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991.
The head of Anomochilus weberi combines features seen in living uropeltines and scolecophidians, two clades of fossorial snakes that appear to have the most specialized and, at the same time, the most divergent modifications of the head. However, the weakly supported premaxilla of Anomochilus departs from both scolecophidian and uropeltine modes of reinforcing the anterior tip of the snout, suggesting that Anomochilus is a less specialized burrower. Its skull also has a number of features unusual among snakes, including a unique buttress on the anterior ends of the septomaxillae, an ectopterygoid reduced to a splint that touches neither maxilla nor pterygoid, a short maxillary tooth row oriented at 45° to the long axis of the skull, and a braincase and snout complex that are uniformly wide. The features of the upper jaw are predicted to confer behavioural and mechanical attributes intermediate between those of typhlopid scolecophidians and uropeltines. 相似文献
992.
993.
DIDIER NÉRAUDEAU BRUNO DAVID CÉLINE MADON 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1998,31(4):323-333
The existing definition of spatangoid fascioles as a narrow band of minute tubercles (miliaries) is inadequate. One reason is that many intermediates between the presence of indisputable fascioles and their total absence are known. Although fascioles are widely used in the classification of spatangoids, diversity of fasciole tuberculation has largely been ignored. We examine fascioles in about 100 spatangoid species, focusing on the earliest manifestations of fascioles (both developmentally and phylogenetically) and on their variable tuberculation. Qualitative observations are complemented by quantitative analyses (ANOVA and PCA) of 21 species. Three types of fascioles are defined according to tubercle pattern: protofascioles for localized concentrations of miliaries; parafascioles for bands of miliaries with a progressive transition to the surrounding tuberculation; orthofascioles for strongly differentiated, well-circumscribed bands of miliaries. Ontogenetic, architectural, ecological, and taxonomic variations of these three patterns are qualitatively and quantitatively investigated. We attempt to delineate plausible homologies, origins, and subsequent evolution of the different kinds of fascioles. 相似文献
994.
Cold-hardiness: a component of the diapause syndrome in pupae of the flesh flies, Sarcophaga crassipalpis and S. bullata 总被引:1,自引:0,他引:1
ABSTRACT. Diapausing pupae of Sarcophaga crassipalpis Macquart and S. bullata Parker reared at 20 or 25C readily survive exposure to - 10C for at least 25 days. In contrast, non-diapausing pupae produced by a variety of means are consistently intolerant of the low temperature. Non-diapausing pupae are not immediately killed by exposure to -10C: pupae exposed to the low temperature for up to 3 days proceed with pharate adult development but ultimately die before adult eclosion. Unlike many temperate zone insects, diapausing flesh fly pupae do not require a period of chilling for induction of cold-hardiness, and the attribute of cold-hardiness cannot be separated from other features of the diapause syndrome. Some cold-hardiness is already acquired during the third larval instar: diapause-destined larvae exposed to -10C are more successful in pupariating than non-diapause-destined larvae of the same age. 相似文献
995.
STANDARD SHEILA A.; PERRET DAVID; BRAY CLIFFORD M. 《Journal of experimental botany》1983,34(8):1047-1054
At an optimal germination temperature loss of viability in wheatseed is reflected in reduced levels of nucleoside triphosphatesand nucleotide sugars in the embryo compared to the levels foundin high viability embryos during the early hours of imbibition.These differences are magnified on germination at 10° Cand are accompanied by a greatly reduced rate of protein synthesisin embryos of low viability compared with the correspondingrate in embryos of high viability. Loss of vigour precedes lossof viability in seed but differences in biochemical parametersbetween high and medium vigour seed do not become apparent unlessgermination under stress conditions, e. g. low temperature,occurs. Under these stress conditions, wheat seed of reducedvigour can be distinguished from high vigour seed lots of similarviability by the decreased levels of nucleotides and nucleotidesugars found in embryos from reduced vigour seed lots duringthe early hours of imbibition and by reduced rates of proteinsynthesis in these embryos during this same period. Nucleotideanalysis is a potentially useful method for rapid assessmentof the viability or vigour of a seed lot. Key words: Nucleotides, Vigour, Viability, Wheat 相似文献
996.
Regulation of Sulphate Transport in a Tropical Legume, Macroptilium atropurpureum, cv. Siratro 总被引:2,自引:0,他引:2
CLARKSON DAVID T.; SMITH FRANK W.; BERG PETER J. VANDEN 《Journal of experimental botany》1983,34(11):1463-1483
When young plants of Macroptilium atropurpureum, cv. Siratrowere deprived of external sulphate (-S plants) growth of shootsand roots continued at rates comparable to those in plants wellsupplied with sulphate (control) for 3 d and 5 d respectively.Dilution of internal sulphur therefore took place and redistributionof sulphur occurred between inorganic and organic forms andbetween roots and younger leaves. Even when S-deficiency limitedgrowth, plants contained 16% of their total sulphur as sulphate,but most of this was retained in old leaves and redistributedslowly to growing zones. The capacity for sulphate uptake increased in roots of Splants very soon after they were deprived of external sulphate;within 24 h the absorption from 0.25 mol m3 SO42was more than five times that of control roots. Maximum increasedcapacity was reached after 23 d stress when the Vmaxof system 1 was 1948 nmol h1g1root fr. wt. inS plants and 337 nmol h1g1root fr. wt.in controls. The Kmfor system 1 did not change significantlywith S-stress being between 58 µM in both setsof plants. Absorption of L-cysteine was not stimulated by S-stress. There was a close, positive relationship between plant growthrate and the rate at which sulphate uptake capacity was enhancedby withholding sulphate from culture solutions. When S plants were replaced in sulphate-containing solutiontheir capacity for SO42 declined to the control levelwithin 24 h. Very marked repression of capacity was also foundwhen S plants were treated with L-cysteine, but therewas no immediate effect with methionine. Roots of this species appear to have a very active system fordegrading L-cysteine to sulphate, 30% of the label in 35S-cysteineabsorbed by roots was recovered in 35SO42 after 20 minor 2 h incubation. By contrast, roots had a very weak abilityto reduce sulphate. When part of the root system was in solution lacking sulphatethere was enhanced uptake of sulphate by other parts which themselveswere amply supplied with sulphate. This is seen as an exampleof compensatory absorption. The response to S-stress is specific and there were no positiveinteractions between S-stress and the absorption of phosphate,or P-stress and the uptake of sulphate. The results are discussed in relation to the close control ofsulphate uptake by internal sulphate concentration, redistributionof forms of sulphur during stress and mobility of sulphate inthe phloem. Key words: Kinetics, Amino-S, Sulpholipid, Repression;, Deficiency 相似文献
997.
998.
Primary productivity studies during early years of West Point Reservoir, Alabama-Georgia 总被引:1,自引:0,他引:1
SUMMARY. 1. Phytoplankton density (organisms ml?1), standing crop (chlorophyll a mg m?2) and primary productivity (mg C m?2 d?1) were measured during years 2 (1976) to 5 (1979) after impoundment on West Point Lake. 2. West Point waters had low alkalinity (<0.4 meq 1–1) and low conductivity (<75 μs cm?1 at 20°C) but N and P concentrations typically exceeded those considered apt to cause nuisance blooms of algae. Abiogenic turbidity was normally higher in the upstream areas of the reservoir than in the downstream areas and was several times higher in winter-spring than in summer-autumn due to increased rains and runoff. 3. Primary productivity varied greatly both temporally and spatially. A mean value of 684 mg C m?2 d?1 was well within the mesotrophic range and did not approach the highly eutrophic state predicted. Productivity increased from a low of 550 mg C m?2 d?1 in 1976 to high of 763 mg Cm?2d?1 in 1979. 4. Observed variation in both chlorophyll a and primary productivity was more predictable in the cool (December-March) than in the warm (June-September) season and with plant nutrient data than without it. With plant nutrient data in the cool season 84% and 86% of the variation (R2) in chlorophyll a and productivity, respectively, were accounted for by the regression equations. During the warm season, with plant nutrient data, regression equations accounted for 44% and 68% of the variation in chlorophyll a and productivity, respectively. Higher R2 values in cool seasons resulted from the overriding influence of abiogenic turbidity on phytoplankton communities. 相似文献
999.
JOHN RINGO MARY KING KANANEN DAVID WOOD 《Ethology : formerly Zeitschrift fur Tierpsychologie》1983,61(4):341-350
Three closely related species of Drosophila: D. virilis, D. americana, and D. novamexicana, are known to differ in levels of male-male aggression. Through direct observation in the laboratory, we attempted to determine and characterize the relationships between intrasexual aggression and mating success in males of each of these species. Our results indicated that the most important determinant of male mating success was not the amount of aggression performed by a male, but rather the amount of aggression directed towards him. 相似文献
1000.
This paper describes the traditional and modern ideology of conception and parenting among the Kaliai of West New Britain Province, Papua New Guinea. A pervasive set of beliefs hinges on male primacy and includes the assignment of the principal role in conception to the male. Females become kin to the children they bear only secondarily, through nurturance of their infants. Mother's milk and semen, then, are equivalent in their capacity to establish links of kinship. Despite the ideology of male dominance, food given is so loaded with significance for the establishment of kin ties that adoptive parents, male and female, must feed a nursing mother or risk the lapse of their claim on her infant. A mother's milk is therefore truly equal to a father's semen — his ‘water’ — and different aspects of Kaliai ideology are used more to justify past behaviour rather than to constrain it in the present. 相似文献