interglacial cycle. A likelihood-ratio test rejected a model of simultaneous species origins, the predicted branching pattern if species arose from the fragmentation of a widespread ancestor. These grasshoppers live in an area that was previously glaciated and, as inhabitants of the northern Rocky Mountain sky islands, underwent latitudinal and probably altitudinal shifts in distribution in response to climatic fluctuations. Given the repeated distributional shifts and range overlap of the taxa, there most likely has been ample opportunity for population mixing. However, despite periodic glacial cycles, with more than 10 major glaciations over the past million years and climatic fluctuations over as short a time scale as 10(3) to 10(4) years, the dynamic history of the Pleistocene did not preclude speciation. Although relationships among some taxa remain unresolved, these grasshopper species, even with their recent origins, exhibit genetic coherence and monophyletic or paraphyletic gene trees. The frequency of glacial cycles suggests that the speciation process must have been extremely rapid. These species of grasshoppers are morphologically very similar, differing primarily in the shape of the male genitalia. These characters are posited to be under sexual selection, may play an important role in reproductive isolation, and are known to diverge rapidly. This suggests the rapidity of evolution of reproductive isolation may determine whether species divergences occurred during the Pleistocene glaciations.

Shifting distributions and speciation: species divergence during rapid climate change

Questions about how shifting distributions contribute to species diversification remain virtually without answer, even though rapid climate change during the Pleistocene clearly impacted genetic variation within many species. One factor that has prevented this question from being adequately addressed is the lack of precision associated with estimates of species divergence made from a single genetic locus and without incorporating processes that are biologically important as populations diverge. Analysis of DNA sequences from multiple variable loci in a coalescent framework that (i) corrects for gene divergence pre-dating speciation, and (ii) derives divergence-time estimates without making a priori assumptions about the processes underlying patterns of incomplete lineage sorting between species (i.e. allows for the possibility of gene flow during speciation), is critical to overcoming the inherent logistical and analytical difficulties of inferring the timing and mode of speciation during the dynamic Pleistocene. Estimates of species divergence that ignore these processes, use single locus data, or do both can dramatically overestimate species divergence. For example, using a coalescent approach with data from six loci, the divergence between two species of montane Melanoplus grasshoppers is estimated at between 200,000 and 300,000 years before present, far more recently than divergence estimates made using single-locus data or without the incorporation of population-level processes. Melanoplus grasshoppers radiated in the sky islands of the Rocky Mountains, and the analysis of divergence between these species suggests that the isolation of populations in multiple glacial refugia was an important factor in promoting speciation. Furthermore, the low estimates of gene flow between the species indicate that reproductive isolation must have evolved rapidly for the incipient species boundaries to be maintained through the subsequent glacial periods and shifts in species distributions.

Identification, functional characterization and phylogenetic analysis of double stranded RNA degrading enzymes present in the gut of the desert locust, Schistocerca gregaria

RNA interference (RNAi) has become a widely used reverse genetics tool in eukaryotes and holds great potential to contribute to the development of novel strategies for insect pest control. While previous studies clearly demonstrated that injection of dsRNA into the body cavity of the desert locust, Schistocerca gregaria, is highly effective to induce gene silencing effects, we observed that the RNAi response is much less sensitive to orally delivered dsRNA. In line with this, we report on the presence of a potent dsRNA degrading activity in the midgut juice. Four different dsRNase sequences that belong to the DNA/RNA Non-specific Nuclease superfamily were retrieved from a transcriptome database of the desert locust. Surprisingly, we have found that, in the publicly available eukaryote nucleotide sequence databases, the presence of this group of enzymes is restricted to insects and crustaceans. Nonetheless, phylogenetic analyses predict a common origin of these enzymes with the Endonuclease G (EndoG) Non-specific Nucleases that display a widespread taxonomic distribution. Moreover, in contrast to the Sg-endoG transcript, the four Sg-dsRNase transcripts appear to be specifically expressed in the gut. Finally, by means of RNAi, we provide evidence for an important contribution of dsRNase2 to the dsRNA degrading activity that is present in the gut lumen of S. gregaria.

Final steps in juvenile hormone biosynthesis in the desert locust, Schistocerca gregaria

Two genes coding for enzymes previously reported to be involved in the final steps of juvenile hormone (JH) biosynthesis in different insect species, were characterised in the desert locust, Schistocerca gregaria. Juvenile hormone acid O-methyltransferase (JHAMT) was previously described to catalyse the conversion of farnesoic acid (FA) and JH acid to their methyl esters, methyl farnesoate (MF) and JH respectively. A second gene, CYP15A1 was reported to encode a cytochrome P450 enzyme responsible for the epoxidation of MF to JH. Additionally, a third gene, FAMeT (originally reported to encode a farnesoic acid methyltransferase) was included in this study. Using q-RT-PCR, all three genes (JHAMT, CYP15A1 and FAMeT) were found to be primarily expressed in the CA of the desert locust, the main biosynthetic tissue of JH. An RNA interference approach was used to verify the orthologous function of these genes in S. gregaria. Knockdown of the three genes in adult animals followed by the radiochemical assay (RCA) for JH biosynthesis and release showed that SgJHAMT and SgCYP15A1 are responsible for synthesis of MF and JH respectively. Our experiments did not show any involvement of SgFAMeT in JH biosynthesis in the desert locust. Effective and selective inhibitors of SgJHAMT and SgCYP15A1 would likely represent selective biorational locust control agents.

A feasibility study of the use of random amplified polymorphic DNA in the population genetics and systematics of grasshoppers

Single, short primers of arbitrary nucleotide sequence were used in polymerase chain reactions to amplify regions of DNA isolated from several melanopline and oedipodine grasshoppers collected from local Saskatchewan populations. This represents one of the first applications of the method, called randomly amplified polymorphic DNA (or RAPD), to natural populations. Twenty-four different oligonucleotide primers, nine nucleotides in length, yielded clear and reproducible bands corresponding to amplified products and separable by agarose gel electrophoresis. On average, about 8.1 bands (range 0-17) were obtained per primer per individual. The mean percent similarity between band profiles of conspecific individuals was 51.2%, whereas the mean value for individuals representing different species or genera was 35.0%. Clearly, greater numbers of insects and primers will be required to achieve a satisfactory level of phylogenetic resolution. Given RAPDs technical advantages and ease of execution, however, this should not be problematic to the molecular systematist.

The complete mitochondrial genomes of two band-winged grasshoppers, Gastrimargus marmoratus and Oedaleus asiaticus

BACKGROUND

The two closely related species of band-winged grasshoppers, Gastrimargus marmoratus and Oedaleus asiaticus, display significant differences in distribution, biological characteristics and habitat preferences. They are so similar to their respective congeneric species that it is difficult to differentiate them from other species within each genus. Hoppers of the two species have quite similar morphologies to that of Locusta migratoria, hence causing confusion in species identification. Thus we determined and compared the mitochondrial genomes of G. marmoratus and O. asiaticus to address these questions.

RESULTS

The complete mitochondrial genomes of G. marmoratus and O. asiaticus are 15,924 bp and 16,259 bp in size, respectively, with O. asiaticus being the largest among all known mitochondrial genomes in Orthoptera. Both mitochondrial genomes contain a standard set of 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes and an A+T-rich region in the same order as those of the other analysed caeliferan species, but different from those of the ensiferan species by the rearrangement of trnD and trnK. The putative initiation codon for the cox1 gene in the two species is ATC. The presence of different sized tandem repeats in the A+T-rich region leads to size variation between their mitochondrial genomes. Except for nad2, nad4L, and nad6, most of the caeliferan mtDNA genes exhibit low levels of divergence. In phylogenetic analyses, the species from the suborder Caelifera form a monophyletic group, as is the case for the Ensifera. Furthermore, the two suborders cluster as sister groups, supporting the monophyly of Orthoptera.

CONCLUSION

The mitochondrial genomes of both G. marmoratus and O. asiaticus harbor the typical 37 genes and an A+T-rich region, exhibiting similar characters to those of other grasshopper species. Characterization of the two mitochondrial genomes has enriched our knowledge on mitochondrial genomes of Orthoptera.

mtDNA phylogeography and postglacial patterns of subdivision in the meadow grasshopper Chorthippus parallelus

A 300 bp portion of the mitochondrial cytochrome oxidase subunit I (COI) gene was used to investigate the intraspecific genetic structure of the European meadow grasshopper Chorthippus parallelus. Levels of genetic subdivision between geographical regions in Europe were assessed using the KST statistic and revealed patterns indicative of the postglacial history of this organism. Northern European populations are shown to share a very recent common ancestor with, and hence originate from, a Balkan expansion. Genetic distances between these areas and both southern Italy and central Spain are shown to be approximately equal, even though only the Spanish form is recognized as a distinct subspecies. Distance estimates indicate that the common ancestor of the two subspecies lived more than one glacial cycle ago, and the refugial populations have probably been diverging in isolation for five or six glacial cycles (approximately equal to 550,000 years). Comparisons are made to the analysis of a similar data set using an anonymous nuclear DNA marker (Cooper et al., 1995). Although the structure revealed is generally very similar, differences in the location of transition zones between different genetic forms of C. parallelus may reflect the different historical assortment of these molecules.

Phylogenomic analysis sheds light on the evolutionary pathways towards acoustic communication in Orthoptera

Acoustic communication is enabled by the evolution of specialised hearing and sound producing organs. In this study, we performed a large-scale macroevolutionary study to understand how both hearing and sound production evolved and affected diversification in the insect order Orthoptera, which includes many familiar singing insects, such as crickets, katydids, and grasshoppers. Using phylogenomic data, we firmly establish phylogenetic relationships among the major lineages and divergence time estimates within Orthoptera, as well as the lineage-specific and dynamic patterns of evolution for hearing and sound producing organs. In the suborder Ensifera, we infer that forewing-based stridulation and tibial tympanal ears co-evolved, but in the suborder Caelifera, abdominal tympanal ears first evolved in a non-sexual context, and later co-opted for sexual signalling when sound producing organs evolved. However, we find little evidence that the evolution of hearing and sound producing organs increased diversification rates in those lineages with known acoustic communication.

Relationships between species richness, evenness, and abundance in a southwestern savanna

Species richness and evenness are components of biological diversity that may or may not be correlated with one another and with patterns of species abundance. We compared these attributes among flowering plants, grasshoppers, butterflies, lizards, summer birds, winter birds, and rodents across 48 plots in the grasslands and mesquite-oak savannas of southeastern Arizona. Species richness and evenness were uncorrelated or weakly negatively correlated for each taxonomic group, supporting the conclusion that richness alone is an incomplete measure of diversity. In each case, richness was positively correlated with one or more measures of abundance. By contrast, evenness usually was negatively correlated with the abundance variables, reflecting the fact that plots with high evenness generally were those where all species present were about equally uncommon. Therefore richness, but not evenness, usually was a positive predictor of places of conservation value, if these are defined as places where species of interest are especially abundant. Species diversity was more positively correlated with evenness than with richness among grasshoppers and flowering plants, in contrast to the other taxonomic groups, and the positive correlations between richness and abundance were comparatively weak for grasshoppers and plants as well. Both of these differences can be attributed to the fact that assemblages of plants and grasshoppers were numerically dominated by small subsets of common species (grasses and certain spur-throated grasshoppers) whose abundances differed greatly among plots in ways unrelated to species richness of the groups as a whole.

Climate-driven geographic distribution of the desert locust during recession periods: Subspecies' niche differentiation and relative risks under scenarios of climate change

The desert locust is an agricultural pest that is able to switch from a harmless solitarious stage, during recession periods, to swarms of gregarious individuals that disperse long distances and affect areas from western Africa to India during outbreak periods. Large outbreaks have been recorded through centuries, and the Food and Agriculture Organization keeps a long-term, large-scale monitoring survey database in the area. However, there is also a much less known subspecies that occupies a limited area in Southern Africa. We used large-scale climatic and occurrence data of the solitarious phase of each subspecies during recession periods to understand whether both subspecies climatic niches differ from each other, what is the current potential geographical distribution of each subspecies, and how climate change is likely to shift their potential distribution with respect to current conditions. We evaluated whether subspecies are significantly specialized along available climate gradients by using null models of background climatic differences within and between southern and northern ranges and applying niche similarity and niche equivalency tests. The results point to climatic niche conservatism between the two clades. We complemented this analysis with species distribution modeling to characterize current solitarious distributions and forecast potential recession range shifts under two extreme climate change scenarios at the 2050 and 2090 time horizon. Projections suggest that, at a global scale, the northern clade could contract its solitarious recession range, while the southern clade is likely to expand its recession range. However, local expansions were also predicted in the northern clade, in particular in southern and northern margins of the current geographical distribution. In conclusion, monitoring and management practices should remain in place in northern Africa, while in Southern Africa the potential for the subspecies to pose a threat in the future should be investigated more closely.

Organization of the Hox gene cluster in the grasshopper, Schistocerca gregaria

The conserved organization of the Hox genes throughout the animal kingdom has become one of the major paradigms of evolutionary developmental biology. We have examined the organization of the Hox genes of the grasshopper, Schistocerca gregaria. We find that the grasshopper Hox cluster is over 700 kb long, and is not split into equivalents of the Antennapedia complex and the bithorax complex of Drosophila melanogaster. SgDax and probably also Sgzen, the grasshopper homologues of fushi-tarazu (ftz) and Zerknüllt (zen), respectively, are also in the cluster, showing that the non-homeotic Antp-class genes, "accessory genes," are an ancient feature of insect Hox clusters.

Ancient trans-Atlantic flight explains locust biogeography: molecular phylogenetics of Schistocerca

The desert locust (Schistocerca gregaria) has been an important agricultural pest at least since biblical times. Although the ecology, physiology and behaviour of this insect species have been well characterized, its biogeographical origins and evolutionary history are more obscure. Schistocerca gregaria occurs throughout Africa, the Middle East and Western Asia, but all other species in the genus Schistocerca are found in the New World. Because S. gregaria has the capacity for extreme long-distance movement associated with swarming behaviour, dispersal may have played an important role in determining current distribution patterns. Some authors have argued that S. gregaria is the product of an eastward trans-Atlantic dispersal from North America to Africa; others consider it more likely that the New World taxa are the product of westward dispersal from Africa. Here, we present a mitochondrial DNA phylogeny of Schistocerca species that supports the monophyly of New World species (including the Galapagos endemic Halmenus) relative to S. gregaria. In concert with observed patterns of molecular divergence, and in contrast to previous morphological studies, our analysis indicates a single trans-Atlantic flight from Africa to South America, followed by extensive speciation and ecological divergence in the New World.

Digital particle image velocimetry measurements of the downwash distribution of a desert locust Schistocerca gregaria

Actuator disc models of insect flight are concerned solely with the rate of momentum transfer to the air that passes through the disc. These simple models assume that an even pressure is applied across the disc, resulting in a uniform downwash distribution. However, a correction factor, k, is often included to correct for the difference in efficiency between the assumed even downwash distribution, and the real downwash distribution. In the absence of any empirical measurements of the downwash distribution behind a real insect, the values of k used in the literature have been necessarily speculative. Direct measurement of this efficiency factor is now possible, and could be used to compare the relative efficiencies of insect flight across the Class. Here, we use Digital Particle Image Velocimetry to measure the instantaneous downwash distribution, mid-downstroke, of a tethered desert locust (Schistocerca gregaria). By integrating the downwash distribution, we are thereby able to provide the first direct empirical measurement of k for an insect. The measured value of k = 1.12 corresponds reasonably well with that predicted by previous theoretical studies.

Neurotoxic and neurobehavioral effects of kynurenines in adult insects

Kynurenines are endogenous metabolites of tryptophan, which are studied extensively in vertebrates with respect to their etiological role in the pathology of various neurodegenerative disorders. In insects, metabolites of the kynurenic pathway are present in peak concentrations in the hemolymph of holometabolic species during pupation and just before eclosion. Unlike in larvae, these compounds cause severe motor dysfunction in adult species. Adult flesh flies were injected with various concentrations of these endogenous toxins and the effects on motor function were assessed. For tryptophan, L-kynurenine, 3-hydroxy-kynurenine, and anthranilic acid, the effects ranged from reversible to irreversible motor dysfunction, to instant paralysis and death. 3-Hydroxy-anthranilic acid could induce a tetanus like spasm of the wings. Tryptophan, 3-hydroxykynurenine, and 3-hydroxy-anthranilic acid were toxic to primary cultures of insect neurons. It is possible that some of these metabolites have a distinct role in larvae during the apoptotic events related to neurometamorphosis.

Antioxidants in grasshoppers: higher levels defend the midgut tissues of a polyphagous species than a graminivorous species

Polyphagous grasshoppers consume plants that contain markedly greater amounts of potentially prooxidant allelochemicals than the grasses eaten by graminivorous grasshoppers. Therefore, levels of antioxidant defenses maintained by these herbivores might be expected to differ in accordance with host plant ranges. Antioxidant levels were compared in midgut tissues and gut fluids of a polyphagous grasshopper. Melanoplus sanguinipes, and a graminivorous grasshopper, Aulocara ellioti. Glutathione concentrations in midgut tissues of M. sanguinipes (10.6 mM) are among the highest measured in animal tissues and are twice as high as those in A. ellioti. Alpha-tocopherol levels are 126% higher in midgut tissues of M. sanguinipes than in those of A. ellioti, and remain at high levels when M. sanguinipes is reared on plants containing a wide range of alpha-tocopherol concentrations. Ascorbate levels in M. sanguinipes midgut tissues are 27% higher than in those of A. ellioti, but vary depending on the host plant on which they are reared. Midgut fluids of both species contain elevated levels of glutathione, as well as large (millimolar) amounts of undetermined antioxidants that are produced in the insects. The consumption of tannic acid decreases ascorbate concentrations in midgut tisssues and gut fluids of A. ellioti but has no effect on ascorbate levels in M. sanguinipes. The results of this study provide the first measurements of antioxidants in grasshoppers and suggest that the maintenance of high levels of antioxidants in the midgut tissues of polyphagous grasshoppers might effectively protect them from oxidative stress.

A molecular biogeographic analysis of the relationship between North American melanoploid grasshoppers and their Eurasian and South American relatives

The Melanoplinae constitute one of the two largest subfamilies of Acrididae. Distributed mainly throughout the New World and parts of Eurasia, this group of grasshoppers includes over 100 genera and 800 species. Over the past five decades there has been considerable speculation on the origins of North and South American taxa. The most favored hypothesis proposes an ancient division of Laurasian taxa accompanying the separation of North America and Eurasia, with subsequent radiations within those continents, followed by a recent incursion of Nearctic melanoplines into the southern hemisphere with the establishment of the Isthmus of Panama. This research tests that scenario by phylogenetic analysis using as characters portions of five mitochondrial gene sequences, totaling 2285 bp. Three tree-building methods, maximum-parsimony, neighbor-joining, and maximum-likelihood, strongly support the different view that melanopline grasshoppers originated somewhere in the Americas and spread to the Old World. The feasibility of these findings is discussed within a geological context.

The importance of the ontogenetic niche in resource-associated divergence: evidence from a generalist grasshopper

Geographic variation in resource use can produce locally adapted populations that exhibit genetic and phenotypic divergence. In the bird-winged grasshopper (Schistocerca emarginata = [lineata]), we investigate whether genetic data exist in accordance with geographic variation in resource (host) use and coloration. In Texas, juvenile grasshoppers feed almost exclusively on one of two host plants, Rubus trivialis (Rosaceae) or Ptelea trifoliata (Rutaceae), whereas adults of both forms are dietary generalists and consume many plants from unrelated families. Along with differences in juvenile feeding, differences in a density-dependent color polyphenism are concordant with genetic (mitochondrial DNA) variation among eight populations of the bird-winged grasshopper. Forms feeding on R. trivialis and those feeding on P. trifoliata represent monophyletic lineages according to phylogenetic analysis and maximum-likelihood tests of two alternative phylogeographic hypotheses for geographic variation in host use. Character-state optimization of host-plant acceptability on a phylogeny containing S. emarginata and outgroup taxa indicates that populations consuming R. trivialis gave rise to populations consuming P. trifoliata. Juvenile grasshoppers that consume P. trifoliata acquire deterrence against predation, suggesting that enemy-free space facilitated this host shift. In extant populations, adaptations stemming from alternative resource use during ontogeny present possible barriers to gene exchange. This study represents the first demonstration of resource-associated divergence in an otherwise generalist insect that exhibits temporal variation in resource use, characterized as developmental changes in host specialization. Our findings suggest that exploitation of different resources may have unexplored significance for generalist species that compartmentalize specialization to particular life stages.

Out of South America? Additional evidence for a southern origin of melanopline grasshoppers

Molecular phylogenetic methods provide a useful tool for critically evaluating competing biogeographic hypotheses. This paper focuses on conjectures at the intercontinental level. An earlier phylogeographic study of the grasshopper subfamily Melanoplinae examined relationships among taxa occupying the Americas and Eurasia. The objective was to test which of three scenarios best described the subfamily's origins and patterns of intercontinental movement. It was tentatively proposed that the melanopline grasshoppers evolved somewhere in the Americas and spread to the Old World. The present article, by including additional Neotropical species, not only upholds that conjecture, but is able to identify South America as the site of origin. Phylogenetic analysis indicates a direction of dispersal: South America-->North America-->Eurasia, that is opposite to what was previously believed. This study also provides, for the first time, a preliminary molecular phylogeny of selected South American melanopline genera.

MicroRNA-dependent development revealed by RNA interference-mediated gene silencing of LmDicer1 in the migratory locust

MicroRNAs (miRNAs) are small noncoding RNAs, which participate in many biological processes. The small RNA transcriptome in the migratory locust has been characterized and 50 conserved miRNA families and 185 potential locust-specific miRNA family candidates have been identified using high-throughput sequencing. However, it is unclear whether miRNAs influence a wide variety of locusts' biological processes, such as growth or development. In insects, Dicer1 ribonuclease transforms miRNA precursors into mature miRNAs. Thus, using systemic RNA interference (RNAi) to silence the expression of Dicer1 in the migratory locust, Locusta migratoria, we reduced miRNA contents in the locust and disrupted two types of molt (nymph-nymph, and nymph-adult). The RNAi of LmDicer1 also resulted in a high mortality in L. migratora. Our study revealed that LmDicer1 was essential for miRNA regulation and development of L. migratoria. These results further support our notion that LmDicer1 could serve as an excellent target for developing novel strategies for controlling this important insect pest.

Transcript profiling of pacifastin-like peptide precursors in crowd- and isolated-reared desert locusts

Locusts have fascinated researchers for several decades, because they have the remarkable ability to undergo phase transition from the harmless solitary to the swarm-forming gregarious phase. However, the physiological and endocrine mechanisms, underlying phase polymorphism, are only partially unravelled. Nevertheless, besides the 'classical' hormones, pacifastin-related peptides have been suggested to play a role in phase transition. Here, we present the first quantitative and comparative analysis of locust transcripts, in particular pacifastin-related precursor (SGPP-1-3) mRNAs, between isolated-reared (solitary) and crowd-reared (gregarious) desert locusts, revealing a phase-dependent transcriptional regulation of the corresponding genes. While the SGPP-1 and SGPP-3 transcripts were most abundant in fat body from crowd-reared males, corresponding to significantly higher levels than in isolated-reared males, the SGPP-2 transcript was detected most abundantly in brain from crowd-reared male locusts. Furthermore, SGPP-2 transcript levels in brain, testes, fat body, and accessory glands from crowd-reared males significantly exceeded the levels in solitary locusts.

A molecular phylogeographic perspective on a fifty-year-old taxonomic issue in grasshopper systematics

This paper addresses a decades-old taxonomic controversy surrounding a species in the grasshopper subfamily Melanoplinae. Melanoploid grasshoppers fall into two tribes, the Nearctic-restricted Melanoplini and the Holarctically distributed Podismini. The current view regarding one member, Bohemanella frigida, is that it belongs to the latter tribe and that North American populations were established by dispersal from Eurasia via the Bering Land Bridge. Over the past 50 years, this opinion has changed a few times; this species was once regarded as part of the tribe Melanoplini and, as such, deemed to be the only Holarctically distributed Orthopteran insect with New World antecedents. A molecular phylogenetic study of this species was thus performed to verify its phylogenetic position and to establish a probable direction of dispersal. Portions of three mitochondrial genes (cyt b, COII, and ND2) were sequenced and phylogenetically analysed using weighted and unweighted parsimony, neighbour-joining, and maximum likelihood methods. Support for the inclusion of B. frigida within the tribe Melanoplini and the use of its original name, Melanoplus frigidus, was strong using all methods. Placement in the tribe Melanoplini leads to an acceptance of an earlier hypothesis regarding direction of dispersal across the Bering Land Bridge, making this grasshopper a unique case in orthopteran insects in this respect.

Geographic distribution of Robertsonian fusions in Dichroplus pratensis (Melanoplinae, Acrididae): the central-marginal hypothesis reanalysed

The South American acridid grasshopper Dichroplus pratensis (Melanoplinae) is polymorphic and polytypic for a system of Robertsonian fusions across most of its distribution range. Several chromosomal races and hybrid zones have been identified. Since the fusions exert profound inter- and intrachromosomal effects on recombination, it has been proposed that these fusion systems could preserve sets of adaptive gene combinations in central (ecologically optimal) populations, and that marginal populations would show lower levels of chromosomal polymorphism and thus, increased recombination potential to cope with the harsher conditions of marginal habitats. In this paper, we describe a series of central and marginal populations which display typical features of each type and also, identify for the first time completely standard telocentric marginal populations at the southernmost and northernmost limits of the species distribution and show, as expected, the highest recombination indices. However, this modification of chiasma patterns, is only true of the male sex since females of both standard and Robertsonian populations show low chiasma frequencies. The hypothesis that higher levels of recombination would be adaptive in marginal populations is reinforced by the fact that the latter also show unusually high frequencies of B chromosomes some of which increase mean cell chiasma frequency.