Colour-pattern variation in relation to habitat in the grasshopper Chorthippus brunneus (Thunberg)

Abstract. 1. Chorthippus brunneus were collected from twenty-two different sites in Nottinghamshire, Derbyshire and Essex.
2. Discrete characters of the head, pronotum and forewings and hind femora were scored. The results were compared with the types of habitat from which the grasshoppers were collected.
3. Associations between striped and mottle-winged varieties were found.
4. The relationships between colour and habitat were examined.     

Population density, phenotype and reproductive output in the grasshopper Chorthippus brunneus

ABSTRACT. 1. The effects of population density on the reproductive output of individual female grasshoppers ( Chorthippus brunneus Thunberg) and the relationships between reproductive output and component elements of each female's phenotype, were investigated.
2. Reproductive output was primarily determined by the rate of egg-pod production. Increased density led to significant reductions in the rate of egg-pod production and reproductive output.
3. Exoskeleton size (reflecting nymphal experience) was positively correlated with clutch size at both high and low densities, but condition (reflecting adult experience) showed no such correlation. At high density, exoskeleton size was more strongly correlated with the rate of egg-pod production and reproductive output than condition. It is concluded that the nymphal aspects of size are more important than the adult aspects.
4. At low density, females with small exoskeletons compensated for their smaller clutches by producing egg-pods at a faster rate. Thus, there was no overall relationship between reproductive output and any of the phenotypic characteristics.
5. The effects of competition were weakly asymmetric in high density populations. The weakness of the asymmetry suggests scramble-like interactions for resources. It is concluded that not only are the effects of competition influenced by individual differences, but also that competition may reveal differences that would not otherwise be apparent.     

The genetics of colour-patterns in the grasshopper Chorthippus brunneus

Several alleles were found to determine the colour of the dorsal pronotum in Chorthippus brunneus; there was evidence for at least two loci ( C and V ). Brown ( C^B )was the universal recessive and green ( C^C ) was dominant to all other colours. The white allele ( C^W )was codominant with green( C^G )and purple ( C^P ). Wing-patterns were determined by a separate, probably linked locus ( W ). A dominant plain wing-pattern ( W^P ) was associated with colours other than brown. Striped( W^S )and mottled( W^mo ) were codominant and a plain recessive allele ( W^P ) was also found. All three alleles were associated with the brown phenotype. A purple-sided allele ( S^Pu ) was sometimes obmd with C^pu.. S ^Pu was dominant to brown sides ( S^B ), A series of markings on the dorsal and lateral pronotum ( linea intermedia, fascia postocularis, linea media, carina media and zona lateralis ) were investigated and found to be controlled at separate loci which may be linked to W . These characters were expressed by dominant alleles.
Epistatic effects by modifier loci were shown to have an important effect on the determination of wing phenotype. Allele Wo⁺ , for example, suppressed the stripe-wing pattern, linea media, carina media and zona lateralis .
It was concluded that colour patterns appear to be under genetic control and that dominant alleles were rare in the wild. Changes in shades of colours were shown to be age-dependent and minor.     

Enzyme variation in the grasshopper Chorthippus brunneus (Thunberg)

Forty-two populations of the grasshopper Chorthippus brunneus from four different areas were scored for polymorphism at 15 enzyme loci. The areas sampled were Nottinghamshire, inland Essex, the Essex coast and Dovedale in Derbyshire. Five loci were found to be polymorphic (isocitrate dehydrogenase (2), malate dehydrogenase, glyceroI-3-phosphate dehydrogenase and phosphoglucomutase) but levels of heterozygosity were generally low. Differences in enzyme variation between different areas were demonstrated using multivariate analysis.     

Population density, phenotype and mortality in the grasshopper Chorthippus brunneus

ABSTRACT.

• 1 The patterns of mortality in laboratory populations of the grasshopper Chorthippus brunneus Thunberg are examined at a range of densities and at different stages of nymphal development with particular reference to the phenotypes of nymphs that die or survive.
• 2 Total mortality during nymphal development rises from density-independence at the lowest densities to approximately compensating density-dependence at the highest densities.
• 3 The greatest proportion of total mortality occurs in the first two instars. The stage broadly covering the second instar is the ‘key-stage’ determining adult density. The mortality during these stages is largely density-independent. There is relatively little mortality during stages broadly covering the final instar, but it is density-dependent and also plays a significant part in determining final adult density.
• 4 As the mortality becomes more density-dependent, either with density itself or with cohort age, the smallest individuals become increasingly disproportionately prone to mortality.
• 5 Males, which are smaller, are more susceptible to mortality than females, but their susceptibility relative to their size is less than that of females.

     

Timing of life cycles in a seasonal environment: the temperature-dependence of embryogenesis and diapause in a grasshopper (Chorthippus brunneus Thunberg)

Summary The durations of the stages in the embryonic development of Chorthippus brunneus (Thunberg) have been estimated at constant temperatures of 20° C and 30° C. There was stage-dependent variation in the temperaturedependence of morphogenesis-a pattern apparently not previously described. The earliest and latest stages of morphogenesis proceeded relatively rapidly at higher temperatures. But intermediate stages, which would tend to occur around the diapause stage in a temperate winter, proceeded relatively rapidly at lower temperatures, as did diapause development. At a given temperature, there was individual variation between eggs such that some developed consistently faster than others. However, these intrinsic differences could be altered by exposure to diapause-breaking conditions at different morphological stages. The results are discussed in terms of their adaptive significance, their effect on population dynamics in a seasonal environment, and their implications for the nature of diapause in insects generally.     

Relationships between oviposition date, hatch date, and offspring size in the grasshopper Chorthippus brunneus

Abstract 1. The grasshopper Chorthippus brunneus has been shown to increase egg size with maternal age under constant laboratory conditions, such that late-laid eggs are larger than early laid eggs. In this study, an increase in the size of eggs (and hatchlings from those eggs) was recorded with date of oviposition in a field cage population. This suggests that the relationship between maternal age and egg size, observed previously in the laboratory, also occurs in the field. There was, however, some evidence that the behaviour of the maternal females in field cages was modified by the onset of autumnal weather at the end of the breeding season. Only a small number of eggs was laid in the last 3 weeks of the summer but these yielded relatively small hatchlings.
2. The date on which eggs were laid was correlated positively with their date of hatch in the following year. A consequence of this relationship, and that between oviposition date and egg size, was that size at hatch increased with date of hatch through most of the spring but then declined as the last few eggs hatched. Temporal variation in size at hatch parallelled temporal variation in the maternal females' investment in egg size in the previous year.
3. An undisturbed field population was monitored to assess whether the temporal variation in size at hatch resulted in size variation at eclosion in subsequent developmental stages. There were negative correlations between size at eclosion and date of eclosion at the third and fourth instars, suggesting that despite their smaller size at hatch, early hatchers experienced more favourable conditions for juvenile growth than late hatchers. The larger size at hatch of late hatchers may enhance their survival and compensate (albeit incompletely) for their reduced opportunity for growth. Female reproductive behaviour may represent an adaptive response to a predictable seasonal decline in offspring fitness at hatch.     

Visual behaviors of the migratory grasshopper,Melanoplus sanguinipes F. (Orthoptera: Acrididae)

The visual behavior of adult Melanoplus sanguinipesF. (Orthoptera: Acrididae) was investigated by placing individuals in the center of an arena and recording their orientation responses to visual targets at the perimeter of the arena. Targets that reflected more 540- to 570-nm light were approached more frequently; however, when reflectance in the 540 -to 570-nm region was combined with reflectance in the 400- to 520-nm region, orientation responses were reduced significantly. This suggests that spectral discrimination in M. sanguinipesinvolves at least two classes of photoreceptors, which respond to different regions of the wavelength spectrum. In addition, grasshoppers oriented to vertical, but not horizontal, contrasting stripes. However, when vertical stripes were added to targets reflecting 520- to 650-nm light, responses to verticals on these targets were not enhanced relative to verticals presented against a target background of 400- to 520-nm + 520- to 650-nm light. Thus, spectral discrimination and vertical stripe fixation appear to be two distinct visual behaviors, controlled by outputs from two classes of photoreceptors and a single class of photoreceptors, respectively, and may be used in different physiological or ecological contexts.     

Ecotypic differentiation between urban and rural populations of the grasshopper <Emphasis Type="Italic">Chorthippus brunneus</Emphasis> relative to climate and habitat fragmentation

Urbanization alters environmental conditions in multiple ways and offers an ecological or evolutionary challenge for organisms to cope with. Urban areas typically have a warmer climate and strongly fragmented herbaceous vegetation; the urban landscape matrix is often assumed to be hostile for many organisms. Here, we addressed the issue of evolutionary differentiation between urban and rural populations of an ectotherm insect, the grasshopper Chorthippus brunneus. We compared mobility-related morphology and climate-related life history traits measured on the first generation offspring of grasshoppers from urban and rural populations reared in a common garden laboratory experiment. We predicted (1) the urban phenotype to be more mobile (i.e., lower mass allocation to the abdomen, longer relative femur and wing lengths) than the rural phenotype; (2) the urban phenotype to be more warm adapted (e.g., higher female body mass); and (3) further evidence of local adaptation in the form of significant interaction effects between landscape of origin and breeding temperature. Both males and females of urban origin had significantly longer relative femur and wing lengths and lower mass allocation to the abdomen (i.e., higher investment in thorax and flight muscles) relative to individuals of rural origin. The results were overall significant but small (2–4%). Body mass and larval growth rate were much higher (+10%) in females of urban origin. For the life history traits, we did not find evidence for significant interaction effects between the landscape of origin and the two breeding temperatures. Our results point to ecotypic differentiation with urbanization for mobility-related morphology and climate-related life history traits. We argue that the warmer urban environment has an indirect effect through longer growth season rather than direct effects on the development.     

Reproductive life history variation among colour morphs of the pygmy grasshopper Tetrix subulata

Individuals of pygmy grasshoppers ( Tetrix subulata [L.] Orthoptera: Tetrigidae) exhibit genetically coded discontinuous variation in colour pattern. To determine whether reproductive performance is likely to be affected by colour pattern, this study investigated variation in body size and reproductive life-history characteristics among individuals belonging to five different colour morphs. The proportion of reproductive females (i.e. females with eggs) declined significantly as the season progressed (from 100% in mid-May to 40% in mid-June), but no such seasonal trend was apparent for body size, clutch size or egg size. Colour morphs differed significantly in body size, and these size differences accounted for most of the variation in clutch size and egg size. Colour morphs also differed in the regression of egg size on clutch size, suggesting that trade-offs between number and size of offspring might vary among morphs. Finally, I found a negative relationship across colour morphs between the proportion of females with eggs and average clutch size. This suggests that individuals belonging to certain colour morphs produce a relatively large number of clutches per unit time, at the expense of fewer offspring in each clutch, compared to other morphs. Collectively, my results indicate that different colour morphs of T. subulata may have different reproductive strategies. These differences may reflect variation in thermoregulatory capacity or differences in probability of survival induced by visual predators.     

Chromosomal differentiation through an Alpine hybrid zone in the grasshopper Chorthippus parallelus

The grasshopper Chorthippus parallelus is genetically differentiated over its range into at least five major geographical subdivisions. Two of these subdivisions, designated as subspecies, meet and form a hybrid zone in the Pyrenees. These subspecies differ for a wide range of morphological, behavioural and chromosomal characters, which vary clinally across the zone. A further geographical subdivision exists within Italy. Here we present the first evidence for chromosomal divergence between populations of the grasshopper north and south of the Alps. Across two Alpine cols (Col de Larche, between France and Italy; Passo de Resia, between Austria and Italy), these populations differ in both structural and functional components of the X-chromosome. Northern Alpine individuals possess an active nucleolar organizing region (NOR) at the distal end of the X-chromosome and an associated region of heterochromatin (C-band). Both these features are absent from individuals from the south of the Alps. However, all individuals examined carry distally located rDNA on the X-chromosome. Clinal transition was examined in the distal C-band in transects through the two cols. The cline centres are roughly coincident with the tops of the cols. Both clines were of similar widths (Col de Larche, 21.88 km; Passo de Resia, 24.05 km), and therefore much wider than those for an X-linked distal C-band in the Pyrenean hybrid zone. This suggests that there are different selective pressures on the cytogenetic characters in the Alps. The results are discussed in the context of the historical population dynamics of the species in relation to the climatic changes associated with the Pleistocene ice ages.     

Ecotypic differentiation determines the outcome of positive interactions in a dryland annual plant species

Positive interactions among plants have rarely been investigated with respect to their evolutionary consequences and vice versa. The outcome of facilitative interactions depends on the competitive ability and stress tolerance of the species. We tested whether this also applies to populations of conspecifics that are locally adapted to different environments and thereby differ in these traits. We hypothesised that ecotypes from less stressful environments experience a greater effect of facilitation when grown in stressful environments compared to populations adapted to these conditions.Seeds of two ecotypes of the annual grass species, Brachypodium distachyon, were collected from Mediterranean and arid origins and transplanted at an arid environment within the species’ distribution range. To examine the effect of biotic interactions on these ecotypes, we transplanted the individuals with and without the presence of the shrub Gymnocarpos decander (underneath or away from the shrub), and with and without the presence of annual vegetation (removal experiment). We examined the effect of these interactions on the two B. distachyon ecotypes by comparison of emergence success, biomass, and survival to reproduction.The presence of shrubs had a positive effect on all three variables in both ecotypes. Facilitation by shrubs enabled individuals from Mediterranean origin to grow and reproduce in arid conditions. Unlike the locals, they failed to survive to reproduction away from the shrubs, because of the markedly shorter growing season in open areas. The annual vegetation did not affect emergence or survival to reproduction in either ecotype; however, the positive effect of shrubs on biomass was reduced in the presence annual vegetation in the Mediterranean ecotype.This demonstrates that ecotypes adapted to arid conditions respond differently to these biotic interactions compared to Mediterranean populations. We argue that facilitation may have important evolutionary consequences by enabling maladapted ecotypes to invade and colonize stressful habitats.     

Geographic variation in the life history of the sagebrush lizard: the role of thermal constraints on activity

Thermal constraints on the time available for activity have been proposed as a proximate mechanism to explain variation in suites of life history traits. The longer that an ectotherm can maintain activity, the more time it has to forage and the greater chance that it will encounter a predator and be eaten. Thus, the thermal environment may produce a trade off between growth and survival when variation in the environment favors increased activity. I used mark-recapture data from a demographic study of three natural populations of the sagebrush lizard (Sceloporus graciosus) and estimates of thermal opportunity for each population to evaluate whether variation in the thermal environment can explain patterns of growth and survival that occur over an elevational gradient. Lizards from the highest elevation population exhibited higher individual growth rates than those of lizards from lower elevation, while mortality rates increased with elevation for these populations. The covariation of fast growth and high mortality with increased thermal opportunity is the opposite trend expected if the thermal environment alone is to explain patterns of life history in these lizards. Additional factors including thermal heterogeneity in the distribution of microhabitats of lizards, adaptation to local environmental conditions, and a potential trade-off between resource acquisition and predation risk need to be addressed to obtain a satisfactory explanation of the causative mechanisms producing life history variation.     

Variation in dietary patterns among and within polyphagous grasshopper species (Orthoptera: Acrididae)

Individuals of two polyphagous grasshopper species,Melanoplus differentialis andSchistocerca albolineata, were reared under standardized conditions to eliminate prior experience as an influence on feeding behavior. Individuals were offered four plants in simultaneous choice tests from 8 to 14 times during development to adulthood. Individual insects varied in the preferred plant and the strength of preference, in the strength of the preference hierarchy among the four plants, and in breadth of feeding in choice tests. Average feeding diversity in choice tests increased significantly in later instars, but the sexes did not differ in feeding pattern. In both species a significant preference for one plant was generally but not invariably associated with a consistent preference hierarchy. Breadth of feeding in all tests was inversely related to the strength of preference and of the preference hierarchy. Although the two species differed in feeding diversity and in the relationship between preference and strength of preference hierarchy, evidence suggests that these differences were due to the specific plants used rather than to true interspecific differences. The existence of such variation under highly standardized rearing conditions suggests that genetic variation for these characteristics may exist in natural populations of polyphagous grasshoppers.     

Recognition of sex in the acoustic communication of the grasshopper Chorthippus biguttulus (Orthoptera, Acrididae)

Many gomphocerine grasshoppers communicate acoustically: a male's calling song is answered by a female which is approached phonotactically by the male. Signals and recognition mechanisms were investigated in Chorthippus biguttulus with regard to the cues which allow sex discrimination. (1) The stridulatory files on the hindfemur of both sexes are homologous in that they are derived from the same row of bristles, but convergent with respect to the “pegs”. In males the pegs are derived from the bristles, and in females from the wall of the bristle's cup. (2) Male and female songs are generated by similar, probably homologous motor programs, but differ in the duration, intensity, “gappyness” of syllables, risetime of pulses, and the frequency spectra. The hindleg co-ordination during stridulation and the resulting temporal song patterns are less variable in males than in females. (3) For both sexes, recognition of a mate's signal depends on species-specific syllable structure. For males it is essential that the female syllables consist of distinct short pulses, whereas females reject “gappy” syllables. Males strongly prefer “ramped” pulses, females respond to syllables irrespective of steeply or slowly rising ramps. Males react only to the low-frequency component, whereas females prefer spectra containing both, low and high frequency components. Accepted: 20 November 1996     

Effect of photoperiod on the maternal induction of an egg diapause in the grasshopper Chorthippus bornhalmi

The effect of the photoperiod experienced maternally on the induction of an egg diapause was studied in the grashopper Chorthippus bornhalmi Harz (Acridoidea: Gomphocerinae), which lives on the southern Balkan peninsula. Photoperiods used ranged from L12:D12 to L20:D4 and were kept constant, or were increased or decreased after the imaginal ecdysis in other experiments. Under most conditions in the study, the females laid almost only diapause eggs (not less than 93%). Using constant day-lengths, only at L14:D10 the percentage of non-diapause eggs was somewhat higher (20%). An increase in day-length from moderately long (L14:D10) to long day (L16:D8) was necessary for non-diapause eggs to predominate. However, the percentage of non-diapause eggs decreased with the age of the females, except when the day-length was raised a second time. An increase from short day (L12:D12) to moderately long day (L14:D10) or from long day (L16:D8) to extremely long day (L18:D6) as well as a decrease of day-length, all resulted in the production of diapause eggs. The consequences for the life cycle are discussed.

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Zusammenfassung Der einfluß der Photoperiode auf die maternelle Induktion einer Eidiapause beim Grashüpfer Chorthippus bornhalmi wurde untersucht. Die Art lebt auf der südöstlichen Balkanhalbinsel. Die getesteten Photoperioden reichten von L12:D12 bis L20:D4. In einem Teil der Versuche wurde die Photoperiode während des gesamten Lebens der Grashüpfer konstant gehalten, in anderen nach der Imaginalhäutung erhöht oder erniedrigt. Unter den meisten Bedingungen legten die Grashüpfer-Weibchen fast ausschließlich Diapause-Eier (mehr als 93%). Bei konstanten Tageslängen stieg der Anteil der Subitaneier lediglich nach einer Eiablage bei L14:D10 auf 20%. Eine Erhöhung der Photophase von 14 auf 16 Stunden war notwendig, damit der Anteil an Subitaneier überwog. Aber auch unter diesen Bedingungen nahm ihr Anteil mit dem Alter der Weibchen ab, außer wenn die Photophase noch ein zweites Mal (auf 18 Stunden) verlängert worden war. Eine Zunahme der Tageslänge von Kurztag (L12:D12) auf mäßigen Langtag (L14:D10) oder auch von Langtag (L16:D8) auf extremen Langtag (L18:D6) sowie eine Abnahme der Tageslänge hatten zur Folge, daß die Weibchen fast ausschließlich Diapause-Eier legten. Auf grund der spezialisierten Form der Diapause-Induktion können die Grashüpfer im Freiland nur im Frühjahr Subitaneier legen.

     

Low levels of chromosomal differentiation between the grasshoppers Chorthippus brunneus and Chorthippusjacobsi (Orthoptera; Acrididae) in northern Spain

The grasshopper species Chorthippus brunneus and C. jacobsi (Orthoptera: Acrididae) form a hybrid zone in northern Spain. These species probably diverged while isolated in southern refugia during one of the recent ice ages, and are clearly distinguished by morphology and male calling song. However, in contrast to other Chorthippus taxa that form hybrid zones in Europe, these two species cannot be reliably distinguished on the basis of characteristics of the karyotype such as heterochromatin banding patterns and composition, as revealed by C-banding and fluorochrome staining. Silver staining also reveals the presence of two autosomal nucleolar organiser regions (NORs) in both species. However, differentiation between C. brunneus and C. jacobsi was revealed on the X chromosome using fluorescent in situ hybridisation (FISH). C. brunneus individuals showed additional rDNA sequences on the X chromosome that were not observed in any C. jacobsi individuals. These sequences are not transcribed, indicating either mutational silencing of an ancestral NOR on the X chromosome, or the transposition of non-functional sequences from the autosomes. The implications of these results for the evolution of NOR number in Chorthippus are discussed.     

Ecotypic differentiation of response to enhanced CO2 and temperature levels in Arabidopsis thaliana

Five ecotypes of Arabidopsis thaliana, from widely dispersed origins, were grown under combinations of ambient and elevated atmospheric CO₂ concentrations and ambient and elevated temperatures within solardomes. Total above-ground plant biomass was measured when the majority of plants across all ecotypes and treatments had formed seed pods. There were substantial differences in biomass between the ecotypes across all treatments. Temperature had no effect on biomass whilst CO₂ had a significant effect both alone and in interaction with ecotype. The CO₂ x ecotype interaction was mostly due to the enhancement of a single ecotype from the Cape Verde Islands.     

Divergence in morphometric and life history traits in two thermally contrasting Andean populations of Rhinella spinulosa (Anura: Bufonidae)

(1) We studied the variation in characters of two Andean populations of Rhinella spinulosa with different larval thermal regimes as a function of geographic origin and temperature.

(2) In both populations, survival and growth rate were greater at the higher temperature. Size at metamorphosis was only determined by locality, while there was a divergence in growth rate and age at metamorphosis as a function of locality and temperature.

(3) Variation was found in seven of the 12 morphological characters evaluated in post-metamorphic toadlets, which was determined only by their locality of origin.

Assortative preferences and discrimination by females against hybrid male song in the grasshoppers Chorthippus brunneus and Chorthippus jacobsi (Orthoptera: Acrididae)

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are highly differentiated for male mating signals, and form a mosaic hybrid zone in northern Spain. At some sites within this zone, many hybrids are observed. At others, few hybrids are observed. Such bimodal sites may reflect recent contacts between parental genotypes, or local variation in levels of assortative mating or selection against hybrids. Playback of 12 parental and F1 male songs to 296 parental and hybrid females revealed positive assortative preferences in C. brunneus and C. jacobsi females, supporting a direct role of male mating signals in female choice. However, all female genotypic classes showed reduced responsiveness to F1 male songs. Such sexual selection against hybrids is consistent with the narrow cline width observed in the field for song characters relative to morphology. These results have implications for the genetic structure of the hybrid zone and for models of speciation by reinforcement.