Gryllus Pennsylvanicus Research Articles

THE EFFECT OF A VARIABLE ENVIRONMENT ON THE GENETIC CORRELATION STRUCTURE IN A FIELD CRICKET.

The evolutionary trajectory of a trait depends not only on the presence of genetic variation, but also on the pattern of genetic correlations (rg ) among traits. Genetic correlations are most easily measured under homogeneous, controlled laboratory conditions, whereas natural populations typically experience a higher degree of environmental variability. The effect of environmental variability on genetic correlations in the cricket, Gryllus pennsylvanicus, was studied by measuring genetic correlations within and between two environments differing in levels of environmental heterogeneity. Within-environment rg among morphological traits measured in the homogeneous laboratory environment were found to be reliable predictors of rg measured in the experimental field environment. Laboratory measures of rg involving life-history traits, though, were not found to reflect the same correlations measured in the heterogeneous environment. A significant negative genetic correlation between fecundity and developmental time was found in the field environment, yet was not detectable when measured in the laboratory. Phenotypic correlations may be obtained much more easily than genetic correlations, but their usefulness in evolutionary inference depends on the pattern of similarity between the two correlations. A comparison of genetic and phenotypic correlations revealed a close match between the two measures for morphological traits, but revealed only broad similarities when considering life-history traits. Male-female genetic correlations between morphological traits were high (all rg > 0.73) and were consistently higher in the field environment than in the laboratory. The genetic correlations between the sexes in developmental time followed the same trend, but the male-female genetic correlation of gonad weights was low in both environments. Across-environment correlations were found to be strong for morphological traits and for gonad weight, whereas the genetic expression of developmental time was found to be dependent on the environment in which the crickets were raised.

Mitochondrial DNA phylogeny of North American field crickets: perspectives on the evolution of life cycles, songs, and habitat associations

AbstractNorth American field crickets (genus Gryllus) exhibit a diversity of life cycles, habitat associations, and calling songs. However, patterns of evolution for these ecological and behavioral traits remain uncertain in the absence of a robust phylogenetic framework. Analyses of morphological variation have provided few clues about species relationships in the genus Gryllus. Here we use comparisons of mitochondrial DNA restriction site maps for 29 individuals representing 11 species (including potential outgroups) to examine relationships among eastern North American field crickets. Initially chosen as likely outgroup taxa, the two European species of Gryllus do not obviously fall outside of an exclusively North American clade and (based on amount of sequence divergence) appear to have diverged from North American lineages at about the same time that major North American lineages diverged from each other. The egg‐overwintering crickets comprise a strongly supported monophyletic group, but relationships among these three closely related species cannot be resolved. The mtDNA data are consistent with a single origin of egg diapause and do not support a model of recent life cycle divergence and allochronic speciation for Gryllus pennsylvanicus and G. veletis. The two crickets are not sister species, despite remarkable similarity in morphology, habitat, and calling song. This conclusion is consistent with published data on allozyme variation in North American field crickets. The habitat associations of eastern North American field crickets have been labile, but calling songs sometimes have remained virtually unchanged across multiple speciation events.

THE EFFECT OF ENVIRONMENTAL VARIABILITY ON THE HERITABILITIES OF TRAITS OF A FIELD CRICKET.

The presence of heritable variation in traits is a prerequisite for evolution. The great majority of heritability (h2 ) estimates are performed under laboratory conditions that are characterized by low levels of environmental variability. Very little is known about the effect of environmental variability on the estimation of components of quantitative variation, although theoretical extrapolations from lab studies have been attempted. Here we investigate the effects of environmental heterogeneity on variance component estimation using full-sib families of Gryllus pennsylvanicus split between a homogeneous laboratory environment and a more variable field environment. Although large standard errors prevent demonstration of statistically significant differences among h2 of traits measured in the two environments for all but one trait, the values of h2 are, on average, lower in the variable field environment, with a mean reduction of 19%. Developmental time is an exception, exhibiting high levels of additive variance in the field, leading to a higher value of h2 in the variable environment. Underlying the lower field h2 estimates are greater components of environmental variance as expected, as well as lower components of genetic variance. In this study, there is no evidence that the increase in the environmental component of variance in the field is any more important in the reduction of h2 than is the decrease in the additive genetic component. The implications of the relative changes in the two components of variance are discussed.

Female mating behavior in the field cricket,Gryllus pennsylvanicus (Orthoptera: Gryllidae) at different operational sex ratios

The influence of operational sex ratio on the mating behavior of female field crickets,Gryllus pennsylvanicus, was investigated. Females were predicted to be more discriminating under conditions of high mate availability and show less selectivity when males were rare. Such selectivity was indicated in this study with the proportion of courtships leading to a mating changing with sex ratio. Females accepted almost 70% of all courtships at the female-biased sex ratio, but only about half of all courtships were successful at even or male-biased sex ratios. Females moved least at the female-biased sex ratio. There was also a trend for females to be guarded more under male-biased conditions. Female weight did not influence any of the behaviors examined.

Natural variation in the temporal patterning of calling song structure in the field cricket Gryllus pennsylvanicus: effects of temperature, age, mass, time of day, and nearest neighbour

Genetic and environmental sources of variation in the temporal patterning of song structure may be important variables influencing male field cricket reproductive success. Song structure in both field and laboratory populations of Gryllus pennsylvanicus was examined to assess possible sources of variation. Factors examined included temperature, male age, body mass, time of day, and male spacing patterns. Temperature was positively correlated with pulse rate and negatively correlated with interchirp interval for both field and laboratory populations. Temperature was negatively correlated with chirp duration only in the field population. Calling song structure did not vary with male age or mass. Time of day had a significant effect on the song parameters examined, even when data were corrected for temperature differences. Males calling in the morning had faster pulse rates and shorter chirp durations than males recorded at night time. Male spacing patterns also influenced calling; isolated males had longer intervals between consecutive chirps than clumped males. Data are discussed in terms of acoustical competition between males and female choice.

Reproductive Competition and Selection On Male Traits At Varying Sex Ratios in the Field Cricket, Gryllus Pennsylvanicus

Abstract Intensity of male-male competition and sexual selection were studied in the field cricket, Gryllus pennsylvanicus, in an outdoor arena at four sex ratios, male-only (5:0), male-biased (5:2), unity (5:5) and female-biased (5:10). Fighting frequency was highest at male-biased and unity sex ratios. Fighting success was correlated with male body weight at all sex ratios. Calling duration and searching distance decreased with increased female numbers. Opportunity for selection was highest at the male-biased and lowest at the female-biased sex ratio. Selection gradients and differentials were calculated and demonstrated that direct and total selection was highly variable and often relaxed. Direct selection favored male weight at the male-biased sex ratio and total selection for weight occurred at unity. There was no selection on male weight at the female-biased sex ratio. Total and direct selection for increased calling duration occurred at the male-biased sex ratio. Only total selection for calling duration was found at unity, whereas direct selection acted against calling duration at the female-biased sex ratio. Selection did not act on searching at any sex ratio. Natural variations in sex ratios occur and fluctuations in selection on correlated male traits may maintain additive genetic variation for traits important in male-male competition.

Spatial Distribution of Calling Males in Two Species of Hawaiian Crickets

in the habitat or reduced predation risks and/or increased mate attraction relative to solitary individuals (Greenfield and Shaw 1983). In contrast, French et. al. (1986) reported uniform spacing of male Gryllus pennsylvanicus in two of three populations studied. This finding indicates that male spacing patterns may vary considerably a ong cricket species and that data for additional sp cies is needed to fully describe and account for this variation.

An Experimental Study on the Effects of Predation Risk and Feeding Regime on the Mating Behavior of the Water Strider

Influence du risque du a la presence de predateurs et a au jeune subit sur le taux d'accouplement et sur sa duree

ECOLOGICAL GENETICS OF A MOSAIC HYBRID ZONE: MITOCHONDRIAL, NUCLEAR, AND REPRODUCTIVE DIFFERENTIATION OF CRICKETS BY SOIL TYPE.

We investigated the effects that habitat variation has on the structure and dynamics of a hybrid zone between two closely related crickets in Connecticut. A collecting protocol was developed in which crickets were sampled from characteristic habitats on either side of the hybrid zone and from two distinct habitat types within the zone. Presumptive pure Gryllus pennsylvanicus were sampled from fields in northwestern Connecticut and represent "inland" populations. "Pure" Gryllus firmus were sampled from beaches along the coast and represent the "coastal" populations. Crickets from within the hybrid zone were sampled from two different soil types: the "loam" populations from loamy soils and the "sand" populations from sandy soils. Moreover, an attempt was made to identify closely adjacent sand and loam localities to determine the scale of habitat variation and its possible effects on hybrid-zone structure. In general, there was little variation in morphological traits or in allozyme and mtDNA genotype frequencies among localities from within each of the four habitat types. Between each of the closely situated sand and loam localities within the hybrid zone, however, there were very significant differences in each of these sets of markers. In addition, crickets from hybrid-zone populations were tested for reproductive isolation. The asymmetric outcome of hybrid crosses that exists across the zone (Harrison, 1983) also exists on a finer ecological scale within the zone. Thus, this hybrid zone is a mosaic of strikingly differentiated populations. The dynamics of hybrid zones with mosaic structures are discussed in contrast to the traditional clinal models. The data are also discussed in light of the semipermeable nature of species boundaries. The extent to which a species boundary is permeable varies not only from one genetic marker to the next, but also with the ecological and geographic context of species interaction.

Molecular population genetics of mtDNA size variation in crickets.

Nucleotide sequence analysis of a region of cricket (Gryllus firmus) mtDNA showing discrete length variation revealed tandemly repeated sequences 220 base pairs (bp) in length. The repeats consist of 206 bp sequences bounded by the dyad symmetric sequence 5'GGGGGCATGCCCCC3'. The sequence data showed that mtDNA size variation in this species is due to variation in the number of copies of tandem repeats. Southern blot analysis was used to document the frequency of crickets heteroplasmic for two or more different-sized mtDNAs. In New England populations of G. firmus and a close relative Gryllus pennsylvanicus approximately 60% of the former and 45% of the latter were heteroplasmic. From densitometry of autoradiographs the frequencies of mtDNA size classes were determined for the population samples and are shown to very different in the two species. However, in populations where hybridization between the two species has occurred, the frequencies of size classes and cytoplasmic genotypes in each species' distinct mtDNA lineage were shifted in a manner suggesting nuclear-cytoplasmic interactions. The data were applied to reported diversity indices and hierarchical statistics. The hierarchical statistics indicated that the greatest proportion of variation for mtDNA size was due to variation among individuals in their cytoplasmic genotypes (heteroplasmic or homoplasmic state). The diversity indices were used to estimate a per-generation mutation rate for size variants of 10(-4). The data are discussed in light of the relationship between genetic drift and mutation in maintaining variation for mtDNA size.

The effects of gregarine parasites on longevity, weight loss, fecundity and developmental time in the field crickets Gryllus veletis and G.pennsylvanicus

ABSTRACT. 1. Gregarines, debilitating gut parasites, significantly reduced longevity and increased weight loss in the field cricket Gryllus pennsylvanicus Burmeiser when adults were kept on suboptimal diets, but in G.pennsylvanicus and G.veletis (Alexander and Bigelow) fed ad libitum, weight change, longevity, and fecundity were not significantly different in infected and control individuals.2. Adults harbouring gregarines at eclosion took significantly longer to develop from the second and third instars than did uninfected adults.3. Longevity of nymphs kept in the laboratory without food was decreased in infected individuals compared with uninfected ones, but not significantly so.4. The evolutionary and ecological implications of nonlethal parasites are discussed.

Age determination of adult field crickets: methodology and field applications

Details of a method originated by A.C. Neville for aging adult insects by counting daily growth rings in tibial or other body sections are given. A test of the method's accuracy using laboratory-reared field crickets (Gryllus pennsylvanicus and Gryllus veletis) showed that the number of growth rings counted is equivalent to the number of days past adult molt until the insect is approximately 25–30 days old, when cuticle growth is completed and rings are no longer added. Field populations of the two cricket species sampled in 2 years seldom contained individuals with more than 18 rings. Several applications for the technique to ecological and behavioral studies are given, using examples from data on G. veletis and G. pennsylvanicus.

PREDATION ON ADULTS OF THE CRUCIFER FLEA BEETLE, PHYLLOTRETA CRUCIFERAE (GOEZE), BY THE NORTHERN FALL FIELD CRICKET, GRYLLUS PENNSYLVANICUS BURMEISTER (ORTHOPTERA: GRYLLIDAE)

Predation on adults of the crucifer flea beetle, Phyllotreta cruciferae (Goeze), by the northern fall field cricket, Gryllus pennsylvanicus Burmeister, was recorded in laboratory tests to identify predators of flea beetles that attack canola and mustard crops. In these tests, four field-collected adult crickets all ate live adult P. icruciferae, as did 15 of 16 lateinstar cricket nymphs. The tests were carried out in 60 by 20 mm disposable plastic Petri dishes, with a stoppered hole to facilitate introduction of flea beetles. A filter paper liner in the bottom of the dish gave the insects a firm footing.

BARRIERS TO GENE EXCHANGE BETWEEN CLOSELY RELATED CRICKET SPECIES. II. LIFE CYCLE VARIATION AND TEMPORAL ISOLATION

The closely related field crickets Gryllus firmus and Gryllus pennsylvanicus are known to hybridize in a zone of contact that extends over more than 800 km from the Blue Ridge in Virginia to southern Connecticut. Here I present evidence that the extent of temporal reproductive isolation of the two cricket species varies along the length of the zone. Adults of G. firmus and G. pennsylvanicus occur synchronously in Connecticut but G. firmus matures significantly later than G. pennsylvanicus along the Blue Ridge in Virginia. Variation in the extent of temporal isolation is a consequence of intrinsic differences in the egg-to-adult development time of G. firmus from the two localities. In laboratory rearing experiments, there is little variation in development time among crickets from G. pennsylvanicus populations ranging from Vermont to Virginia. However, G. firmus from Virginia takes significantly longer to mature than G. firmus from Connecticut. Comparisons between species from neighboring localities show that lowland Virginia G. firmus take much longer to develop and are larger as adults than montane Virginia G. pennsylvanicus. In Connecticut, crickets of the two species differ very little in development time and body size. Patterns of variation in development time and body size are compared with similar data for frogs along one of the same environmental gradients and for field crickets along similar gradients elsewhere. Although G. firmus and G. pennsylvanicus are temporally isolated in Virginia, adults of the two species do occur together. Examination of Esterase genotypes of field-inseminated females and their progeny from a mixed population on the Blue Ridge suggests that pre-mating barriers other than temporal isolation are not effective in preventing gene exchange.

Persistence and Transfer of 36 C1‐DDT in the Soil and Biota of an Old‐Field Ecosystem: A Six‐Year Balance Study

The fate of a 1 kg/ha application of granular chlorine—36—labeled DDT made by helicopter on 10 June 1969 to a 4—ha old—field study are near Urbana, Ohio was traced and quantified in soil and biota through November 1974. Between 1970 and 1974, residues of DDT (DDTR, includes DDT plus metabolites) declined from 22.0 to 3.8 mg/kg tissue in earthworms (Lumbricus terrestris) and from 9.3 to 2.1 mg/kg in slugs (Decoceras laeve). Residues also declined from 12.1 to 4.7 mg/kg in firefly larvae (Photuris sp.), and from 32.3 mg/kg whole body in 1970 to 18.9 mg/kg in 1974 in short—tailed shrews (Blarina brevicauda), two predators of slugs and earthworms. The fact of moles (Scalopus aquaticus) and garter snakes (Thamnophis sirtalis), which fed primarily on earthworms, contained less DDTR (69.7 and 53.3 mg/kg, respectively) than did that of Blarina (308.5 mg/kg) but more than that of the other vertebrates. Levels of DDTR in foilage of grasses and forbs increased from 2—3 mg/kg in 1970 to 7.6 mg/kg in 1974, but remained relatively constant at 1.6 mg/kg in roots. Residues increased from 2.5 mg/kg in 1971 to 10.8 mg/kg in 1974 in isopods (Tracheoniscus rathkei); from 1.5 mg/kg in 1970 to 8.1 mg/kg in 1973 in crickets (Gryllus pennsylvanicus and Nemobius allardi); and from 1.4 mg/kg in 1970 to 5.4 mg/kg in 1973 in ground beetles (Carabidae), which were predators of isopods, crickets, and other herbivorous arthropods. Whole body residues increased in meadow voles (Microtus pennsylvanicus), which fed primarily on grasses, from 2.7 mg/kg in 1970 to 6.8 mg/kg in 1974; and in masked shrews (Sorex cinereus), which were predators of herbivorous arthropods, from 4.4 mg/kg in 1970 to 9.8 mg/kg in 1974. Cottontail rabbits (Sylvilagus floridanus), collected only in 1969 and 1970, contained DDTR levels similar to those of voles. Weasels (Mustela nivalis) contained about twice the residue levels of voles, their principal prey. Amounts of residues in samples of air collected at the surface of the soil were positively correlated with amounts in soil and with air temperature. The total quantity of DDTR in the top 12 cm of soil was estimated to be 1779 g in OCtober 1974, or 38% of the amount applied in 1969. Earthworms, which comprised the largest component of animal biomass, contained 5% of the total DDTR in the ecosystem in 1969, compared to 3% in the plants and other biota. As residues declined in earthworms and increased in plants over time, the total DDTR bound in the biota increased until it accounted for 22% of the total DDTR in the ecosystem in 1974. Losses of DDTR from the ecosystem eary year were attributed primarily to volatilization from soil, because losses in runoff and emigration insects and small mammals were negligible.

Cellular reactions of the field cricket (Gryllus pennsylvanicus (Burmeister)) to Turgida turgida (Rudolphi, 1819) (Nematoda: Physalopteroidea)

Cellular reactions to infections of Turgida turgida (Rudolphi, 1819) in field crickets (Gryllus pennsylvanicus (Burmeister) (=Acheta pennsylvanicus Burmeister)) were studied. Most larvae reached the epithelial cells of the ileum. These larvae caused little cellular destruction or haemocytic response until 18 h after infection. Syncytia of epithelial cell origin had formed around larvae by 28 h after infection. Initially, each syncytium was surrounded by haemocytes and later, by a wall with two well-defined layers. The epithelial layer of the alimentary tract had regenerated beneath the capsule by 48 days. Occasionally larvae penetrated directly into the haemocoel and were surrounded by haemocytes and(or) became melanized.

Survivorship of Experimental Green Cloverworm (Lepidoptera: Noctuidae) Pupal Cohorts in Soybeans1

The survivorship of pupal green cloverworms (GCW), Plathypena scabra (F.), was studied experimentally in Iowa soybean fields during 1978 to 1980. During 1978 and 1980, predation was the primary pupal mortality factor, accounting for 37.8 and 60.0% mortality, respectively. Two categories of predation were identified: “eaten” and “missing” pupae. More pupae were “missing” and fewer pupae were “eaten” in field plots 0 to 4 m from the fencerow than in plots 30 to 34 m or 76 to 80 m from the fencerow. During 1979, a single severe thunderstorm destroyed 82.8% of the cohorts. Laboratory feeding trials identified 10 species of crickets, ground beetles, and rodents as GCW pupal predators. Exclusion cage experiments during 1980 showed that the northern field cricket, Gryllus pennsylvanicus Burmeister, accounted for 60 to 87% of total pupal predation. The combined impact of this cricket and several ground-foraging birds seemed to account for the high levels of pupal predation observed adjacent to the fencerow.

A NARROW HYBRID ZONE BETWEEN CLOSELY RELATED CRICKET SPECIES.

Our understanding of speciation events derives in large part from observations of closely related species or of differentiated populations that are thought to be incipient species. Such observations are particularly useful if they allow us to identify critical genetic changes that result in intrinsic barriers to gene exchange and to distinguish these from changes that simply accompany speciation (and might well occur in its absence). One approach is to examine interactions between closely related species or presumed incipient species where they occur sympatrically. With appropriate laboratory and/or field manipulations it may be possible to isolate the effects on degree of reproductive isolation of particular morphological, developmental or behavioral differences and then proceed to examine the genetic basis for such differences. This paper is the first in a series in which we examine the nature of barriers to gene exchange between egg-overwintering, fall adult field crickets (genus Gryllus). North American field crickets provide excellent material for evolutionary studies (Alexander, 1968; Harrison, 1978). Despite the existence of considerable morphological variation within this group, orthopteran taxonomists in the early part of this century concluded that Gryllus in North America consisted of a single, highly variable species (Lutz, 1908; Rehn and Hebard, 1915). Subsequent work, using calling song, life cycle and habitat as distinguishing characters, established the existence of at least eight distinct species in eastern North America alone (Fulton, 1952; Alexander, 1957; Alexander and Bigelow, 1960; Alexander and Walker, 1962; Walker, 1974). Here we are concerned with two of these species-the very closely related pair, G. pennsylvanicus and G. firmus. Gryllus pennsylvanicus occurs throughout the northeastern United States and extends south in the mountains to North Carolina and Georgia (Alexander, 1968). Throughout its range this species is univoltine, overwintering in the egg stage with adults appearing in late summer or early fall. Gryllus firmus, the 'beach cricket' (Fulton, 1952), is found along the Gulf Coast of the United States and along the Atlantic Coast as least as far north as the eastern shore of Maryland, where it is reported to occur together with G. pennsylvanicus (Alexander, 1957, 1968). In the northern part of the range the life cycle of G. firmus is nearly identical to that of G. pennsylvanicus. Further south adults of G. firmus appear in spring as well as fall (North Carolina) or throughout the year (Florida) and females lay both diapause and non-diapause eggs (Fulton, 1952; Alexander, 1968; Walker, 1981). Although populations of G. firmus and G. pennsylvanicus are morphologically distinct, no single morphological character is clearly diagnostic. The most reliable character for distinguishing the species appears to be ovipositor length in females (Alexander, 1957). In males, the number of teeth on the stridulatory file is greater in G. firmus (Rakshpal, 1960; Alexander and Walker, 1962; Nickle and Walker, 1974). In both sexes, G. firmus tends to be

Major unsaturated cuticular hydrocarbons of the field crickets,Gryllus pennsylvanicus andNemobius fasciatus

AbstractAdult male field crickets,Gryllus pennsylvanicus Burmeister, have more unsaturated cuticular hydrocarbons than adult females, and each has more unsaturates than last‐instar male and female nymphs. The 2 most abundant unsaturated hydrocarbons from each adult were (Z)‐7‐nonacosene and (Z,Z)‐6,22‐nonacosadiene. Last‐instar male nymphal field crickets,Nemobius fasciatus (De Geer), were almost devoid of cuticular alkenes compared to last instar female nymphs and adult males and females. The major unsaturated hydrocarbon from each was (Z,Z)‐6,9‐pentacosadiene.

Flight polymorphism in the field cricket Gryllus pennsylvanicus.

Wing length polymorphisms are common in many groups of insects. In the field cricket Gryllus pennsylvanicus the long-winged morph occurs in low frequency in most populations but seems not to occur at all in certain areas and to become relatively abundant in others. Laboratory rearing experiments and single-pair crosses suggest that both inter-and intrapopulation variation can be explained at least in part by genetic differences. A model of genetic variation in threshold response is consistent with all available data. One possible mechanism for maintenance of the flight polymorphism is discussed.