荒漠草原蝗虫营养生态位及种间食物竞争模型的研究

以宁夏荒漠草原 1 2种蝗虫为对象 ,对荒漠草原蝗虫的营养生态位和种间食物竞争模型进行了研究 .采用嗉囊内含物分析技术分析了 1 2种蝗虫的取食特性和食物利用谱 ,并根据嗉囊内含物的分析结果 ,定量研究了蝗虫的营养生态位重叠和宽度 .依据生态位分化的特点 ,1 2种蝗虫可划分为 4个不同营养需求类群 :杂草取食者、杂草 禾草取食者、禾草 杂草取食者、禾草取食者 .通过蝗虫的取食频率、生物量以及种群密度 ,提出了蝗虫种间食物竞争力评估模型 ,对 1 2种蝗虫种间食物竞争的作用力进行了讨论 .     

Stage-based mortality of grassland grasshoppers (Acrididae) from wandering spider (Lycosidae) predation

Mortality rates in insects, including grasshoppers (Acrididae), are often stage- or size-specific. We estimated stage-specific mortality rates for three common grasshopper species from a Nebraska (USA) sandhills grassland (Ageneotettix deorum, Melanoplus sanguinipes and Phoetaliotes nebrascensis), and partitioned the impact due to wandering spider predation from remaining sources. Survivorship was estimated for multiple developmental stages (3rd instar through adult) under experimental conditions that either prevented or permitted predation from free-living, wandering spiders (primarily Schizocosa species). Total stage-specific mortality, including spider predation, examined over the period of single stages was greatest for the youngest stages (91% for 3rd instar, 73% for 4th instar, 63.5% for 5th instar and 30.4% for adults). For the developmental stages considered and averaged for all species, the contribution to total mortality from spider predation over the 10-d period (approximately the length of a developmental stage) ranged from 17% for 3rd instar nymphs to 23% for 4th and 5th instars, and an undetectable level for adults. While spiders may depress grasshopper numbers, contributions from spider predation to grasshopper population dynamics are uncertain.     

Competition among the adults of three grasshoppers (Orthop., Acrididae) on an alpine grassland

Abstract:  The intraspecific and interspecific competition among the adults of three common grasshoppers, Angaracris rhodopa (Fischer-Waldheim), Chorthippus dubius (Zubovsky) and Chorthippus fallax (Zubovsky) was investigated on Ganjia High Mountain Grassland in north-west China. The results indicated a strong intraspecific competition within species at high densities. The interspecific competition between the larger-sized species, A. rhodopa , and the smaller-sized species, C. dubius or C. fallax , was weak, while competition between C. dubius and C. fallax was strong. An asymmetric competitive interaction in mortality and fecundity associated with the diet and size was observed among the three species. Competition was strong between the two species that had a similar diet. The large-sized species had higher mortality rates and lower fecundity than the smaller-sized species. Intraspecific competition between the three species was mainly affected by food limitation, while interspecific competition was mainly associated with food limitation as well as the grasshoppers' adaptation to the environment.     

Fish mortality and physicochemistry in a managed floodplain wetland

Patterns of fish mortality and associated physicochemical factors werestudied during late spring in a managed wetland canal along the lowerMissouri River, Missouri. Mean dawn dissolved oxygen was lower and meanun-ionized ammonia and turbidity were higher during the fish kill thanbefore or after the kill, or than was observed in a nearby wetland canalwhere no fish kill occurred. Dissolved oxygen at dawn and un-ionizedammonia concentrations were at critically low and high levels respectively,so that both likely contributed to the fish mortality. Timing and magnitudeof observed carcasses suggested that Ameiurus melas Rafinesques wasthe most tolerant species for the sizes observed compared to Ictiobuscyprinellus Valenciennes, Lepomis macrochirus Rafinesque, Cyprinus carpio Linneaus, and Lepomis cyanellus Rafinesque.Decreasing mean lengths of fish carcasses during the fish kill for C.carpio, L. cyanellus, and A. melas, indicate that smaller fishes mayhave been more tolerant of harsh environmental conditions than largerindividuals of the same species. Differential mortalities among species andsizes during drawdowns in actively managed wetland pools may haveintentional and unintentional ramifications on wetland and riverine fishcommunity structure, fish-avian interactions, and implementing anecosystem management perspective to restoring more naturalized riverfloodplain wetland functions. Late summer and early autumn draining ofmanaged wetlands might be used to benefit a wider diversity of wildlife andfishes.     

Humidity selection by thermoregulating grasshoppers

1. 1.|To make the most effective use of evaporative cooling, an insect must be in an environment of the lowest humidity.

2. 2.|To test the hypothesis that, at temperatures requiring evaporative cooling, grasshoppers were able to select such a favourable environment, we observed the selection of, and time spent in dry (RH 5%) or humid (RH 97%) alternative chambers of a shuttle box at a range of temperatures from 28 to 50°C, in two species, Schistocerca americana and Romalea microptera.

3. 3.|Below 45°C, both species tended to remain in the chamber in which they began the trial; above 48°C, they all selected the arid chamber.

4. 4.|These findings suggest that grasshoppers can select the environment best for maintaining their body temperature below lethal levels but do not necessarily mean that they can actually sense relative humidity.

Chiasma distribution in Truxaline grasshoppers

Similar patterns of chiasma distribution are found within the individual arms of the chromosome complement in four species of Truxaline grasshopper. There is a linear relationship between chiasma frequency and chromosome arm length although the telocentric elements have a consistently higher mean number of chiasmata per unit of arm length. The positions of successive chiasmata can be defined in terms of residual (r.c. and r.t.) and interference (T) distances which vary in value according to both arm length and chiasma frequency. There is a tendency for one chiasma to lie in a distal position which is accentuated when additional chiasmata form. Supernumerary B chromosomes do not appear to influence the overall control mechanism of chiasma distribution. There is no indication that bivalents within a nucleus compete for chiasmata nor does the chiasma distribution in one arm of the metacentric members influence that in the other. It is suggested that the control of chiasma formation is determined mainly by interference factors.     

Spontaneous chromosome mutations in Truxaline grasshoppers

Three distinct mutant conditions are described in single male individuals from three species of short horn grasshopper. Of these, one is an entire germ line mutant of Myrmeleotettix maculatus, heterozygous for a centric fusion between single M₄ and M₅ telocentric chromosomes. In contrast, the remaining two mutants are present in mosaic form. One is heterozygous for an L₁-M₄ interchange in Omocestus viridulus, the other tetrasomic for the M₄ chromosome in Chorthippus parallelus which in addition is characterised by the inclusion of a supernumerary heterochromatic segment on one S₈ homologue. Centric fusion in Myrmehotettix maculatus has neither disturbed the chiasma potential of the elements constituting the fusion multiple nor, has it apparently influenced the production of balanced gametes. The pattern of chiasma formation in the L₁-M₄ interchange multiple lends support to the contention that the process of chiasma formation originates near the distal end of chromosome arms in Omocestus viridulus. There is no interaction between the two mutant conditions of tetrasomy and the presence of supernumerary segments in Chorthippus parallelus. Moreover, because of the precocious nature of two of the four M₄ homologues there is little tendency to form multivalents. The two M₄ bivalents share a similar mean chiasma frequency.     

Male and female meiosis in grasshoppers

Male meiosis in the grasshopper Stethophyma grossum is well known as an example of proximal chiasma localisation. An investigation of female meiosis in oocytes of this species shows that both the frequency and distribution of chiasmata are quite different from the male situation. Mean chiasma frequency per cell (14.98) in considerably higher in females than in males (11.28) which agrees with the trend established in other comparative studies of male and female meiosis. More strikingly, males and females also show not only different but quite opposite patterns of chiasma distribution. In spermatocytes of males, chiasmata are strictly localised proximally in most bivalents, but in oocytes of females very few chiasmata form in proximal regions and nearly all chiasmata form either in distal or interstitial regions. The genetical significance of these findings is considered.     

The cytogenetic systems of grasshoppers and locusts

The australian plague locust (2n=23 male, 24 female) is distinctive in possessing three pairs of two-armed, short autosomes (S₉, S₁₀ and S₁₁). In two of these pairs (S₉, S₁₀) these arms are a constant feature but in the shortest (S₉) pair most individuals are either heterozygous for them or else are homozygous telocentric. Coupled with this five of the heterozygous individuals give evidence of occasional short-arm detachment.—In all the S-pairs the shorter of the two arms is invariably heterochromatic in character and in the S₉ and S₁₁ shows a bi- or tri-partite sub-structure which suggests they may have originated by tandem duplication. — Three of the other autosomes (L₂, M₃ and M₆) also have small heterochromatin(het)-blocks associated with them. At first meiotic prophase these frequently associate with the univalent X chromosome which itself displays an unconventional pattern of allocycly, its centric end appearing negatively heteropycnotic from leptotene through diplotene.—At metaphase I the het-blocks on the telocentric autosomes sometimes transform into swollen, negatively heteropycnotic, segments equivalent in appearance to that shown by the entire X at this stage. It is suggested that these puff-like structures represent an inter-chromosomal position effect conditional upon prior X/A het-association at first prophase.     

The cytogenetic systems of grasshoppers and locusts

Two new cases of supernumerary heterochromatic segments are described. One of these, found in a heterozygous state in eight males of Chorthippus jucundus, is present terminally on the short arm of the longest autosome. The other, present in a single male heterozygote of Trimerotropis tolteca modesta, is again terminally sited, this time on the long arm of the second smallest auto-some. Both segments are considered to be products of tandem duplication rather than translocation. The segment system of C. jucundus, like that of a number of other categories of heterochromatic material, produces a striking increase in mean cell chiasma frequency compared to basic homozygotes from the same population. It is argued that this effect of the segment on recombination provides a potential basis for selection leading to altered fitness. This, in turn, may well have determined the evolution of at least some forms of supernumerary material in natural populations.     

Kinetochores of grasshoppers with Robertsonian chromosome fusions

The pachytene karyotypes of three grasshopper species with 2 and 3 Robertsonian fusions were constructed from electron micrographs of serially sectioned spermatocyte nuclei. Tracings of the synaptonemal complexes permitted identification of each bivalent and its centromeric region. Chromosomes with the centromere in a terminal position have a knob of centric heterochromatin on the synaptonemal complex where it ends at the nuclear envelope. In Chorthippus and in Chloealtis the submetacentric Robertsonian fusion chromosomes each have a single centric knob in the appropriate place. In Neopodismopsis each of the 2 submetacentric chromosomes have a centric knob which is double in size and structure. In spermatogonial metaphases the submetacentric chromosomes of Neopodismopsis have 70–80 microtubules per kinetochore while the telocentric chromosomes have 30–40 tubules per kinetochore. These observations are correlated with evidence from light microscopy that Robertsonian fusions may produce mono- or dicentric chromosomes.     

Transneuronal induction of muscle atrophy in grasshoppers

Autotomy is a process in grasshoppers whereby one or both hindlimbs can be shed to escape a predator or can be abandoned if damaged. It occurs between the trochanter and the femur (second and third leg segments) and once lost, the legs never regenerate. Autotomy severs branches of the leg nerve (N5) but damages no muscles since none span the autotomy plane. We find, however, that undamaged muscles intrinsic to the thorax of grasshoppers, Barytettix psolus, atrophy to less than 15% of their normal mass after autotomy of a hindlimb. These muscles operate the coxa and trochanter (first and second leg segments) and are innervated by branches of nerves 3 and 4; nerve branches that are not damaged by autotomy. Atrophy is localized to the side and body segment where autotomy occurs. Atrophy is evident 7-10 days after loss of a limb, is complete by about 30 days, and follows a similar time course whether induced in young adult, or sexually mature grasshoppers. During autotomy, leg nerve 5 is served distal to the trochanter, the thoracic muscles lose their normal static and dynamic load, and these muscles are subsequently no longer used to support the weight of the insect during posture and locomotion. Experimental loading and unloading of the affected muscles, and cutting of nerves indicated that it is the severing of leg nerve 5 during autotomy that transneuronally induces muscle atrophy.     

The cytogenetic systems of grasshoppers and locusts

The three endemic species of the Australian genusTolgadia are all distributed in the northern tropical and subtropical areas. They are distinguishable both on morphological and cytological grounds. All three have a derived neo XY, neo XX sex chromosome system involving distinct elements of a basically 11-membered autosome set, namely (spacies-1) (bivittata) and (infirma). Additionallybivittata is homozygous for two autosomal fusions involving and giving 2n=18 as compared to the complement of 2n=22 present in the other two species. Two of the species,bivittata and species-1, have a comparable mean cell chiasma frequency despite their difference in chromosome number. That ofinfirma is significantly higher. Coupled with this, some of the populations ofinfirma are polymorphic for supernumerary heterochromatic segments, principally on the smallest autosome. Such segments increase the mean cell chiasma frequency still further. Thusinfirma, which is the least habitat restricted despite its brachypterous nature, not only has the highest mean cell chiasma frequency but, in addition, has at its disposal a polymorphism capable of magnifying this difference.     

Visually targeted reaching in horse-head grasshoppers

Visually targeted reaching to a specific object is a demanding neuronal task requiring the translation of the location of the object from a two-dimensionsal set of retinotopic coordinates to a motor pattern that guides a limb to that point in three-dimensional space. This sensorimotor transformation has been intensively studied in mammals, but was not previously thought to occur in animals with smaller nervous systems such as insects. We studied horse-head grasshoppers (Orthoptera: Proscopididae) crossing gaps and found that visual inputs are sufficient for them to target their forelimbs to a foothold on the opposite side of the gap. High-speed video analysis showed that these reaches were targeted accurately and directly to footholds at different locations within the visual field through changes in forelimb trajectory and body position, and did not involve stereotyped searching movements. The proscopids estimated distant locations using peering to generate motion parallax, a monocular distance cue, but appeared to use binocular visual cues to estimate the distance of nearby footholds. Following occlusion of regions of binocular overlap, the proscopids resorted to peering to target reaches even to nearby locations. Monocular cues were sufficient for accurate targeting of the ipsilateral but not the contralateral forelimb. Thus, proscopids are capable not only of the sensorimotor transformations necessary for visually targeted reaching with their forelimbs but also of flexibly using different visual cues to target reaches.