MATING SYSTEM ANALYSIS USING PROTEIN ELECTROPHORESIS IN THE SELF-FERTILE HERMAPHRODITE SPECIES BULINUS TRUNCATUS (GASTROPODA: PLANORBIDAE)

Uniparental reproduction in the tetraploid hermaphrodite speciesBulinus truncatus has been suggested to occur via self-fertilization,on the basis of cytological and genetic studies. However, recentanalyses of population genetic structure by protein electrophoresisindicated the occurrence of multi-banded phenotypes referredto as ‘fixed hetero-zygosity’. Although intrapopulationand geographical variation of multibanded phenotypes occur,many populations bear only one type of such patterns. This ledto the suggestion that parthenogenesis may well be the matingsyste in B. truncatus. However, such fixed heterozygosity patternsare expected in some tetraploid species in which double disomicinheritance of alleles occurs. It is therefore not possibleto determine from population genetic structure analysis alonewhether segregation occurs or not. Here, we investigate thestability of such patterns over one generation of uniparentalreproduction among four populations. We also present resultsof crossing experiments between individuals from two populations,using two diagnostic loci to analyse their offspring. Our resultsclearly indicate Mendelian segregation of alleles, and confirmsexual reproduction by self-fertilization and cross-fertilization.We interpret the multibanded patterns observed in populationsas the product of both diploid loci of the tetraploid genomewhen they are monomorphic for different alleles. Our study alsoallows us to suggest that partial selfing may be the regularmating system in B. truncatus. (Received 12 February 1992; accepted 7 September 1992)     

Symbiotic Performance of Supernoclulating Soybean (Glycine max (L.) Merrill) Mutants during Development on Different Nitrogen Regimes

Growth and symbiotic performance of soybean (Glycine max (L.)Merrill) cv. Bragg and three of its induced nodulation mutants(nod49, non-nodulating; ntsl 116, intermediate supernodulator;nts1007, extreme supernodulator) were compared throughout developmentunder different nitrogen regimes (0, 2, 5 and 10 mol nitratem^–3). Nitrogen fixation was assessed using ¹⁵N-isotopedilution and xylem sap analysis for ureide content. Both techniquesconfirmed a complete lack of N₂ fixation activity in nod49.Plant reliance on nitrogen fixation by the other genotypes wasdependent on the nitrate regime and the developmental stage.The ntsl007 and ntsl 116 mutants fixed more nitrogen than theparent cultivar in the presence of 10 mol m^–3 nitratein the nutrient solution, but higher input of symbioticallyderived nitrogen was still insufficient to offset the amountof nitrogen removed in the harvested seed. However, the mutantsutilized less nitrate for growth than Bragg. Comparison of estimatesof N₂ fixation derived from the ¹⁵N-dilution technique withthose based on relative ureide content of xylem sap indicatedthat the latter offered a simple and reliable procedure forevaluating the symbiotic performance of supernodulating plants. Key words: ¹⁵N-isotope dilution, supernodulation, ureides     

Phylogenetics of gall-inducing thrips on Australian Acacia

Analysis of DNA sequence data from four genes ( Elongation Factor-1 α, wingless , 16S rDNA and cytochrome oxidase I ) yielded a well-resolved, well-supported phylogeny for all 21 species of gall-inducing thrips found on Australian Acacia. This phylogeny was then used to investigate the evolution of various behavioural and life history traits, and to examine the level of agreement with the taxonomy of the group. Our results suggest that there may have been a single origin of soldier castes in gall-inducing thrips. Examination of the distribution of the three primary life history strategies employed by these thrips (pupating in the gall, pupating in soil with soldier castes and pupating in soil without soldier castes) indicates that two of the strategies may have evolved as a result of factors associated with host plant affiliations or through parasite pressure. Our phylogeny does not support the existing generic classification of the group in that the genera are not monophyletic, nor does it lend itself to a clear solution to improve the classification in accordance with the phylogeny.     

Non-interactive fish communities in the coastal streams of North-western France

1. Spatial patterns of freshwater fish species at regional and local scales were investigated to explore the possible role of interspecific interactions in influencing distribution and abundance within communities occupying coastal streams of North-Western France.
2. Nine sites from nine streams situated in the same biogeographical region were sampled annually over the 6-year period from 1990 to 1995.
3. Similar habitats (sites) with richer regional colonization pools exhibited proportionally richer local communities in terms of number of species, total density and total biomass of individuals. Furthermore, no negative relationships were found between density and biomass of each of the most common species and local species richness.
4. Results of dynamic regression models (applied to the above-mentioned species) suggest an absence of strong competition between all pairs of species.
5. The evidence on lack of density compensation for species-poor communities and absence of perceptible interspecific competition between species suggest that the communities studied are non-interactive.
6. Two main explanations can be advanced. First, the local abundance of species in the communities studied could be determined through differential responses to unpredictable environmental changes, rather than through biological interactions. Second, as a result of historical events, the communities studied are reduced in congeneric species which can limit, in turn, the influence of interspecific competition in structuring these communities.
7. These results underline the strong influence of regional processes in shaping local riverine fish communities and minimize the possible influence of species interactions in governing these communities.     

Role of Glycerol Permeation in the Bloodstream Form of Trypanosoma brucei*

SYNOPSIS. Under aerobic conditions, we have determined glycerol uptake in the long slender (LS) bloodstream form of Trypanosoma (Trypanozoon) brucei brucei by studying glycerophosphate accumulation in the parasites. The coupled enzyme theory applies to the permeation-phosphorylation sequence. Glycerol passage through the plasma membrane is asymmetric, the efflux process being favored over the influx process. No free diffusion of glycerol can be detected even under conditions under which free glycerol accumulates within the cells; most probably, glycerol permeation is mediated by a specific transport system. In the absence of respiratory activities, glycerol is known to be an end-product of T. brucei glycolysis; its production from glycerophosphate should allow ATP synthesis. The observed efflux of free glycerol following intracellular accumulation of glycerophosphate confirms the hypothesis that glycerol production occurs through reversal of glycerol kinase activity. We conclude that in vivo the role of the carrier-mediated asymmetric permeation process is to prevent inhibition of the reversal of the glycerol kinase-mediated reaction by removing free glycerol.     

Common canonical variates

Canonical correlation analysis measures the linear relationshipbetween two random vectors X₁ and X₂ as the maximum correlationbetween linear combinations of X₁ and linear combinations ofX₂. Several generalisations of canonical correlation analysisto k2 random vectors X₁ ..., X_k have been proposed in the literature(Kettenring, 1971, 1985), based on the principle of maximisingsome generalised measure of correlation. In this paper we proposean alternative generalisation, called common canonical variates,based on the assumption that the canonical variates have thesame coefficients in all k sets of variables. This generalisationis applicable in situations where all X_i have the same dimension.We present normal theory maximum likelihood estimation of commoncanonical variates, and illustrate their use on a morphometricdata set.     

The roles of redox processes in pea nodule development and senescence

Nodule senescence is triggered by developmental and environmental cues. It is orchestrated through complex but poorly characterized genetic controls that involve changes in the endogenous levels of reactive oxygen species (ROS) and antioxidants. To elucidate the importance of such redox control mechanisms in pea root nodule senescence, redox metabolites were analysed throughout nodule development in a commercial pea variety ( Pisum sativum cv. Phoenix) inoculated with a commercial rhizobial strain ( Rhizobium leguminosarum bv. viciae ). Although a strong positive correlation between nitrogenase activity and nodule ascorbate and glutathione contents was observed, the progressive loss of these metabolites during nodule senescence was not accompanied by an increase in nodule superoxide or hydrogen peroxide. These oxidants were only detected in nodule meristem and cortex tissues, and the abundance of superoxide or hydrogen peroxide strongly declined with age. No evidence could be found of programmed cell death in nodule senescence and the protein carbonyl groups were more or less constant throughout nodule development. Pea nodules appear to have little capacity to synthesize ascorbate de novo . l -galactono-1, 4-lactone dehydrogenase (GalLDH), which catalyses the last step of ascorbate synthesis could not be detected in nodules. Moreover, when infiltrated with the substrates l -galactono-1, 4-lactone or l -gulonolactone, ascorbate did not accumulate. These data suggest that ROS, ascorbate and glutathione, which fulfil well recognized, signalling functions in plants, decline in a regulated manner during nodule development. This does not necessarily cause oxidative stress but rather indicates a development-related shift in redox-linked metabolite cross-talk that underpins the development and aging processes.