Niche Shape and Genetic Aspects of Character Displacement

Character displacement involving a single, diallelic locus ineach of two competing species is investigated via computer simulation.The niche, as the sum of the utilization efficiencies of thepopulation for combinations of environmental variables, is distinguishedfrom the resource peak, which is a set of combinations of environmentalvariables actually present at exploitable frequencies in theenvironment. The two populations compete for a single resourcepeak made up of five subunits. Each genotype in each specieshas an optimum peak subunit, but survives in all of them. Theintermediate subunit is optimal for a genotype in each species.Movement is restricted between subunits, which are thus treatedhere as microhabitats. The simulation covers a geographicalrange with each species occurring alone where its birth rateis high, with the birth rate declining as the range of the otherspecies is approached; sympatry occurs in a region of intermediatebirth rates for both species. The character displacement involvescharacters determined by the genotypes at the competition locus.The shape of the resource peak has a profund effect on the formtaken by character displacement. A "steep" peak (one with theintermediate subunit much more frequent than the rest) resultsin a sharp step in the morphoclines, with two stable equilibriumpoints at the point of equal birth rates. A "bimodal" peak (onewith equally frequent subunits, each optimum for a genotypefor one species only) leads to a gradual change. Other peaktypes also have characteristic effects, showing that ecologicalinferences can be drawn from the form taken by character displacement.     

Efficiency of Countercurrent Distribution, Sephadex G-10, and Silicic Acid Partition Chromatography in the Purification and Separation of Gibberellin-like Substances from Plant Tissue

The effectiveness of countercurrent distribution, Sephadex G-10column chromatography and silicic acid partition column chromatographyin the purification of gibberellin-like substances from extractsof etiolated Phaseoltu multiflorus seedlings, and elongatingvegetative shoots of Arizona cypress (Cupressus arizonica Greene)and coastal Douglas-fir (Pseudotsuga menziesii var. menziesii)was followed by the use of the barley half-seed -amylase bioassayand dry-weight measurements. Countercurrent distribution resultedin a 10- to 30-fold reduction in the dry weight of the acidic,ethyl acetate-soluble fraction. Sephadex G-10 column chromatographyfurther lowered the dry weight by about two-thirds. Silicicacid partition column chromatography separated gibberellin-likesubstances from each other and again reduced the dry weight.Enhancement of bioassay activity was noted at each step of thepurification procedure. It is concluded that the above proceduresconstitute useful and efficient tools for the initial purificationof gibberellin-like substances from plant tissue.     

Catabolism of indole-3-acetic acid in chloroplast fractions from light-grown Pisum sativum L. seedlings

Abstract The catabolism of indole-3-acetic acid was investigated in chloroplast preparations and a crude enzyme fraction derived from chloroplasts of Pisum sativum seedlings. Data obtained with both systems indicate that indole-3-acetic acid undergoes decarboxylative oxidation in pea chloroplast preparations. An enhanced rate of decarboxylation of [1′-¹C]indole-3-acetic acid was obtained when chloroplast preparations were incubated in the light rather than in darkness. Results from control experiments discounted the possibility of this being due to light-induced breakdown of indole-3-acetic acid. High performance liquid chromatography analysis of [2′-¹⁴C]indole-3-acetic acid-fed incubates showed that indole-3-methanol was the major catabolite in both the chloroplast and the crude enzyme preparations. The identification of this reaction product was confirmed by gas chromatography-mass spectrometry when [²H₅]indole-3-methanol was detected in a purified extract derived from the incubation of an enzyme preparation with ³²H₅]indole-3-acetic acid.     

Microsatellite markers for the polygamous termite Nasutitermes corniger (Isoptera: Termitidae)

We developed eight highly variable microsatellite markers for the termite Nasutitermes corniger. Allele number per locus ranged from nine to 34, and expected heterozygosity from 0.45 to 0.94, in samples from seven sites in the former canal zone of Panama. The utility of these markers was assessed for five congeners varying in phylogenetic distance to N. corniger. The markers will be useful for fine‐scale examination of population and colony genetic structure in N. corniger and other closely related species.     

Predicting differential effects of climate change at the population level with life-cycle models of spring Chinook salmon

Habitat conditions mediate the effects of climate, so neighboring populations with differing habitat conditions may differ in their responses to climate change. We have previously observed that juvenile survival in Snake River spring/summer Chinook salmon is strongly correlated with summer temperature in some populations and with fall streamflow in others. Here, we explore potential differential responses of the viability of four of these populations to changes in streamflow and temperature that might result from climate change. First, we linked predicted changes in air temperature and precipitation from several General Circulation Models to a local hydrological model to project streamflow and air temperature under two climate‐change scenarios. Then, we developed a stochastic, density‐dependent life‐cycle model with independent environmental effects in juvenile and ocean stages, and parameterized the model for each population. We found that mean abundance decreased 20–50% and the probability of quasi‐extinction increased dramatically (from 0.1–0.4 to 0.3–0.9) for all populations in both scenarios. Differences between populations were greater in the more moderate climate scenario than in the more extreme, hot/dry scenario. Model results were relatively robust to realistic uncertainty in freshwater survival parameters in all scenarios. Our results demonstrate that detailed population models can usefully incorporate climate‐change predictions, and that global warming poses a direct threat to freshwater stages in these fish, increasing their risk of extinction. Because differences in habitat may contribute to the individualistic population responses we observed, we infer that maintaining habitat diversity will help buffer some species from the impacts of climate change.     

An Assessment of Gibberellin Structure-activity Relationships

Information on the biological activities of gibberellins (GAs)in the barley aleurone, Tangin-bozu dwarf rice, dwarf pea, lettucehypocotyl and cucumber hypocotyl bioassays is reviewed and discussedin the context of GA structure-activity relationships. The barley aleurone bioassay exhibits a limited response toGAs and it is suggested that this may be because the aleuronecells are able to carry out few GA interconversions. Consequentlyactivity is determined by the degree of compatibility betweenthe GAs and a receptor site. In this assay high biological activityis associated with GAs having a 3ß-hydroxy--lactonestructure. This activity is substantially enhanced by the additionalpresence of a 13-hydroxyl group. The substitution of a -lactoneor a -lactol for a -lactone results in reduced activity while3ß,13-dihydroxy GAs with either 20-carboxyl or 20-methylfunctions are completely inactive. The Tanginbozu dwarf ricebioassay responds to many more GAs than the barley aleuronesystem possibly because the rice seedlings can carry out extensiveGA interconversions. Under these circumstances GAs that areinactive per se can be metabolically converted to active forms.There is no interaction between the 3ß- and 13-hydroxyfunctions of GA molecules in the rice assay. Activity appearsto be determined by the degree oxidation of the C-20 group.The order of activity is usually -lactone > -lactol >-lactone > methyl > carboxyl. It is suggested this mayindicate that in rice seedlings C₂₀-GAs are converted to C₁₉-GAsvia a Baeyer-Villiger type oxidation. Activity in the dwarfpea bioassay is dependent upon GAs possessing both 3ß-and 13-hydroxyl groups and is again related to the state ofoxidation at the C-20 locus. In the lettuce bioassay activityis restricted to GAs with a -lactone function. In some instancesa -lactone, but not a -lactol, can substitute effectively. Thismay imply that the applied C₂₀-GAs are not converted to C₁₉-GAsand that the response to the -lactone results from the six-memberedring mimicking the -lactone at the receptor site. Only GAs havinga 19,10 or a 19,20 lactonic bridge show substantial activityin the cucumber bioassay. The additional presence of eithera 12- or a 13-hydroxyl group severely reduces activity.     

Mitochondrial Sequence Characterisation of Australian Commercial and Feral Honeybee Strains, Apis mellifera L. (Hymenoptera: Apidae), in the Context of the Species Worldwide

The history of honeybee ( Apis mellifera ) importations and management in Australia is largely anecdotal and therefore a survey and characterisation of this agriculturally important insect is of value. We give information on the genetic composition of 42 feral and commercial strains by sequencing sections of the ATPase 6, cytochrome oxidase III, cytochrome b and ND2 mitochondrial genes to determine the relationship of the strains to each other. Our phylogenetic analysis shows novel associations between A. m. mellifera, A. m. scutellata, A. m. ligustica and A. m. caucasica.     

Effects of Waterlogging on the Gibberellin Content and Growth of Tomato Plants

Flooding of tomato roots results in decreased stem growth. Wehave shown that flooding will reduce levels of gibberellins(GA) in the roots, shoots, and bleeding sap of tomato plants.The adventitious roots that appear on the third day of waterloggingmay be responsible for the production of GA that accumulatein the shoot after 3 to 4 days of flooding. The endogenous GAof tomato will stimulate stem growth of tomato plants. Initially,application of gibberellic acid (GA₃) will stimulate the growthof flooded plants to a greater extent than that of nonwaterloggedplants. It is suggested that one of the first effects of floodingis to reduce GA levels and so inhibit stem elongation. At alater stage of waterlogging GA₃ is less effective and otherfactors appear to inhibit shoot growth.