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31.
Summary The seeds in fruits consumed by primates may be chewed and digested, swallowed and defecated intact, or separated from the flesh and spat out. We show by a combination of close field observations and experiments with caged animals, that long-tailed macaques (Macaca fascicularis) have a remarkably low threshold of 3–4 mm for swallowing seeds and also that wild macaques rarely break them. The seeds of 69% of the ripe fruit species eaten are spat out intact or cleaned outside the mouth and dropped. Seed-spitting significantly reduces the swallowed food bulk and may lessen the risk of releasing seed toxins during mastication. However, it requires that even small fruits are processed in the mouth one or a few at a time. We suggest that fruit storage in the cheek pouches of cercopithecine monkeys allows them to spit seeds individually without excessively slowing fruit intake while feeding on patchily distributed fruit. In contrast, Apes and New World monkeys apparently swallow and defecate most ripe seeds in their diet and colobine monkeys break and digest them, detoxifying seed defenses by bacterial fermentation. 相似文献
32.
An alternating (asymmetric) bipolar staircase voltage clamppulse series was used to investigate the action potential inChara corallina. Using this protocol, we found that the actionpotential was present in the hyperpolarized region of the current-voltagerelationship of the whole cell membrane. Effects of strong hyperpolarizingvoltage steps, during the excitation process, can thus be studied. (Received August 22, 1989; Accepted October 14, 1989) 相似文献
33.
Begoña Granadino Luiz O. F. Penalva Lucas Sánchez 《Molecular & general genetics : MGG》1996,250(1):89-96
Crosses betweenDrosophila melanogaster females andD. simulans males produce viable hybrid females, while males are lethal. These males are rescued if they carry theD. simulans Lhr gene. This paper reports that females of the wild-typeD. melanogaster population Staket do not produce viable hybrid males when crossed withD. simulans Lhr males, a phenomenon which we designate as the Staket phenotype. The agent responsible for this phenomenon was found to be the StaketX chromosome (X
mel
,Stk). Analysis of the Staket phenotype showed that it is suppressed by extra copies ofD. melanogaster rDNA genes and that theX
mel
,Stk chromosome manifests a weak bobbed phenotype inD. melanogaster X
mel
,Stk/0 males. The numbers of functional rDNA genes inX
mel
,Stk andX
mel
,y w (control) chromosomes were found not to differ significantly. Thus a reduction in rDNA gene number cannot account for the weak bobbedX
mel
,Stk phenotype let alone the Staket phenotype. The rRNA precursor molecules transcribed from theX
mel
,Stk rDNA genes seem to be correctly processed in both intraspecific (melanogaster) and interspecific (melanogaster-simulans) conditions. It is therefore suggested that theX
mel
,Stk rDNA genes are inefficiently transcribed in themelanogaster-simulans hybrids. 相似文献
34.
Sedimentation rates were estimated in a Central Amazonian Black-water inundation forest. Sediment deposition on the forest ground, remote from the river bed, during an annual flood period, is of the order of 1 to 10 tons per hectare, depending on water depth and duration of flooding. The sediments consisted of fine organic matter, kaolinite, quartz sands and biogenic particles of silica. Their genesis and deposition depend on the interplay between pedogenic, limnological and biological processes. Sediments derive primarily from the materials leached from the soils. Clay soils are the main source of dissolved silica, and the sandy soils are the main sources of organic coumpounds and mineral particles. The physical sedimentation of particles as quartz sand grains only occurs in the upper reaches of the studied river. In the flood plain, the sedimentation is due to the coagulation and deposition of combined mineral particles and humic substances, and to the biological precipitation of the silica leached from the soil by sponges. 相似文献
35.
Two species of the dicynodontDinodontosaurus from the Middle Triassic interval of the Santa Maria Formation in Rio Grande do Sul, southern Brazil,D. tener (von Huene 1935) andD. turpior (von Huene 1935), are based on undiagnostic lectotypes and thus arenomina dubia. The oldest valid, available name for a species ofDinodontosaurus isD. oliveirai Romer 1943, the type species of the genus. (The unused senior subjective synonymDiodontosaurus pedroanum Caldas, 1936 has been suppressed by the International Commission on Zoological Nomenclature).Chanaria platyceps Cox 1968 andDinodontosaurus brevirostris Cox 1968 are junior subjective synonyms ofD. oliveirai Romer 1943.Dinodontosaurus thus is a monospecific genus known from the Santa Maria Formation and the Ischichuca (= Chañares) Formation of northwestern Argentina. This dicynodont and associated tetrapods characterize the Chanarian land-vertebrate faunachron, which is of Middle Triassic age, probably Ladinian. 相似文献
36.
Plasmodesmal-mediated cell-to-cell transport in wheat roots is modulated by anaerobic stress 总被引:10,自引:0,他引:10
Summary Cell-to-cell transport of small molecules and ions occurs in plants through plasmodesmata. Plant roots are frequently subjected to localized anaerobic stress, with a resultant decrease in ATP. In order to determine the effect of this stress on plasmodesmal transport, fluorescent dyes of increasing molecular weight (0.46 to 10 kDa) were injected into epidermal and cortical cells of 3-day-old wheat roots, and their movement into neighboring cells was determined by fluorescence microscopy. Anaerobiosis was generated by N2 gas or simulated by the presence of sodium azide, both of which reduced the ATP levels in the tissue by over 80%. In the absence of such stress, the upper limit for movement, or size exclusion limit (SEL), of cortical plasmodesmata was <1 kDa. The ATP analogue TNP-ADP (mw 681) moved across the plasmodesmata of unstressed roots, indicating that plasmodesmata may be conduits for nucleotide (ATP and ADP) exchange between cells. Upon imposition of stress, the SEL rose to between 5 and 10 kDa. This response of plasmodesmata to a decrease in the level of ATP suggests that they are constricted by an ATP-dependent process so as to maintain a restricted SEL. When roots are subjected to anaerobic stress, an increase in SEL may permit enhanced delivery of sugars to the affected cells of the root where anaerobic respiration could regenerate the needed ATP.Abbreviations F-dextran
fluorescein-coupled dextran
- LYCH
Lucifer Yellow CH
- SEL
size exclusion limit
- TNP-ADP
2-O-(trinitrophenyl)adenosine-5-diphosphate 相似文献
37.
We have analysed the viability of cellular clones induced by mitotic recombination in Drosophila melanogaster/D. simulans hybrid females during larval growth. These clones contain a portion of either melanogaster or simulans genomes in homozygosity. Analysis has been carried out for the X and the second chromosomes, as well as for the 3L chromosome arm. Clones were not found in certain structures, and in others they appeared in a very low frequency. Only in abdominal tergites was a significant number of clones observed, although their frequency was lower than in melanogaster abdomens. The bigger the portion of the genome that is homozygous, the less viable is the recombinant melano-gaster/simulans hybrid clone. The few clones that appeared may represent cases in which mitotic recombination took place in distal chromosome intervals, so that the clones contained a small portion of either melanogaster or simulans chromosomes in homozygosity. Moreover, Lhr, a gene of D. simulans that suppresses the lethality of male and female melanogaster/simulans hybrids, does not suppress the lethality of the recombinant melanogaster/simulans clones. Thus, it appears that there is not just a single gene, but at least one per tested chromosome arm (and maybe more) that cause hybrid lethality. Therefore, the two species, D. melanogaster and D. simulans, have diverged to such a degree that the absence of part of the genome of one species cannot be substituted by the corresponding part of the genome of the other, probably due to the formation of co-adapted gene complexes in both species following their divergent evolution after speciation. The disruption of those coadapted gene complexes would cause the lethality of the recombinant hybrid clones. 相似文献
38.
39.
Lucas P. Medeiros Stefano Allesina Vasilis Dakos George Sugihara Serguei Saavedra 《Ecology letters》2023,26(1):170-183
Managing ecological communities requires fast detection of species that are sensitive to perturbations. Yet, the focus on recovery to equilibrium has prevented us from assessing species responses to perturbations when abundances fluctuate over time. Here, we introduce two data-driven approaches (expected sensitivity and eigenvector rankings) based on the time-varying Jacobian matrix to rank species over time according to their sensitivity to perturbations on abundances. Using several population dynamics models, we demonstrate that we can infer these rankings from time-series data to predict the order of species sensitivities. We find that the most sensitive species are not always the ones with the most rapidly changing or lowest abundance, which are typical criteria used to monitor populations. Finally, using two empirical time series, we show that sensitive species tend to be harder to forecast. Our results suggest that incorporating information on species interactions can improve how we manage communities out of equilibrium. 相似文献