刺激隐神经中C类纤维诱发的小脑浦肯野细胞简单锋电位反应

用玻璃微电极记录了猫小脑浦肯野细胞的简单锋电位(PC-SS)。在标准化互协方差函数图中,PC-SS自发放电无明显波峰;弱刺激隐神经只引起A类纤维传入时,PC-SS出现A类诱发放电反应(A-CED),它包括潜伏期为16.7±0.9ms的早反应和270.8±12.8ms的晚反应。用极化电流选择性阻滞A类纤维传导后,强刺激只引起C类纤维单独传入时,出现潜伏期为142.4±4.3ms的C类诱发反应(C-CED)。强刺激同时引起A类和C类纤维传入时,只出现A-CED而不出现C-CED。按标准化功率谱密度函数分析,PC-SS自发放电可分为两种类型。一类为高峰型,最大能量峰值平均为15.7±4.7×10~(-3),峰频为4.07±1.67Hz;刺激A类纤维使峰值增大,而刺激C类纤维却使峰值减小。另一类为低峰型,峰值为8.4±1.4×10~(-3),峰频为3.67±2.90Hz。刺激A类和C类纤维均使峰值增大,前者增大更多,但峰频均无显著性变化。上述结果表明,C类纤维传入可以到达小脑浦肯野细胞,引起特异的PC-SS放电反应。     

Analysis of sibling cannibalism among pike,Esox lucius,juveniles reared under semi-natural conditions

Synopsis Sibling cannibalism in pike, Esox lucius, larvae and juveniles living in outdoor rearing ponds was studied using stomach contents analysis. For the two initial densities tested (6 and 18 larvae m^–2, equivalent to 12 and 36 larvae m^–3), cannibalism was non-existent during the larval period (13 to 35 mm total length) and was observed only during the juvenile stages. Initial density of larvae influenced both the date of first detection of cannibalistic individuals and the rate of development of cannibalism in the population. At initial stocking densities of 18 larvae m^–2 (36 larvae m^–3), cannibalism was observed from 21 days after the start of exogenous feeding (mean total length: 60 mm) onwards. At a mean total length of 100 mm and for initial stocking densities of 6 and 18 larvae m^–2, (12 and 36 larvae m^–3), the average proportions of cannibals in the populations of juveniles were 7.8% and 41.3% and the cannibals accounted for 15.5% and 65.9% of the total pike biomass, respectively. In stomachs of cannibals, young pike were the dominant prey in terms of weight. Dry weights of invertebrate-prey were lower in cannibals than in non-cannibals of similar size. Cannibalism among pike juveniles was characterized by the prey being swallowed whole and head first in the vast majority of cases. There was a strong positive correlation between predator and prey size and the mouth size of a cannibal was found to be an important constraint determining maximum victim size. The overall mean ratio of pike prey length to pike cannibal length was 66.2% and the average ratio of prey head depth to predator mouth width amounted to 87.6%. Prey size selection could be demonstrated for several length-groups of cannibals. These results are compared with the characteristics of early cannibalism in other fish species.     

Succession of sessile organisms on experimental plates immersed in Nabeta Bay,Izu Peninsula,Japan V. An integrated consideration on the definition and prediction of succession

Successional changes of sessile organisms over about 3 years on concrete plates immersed at depths of 1.0, 2.5, 4.0 and 5.5 m in Nabeta Bay, Shimoda, Pacific coast of Japan, were investigated from their species composition, percentage cover, and the structure, metabolism, biomass and maturity of the community for the purpose of verifying the hypothesis of succession by Margalef (1968) and Odum (1969). The process of succession was divided into five stages from a cluster analysis based on Horn's (1966) similarity in community structure. The five stages were characterized from dominant, species and 18 community attributes in terms of structure, metabolism, biomass and maturity. With the advance of stages, two large-sized, long-lived species, the kelpEisenia bicyclis and the oysterCrassostrea nippona, dominated; 18 community attributes showed a directional succession ending in a constant community structure, low community metabolism, accumulation of community biomass except chlorophylla and an enhanced degree of community maturity. This directionality in succession of community attributes was valid for the prediction of Margalef and Odum, despite a tendency for estimated daily energy budget to be more heterotrophic in such an open system. From these results, it was suggested that the definition of succession by Odum (1969) should be interpreted as the regularity in shift of dominant species, not individual species, and as the control of system by feedback mechanism developing with succession rather than community-controlled mechanism.     

Importance of communal foraging grounds outside the reed marsh for breeding great reed warblers

Foraging habitat selection of breeding great reed warblers was studied at a shore of Lake Biwa. The foraging grounds of parent warblers during the nesting period were not restricted to the breeding territory of the reed marsh, their nestling habitat. The paddy field outside the reed marsh was used communally by them throughout the breeding season. Females with early stage nestlings did not visit the paddy field whereas when nestlings were older than 3 days, more than half of their total food was collected there. Females with nests adjacent to the paddy field tended to exploit the paddy field more often than those with nests distant from it. Monogamously mated females tended to exploit the paddy field more often than polygynously mated females. Food collected in the paddy field was larger than that in the reed marsh and parent birds were prepared to travel longer distances to exploit the rich source of food in the paddy field. The importance of the communal foraging ground outside the reed marsh as a background of the polygynous mating system of this species is discussed.     

Morphological and physiological responses to increased salinity in marsh and dune ecotypes ofSporobolus virginicus (L.) Kunth

Summary Sporobolus virginicus (L.) Kunth is a halophytic grass native to tropical and warm temperate coasts throughout the world. A rhizomatous perennial with erect culms,S. virginicus occurs as two genetically distinct growth forms, which are designated by their characteristic habitats as marsh and dune. What accounts for the specific distribution and maintenance of two separate ecotypes ofS. virginicus is not known. The present study examined the effects of seawater salinity on several morphological and physiological responses of hydroponically cultivated marsh and dune plants to determine whether differential tolerance to substrate salinity might contribute to the observed pattern of habitation. Both marsh and dune form plants survived prolonged exposure to full-strength seawater and reproduced vegetatively via culms and rhizomes. Salinity-induced reductions in culm height, internode length, and leaf size led to a miniaturization of marsh and dune plants. Sodium ion levels were low (<1.0 mmol/g dry weight) in various organs of salinized plants irrespective of ecotype, and potassium ion content increased in all salt-challenged plants, as did quarternary ammonium compounds and proline. Significant differences, however, between marsh and dune plants with respect to the effects of salinity on resource allocation, flowering phenology, and protein composition suggested that external salt concentration has a role in determining ecotype distribution.     

Fish size and habitat depth relationships in headwater streams

Summary Surveys of 262 pools in 3 small streams in eastern Tennessee demonstrated a strong positive relationship between pool depth and the size of the largest fish within a pool (P<0.001). Similarly, the largest colonizers of newly-created deep pools were larger than the colonizers of shallow pools. We explored the role of predation risk in contributing to the bigger fish — deeper habitat pattern, which has been noted by others, by conducting five manipulative field experiments in two streams. Three experiments used stoneroller minnows (Campostoma anomalum); one used creek chubs (Semotilus atromaculatus); and one used striped shiners (Notropis chrysocephalus). The stoneroller experiments showed that survival of fish approximately 100 mm in total length (TL) was much lower in shallow pools (10 cm deep) than in deep (40 cm maximum) pools (19% versus 80% survival over 12 d in one experiment) and added cover markedly increased stoneroller survival in shallow pools (from 49% to 96% in an 11-d experiment). The creek chub experiment showed that, as for stonerollers, pool depth markedly influenced survival: the chubs survived an average of 4.9 d in shallow pools and >10.8 d in deep pools. In the striped shiner experiment in shallow artificial streamside troughs, no individuals 75–100 mm TL survived as long as 13 d, where-as smaller (20–25 mm) fish had 100% survival over 13 d. The results of the experiments show that predation risk from wading/diving animals (e.g., herons and raccoons) is much higher for larger fishes in shallow water than for these fishes in deeper water or for smaller fish in shallow water. We discuss the role of predation risk from two sources (piscivorous fish, which are more effective in deeper habitats, and diving/wading predators, which are more effective in shallow habitats) in contributing to the bigger fish — deeper habitat pattern in streams.     

Resource limitation of tephritid flies on lesser burdock,Arctium minus (Hill) Bernh. (Compositae)

Summary The intensity of resource exploitation by phytophagous insects is usually considered to reflect population size. For populations of two flowerhead-attacking tephritid flies, however, the resources utilised were not related to the numbers of searching adults. Tephritis bardanae Schrank attacked 11–13% of the total flowerheads each year, and Cerajocera tussilaginis (Fab) 17–65%, despite much wider and uncorrelated variation in adult numbers. Analysis of field data showed that the proportion of flowerheads used was not limited by poor flowerhead quality, but was restricted by (1) the synchronisation of adult activity with the appearance of flowerheads at the correct age for oviposition, and (2) by factors which influenced the ability of female flies to locate available heads. These restrictions were more severe in T. bardanae and explained its relatively low rate of infestation. Both tephritids tended to avoid flowerheads in open areas. The processes governing resource exploitation in each tephritid operated independently of the other, and a partial separation of the two species between flowerhead types and habitats arose simply because of their different timing of attack.     

Current perspectives on plasmodesmata: structure and function

Recent studies on plasmodesmata have shown that these important intercellular passages for communication and transport are much more sophisticated in both structure and regulatory abilities than previously imagined. A complex, but not well understood, substructure has been revealed by a variety of increasingly reliable ultrastructural techniques. Proteinaceous particles are seen within the cytoplasmic sleeve surrounding the desmotubule. Dye-coupling studies have provided experimental evidence for the physical pathway of solute movement, supporting conclusions about substructural dimensions within plasmodesmata drawn from the ultrastructural studies. Calcium has been identified as a major factor in the regulation of intercellular communication via plasmodesmata. Evidence from studies on virus movement through plasmodesmata suggests a direct interaction between virallycoded movement proteins and plasmodesmata in the systemic spread of many viruses. There is increasing evidence, albeit indirect, that in some plant species phloem loading may involve transport of photoassimilate entirely within the symplast from mesophyll cells to the sieve element-companion cell complexes of minor veins.     

Prediction of F3 row performance from F2 individual plant data in oats

Summary Parameters estimated from a Gardner-Eberhart analysis of the F₂ generation of a six-parent diallel in oats (Avena sativa L.) were used to compare methods for predicting the performance of F₃ row plots. The prediction methods were: (1) individual F₂ plant performance (F2I), (2) parent average plus F₂ plot deviations (PF2), (3) parent average plus weighted F₂ plot deviations (PF2P), (4) best linear unbiased prediction (BLUP) of parent average plus F₂ plot deviations (BPF2), and (5) BLUP plus weighted F₂ deviations (BF2). The F₂ single-plant traits used for prediction were biological yield to predict F₃ biological yield, whole plant and primary tiller grain yield for prediction of F₃ grain yield, and whole plant and primary tiller harvest index (HI) to predict F₃ HI. Prediction methods were evaluated by correlations between predicted and observed F₃ performance. Prediction methods and traits for which correlations were greater than for F2I included: BF2 for biological yield, PF2, PF2P and BF2 for whole plant grain yield, PF2, BPF2, and BF2 for primary tiller grain yield. None had a correlation significantly greater than F2I for either measure of HI, where heritability was large. PF2 is the recommended method for traits with low heritability because of its simplicity and because it had the largest or nearly the largest correlation for each of the yield traits. F2I is the recommended method for traits with larger heritability.Contribution No. 8821 of the U.S. Regional Pasture Research LaboratoryDeceased     

What is this stuff called fitness?

This paper considers a variety of attempts to define fitness in such a way as to defend the theory of evolution by natural selection from the criticism that it is a circular argument. Each of the definitions is shown to be inconsistent with the others. The paper argues that the environment in which an animal evolves can be defined only with respect to the properties of the phenotype of the animal and that it is therefore not illuminating to try to explain the phenotypic properties of the animal in terms of adaptation to an environment that is defined by those very properties. Furthermore, since there is no way that the environment can be defined independently of the presence of the animal there is no way that the quality of an animal can be assessed; and there can be no objective criteria by whichany form of selection can be carried out, therefore there can be no criteria by whichnatural selection can be carried out. It is proposed that fitness is nothing more than the production of offspring, that this is a phenotypic property like all the others, and if it is heritable then the offspring of the parents that produce the most offspring will themselves produce the most offspring, and that in principle it is impossible to account for this in terms of the other phenotypic properties of the fittest animals except by circular argument. Differential rates of reproduction are the causes of evolution and the phenotypic causes are strictly inexplicable.