Scale dependence of vegetation-environment correlations: A case study of a North Carolina piedmont woodland

Abstract. Vegetation and its correlation with environment has been traditionally studied at a single scale of observation. If different ecological processes are dominant at different spatial and temporal scales, the results obtained from such observations will be specific to the single scale of observation employed and will lack generality. Consequently, it is important to assess whether the processes that determine community structure and function are similar at different scales, or whether, how rapidly, and under what circumstances the dominant processes change with scale of observation. Indeed, early work by Greig-Smith and associates (Greig-Smith 1952; Austin & Greig-Smith 1968; see Greig-Smith 1979; Kershaw & Looney 1985; Austin & Nicholls 1988) suggested that plant-plant interactions are typically important at small scales, but that the physical environment dominates at large scales. Using a gridded and mapped 6.6 ha portion of the Duke Forest on the North Carolina piedmont for a case study, we examined the importance of scale in vegetation studies by testing four hypotheses. First, we hypothesized that the correlation between vegetation composition and environment should increase with increasing grain (quadrat) size. Our results support this hypothesis. Second, we hypothesized that the environmental factors most highly correlated with species composition should be similar at all grain sizes within the 6.6-ha study area, and should be among the environmental factors strongly correlated with species composition over the much larger extent of the ca. 3500 ha Duke Forest. Our data are not consistent with either portion of this hypothesis. Third, we hypothesized that at the smaller grain sizes employed in this study (< 256 m²), the composition of the tree canopy should contribute significantly to the vegetation pattern in the under-story. Our results do not support this hypothesis. Finally, we predicted that with increased extent of sampling, the correlation between environment and vegetation should increase. Our data suggest the opposite may be true. This study confirms that results of vegetation analyses can depend greatly on the grain and extent of the samples employed. Whenever possible, sampling should include a variety of grain sizes and a carefully selected sample extent so as to ensure that the results obtained are robust. Application of the methods used here to a variety of vegetation types could lead to a better understanding of whether different ecological processes typically dominate at different spatial scales.     

Prenatal nicotine affects catecholamine gene expression in newborn rat carotid body and petrosal ganglion

Nicotine exposure modifiesthe expression of catecholamine and opioid neurotransmitter systemsinvolved in attenuation of hypoxic chemosensitivity. We used insitu hybridization histochemistry to determine the effect of prenataland early postnatal nicotine exposure on tyrosine hydroxylase (TH),dopamine -hydroxylase (DH), preproenkephalin (PPE), andD₂-dopamine receptor mRNA levels in the rat carotid bodyand petrosal ganglion during postnatal development. In the carotidbody, nicotine increased TH mRNA expression in animals at 0 and 3 postnatal days (both, P < 0.05 vs. control) withoutaffecting TH mRNA levels at 6 and 15 days. At 15 postnatal days, DHmRNA levels were increased in the carotid body of nicotine-exposed animals. Dopamine D₂-receptor mRNA levels in the carotidbody increased with postnatal age but were unaffected by nicotineexposure. PPE was not expressed in the carotid body at any of the agesstudied in control or treated animals. In the petrosal ganglion,nicotine increased the number of ganglion cells expressing TH mRNA inanimals at 3 days (P < 0.01 vs. control). DH mRNAexpression was not induced nor was PPE mRNA expression increased in thepetrosal ganglion in treated animals. Prenatal nicotine exposureupregulates mRNAs involved in the synthesis of two inhibitoryneuromodulators, dopamine and norepinephrine, in peripheral arterialchemoreceptors, which may contribute to abnormalities incardiorespiratory control observed in nicotine exposed animals.

     

High levels of congenital transmission of Toxoplasma gondii in a commercial sheep flock

Our current understanding of congenital transmission of Toxoplasma gondii from ewe to lamb dictates that infection frequently results in abortion and the death of the developing foetus, that the birth of live infected lambs occurs rarely and that the cat is the predominant source of infection in ewes. Using direct polymerase chain reaction detection of T. gondii, we report high levels of congenital transmission occurring in a commercially managed sheep flock. We sampled foetal-derived placental tissue and tissues from aborted lambs and showed that congenital transmission was detected in these tissues from 61% of all pregnancies. Where pregnancies resulted in the death of one or more lambs, T. gondii was detected in the lamb tissue for all but one of 18 (94%) pregnancies. Of the successful pregnancies resulting in the birth of live lambs we were able to detect T. gondii in foetal-derived placental tissue from 37 of 70 (42%) pregnancies. These results show that congenital transmission is occurring in a high percentage of lambings including normal healthy lambings, at this farm, suggesting that this route of transmission from generation to generation may be much more significant than that reported previously. These results may have implications for sheep husbandry and future epidemiological studies of T. gondii.     

The 'human revolution' in lowland tropical Southeast Asia: the antiquity and behavior of anatomically modern humans at Niah Cave (Sarawak, Borneo)

Recent research in Europe, Africa, and Southeast Asia suggests that we can no longer assume a direct and exclusive link between anatomically modern humans and behavioral modernity (the 'human revolution'), and assume that the presence of either one implies the presence of the other: discussions of the emergence of cultural complexity have to proceed with greater scrutiny of the evidence on a site-by-site basis to establish secure associations between the archaeology present there and the hominins who created it. This paper presents one such case study: Niah Cave in Sarawak on the island of Borneo, famous for the discovery in 1958 in the West Mouth of the Great Cave of a modern human skull, the 'Deep Skull,' controversially associated with radiocarbon dates of ca. 40,000 years before the present. A new chronostratigraphy has been developed through a re-investigation of the lithostratigraphy left by the earlier excavations, AMS-dating using three different comparative pre-treatments including ABOX of charcoal, and U-series using the Diffusion-Absorption model applied to fragments of bones from the Deep Skull itself. Stratigraphic reasons for earlier uncertainties about the antiquity of the skull are examined, and it is shown not to be an 'intrusive' artifact. It was probably excavated from fluvial-pond-desiccation deposits that accumulated episodically in a shallow basin immediately behind the cave entrance lip, in a climate that ranged from times of comparative aridity with complete desiccation, to episodes of greater surface wetness, changes attributed to regional climatic fluctuations. Vegetation outside the cave varied significantly over time, including wet lowland forest, montane forest, savannah, and grassland. The new dates and the lithostratigraphy relate the Deep Skull to evidence of episodes of human activity that range in date from ca. 46,000 to ca. 34,000 years ago. Initial investigations of sediment scorching, pollen, palynomorphs, phytoliths, plant macrofossils, and starch grains recovered from existing exposures, and of vertebrates from the current and the earlier excavations, suggest that human foraging during these times was marked by habitat-tailored hunting technologies, the collection and processing of toxic plants for consumption, and, perhaps, the use of fire at some forest-edges. The Niah evidence demonstrates the sophisticated nature of the subsistence behavior developed by modern humans to exploit the tropical environments that they encountered in Southeast Asia, including rainforest.     

Missense Mutations Allow a Sequence-Blind Mutant of SpoIIIE to Successfully Translocate Chromosomes during Sporulation

SpoIIIE directionally pumps DNA across membranes during Bacillus subtilis sporulation and vegetative growth. The sequence-reading domain (γ domain) is required for directional DNA transport, and its deletion severely impairs sporulation. We selected suppressors of the spoIIIEΔγ sporulation defect. Unexpectedly, many suppressors were intragenic missense mutants, and some restore sporulation to near-wild-type levels. The mutant proteins are likely not more abundant, faster at translocating DNA, or sequence-sensitive, and rescue does not involve the SpoIIIE homolog SftA. Some mutants behave differently when co-expressed with spoIIIEΔγ, consistent with the idea that some, but not all, variants may form mixed oligomers. In full-length spoIIIE, these mutations do not affect sporulation, and yet the corresponding residues are rarely found in other SpoIIIE/FtsK family members. The suppressors do not rescue chromosome translocation defects during vegetative growth, indicating that the role of the γ domain cannot be fully replaced by these mutations. We present two models consistent with our findings: that the suppressors commit to transport in one arbitrarily-determined direction or delay spore development. It is surprising that missense mutations somehow rescue loss of an entire domain with a complex function, and this raises new questions about the mechanism by which SpoIIIE pumps DNA and the roles SpoIIIE plays in vivo.     

Low-molecular mass carbohydrate accumulation in cyanobacteria from a marine microbial mat in response to salt

Forty seven strains of cyanobacteria, all isolated from microbial mats of intertidal sediments of the island of Mellum (North Sea), were analyzed for the presence of organic osmotica. The cyanobacteria examined belonged to taxonomically different groups and were classified according to their salt optimum and salt tolerance as either freshwater, brackish or marine. Except betaine, all organic osmotica known to occur in cyanobacteria, were found. The results showed no clear correlation between the chemical nature of the organic solute and the salt optimum or salt tolerance of the cyanobacteria examined, indicating that these solutes are not specific to this marine habitat. All strains belonging to the Nostoc/Anabea-group accumulated sucrose as the sole organic osmoticum. The marine, heterocystous Calothrix sp. accumulated trehalose. All strains of the LPP-group (Lyngbya, Plectonema, Phormidium) accumulated glucosylglycerol as sole or primary organic solute. Some LPP-strains accumulated a disaccharide as a secundary solute, e.g. sucrose or trehalose. Gloeocapsa, Synechocystis and Spirulina accumulated glucosylglycerol. Two marine Oscillatoria accumulated trehalose, whereas a freshwater Oscillatoria with a broad salinity tolerance, accumulated sucrose.Analysis of field samples of the microbial mats demonstrated the presence of glycerol, glucosylglycerol, sucrose and trehalose. The relative abundance of the different compounds was related to the species composition as could be predicted from laboratory observations. These data suggest that these carbohydrates have a function in maintaining osmotic balance in the organisms within the microbial mat.     

Mapping of antibody responses to the protective antigen of Bacillus anthracis by flow cytometric analysis

BACKGROUND: Different plant species vary as to the ratio of nucleotide base pairs of genomic DNA. A correlation between genome size and base pair ratio has been claimed. Base composition can be analyzed by base-specific dyes. METHODS: Genome size is determined by flow cytometry of suspensions of nuclei stained by the base independent dye, PI. For estimation of the AT frequency, the AT-specific dyes 4,6-diamidino-2-phenylindole, dihydrochloride (DAPI) and Hoechst 33342 (HO) were used. We define a dye factor (DF) as the ratio of the two estimates (peak ratios) of nuclear fluorescence intensities of sample relative to reference plant nuclei using a given dye and an intercalating fluorochrome. RESULTS: No significant correlation between genome size and the DF for DAPI was found when 54 plant species were investigated. However, similarities within and differences among the plant families were shown. The comparison of DAPI and HO DFs gave no consistent differences as would be predicted from the model of different binding site length of dyes. This result may be explained by the nonrandom distribution of base pairs. CONCLUSIONS: There is no general correlation between genome size and AT/GC ratio in higher plants. Similar AT/GC ratios within a plant family result from the general similarity of the DNA sequences within a family. The fluorescence of base-specific dyes is influenced by the nonrandom distribution of bases in the DNA molecule.     

Effects of monensin and forage:concentrate ratio on feed intake, endocrine, and ovarian function in beef heifers

Several reports have suggested that a treatment before in vitro maturation might improve oocyte competence and increase its developmental potential. Therefore, the objectives of the present study were to establish the kinetics of IVM in Zebu oocytes, to assess the effect of 6-dimethylaminopurine (6-DMAP), a phosphorylation inhibitor, on meiotic resumption, and to verify the developmental potential of the blocked oocytes after removal of the inhibitory conditions. To establish the kinetics of in vitro maturation 1422 oocytes were obtained from Nellore cows ovaries and matured in presence and absence of gonadotropins. Samples of oocytes were taken from culture at 0, 6, 9, 12, 15, 18, 21 and 24h, and the oocytes were fixed, stained and evaluated for nuclear morphology. Germinal vesicle break down (GVBD) occurred between 6 and 12h of culture in both groups. By 21h the majority of the oocytes had reached metaphase II in presence (71%) and absence (62%) of gonadotropins. In order to examine the inhibitory effect of 6-DMAP, 585 oocytes were cultured for 12, 18 and 24h in the presence or absence of 2mM of 6-DMAP. At each time point the oocytes were evaluated for nuclear morphology. To test the reversibility of meiotic inhibition 366 oocytes were incubated for 0, 12, 18 and 24h in the presence of 6-DMAP and then were transferred to the maturation medium and cultured for further 24h. A total of 429 oocytes were used to evaluate the developmental potential after meiotic inhibition. The oocytes were cultured in the presence of 6-DMAP for 0, 12, 18 and 24h, and then were matured, fertilized and cultured in vitro. Culture of bovine oocytes in the presence of 6-DMAP up to 24h completely blocked GVBD with more than 90% of the oocytes at GV stage. The inhibitory effect of 6-DMAP was fully reversible since maturation rates were similar (P>0.05) among all treatment groups. The evaluation of embryo development after various periods of meiotic blockage showed that inhibition, regardless the time period, had no effect (P>0.05) on penetration and cleavage rates. However, the proportion of embryos at blastocyst stage was reduced after inhibition for 12 (20.2%), 18 (20.1%) and 24h (19.0%) compared with the control group (35.6%). 6-DMAP has a reversible effect on maintenance of meiotic arrest, but reduced further embryo development.     

Effect of contingent auditory stimuli on concurrent schedule performance: an alternative punisher to electric shock

This study explored whether load auditory stimuli could be used as functional punishing stimuli in place of electric shock. Three experiments examined the effect of a loud auditory stimulus on rats’ responding maintained by a concurrent reinforcement schedule. In Experiment 1, overall response rate decreased when a concurrent 1.5 s tone presentation schedule was superimposed on the concurrent variable interval (VI) 180-s, VI 180-s reinforcement schedule. On the contrary, response rate increased when a click presentation schedule was added. In Experiment 2, the extent of the response suppression with a 1.5 s tone presentation varied as a function of the frequency of the reinforcement schedule maintaining responses; the leaner the schedule employed, the greater the response suppression. In Experiment 3, response suppression was observed to be inversely related to the duration of the tone; response facilitation was observed when a 3.0-s tone was used. In Experiments 1 and 2, a preference shift towards the alternative with richer reinforcement was observed when the tone schedule was added. In contrast, the preference shifted towards the leaner alternative when the click or longer duration stimulus was used. These results imply that both the type and duration of a loud auditory stimulus, as well as the reinforcement schedule maintaining responses, have a critical role in determining the effect of the stimuli on responding. They also suggest that a loud auditory stimulus can be used as a positive punisher in a choice situation for rats, when the duration of the tone is brief, and the reinforcement schedule maintaining responses is lean.     

Olfactory cytochrome P-450. Studies with suicide substrates of the haemoprotein.

1. The olfactory epithelium of male hamsters has been found to be extremely active in the cumene hydroperoxide-supported oxidation of tetramethylphenylenediamine, and this peroxidase activity has been shown to be cytochrome P-450-dependent. 2. The interaction of a series of suicide substrates of cytochrome P-450 with the hepatic and olfactory mono-oxygenase systems has been assessed by determination of peroxidase, 7-ethoxycoumarin O-de-ethylase (ECOD) and 7-ethoxyresorufin O-de-ethylase (EROD) activities after treatment in vivo with these compounds. Chloramphenicol, OOS-trimethylphosphorothiolate and two dihydropyridines [DDC (3,5-diethoxycarbonyl-1,4-dihydrocollidine) and 4-ethyl DDC (3,5-diethoxycarbonyl-4-ethyl-1,4-dihydro-2,6-dimethylpyridine)] all caused similar percentage inhibitions of hepatic and olfactory activities, but the absolute amounts of enzymic activity lost were considerably greater in the latter tissue. In contrast, halothane had little effect upon hepatic cytochrome P-450-dependent reactions, whereas it severely inhibited those of the olfactory epithelium. 3. The time course of loss and recovery of hepatic and olfactory peroxidase, ECOD and EROD activities after a single dose of 4-ethyl DDC was studied. The rates of loss of activity observed were very similar, irrespective of tissue or reaction examined. In the olfactory epithelium, all three activities recovered concurrently and at a rate similar to that of the hepatic peroxidase activity. In contrast, the hepatic de-ethylation of 7-ethoxycoumarin and 7-ethoxy-resorufin recovered significantly more rapidly. 4. It is suggested that this behaviour is due to 4-ethyl DDC acting not only as a suicidal inhibitor but also as an inducer of certain forms of cytochrome P-450 in the liver; in the olfactory epithelium, however, inactivation, but not induction, occurs. Classical inducing agents were reported to have no effect upon olfactory cytochrome P-450, and in the present study neither phenobarbitone nor beta-naphthoflavone treatment had any effect upon olfactory cytochrome P-450-dependent reactions, although it induced those of the liver.