Dispersal differences predict population genetic structure in Mormon crickets

Development of RNAi Methods for the Mormon Cricket, Anabrus simplex (Orthoptera: Tettigoniidae)

Mormon crickets are a major rangeland pest in the western United States and are currently managed by targeted applications of non-specific chemical insecticides, which can potentially have negative effects on the environment. In this study, we took the first steps toward developing RNAi methods for Mormon crickets as a potential alternative to traditional broad-spectrum insecticides. To design an effective RNAi-based insecticide, we first generated a de novo transcriptome for the Mormon cricket and developed dsRNAs that could silence the expression of seven housekeeping genes. We then characterized the RNAi efficiencies and time-course of knockdown using these dsRNAs, and assessed their ability to induce mortality. We have demonstrated that it is possible to elicit RNAi responses in the Mormon cricket by injection, but knockdown efficiencies and the time course of RNAi response varied according to target genes and tissue types. We also show that one of the reasons for the poor knockdown efficiencies could be the presence of dsRNA-degrading enzymes in the hemolymph. RNAi silencing is possible in Mormon cricket, but more work needs to be done before it can be effectively used as a population management method.

Elevational Changes in Mormon Cricket Life Histories: Minimum Temperature for Nymphal Growth Declines With Elevation

As the mean temperature and the duration of the growing season decline with elevation, growth of immature insects should initiate at a lower temperature, but it should also be faster to complete development prior to season's end. Although flightless, Mormon crickets migrate in large aggregations across broad spatial and elevational distances that might limit adaptations to local environments. In addition, selection to be active at cooler temperatures might limit selection to maximize growth rate. I measured growth rate in controlled environments for nymphs from three populations that vary in altitude (87-2,688 m) but are similar in latitude (43.2-45.7°N). Growth rate increased significantly with mean rearing temperature between 22 and 30°C. The intercept of the regression of growth rate on temperature increased with elevation, whereas the slope did not change significantly. For any given rearing temperature, growth rate increased with elevation, which suggests that selection to initiate growth at cooler temperatures did not compromise growth rate. Body mass did not differ between the two lower elevations, whereas the highest elevation population had smaller hatchlings and adults. Critical thermal minimum (base temperature) declined with elevation (0.7°C per 1,000 m), and the degree days were 509 across all elevations. For pest management, a base temperature from midelevation of 15.3°C (60°F) and growing degree days of 509 (equivalent to 916 Fahrenheit-based degree days) are reasonable estimates for applications from sea level to 2,700 m.

Taxonomic identification and biological traits of Platystethynium triclavatum (Donev & Huber, 2002), comb. n. (Hymenoptera, Mymaridae), a newly recorded egg parasitoid of the Italian endemic pest Barbitistes vicetinus (Orthoptera, Tettigoniidae)

The little known fairyfly (Hymenoptera, Mymaridae), Platystethynium (Platystethynium) triclavatum (Donev & Huber, 2002), comb. n. from Pseudocleruchus Donev & Huber, 2002, is newly recorded as an egg parasitoid of Barbitistes vicetinus Galvagni & Fontana, 1993 (Orthoptera, Tettigoniidae). This bush-cricket is endemic to northeastern Italy (mainly Euganean Hills of Veneto Region), where it has recently become an economically significant agricultural and forest pest. Data on discovery, distribution, and some remarkable biological traits of this gregarious egg parasitoid are presented. Its identification and availability of many well-preserved fresh specimens have made possible to re-define Pseudocleruchus Donev & Huber, 2002 syn. n., with type and the only described species Pseudocleruchus triclavatus Donev & Huber, 2002, as a synonym of Platystethynium Ogloblin, 1946 and its nominate subgenus, P. (Platystethynium), and also to describe the brachypterous male of P. (Platystethynium) triclavatum. It is the first known male for the entire genus. Enlarged mandibles of the megacephalous males are used to chew holes in the hard chorion of the host egg, allowing fully winged females, whose mandibles are strongly reduced and do not cross over, to emerge after mating with the males inside it. Up to 136 individual parasitoids (about 77 on average) can hatch from a single egg of B. vicetinus, with their sex ratio being strongly female biased (80–97% females per egg).

Biased dispersal of Metrioptera bicolor, a wing dimorphic bush-cricket

In the highly fragmented landscape of central Europe, dispersal is of particular importance as it determines the long-term survival of animal populations. Dispersal not only secures the recolonization of patches where populations went extinct, it may also rescue small populations and thus prevent local extinction events. As dispersal involves different individual fitness costs, the decision to disperse should not be random but context-dependent and often will be biased toward a certain group of individuals (e.g., sex- and wing morph-biased dispersal). Although biased dispersal has far-reaching consequences for animal populations, immediate studies of sex- and wing morph-biased dispersal in orthopterans are very rare. Here, we used a combined approach of morphological and genetic analyses to investigate biased dispersal of Metrioptera bicolor, a wing dimorphic bush-cricket. Our results clearly show wing morph-biased dispersal for both sexes of M. bicolor. In addition, we found sex-biased dispersal for macropterous individuals, but not for micropters. Both, morphological and genetic data, favor macropterous males as dispersal unit of this bush-cricket species. To get an idea of the flight ability of M. bicolor, we compared our morphological data with that of Locusta migratoria and Schistocerca gregaria, which are very good flyers. Based on our morphological data, we suggest a good flight ability for macropters of M. bicolor, although flying individuals of this species are seldom observed.

Range wide molecular data and niche modeling revealed the Pleistocene history of a global invader (Halyomorpha halys)

Invasive species’ Pleistocene history contains much information on its present population structure, dispersability and adaptability. In this study, the Pleistocene history of a global invasive pest (Brown Marmorated Stink Bug BMSB, Halyomorpha halys) was unveiled using the coupled approach of phylogeography and ecological niche modelling. Rangewide molecular data suggests that the Taiwan and other native populations had diverged in mid-Pleistocene. In mainland China, the native BMSB did not experience population contraction and divergence during last glacial, but persisted in interconnected populations. Combined Bayesian Skyline Plot (BSP) and niche modelling revealed a rapid expansion occurred during the transition of Last Inter Glacial (LIG) to Last Glacial Maximum (LGM). High genetic diversity and multi-reticular haplotypes network exist in the original sources populations of BMSB invasion in northern China. They were speculated to be colonized from the central China, with many derived haplotypes evolved to adapt the novel environment. The ENM future prediction suggest that BMSB may expand northward to higher latitudes in the US and Europe, because of its high invasive ability, together with the available suitable climate space there.

Ecological differentiation and habitat unsuitability maintaining a ground beetle hybrid zone

Exogenous selection via interactions between organisms and environments may influence the dynamics of hybrid zones between species in multiple ways. Two major models of a hybrid zone allowed us to hypothesize that environmental conditions influence hybrid zone dynamics in two ways. In the first model, an environmental gradient determines the mosaic distribution at the boundary between ecologically differentiated species (mosaic hybrid zone model). In the second model, a patch of unsuitable habitat traps a hybrid zone between species whose hybrids are unfit (tension zone model). To test these, we examined the environmental factors influencing the spatial structure of a hybrid zone between the ground beetles Carabus maiyasanus and C. iwawakianus using GIS‐based quantification of environmental factors and a statistical comparison of species distribution models (SDMs). We determined that both of the hypothetical processes can be important in the hybrid zone. We detected interspecific differences in the environmental factors in presence localities and their relative contribution in SDMs. SDMs were not identical between species even within contact areas, but tended to be similar within the range of each species. These results suggest an association between environments and species, and provide evidence that ecological differentiation between species plays a role in the maintenance of the hybrid zone. Contact areas were characterized by a relatively high temperature, low precipitation, and high topological wetness. Thus, the contact areas were regarded as being located in an unsuitable habitat with a drier climate, where those populations are likely to occur in patches with limited precipitation concentrated. A comparison of spatial scales suggests that exogenous selection via environmental factors may be weaker than endogenous selection via genitalic incompatibility.

Consequences of extensive habitat fragmentation in landscape-level patterns of genetic diversity and structure in the Mediterranean esparto grasshopper

Anthropogenic habitat fragmentation has altered the distribution and population sizes in many organisms worldwide. For this reason, understanding the demographic and genetic consequences of this process is necessary to predict the fate of populations and establish management practices aimed to ensure their viability. In this study, we analyse whether the spatial configuration of remnant semi-natural habitat patches within a chronically fragmented landscape has shaped the patterns of genetic diversity and structure in the habitat-specialist esparto grasshopper (Ramburiella hispanica). In particular, we predict that agricultural lands constitute barriers to gene flow and hypothesize that fragmentation has restricted interpopulation dispersal and reduced local levels of genetic diversity. Our results confirmed the expectation that isolation and habitat fragmentation have reduced the genetic diversity of local populations. Landscape genetic analyses based on circuit theory showed that agricultural land offers ∽1000 times more resistance to gene flow than semi-natural habitats, indicating that patterns of dispersal are constrained by the spatial configuration of remnant patches of suitable habitat. Overall, this study shows that semi-natural habitat patches act as corridors for interpopulation gene flow and should be preserved due to the disproportionately large ecological function that they provide considering their insignificant area within these human-modified landscapes.

Phylogeography and Population Genetic Structure of Amur Grayling Thymallus grubii in the Amur Basin

Amur grayling, Thymallus grubii, is an important economic cold freshwater fish originally found in the Amur basin. Currently, suffering from loss of habitat and shrinking population size, T. grubii is restricted to the mountain river branches of the Amur basin. In order to assess the genetic diversity, population genetic structure and infer the evolutionary history within the species, we analysised the whole mitochondrial DNA control region (CR) of 95 individuals from 10 rivers in China, as well as 12 individuals from Ingoda/Onon and Bureya River throughout its distribution area. A total of 64 variable sites were observed and 45 haplotypes were identified excluding sites with gaps/missing data. Phylogenetic analysis was able to confidently predict two subclade topologies well supported by maximum-parsimony and Bayesian methods. However, basal branching patterns cannot be unambiguously estimated. Haplotypes from the mitochondrial clades displayed local homogeneity, implying a strong population structure within T. grubii. Analysis of molecular variance detected significant differences among the different geographical rivers, suggesting that T. grubii in each river should be managed and conserved separately.

Genetic diversity of Odontobutis potamophila from different geographic populations inferred from mtDNA control region

Odontobutis potamophila is a Chinese endemic species and an economically important fishery resource in the Yangtze River. The genetic variability of O. potamophila was studied based on the sequence analysis of mitochondrial DNA control region from 150 individuals of five geographical populations including from Dangtu (n=30), Sheyang (n=30), Yuyao (n=30), Tai Lake nearby Dongxishan (n=30) and Minjiang (n=30). Among five populations, the genetic distance between Minjiang population and other populations (0.1186-0.1223) was larger than that among four populations except for Minjiang (0.0015-0.0198). In addition, 23 haplotypes were obtained and each population had special haplotypes. The samples from five sites had high haplotype diversity (0.80510) and low nucleotide diversity (0.04028). Through Tajima's D and Fu's F neutral testing and mismatch distribution test among all geographical populations, O. potamophila did not undergo recent population expansion. During the population evolution, O. potamophila experienced a balanced selection function and maintained a stable state and population size. Moreover, the haplotype Neighbor-Joining (NJ) tree was separated two haplotype groups. The NJ tree, TCS network and median-joining network could clearly separate the haplotypes of the specimens from different areas. Analysis of molecular variance and pairwise FST revealed an obvious genetic differentiation among different geographical populations, suggesting that O. potamophila in different geographical populations should be managed and conserved separately.

Age- and density-dependent prophylaxis in the migratory, cannibalistic Mormon cricket Anabrus simplex (Orthoptera: Tettigoniidae)

As a result of the increased potential for disease transmission, insects are predicted to show an increased constitutive immunity when crowded. Cannibalistic aggressive interactions further increase the risk of wounding and pathogen transmission in crowds. Nymphal Mormon crickets Anabrus simplex Haldeman were collected in Montana and reared in the laboratory either solitarily or at densities similar to that experienced by Mormon crickets in migratory bands. As teneral adults, solitarily-reared Mormon crickets tended to have greater phenoloxidase activity than those reared in groups. Sampling enzyme activity a second time when the adults were nearing reproductive maturity, group-reared Mormon crickets had elevated levels of prophenoloxidase and encapsulated foreign objects faster than solitarily-reared insects. Rearing density did not have a significant effect on either the darkness of the cuticle or antibacterial activity. This is the first report of age-related responses of adult insect immunity to crowding.

A comparative analysis of fine-scale genetic structure in three closely related syntopic species of the grasshopper genus Calliptamus

Landscape analysis and genetics can allow a better understanding of grasshoppers for which ecology is not very well known. We analysed landscape changes between 1990 and 2006 at two areas from southern France where three grasshopper species ( Calliptamus italicus (L., 1758), Calliptamus wattenwylianus Pantel, 1896, and Calliptamus barbarus (Costa, 1836)) occur. We then applied microsatellite markers to the study of 1200 georeferenced samples collected over both areas. We used a recent Bayesian clustering method with correlated allele frequencies to detect weak population genetic structure. We found evidence of breaks in gene flow only in C. wattenwylianus, thought to be sedentary relative to its congenerics. By using different allele frequency models and prior information to different levels of genetic differentiation for our six real data sets, our study also informs on the ability of the newly available Bayesian clustering methods model to detect weak genetic structure in natural field populations.

Contrasting genetic structure in two co-distributed species of old world fruit bat

The fulvous fruit bat (Rousettus leschenaulti) and the greater short-nosed fruit bat (Cynopterus sphinx) are two abundant and widely co-distributed Old World fruit bats in Southeast and East Asia. The former species forms large colonies in caves while the latter roots in small groups in trees. To test whether these differences in social organization and roosting ecology are associated with contrasting patterns of gene flow, we used mtDNA and nuclear loci to characterize population genetic subdivision and phylogeographic histories in both species sampled from China, Vietnam and India. Our analyses from R. leschenaulti using both types of marker revealed little evidence of genetic structure across the study region. On the other hand, C. sphinx showed significant genetic mtDNA differentiation between the samples from India compared with China and Vietnam, as well as greater structuring of microsatellite genotypes within China. Demographic analyses indicated signatures of past rapid population expansion in both taxa, with more recent demographic growth in C. sphinx. Therefore, the relative genetic homogeneity in R. leschenaulti is unlikely to reflect past events. Instead we suggest that the absence of substructure in R. leschenaulti is a consequence of higher levels of gene flow among colonies, and that greater vagility in this species is an adaptation associated with cave roosting.

Differential threshold effects of habitat fragmentation on gene flow in two widespread species of bush crickets

Effects of habitat fragmentation on genetic diversity vary among species. This may be attributed to the interacting effects of species traits and landscape structure. While widely distributed and abundant species are often considered less susceptible to fragmentation, this may be different if they are small sized and show limited dispersal. Under intensive land use, habitat fragmentation may reach thresholds at which gene flow among populations of small-sized and dispersal-limited species becomes disrupted. Here, we studied the genetic diversity of two abundant and widespread bush crickets along a gradient of habitat fragmentation in an agricultural landscape. We applied traditional (G(ST), θ) and recently developed (G'ST', D) estimators of genetic differentiation on microsatellite data from each of twelve populations of the grassland species Metrioptera roeselii and the forest-edge species Pholidoptera griseoaptera to identify thresholds of habitat fragmentation below which genetic population structure is affected. Whereas the grassland species exhibited a uniform genetic structuring (G(ST) = 0.020-0.033; D = 0.085-0.149) along the whole fragmentation gradient, the forest-edge species' genetic differentiation increased significantly from D < 0.063 (G(ST) < 0.018) to D = 0.166 (G(ST) = 0.074), once the amount of suitable habitat dropped below a threshold of 20% and its proximity decreased substantially at the landscape scale. The influence of fragmentation on genetic differentiation was qualitatively unaffected by the choice of estimators of genetic differentiation but quantitatively underestimated by the traditional estimators. These results indicate that even for widespread species in modern agricultural landscapes fragmentation thresholds exist at which gene flow among suitable habitat patches becomes restricted.

Population fragmentation leads to isolation by distance but not genetic impoverishment in the philopatric Lesser Kestrel: a comparison with the widespread and sympatric Eurasian Kestrel

Population fragmentation is a widespread phenomenon usually associated with human activity. As a result of habitat transformation, the philopatric and steppe-specialist Lesser Kestrel Falco naumanni underwent a severe population decline during the last century that increased population fragmentation throughout its breeding range. In contrast, the ubiquitous Eurasian Kestrel Falco tinnunculus did not suffer such adverse effects, its breeding range still remaining rather continuous. Using microsatellites, we tested the effects of population fragmentation on large-scale spatial patterns of genetic differentiation and diversity by comparing these two sympatric and phylogenetically related species. Our results suggest that habitat fragmentation has increased genetic differentiation between Lesser Kestrel populations, following an isolation-by-distance pattern, while the population of Eurasian Kestrels is panmictic. Contrary to expectations, we did not detect significant evidence of reduced genetic variation or increased inbreeding in Lesser Kestrels. Although this study reports genetic differentiation in a species that has potential for long-distance dispersal but philopatry-limited gene flow, large enough effective population sizes and migration may have been sufficient to mitigate genetic depauperation. A serious reduction of genetic diversity in Lesser Kestrels would, therefore, only be expected after severe population bottlenecks following extreme geographic isolation.

Sex and differentiation: population genetic divergence and sexual dimorphism in Mexican goodeid fish

Genetic differentiation arises due to the interaction between natural and sexual selection, migration and genetic drift. A potential role of sexual selection in speciation has received much interest, although comparative studies are inconsistent in finding supporting evidence. A poorly tested prediction is that species subject to a higher intensity of sexual selection should show greater genetic differentiation amongst populations because females from these populations should be more choosy in mate choice. The Goodeinae is a group of endemic Mexican fishes in which female choice has driven some species to be morphologically sexually dimorphic, whereas others are relatively monomorphic. Here, we measured population divergence, using microsatellite loci, within four goodeid species which show contrasting levels of sexual dimorphism. We found higher levels of differentiation between populations of the more dimorphic species, implying less gene flow between populations. We also found evidence of higher levels of genetic differences between the sexes within populations of the dimorphic species, consistent with greater dispersal in males. Adjusted for geographic distance, the mean F(ST) for the dimorphic species is 0.25 compared with 0.16 for the less dimorphic species. We conclude that population differentiation is accelerated in more sexually dimorphic species, and that comparative phylogeography may provide a more powerful approach to detecting processes, such as an influence of sexual selection on differentiation, than broad-scale comparative studies.