Grasshopper Species Research Articles

The host and geographical range of the grasshopper pathogen Paranosema (Nosema) locustae revisited

Host and geographical ranges are updated for the microsporidium Paranosema locustae; this pathogen was developed in the USA as a long-term microbial control agent of grasshoppers. Currently known to be susceptible to P. locustae, either naturally or experimentally, are 121 species of Orthoptera from North and South America, Africa, Australia, China, and India. Most belong to the Acrididae (112), and within this family, to the Melanoplinae (36), Oedipodinae (35), and Gomphocerinae (35). The host range of P. locustae, as presently understood, is based largely on morphology and could change if molecular techniques revealed cryptic species. The North American isolate is not only the best studied, but the one established after its introduction into Argentina, and produced and used in China: it can be considered a generalist pathogen. As such, P. locustae may have the ability to alter, through differences in host susceptibilities, the structure of grasshopper assemblages in areas where it was not present before. Long-term careful monitoring of key grasshopper species in areas of pathogen introduction/establishment may reveal such effects.

Body Size and Phenology of the Grasshopper species Chorthippus brunneus with Variable Numbers of Female Instars (Orthoptera: Acrididae)

Body Size and Phenology of the Grasshopper species Chorthippus brunneus with Variable Numbers of Female Instars (Orthoptera: Acrididae)

A Comparative Cytogenetic Analysis between the Grasshopper Species Chromacris nuptialis and C. speciosa (Romaleidae): Constitutive Heterochromatin Variability and rDNA Sites

The chromosomes of Chromacris nuptialis and C. speciosa were comparatively analyzed using different cytogenetic techniques, in order to determine the level of karyotypic similarities and differences between the species. The results show similarities in chromosome number (2n=23,X0) and acrocentric morphology. In some C. nuptialis individuals meiotic irregularities were detected involving the L(2) bivalent. This bivalent was delayed and presented anaphasic bridges and other aberrations. Differences in constitutive heterochromatin (CH) patterns and composition were observed through C-banding and fluorochromes staining. Silver nitrate staining revealed a single medium nucleolar organizer regions (NORs) pair, per species. Differences were also observed in NORs location, which was pericentromeric in C. nuptialis and proximal in C. speciosa. FISH using an rDNA probe confirmed the existence of ribosomal sites coinciding with active regions visualized by silver nitrate. The possible implications of the karyotype differences observed between both species are discussed.

Nymphal RNAi: systemic RNAi mediated gene knockdown in juvenile grasshopper

BackgroundGrasshopper serves as important model system in neuroscience, development and evolution. Representatives of this primitive insect group are also highly relevant targets of pest control efforts. Unfortunately, the lack of genetics or gene specific molecular manipulation imposes major limitations to the study of grasshopper biology.ResultsWe investigated whether juvenile instars of the grasshopper species Schistocerca americana are conducive to gene silencing via the systemic RNAi pathway. Injection of dsRNA corresponding to the eye colour gene vermilion into first instar nymphs triggered suppression of ommochrome formation in the eye lasting through two instars equivalent to 10–14 days in absolute time. QRT-PCR analysis revealed a two fold decrease of target transcript levels in affected animals. Control injections of EGFP dsRNA did not result in detectable phenotypic changes. RT-PCR and in situ hybridization detected ubiquitous expression of the grasshopper homolog of the dsRNA channel protein gene sid-1 in embryos, nymphs and adults.ConclusionOur results demonstrate that systemic dsRNA application elicits specific and long-term gene silencing in juvenile grasshopper instars. The conservation of systemic RNAi in the grasshopper suggests that this pathway can be exploited for gene specific manipulation of juvenile and adult instars in a wide range of primitive insects.

Hunting success of wintering Swainson's hawks: environmental effects on timing and choice of foraging method

We examined the predatory behavior of Swainson's hawks (Buteo swainsoni Bonaparte, 1838) wintering in the Argentine pampas. Aerial and ground foraging were the main hunting methods employed by hawks in this region. The overall hunting success of hawks preying on insects was 50% and age-related differences in hunting success were not significant. The Swainson's hawks, however, hunted more successfully in the air (65% of prey capture attempts) than on the ground (42%). Aerial hunting while soaring was the most successful hunting method based on the number of prey captured per energy unit. Based on the analysis of prey consumed by hawks during the study period, grasshopper species with poor flight capabilities were available in the air as a consequence of the vertical air motion. With regards to daily activity patterns, the time that a hawk spent using each hunting method was not proportional to the cost ratio associated with each method. Hawks foraged in the air only during midday hours when weather conditions permitted the formation of thermals. Thus, the use of soaring flights and the availability of prey in the air were constrained by the physical environment, and hawks could only exploit airborne food sources during limited periods of the day.

Survey of short-horned grasshoppers (Acrididae) from Dakshina Kannada District, Karnataka

© Zoo Outreach Organisation; www.zoosprint.org Manuscript 1068; Received 04 August 2003; Revised received 09 June 2005; Finally accepted 01 July 2005; Date of publication 21 August 2005 1977 ABSTRACT Twenty-eight species of short-horned grasshoppers (Acrididae) were recorded from 250km2 area of Dakshina Kannada district, Karnataka, from September 2000 to June 2002. The surveys in 12 localities indicated differences in diversity and density of grasshoppers pointing to areas with anthropogenic influence, pollution and agriculture to be less diverse compared to less disturbed and polluted areas.

Grasshoppers efficiently process C4 grass leaf tissues: implications for patterns of host‐plant utilization

AbstractLeaf‐chewing insects are commonly believed to be unable to crush the nutrient‐rich bundle sheath cells (BSC) of C4 grasses. This physical constraint on digestion is thought to reduce the nutritional quality of these grasses substantially. However, recent evidence suggests that BSC are digested by grasshoppers. To directly assess the ability of grasshoppers to digest C4 grass BSC, leaf particles of Bouteloua curtipendula (Poaceae) were examined from the digestive tracts of two grasshopper species: Camnula pellucida (Scudder) (primarily a grass feeder) and Melanoplus sanguinipes (Fabricius) (a forb and grass generalist) (Orthoptera: Acrididae). Transmission electron microscopy was used to make the first observations of BSC crushing by herbivorous insects. Camnula pellucida and M. sanguinipes crushed over 58% and 24%, respectively, of the BSC in ingested leaf tissues. In addition, chloroplast and cell membranes were commonly disrupted in uncrushed BSC, permitting soluble nutrients to be extracted, even when BSC walls remain intact. The greater efficiency with which C. pellucida crushes BSC is consistent with the idea that grass‐feeding species are better adapted for handling grass leaf tissues than are generalist species. By demonstrating the effectiveness with which the BSC of B. curtipendula can be crushed and extracted by both species of grasshoppers, this study suggests one reason why C4 grasses are not generally avoided by grasshoppers: at least some C4 grasses can be more easily digested than has been hypothesized.

Testing the efficiency of three 15N‐labeled nitrogen compounds for indirect labeling of grasshoppers via plants in the field

AbstractIn field studies of plant–insect herbivore interactions it is often difficult to establish which herbivore has fed on a particular plant. We investigated the suitability of three different 15N‐labeled nitrogen compounds (ammonium, nitrate, and glycine) for indirect marking of three grasshopper species [Omocestus viridulus (L.), Chorthippus parallelus (Zett.), and Chorthippus biguttulus (L.) (Orthoptera: Acrididae)] through labeling their food plants in the field. In two short‐term experiments grassland plots of 1 m2 were separately labeled with either one of the different nitrogen compounds. Grasshoppers were caged on three food‐plant species [Dactylis glomerata L., Holcus lanatus L. (Poaceae), and Trifolium repens L. (Fabaceae)] present in these plots for 72 h. Significantly enriched δ15N values in grasshoppers were found in all plant/grasshopper combinations. Enrichment in grasshoppers was positively correlated with the enrichment of plants and labeling with nitrate resulted in highest 15N enrichment. In a long‐term experiment, individuals of C. biguttulus were placed in a cage covering an area of 1 m2 for 37 days, with sampling of grasshoppers at regular intervals. δ15N values of the grasshopper and a common food plant, D. glomerata, increased steadily over time, up to 40‐fold by the end of the experiment. Our results demonstrate that 15N‐labeling of plants is an appropriate tool for the investigation of insect–plant interactions under natural conditions.

MANDIBULAR MORPHOLOGY OF SOME FLORIDIAN GRASSHOPPERS (ORTHOPTERA: ACRIDIDAE)

The relationship between mouthpart structure and diet has been known for years. This connection between mouthpart morphology and specific food types is incredibly pronounced in the class Insecta (Snodgrass 1935). As insects have evolved and adapted to new food sources, their mouthparts have changed accordingly. This is an extremely important trait for evolutionary biologists (Brues 1939) as well as systematists (Mulkern 1967). Isley (1944) was one of the first to study grasshopper mouthparts in detail. He described three groups of mandibles according to general structure and characteristic diet. These three groups, still used today, were graminivorous (grass-feeding type) with grinding molars and incisors typically fused into a scythe-like cutting edge, forbivorous (forb or broadleaf plant-feeding type) which have a molar region consisting of a depression surrounded by raised teeth and sharp interlocking incisor teeth, and herbivorous (mixedfeeding type) that have characteristics of both of the aforementioned groups. The original findings by Isley (1944) have since been proven to be widespread in grasshoppers. Additional studies have been conducted by Snodgrass (1928), Gangwere (1965, 1966), Gangwere et al. (1976), and Patterson (1984) in North America; Lieberman (1968) and Gangwere & Ronderos (1975) in South America; Williams (1954), Kaufmann (1965), and Gangwere & Morales (1973) in Europe; Gangwere & Spiller (1995) and Gangwere et al. (1998) in the Mediterranean islands; Feroz & Chaudhry (1975), Gapud (1968), and Kang et al. (1999) in Asia; and Chapman (1964) in Africa. The relationship between grasshopper mouthparts and food is far from precise. Mulkern (1967) was convinced that only the grossest determinations could be made between mandibular structure and diet (i.e., graminivorous, forbivorous, and herbivorous). Occasionally, grasshoppers with forb-feeding mandibles regularly feed on grasses or vice versa (Chapman 1964). Nevertheless, there is some value in assessing mouthpart structure relative to predicting diet and habitat of grasshoppers, especially for the many rare or non-economic species that are unlikely to be studied in detail. Thus, the morphological characteristics and structural adaptations of the mouthparts of 36 of the 71 grasshoppers occurring in Florida were examined. Grasshoppers were collected from various habitats throughout north-central Florida in 2001 and 2002. Thirty-six of the most common Floridian grasshopper species were identified with the taxonomic key found in Smith et al. (2004) and frozen until examination. Mandibles were removed from thawed specimens by lifting the labrum and pulling out each mandible separately with forceps. Only young adults were used in an effort to avoid confusion of mandible type due to mandible erosion (Chapman 1964; Uvarov 1977). An example of moderate erosion can be seen in Figure 1 (I). This process was replicated with 10 individuals from each species. After air-drying, each mandible was glued to the head of a #3 or #2 insect pin, depending on its size, for easier manipulation, and examined microscopically. We used Isley's (1944) description of mandible types and their adaptive functions to divide the mandibles into 3 major categories: forbivorous (forb-feeding), graminivorous (grass-feeding), and herbivorous (mixed-feeding). Mandibles were lightly brushed with 80 percent ETOH and distilled water in an effort to remove most of the sand and debris adhering to the mouthparts. Photographs were taken with the Syncroscopy Auto-Montage system (University of Florida, Entomology and Nematology Dept.). The mandible structure of 36 species of grasshopper, from five subfamilies (Acridinae, Cyrtacanthacridinae, Gomphocerinae, Oedipodinae, and Romaleinae), found in Florida was microscopically examined. These grasshoppers were collected from a variety of habitats including disturbed freshwater marsh, high pine, swamp, and oak hammocks. All grasshoppers had distinctive mouthparts that could be described as forbivorous (forb-feeding type), herbivorous (mixed-feeding type), or graminivorous (grass-feeding type) (Fig. 1, A-L). A list of each species studied and the mandible type is given in Table 1. Of the subfamilies examined, the Cyrtacanthacridinae demonstrated the most diversity in mandible type; however, most of them displayed either herbivorous or forbivorous mandibles, indicating a tendency toward forb-feeding. These grasshoppers can be found in a wide range of habitats, usually in dense vegetation or woodland areas, and are quite active in both walking and flying. It is interesting to note that both the grasshoppers in this subfamily that did display graminivorous type mandibles (L. marginicollis and S. vitreipennis) also have extremely slender, elongated bodies and can be found on the edges of ponds or in freshwater marshes (Isley 1944; Squitier & Capinera 2002b; Smith & Capinera 2005). These grasshoppers typically grasp the stems of emergent grass or grass-like vegetation such as sedges or cattails, blending in almost perfectly.

The evolution of the phenotypic covariance matrix: evidence for selection and drift inMelanoplus

Phenotypic variation in trait means is a common observation for geographically separated populations. Such variation is typically retained under common garden conditions, indicating that there has been evolutionary change in the populations, as a result of selection and/or drift. Much less frequently studied is variation in the phenotypic covariance matrix (hereafter, P matrix), although this is an important component of evolutionary change. In this paper, we examine variation in the phenotypic means and P matrices in two species of grasshopper, Melanoplus sanguinipes and M. devastator. Using the P matrices estimated for 14 populations of M. sanguinipes and three populations of M. devastator we find that (1) significant differences between the sexes can be attributed to scaling effects; (2) there is no significant difference between the two species; (3) there are highly significant differences among populations that cannot be accounted for by scaling effects; (4) these differences are a consequence of statistically significant patterns of covariation with geographic and environmental factors, phenotypic variances and covariances increasing with increased temperature but decreasing with increased latitude and altitude. This covariation suggests that selection has been important in the evolution of the P matrix in these populations Finally, we find a significant positive correlation between the average difference between matrices and the genetic distance between the populations, indicating that drift has caused some of the variation in the P matrices.

DISTURBANCE BY FIRE FREQUENCY AND BISON GRAZING MODULATE GRASSHOPPER ASSEMBLAGES IN TALLGRASS PRAIRIE

Understanding determinants of local species diversity remains central to developing plans to preserve biodiversity. In the continental United States, climate, grazing by large mammals, fire, and topography are important ecosystem drivers that structure North American tallgrass prairie, with major impacts on plant community composition and vegetation structure. Frequency of fire and grazing by bison (Bos bison), through effects on plant community composition and altered spatial and structural heterogeneity of veg- etation in tallgrass prairie, may act as bottom-up processes that modulate insect community species richness. As previously seen for plant species richness, I hypothesized that grazing had more impact than fire frequency in determining species richness of insect herbivore communities. I examined this prediction with grasshoppers at Konza Prairie, a representative tallgrass prairie site in which fire frequency and bison grazing are manipulated over long terms with landscape-level treatments. Topographic position (upland vs. lowland) and fire frequency (1-, 2-, 4-year intervals, and unburned) did not significantly influence grasshopper species richness or indices of diversity, while grazing had significant effects. On average, I found ;45% more grasshopper species and significantly increased values of Shannon H9 diversity at sites with bison grazing. Species abundances were more equally distributed (Shannon's Evenness Index) in grazed sites as well. No significant interactions among burning and grazing treatments explained variation in grasshopper species diversity. Grasshopper species richness respond- ed positively to increased heterogeneity in vegetation structure and plant species richness, and negatively to average canopy height and total grass biomass. Variation in forb biomass did not influence grasshopper species richness. A significant positive relationship between grasshopper species richness and overall grasshopper density was observed. Species rich- ness increased marginally as watershed area of treatments in grazed areas increased, but not in ungrazed areas. Disturbance from ecosystem drivers operating at watershed spatial scales exhibits strong effects on local arthropod species diversity, acting indirectly by mediating changes in the spatial heterogeneity of local vegetation structure and plant species diversity.

Inheritance of song and stridulatory peg number divergence between Chorthippus brunneus and C. jacobsi, two naturally hybridizing grasshopper species (Orthoptera: Acrididae)

Knowledge of the genetic basis of divergence in mating signal characters that contribute to reproductive isolation is critical to understanding speciation. Here, we describe a semi-automated system for characterizing grasshopper acoustic signals. We used this system to study the genetic basis of divergence in three male calling song components [echeme (EL), syllable (SL) and phrase (PL) lengths] between Chorthippus brunneus and C. jacobsi, two species of grasshoppers that hybridize in northern Spain. We also studied the number of pegs in the stridulatory file. For all characters, additive effects accounted for most of the genetic differentiation between species. However, the three song components also showed small but significant epistatic effects. No sex linkage was detected. Wright-Castle-Lande estimates of the minimum numbers of genetic factors underlying song and peg number divergence were low: peg number (n(e)=5.87+/-5.84), SL (n(e)=2.37+/-4.79) and PL (n(e)=0.87+/-0.86). On the other hand, EL appeared to be controlled by many genes. These results suggest that divergence in SL and PL might be driven by sexual selection whereas EL might not be under selection. This is consistent with experimental results on female song preference in related species. However, the fact that few factors appear to underlie the differences in peg number is surprising. Peg number is not closely related to song characteristics. It often varies between closely related grasshopper species and it has been assumed to be a neutral character. The biometrical approaches used here tend to underestimate the number of factors influencing a trait but provide valuable background for subsequent quantitative trait loci analyses.

Host Preferences and Habitat Associations of Some Florida Grasshoppers (Orthoptera: Acrididae)

Host-plant preferences were assessed by field measurement of grasshopper abundance in relation to measurements of floral community and by laboratory host-plant preferences. Correlations between grasshoppers and plants (biomass and percentage cover) were based on data gathered at 29 study sites in five distinct Florida habitats (including disturbed, freshwater marsh, high pine, oak hammock, and swamp). Relationships among plants in these habitats and 10 abundant grasshopper species were examined to clarify differences in grasshopper assemblages among habitats. The grasshoppers studied were Aptenopedes sphenarioides Scudder, Chortophaga australior (Rehn and Hebard), Eritettix obscurus (Scudder), Melanoplus bispinosus Scudder, Melanoplus querneus Rehn and Hebard, Paroxya clavuliger (Serville), Schistocerca americana (Drury), Schistocerca ceratiola Hubbell and Walker, and Spharagemon crepitans (Saussure). In addition to correlations among individual plants and the abundance of grasshoppers, multiple regression analysis was used to assess how groups of plants were related to grasshopper abundance. These analyses identified grasshopper-plant associations, but some plants were found to be host plants, whereas others were indicators of preferred habitats (indicator plants). Host-plant preferences were determined in the laboratory using five plant-choice tests to help distinguish between host and indicator plants. The 10 grasshopper species examined for laboratory host-plant preferences were the same species scrutinized in the field study. In almost every case, grasshoppers showed specific plant preferences, and the preference studies successfully distinguished between host plants and indicator species. Similar results were obtained whether biomass or percent cover measurements were used to assess the floral community, although percent cover is much easier and faster to determine.

Comparative Karyotype Analysis of Grasshoppers in the Genus Oxya (Orthoptera, Catantopidae) by Differential Staining Techniques

The chromosomes of 4 species of grasshopper in the genus Oxya were analyzed by conventional and five differential-staining methods. All 4 species had a chromosome complement of 2n=22+XX(female)/XO(male), with very similar karyotypes. Both O. hyla intricata and O. japonica japonica had acrocentric chromosomes with minute short arms, while the chromosomes of O. chinensis formosana and O. yezoensis were almost all telocentric. In all 4 species, a secondary constriction (SC) was detected at a proximal site in chromosome 8, which had the same staining properties (positive for C- and CMA-banding; negative for G- and QM-banding) in all 4 species. Our C-banding analysis revealed that the short arms of O. hyla intricata and O. japonica japonica consisted of C-heterochromatin. The 4 species yielded species-specific patterns of C-bands, and there appeared to be a close relationship between O. chinensis formosana and O. yezoensis, as suggested by the polymorphism of the distal C-bands of chromosome 2. In all 4 species of Oxya, Ag-NORs were detected on the centromeric regions of all the chromosomes, but not detected on the SC of chromosome 8. The karyosystematic relationships among the 4 species are discussed on the basis of the results of differential staining.

Postdiapause Development and Hatching Rate of Three Grasshopper Species (Orthoptera: Acrididae) in Inner Mongolia

The postdiapause development, hatching characteristics, and survival of the overwintering eggs of the grasshopper species Oedaleus asiaticus Bei-Bienko, Angaracris barabensis (Pallas), and Chorthippus dubius (Zubowsky) from the Inner Mogolian steppe grasslands were studied at six constant temperatures (15, 20, 25, 30, 35, and 40°C). The results show that the three species had different postdiapause embryonic developmental rates, survival curves, and cumulative hatching probabilities. O. asiaticus had the highest developmental threshold at 13.1°C and the least effective accumulated thermal unit, 191.7 degree-days (DD). A. barabensis had the lowest developmental threshold at 11.1°C and the most effective accumulated thermal unit, 329.7 DD. C. dubius, a later hatching species, had a moderate developmental threshold of 11.4°C and an effective accumulated thermal unit of 230.3 DD. The effective thermal unit at which 50% of postdiapause eggs hatched was 202.7 DD for O. asiaticus, 340.8 DD for A. barabensis, and 251.6 DD for C. dubius. The greatest percentage hatch of O. asiaticus (71.06%), A. barabensis (75.28%), and C. dubius (87%) occurred at 27.3, 27.8, and 27.4°C, respectively. Thermal death points of the three grasshopper species were 41.0°C, 40.5, and 44.8°C, respectively. The optimal temperature ranges of each species were different, 21.9 to 32.7°C for O. asiaticus, 22.0 to 33.5°C for A. barabensis, and 17.8 to 37.1°C for C. dubius. These results suggest that postdiapause embryonic developmental rate and accumulated heat cannot help to explain the different hatching sequences of these species. Much variation in springtime emergence could be attributed to the species-specific overwintering egg stage. In addition, results also indicate that C. dubius has a wider adaptive temperature range than O. asiaticus and A. barabensis.

Association of genetic lineages with ecological features in a polyphagous montane grasshopper species

Abstract Understanding the relationships between intraspecific diversity and habitat has been greatly enhanced with the advent of molecular markers. Such understanding may help to elucidate complex microevolutionary processes. Melanoplus alpinus, a montane/alpine grasshopper species found in the central and northern Rocky Mountains, has a disjunct distribution with highly divergent mtDNA lineages, structured among meadows and drainages within mountain ranges. Previous analyses showed that genetic differentiation is not distance driven, so habitat factors may account for genetic structuring and diversity within the species. In this study, 3 mtDNA lineages were analyzed for their association with ecological variables, and PCR-RFLP haplotype genetic diversities were analyzed for relationships with elevation, elevation-latitude index, and meadow size. Chi-square analysis revealed mtDNA lineage predominance in particular soil textures, indicating the potential of soil to function as a limiting environmental fa...

KEY TO THE GRASSHOPPERS (ORTHOPTERA: ACRIDIDAE) OF FLORIDA

A dichotomous key is presented to aid in the identification of the adult stage of the 71 grasshopper species known to occur in Florida. Reflecting recent research one subspecies, Schistocerca alutacea rubiginosa (Scudder), has been elevated to species status Schistocerca rubiginosa (Harris) in this key.

Variation in Grasshopper (Acrididae) Densities in Response to Fire Frequency and Bison Grazing in Tallgrass Prairie

Abstract While weather can contribute significantly to grasshopper population dynamics in North American grasslands, local environmental conditions resulting from land use practices may be equally important. In this study, significant differences in grasshopper density were detected among adjacent watersheds from Kansas Flint Hills tallgrass prairie that differed in fire frequency and especially bison grazing treatments. Grasshopper densities were ≈2.5 times greater in grazed watersheds compared with ungrazed ones. Grasshopper densities also varied somewhat in response to fire frequency, mostly in species-specific ways. No treatment interactions on overall grasshopper density were detected. The effects of fire frequency and bison grazing were implemented in part through their combined effect on the structural heterogeneity of vegetation, and other habitat characteristics. Individual grasshopper species responded uniquely to combinations of fire frequency and bison grazing. Grazing resulted in significant ...

Sexual harassment in heterogeneous landscapes can mediate population regulation in a grasshopper

Population regulation has been related to differences in the quality among habitats, which mediate differences in vital rates such that in poor habitats reproductive rates are lower than those in high-quality habitats. The spatial distribution of animals in such habitats depends on their preferences and the degree to which individuals have a free choice of a particular habitat. The identified mechanisms that lead to a particular spatial distribution and eventually to regulation mainly include foraging-related interference, for example, ideal free distribution, or simple selection of available high-quality habitats, that is, site-dependent habitat selection. However, in insect species these mechanisms might not be applicable, but density-dependent habitat selection still occurs. We therefore suggest a mechanism that refers to the nearly universal observation that matings also bear fitness costs. Although these costs have been investigated on the individual level in many insect species, their consequences for population dynamics have not yet been addressed. In the grasshopper species Stenobothrus lineatus, females in a nonreceptive mating status escape sexually approaching males by undirected jumps. By including such avoidance behavior in a spatially-explicit simulation model, we investigated its potential to result in progressive use of low-quality habitats at increasing population densities. In particular, we show that (1) such behavior changes habitat selection, (2) altered habitat selection results in population regulation, and (3) the degree of habitat heterogeneity influences regulation such that (4) heterogeneous habitats show finetuned regulation and homogeneous habitats tend to support large fluctuations. Key words: habitat quality, habitat use, individual interactions, mating behavior, spatial simulation model, Stenobothrus lineatus. [Behav Ecol]

Cytogeography and the evolutionary significance of B chromosomes in relation to inverted rearrangements in a grasshopper species

The analysis of geographic distribution of polymorphic cytological markers, briefly termed as cytogeography, can be considered an important tool to be applied when studying the evolutionary significance of chromosome variability within a species, either to unravel the adaptive significance of chromosome polymorphisms or to investigate the parasitic nature of some genomic elements. In this article we review cytogeographical studies in Trimerotropis pallidipennis, a grasshopper species whose South American populations display geographical patterns of distribution of inversion and B chromosome polymorphisms. Several lines of evidence that issue from the analysis of the geographic distribution of polymorphic markers suggest that inverted chromosomes are special sequences that are maintained by deterministic forces. On the other hand, the pattern of distribution of B chromosome polymorphism clearly demonstrates its selfish nature, being more frequent in those populations in central environments. We also present the analysis of 272 individuals of T. pallidipennis from Uspallata, and demonstrate that Bs in this population have some influence on body size, enlarging many of the morphometric characters of individuals and we propose it could be the consequence of its genotypic disequilibrium with one inversion. These investigations are finally discussed with regard to the models proposed for the maintenance of B chromosomes in natural populations and in relation to the possible interactions with chromosome inversions.