Some morphological characteristics of Acipenserid fishes: considerations of their variability and utility in taxonomy

The use of traditionally utilized morphological characteristics as diagnostic tools in tetraploid and octaploid sturgeons assumes that they are heterogenous in nature. Octoploid species are supposed to be of independent origin through multiple events of polyploidization and through interspecific hybridization among tetraploid species. In this study probable relationships between tetraploid and octoploid species are suggested by morphological characteristica. The genus Acipenser should include both former genus Acipenser and Huso and this seems to be the only realistic deduction that can be concluded from morphological features.     

Biometric variability of goat populations revealed by means of principal component analysis

The aim was to analyze variation in 12 Brazilian and Moroccan goat populations, and, through principal component analysis (PCA), check the importance of body measures and their indices as a means of distinguishing among individuals and populations. The biometric measurements were wither height (WH), brisket height (BH) and ear length (EL). Thorax depth (WH-BH) and the three indices, TD/WH, EL/TD and EL/WH, were also calculated. Of the seven components extracted, the first three principal components were sufficient to explain 99.5% of the total variance of the data. Graphical dispersion by genetic groups revealed that European dairy breeds clustered together. The Moroccan breeds were separated into two groups, one comprising the Drâa and the other the Zagora and Rhâali breeds. Whereas, on the one side, the Anglo-Nubian and undefined breeds were the closest to one another the goats of the Azul were observed to have the highest variation of all the breeds. The Anglo-Nubian and Boer breeds were similar to each other. The Nambi-type goats remained distinct from all the other populations. In general, the use of graphical representation of PCA values allowed to distinguish genetic groups.     

The morphological characteristics of Artemia shrimps from Siberian populations

Morphological analysis of characteristics of shrimps from parthenogenetic and bisexual Artemia populations from a vast territory from the Urals to the Sayan Mountains was made. A normal distribution of the majority of parameters and a different degree of their interrelation and dependence on some environmental factors (salinity, ion composition, and ratio) were recorded. The analysis included seasonal, interannual, and sexual variability of Artemia. The greatest influence of salinity and separately of main ions (except for carbonates, hydrocarbonates, and calcium) on the abdomen and furca structure is shown. No correlation was found between water salinity and body length. The cluster analysis of a complex of morphological parameters showed grouping of populations by salinity of lakes instead of their geographical position and sexual structure of populations.     

Genetic variability and differentiation of hypogean Cyprinid fishes from Somalia

The genetic structure of populations of two hypogean Somali cyprinid species was compared by analysing genetic variation at 30 allozyme loci. The two species, Phreatichthys andruzzii and Barbopsis devecchii , are of particular interest, representing two different steps in adaptation to cave life, as indicated by several morphological features including eye regression. Phreatichthys is completely anophthalmic, while Barbopsis shows a highly variable microphthalmia. Results showed a close relationship between Phreatichthys and Barbopsis , suggesting their origin from a common epigean ancestor. Population structure of the two species differs and levels of gene flow are much higher between the Barbopsis populations than between the Phreatichthys populations. Two possible scenarios leading to the current situation are hypothesized.     

Genetic analysis of ecologically relevant morphological variability in Plantago lanceolata L.

Summary Morphological variability was studied in two populations of Plantago lanceolata using diallel analysis. In each population, reciprocal crosses between all possible pairs of ten plants were made. In the greenhouse, six members of each family were grown and many characters were measured. Using the model of Cockerham and Weir, the contributions of the different genetic variance components were calculated. From earlier papers it was postulated in advance to what extent and by which effect the characters in both populations were genetically determined. The populations had been differentiated for life history and morphological characters, and varied also in the relative contribution of genetic components to variability. In the Merrevliet (Me) population, where strong biotic selection was assumed, low levels of additive-genetic variability were present and the relative dominance appeared to be high. The contrasting population, Westduinen (Wd), which is abiotically controlled and shows strong environmental variability, possessed higher levels of additive-genetic variability and lower levels of relative dominance. It is possible that differential natural selection has diminished additive-genetic variability to different extents in both populations: plasticity and environmental heterogeneity prevented the loss of additive-genetic variability in Wd, whereas in the stable population, Me, natural selection had the opportunity of not only changing the means of the characters but also of diminishing additive-genetic variability to a great extent.Grassland Species Research Group Publication No. 146     

Genetic analysis of ecological relevant morphological variability in Plantago lanceolata L.

Summary Morphological variability was analysed in an F₂-generation derived from crosses between two ecotypes of Plantago lanceolata L. Six allozyme loci, localised in five linkage groups, were used as markers. For two marker loci, Got-2 and Gpi-1, segregations did not fit monogenic ratios. In the linkage groups to which these two loci belonged, male sterility genes appeared to be present. In these crosses, male sterility (type 3, as described by Van Damme 1983) may be determined by two recessive loci located in the linkage groups of Got-2 and of Gpi-1. Many correlations of morphological and life history characters with allozyme markers were observed. The quantitative trait loci did not appear to be concentrated in major gene complexes. Often many loci were involved, sometimes with effects opposite to those expected from the population values. Main effects of the linkage groups appeared to be more important than interaction effects in determining variability. It also appeared that there is a positive correlation between the number of heterozygous allozyme loci and generative growth.Grassland Species Research Group Publication No. 115     

Genetic analysis of ecological relevant morphological variability in Plantago lanceolata L.

Summary Plants of an F₂ generation derived from crosses between two ecotypes of Plantago lanceolata L. had previously been studied in a greenhouse. In the present experiment, F₂ plants were transplanted into their original habitats (a hayfield and a pasture). Six allozyme loci were used as markers in the analysis of survival and performance of the segregating genotypes. Fitness differences between the plants were large enough to detect natural selection. In both transplantation sites selection appeared to operate, though in different ways. In the hayfield habitat directional selection was hypothesized and both survival and performance of the plants were related to genotype, with the genotypes originating from the hayfield almost always performing better. In the pasture habitat where the habitat is not uniform and unpredictable hazardous droughts occur, survival was nearly genotype independent and environmentally determined, whereas performance of the plants was genotype dependent. The expression of two morphological characteristics, number of leaves and leaf length, was often not in concordance with the greenhouse results and was contradictory in both sites. Expression of both characters in the field, therefore, appeared to be strongly dependent on the general performance and growth conditions of the plant and not on the genotype.Grassland Species Research Group Publication no. 143     

Song characteristics and morphological traits in four populations of the grasshopper Chorthippus biguttulus L.

We investigated four populations of the grasshopper Chorthippus biguttulus with respect to differences in morphological traits and characteristics of their communication signals. A special focus was laid on possible correlations between morphological and song traits of males that could be used by females to infer quality cues of potential mates. We also tested whether females exhibit preferences for males of their own population. Specific song features (onset accentuation, offset, syllable period) of males—but not of females—differed between populations. We observed size differences both in males and females from different populations, but the size ranks of the two sexes were not always correlated. Environmental factors appear to have a strong influence on different size traits, compared to genetic origin. In all populations a specific song feature, the accentuation of syllable onsets, showed a similar correlation with a morphological trait, hind leg size, but its correlation with other size indicators sometimes differed in sign. Females did not prefer songs of males from their own population. The best predictor for song attractiveness was—unexpectedly—not the onset accentuation but the offset depth.     

Variation within teosinte. I. Numerical analysis of morphological data

Principal components analysis of 27 morphological characters for 18 accessions of teosinte and 3 accessions of maize separated teosinte into 6 phenetic groups which showed broad agreement with previous taxonomic groupings. Tests for regression suggested significant linear relationships with altitude; teosintes from higher elevations are generally more maize-like for a combination of characters. Introgression from maize may have blurred racial identities within teosinte, but variation among current teosinte accessions cannot be satisfactorily explained solely on the basis of known maize introgression. It appears instead that racial differentiation in teosinte was well established by the time of the domestication of maize. While current racial classification of teosinte is quite useful, it does not adequately reflect the amount of genetic variation, nor does it accurately portray many of the relationships within teosinte.     

Interannual variability of algal populations and their influence on lake metabolism

• 1 An input-output phosphorus budget is given for Windermere and its two basins based on data available for the late 1980s. The annual areal total phosphorus loading for the whole lake was 1.04 g P m^-2 yr^-1 and for the North and South Basins were 1.08 and 1.70 g P m^-2 yr^-1, respectively. For the whole lake and its South Basin the values were similar to the upper range of critical loads calculated according to the equation of Vollenweider (1976) for the transition between oligotrophy and eutrophy while that for the North Basin (1.08 g P m^-2 yr^-1) was within this range of critical loadings but towards its lower end.
• 2 Changes in the quality of summer phytoplankton are described for Windermere, particularly its South Basin, between 1978 and 1989 in relation to the utilization of nitrate-nitrogen (NO³-N) in the epilimnion, deoxygenarion of the hypolimnion and the ratio of epilimnetic volume to hypolimnetic volume, E_v/H_v The two basins of Windermere with values of E_v/H_v of 0.79 (South Basin) and 0.50 (North Basin) have contrasting conditions of summer deoxygenarion. The shallower South Basin shows marked interannual variability in the development of hypolimnetic anoxia. Years with large hypolimnetic anoxia during autumn are correlated with the production during summer of large populations of the poorly grazed blue-green alga Oscillatoria bourrellyi and exhaustion of NO₃-N in the upper layers. During years when anoxia does not develop the summer phytoplankton consists of small easily grazed algae or larger ones subject to parasitic epidemics. The deeper North Basin never becomes anoxic even though it can contain similar sized populations of O. bourrellyi to the South Basin.
• 3 A possible explanation of the between basin and, for the South Basin, between year variation of utilization of NO₃-N and level of hypolimnetic deoxygenarion is that algal quality can determine lake metabolism dependent upon lake or basin morphology. Poorly grazed large forms such as O. bourrellyi act as sinks for NO₃-N. On sedimentation such populations act as a ‘short circuit’ mechanism descending into deeper layers in sufficient quantities to cause anoxia. Other species subject to crustacean or microbial grazing are mineralized in the epilimnion with little sedimentation to the deeper waters. Subsequent recycling of nitrogen as NH₄-N takes place in the upper layers or thermocline which is more readily taken up by subsequent production. The influence of such ‘short circuit’ mechanisms is reduced in deep lakes and exacerbated in shallow ones.
• 4 The success of species such as O. bourrellyi is dependent upon a sufficient inoculum, an adequate supply of nutrients and the depth of intermittent mixing. The importance of these factors in regulating presence and timing of summer populations is illustrated and discussed.

     

Genetic structure and morphological variation of British populations of the hybrid Potamogeton x salicifolius

Potamogeton x salicifolius Wolfg. is one of the three most frequently recorded Potamogeton hybrids in the British Isles and Europe. It is thought to be the hybrid between P. lucens and P. perfoliatus. Its scattered distribution suggests that it has arisen several times in Britain. Most British populations of P. x salicifolius can be identified by their morphological characteristics, which are intermediate between those of the putative parents P. lucens and P. perfoliatus . However, the population at the Ouse Washes, Cambridgeshire, differs from other populations in its greater similarity to P . lucens . A genetic study of eight British populations, using six isozyme systems, revealed that most populations consist of a single multi-enzyme phenotype. This suggests that they were the result of a single hybridization event and are therefore maintained through vegetative reproduction. By contrast, the Ouse Washes population consists of three multi-enzyme phenotypes. This variation is likely to have resulted from multiple hybridization events, although we cannot exclude the possibility that the plants are partially fertile. The isozyme systems studied were unable to identify P. lucens and P. perfoliatus unambiguously, and consequently did not provide evidence for their putative parentage of P. x salicifolius. However, at a local level the banding patterns of the hybrids were generally consistent with the local multi-enzyme phenotypes of these putative parents.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 99–111.     

Genotypic diversity and environmental variability affect the invasibility of experimental plant populations

The world is experiencing increasing climatic variability, an ongoing loss of biodiversity and a growing spread of invasive species. Previous experimental studies demonstrated that the invasibility of plant populations is reduced with increasing resident genetic diversity and is promoted by environmental fluctuations, but their combined effect has so far not been considered. In a growth chamber experiment, we tested whether the genotypic diversity of experimental populations of Arabidopsis thaliana (1, 3 or 6 genotypes) and temperature fluctuations affect population invasion by Senecio vulgaris, and how these factors interact. We found that genotypic diversity tended to increase the invasion resistance of experimental plant populations in terms of the biomass ratio between the species, and that temperature fluctuations strongly favoured Arabidopsis (biomass: +49%) over Senecio (–28%). However, there were no interactions between environmental fluctuations and genotypic diversity. Nevertheless, the magnitude of net diversity effects and transgressive overyielding depended on temperature conditions, indicating that increased environmental variability can influence diversity mechanisms. Our study shows that, although genotypic diversity and environmental variability did not interact, these two factors independently affected the invasibility of plant populations.     

Physiological studies of a hybrid between populations of Dactylis glomerata from contrasting climatic regions. I. Inter population differences

A study of the physiological responses of a hybrid between a North European population and a colchicine-induced autotetraploid of a Portuguese population of Dactylis glomerata subspecies lusitanica showed an intermediate response of the hybrid for many characters. However, the hybrid resembled one or other of the parents in the more favourable expression of certain characters in controlled environments at 20°C, 16 h photoperiod and 8 °C, 8 h photoperiod. Rate of dry-matter production of the hybrid did not differ significantly from that of the northern parent at 20 °C, 16 h and that of the Portuguese parent at 8 °C, 8 h. Leaf growth of the hybrid at 8 °C, 8 h was greater than that of the northern parent and together with the high percentage survival in a freezing test may indicate a role for similar hybrids in the development of potential varieties with improved seasonal distribution of dry-matter production.     

Separation and quantification of pigments from natural phototrophic microbial populations

Abstract A simple high-performance liquid chromatography (HPLC) method is described for the rapid (approx. 20 min) simultaneous separation and identification of the major chlorophylls and carotenoids from phytoplankton cells and phototrophic sulfur bacteria. Lyophilized samples were extracted with acetone in the dark at room temperature. Pigments were eluted from a silica column with a hexane-acetone mixture (80: 20, v/v). About 20 algal and bacterial chlorophyll and carotenoid pigments could be separated in one run. The method allowed for the detection of trace amounts of major carotenoids (> approx. 6 ng · 1⁻¹) and of chlorophylls and pheophytins (> approx. 200 ng · 1⁻¹) in natural samples. The method has been applied to samples from the metalimnion of Lake Vechten (The Netherlands) and has proved very useful in estimating algal and bacterial pigments simultaneously with respect to depth distribution and biomass changes of the microbial populations.     

Distribution of genetic variability in populations of two chromosomal races of Dichroplus pratensis (Melanoplinae, Acrididae) and their hybrid zone

We examined, through allozyme electrophoresis, the genetic structure of populations of the acridid grasshopper Dichroplus pratensis from two chromosomal races (Northern and Southern) and their hybrid zone in Argentina. No fixed alleles for any particular race were found, although genetic differentiation among parental races was significant (0 = 0.044, 95% CI: 0.004-0.068). Hybrid populations are genetically more similar to the Southern race (0 = 0.008, 95% CI: -0.005-0.018) than to Northern ones (0 = 0.018, 95% CI: 0.002-0.030). Differential viability or fertility of hybrids, or asymmetry in mating preferences in favour of one particular cross would cause a higher proportion of matings between hybrid individuals and those from the Southern race. This would explain the high genetic similarity between those groups, in spite of their geographical vicinity with northern race populations.     

Phenotypical and genetic differentiation of human populations for morphological and psychophysiological traits. Factor analysis

The multivariate genetic factor analysis is used, as first attempt, to study genetic bases of correlation variability of neurodynamic and psychodynamic levels of individual organization among isolates of Daghestan. Closer similarity between factors described in templates of phenotypic correlations is explained by lower heritability of the parameters under study. Interpopulation differences revealed by the multivariate genetic analysis are the result of differences in the genetic structure of the populations.