A comparison of variability in size dimensions of intertidal and subtidal mussels (Mytilus edulis) (Mollusca: Bivahia)

Variability in size dimensions of bivalve species has previously been claimed (1) to decrease with size and (2) to be greater for individuals in an intertidal habitat than in a subtidal habitat. Results from this study showed that the decrease in variability with size was an artifact of the techniques previously used, and that variability was the same for all sizes of Mytilus edulis. The previous study utilized an interspecific comparison to examine the effects of habitat on variability, which is considered unacceptable because differences in variability are likely to be a consequence of species differences rather than the effects of different habitats. Results presented here from the intraspecific comparison of M. edulis showed that variability was the same for mussels from an intertidal habitat and from a subtidal habitat.     

A comparative study of soil formation in primary stands of Scots pine (planted) and poplar (natural) on calcareous dune sands in the Netherlands

Initial soil formation under primary stands of Scots pine (planted) and European black poplar (natural) on calcareous dune sands was studied, paying particular attention to the humus forms and their spatial variability. The stands studied are both about 80 years old and are situated, at close distance, in the coastal dunes near Wassenaar (the Netherlands).Under Scots pine, soils with a mor-type humus form were observed, exhibiting slight podzolisation. Soil variability is rather slight and soil development is comparable to that under primary Scots pine stands on non-calcareous inland drift sands. Under poplar, mull-type humus forms occur which tend towards moder and exhibit a markedly stronger litter decomposition and bioturbation. In contrast to the soils under pine, soil variability is considerable. Results from chemical analyses of two representative soil profiles are in conformance with these trends.It is concluded that the observed trends in soil formation are in line with those described in the literature, and that a period of 80 years is sufficient for a strong vegetation related divergence in soil properties. Soil variability within the stands probably results from redistribution of litter by wind and/or gravity and will be rather site-dependent.     

Spatio-temporal distribution of recruits (0 group) of Merluccius merluccius and Phycis blennoides (Pisces, Gadiformes) in the Strait of Sicily (Central Mediterranean)

Aspects of the recruitment of hake (Merluccius merluccius L., 1758) and greater fork beard (Phycis blennoides Brunnich, 1768) in the Strait of Sicily (Central Mediterranean) are presented. Data were collected from 1994 to 1999 during the international bottom trawl survey program MEDITS. In view of the available literature on juvenile growth of these two species in the Mediterranean area, a length-based criterion was adopted to separate fish belonging to the 0 group (recruits). Recruit density indices (R/km²) by haul were calculated based upon the likely variability of recruit growth among years and used to study abundance variability and spatial pattern of recruitment and to identify the main nursery areas. Although there was inter-annual variability, two stable areas for M. merluccius were identified on the eastern side of the Adventure Bank and the Malta Bank at depths ranging between 100 and 200 m. The main nursery areas for P. blennoides were deeper (from 200 to 400 m) and two stable nursery areas were identified on the western and eastern side of the Adventure Bank; other nurseries were found in the easternmost part of the Strait in 1998 and 1999. Recruitments of the two species were significantly correlated, with the strongest recruitment occurring in 1998 and 1999 for each species.     

Isolation of microsatellite loci in spotted salamanders (Ambystoma maculatum)

To assess the level and spatial pattern of genetic diversity in the spotted salamander, Ambystoma maculatum, we characterized hypervariable molecular markers by screening genomic libraries enriched for microsatellite motifs. We designed primers that reliably amplify twelve polymorphic loci and checked for variability in individuals from populations in the vicinity of Ithaca, New York. Loci show high variability in the number of alleles and heterozygosities, suggesting they will be useful for determining local population differentiation and mating systems in this pond‐breeding amphibian.     

Genetic Diversity in Alpine and Foothill Populations of Campanula rotundifolia (Campanulaceae)

Climatic constraints on insects in alpine environments have important consequences for the biology of their plant mutualists; in particular, reduced insect diversity and activity in alpine plant populations can result in pollinator-limited seed set and, potentially, in low genetic diversity. However, highly effective pollination by bumblebees in alpine populations can compensate for low visitation rates. In this study we hypothesized that, because of highly effective pollination by bumblebees, alpine populations of Campanula rotundifolia would not experience more frequent cycles of pollinator limitation than low-elevation populations and would therefore exhibit comparable levels of genetic variability and inbreeding to those found in foothill populations. Enzyme electrophoresis was used to assess genetic variability at nine putative loci in alpine and foothill populations of C. rotundifolia in Colorado. Genetic variability in C. rotundifolia was found to be comparable to that reported for other long-lived herbaceous perennials. Measures of genetic variability and fixation indices did not differ between high- and low-elevation populations and were consistent with Hardy-Weinberg expectations. Nonsignificant F(ST) values indicated no genetic differentiation among all populations.     

Environmental Heterogeneity and Morphological Variability in Pisidium subtruncatum (Sphaeriidae,Bivalvia)

On the example of P. subtruncatum, a widely distributed bivalve, we studied the relationship between environmental and morphological variability. The main questions addressed were: (1) are there differences in shell morphology between different populations, (2) are they dependent on sediment composition, hydrology or water chemistry, (3) are there differences in morphological variability between stable and unstable environments. Measurements of specimen from nine sampling sites showed high variability in shell shape and size. Length‐height relation, symmetry, width and dry weight of the shell all varied significantly. Shell shape was significantly correlated with sediment composition and dependent on hydrological connectivity, with higher, asymmetric shells occurring in sandy sediments and lower, rounded shells in muddy sediments. Analysis of intrapopulation morphometric variation showed that variability is higher in habitats with high temporal and spatial environmental variability and lower in habitats with low or reduced environmental heterogeneity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chromosomal Variability in Chironomus plumosus (Linnaeus, 1758) (Diptera,Chironomidae) from a Coastal Lagoon of the Baltic Sea (Curonian Lagoon)

Entomological Review - Chromosomal variability of Chironomus plumosus (Linnaeus, 1758) population from the coastal Curonian Lagoon of the Baltic Sea was studied. The karyotype pool comprises 19...     

Investigation of genetic diversity in fragmented geometric tortoise (Psammobates geometricus) populations

Microsatellite DNA was used to investigatelevels of genetic variability in severelyfragmented populations of the geometrictortoise, Psammobates geometricus, themost endangered tortoise on mainland Africa.Eight microsatellite markers were used toassess genetic variability within and betweenthree naturally occurring populations of P. geometricus. These populations areseparated by the Cape Fold mountain ranges inthe western Cape region of South Africa. Levels of variability were quantified usingallelic diversity, genotypic frequencies andheterozygosity. Evidence for populationsub-structuring was examined using Fstatistics, R_st and ².High levels of variability were found in allthree populations. Low levels of populationdifferentiation were found suggestingsignificant gene flow between the populations.     

Host specificity is linked to intraspecific variability in the genus Lamellodiscus (Monogenea)

SUMMARYWe investigated whether host specificity is linked to variability within species of Lamellodiscus monogeneans, which are gill ectoparasites of the Sparidae. We sampled fish parasites in the northeastern part of the Mediterranean Sea: 4 specialist species, using 1 single host species, and 3 generalist species, using 2 distinct host species. Intraspecific variability was assessed from 2 different datasets. Morphometric variability of the attachment organ, called the haptor, was estimated first from measurements of several sclerified haptoral parts on 102 individuals. Genetic variability was calculated based on comparisons of sequences derived from the first internal transcribed spacer (ITS-1) of nuclear ribosomal DNA of 62 individuals. Morphometric variances in the specialist versus generalist species were compared via principal component analysis and F-tests, and uncorrected genetic distances (p-distances) were estimated within each species. We showed that the inter-individual variance of morphometric characters, as well as p-distances, are clearly greater within generalist species than specialist ones. These findings suggest that a relative increase in morphological and molecular variability enhances the possibility to colonize new host species in monogeneans, and supports the hypothesis that intraspecific variability could be a potential determinant of host specificity.     

Isolation of polymorphic microsatellite loci in Crossosoma californicum (Crossosomataceae)

Crossosoma californicum (Crossosomataceae) is a rare shrub species endemic to the California Channel Islands. Previous studies based on allozymes revealed little genetic variability in this plant species. We have isolated 13 polymorphic microsatellite loci from C. californicum. These loci show intermediate levels of variability, averaging 4.2 alleles per locus and expected heterozygosity of 0.376. Two loci did not fit Hardy–Weinberg expectations with significant deficits of heterozygous genotypes consistent with the presence of null alleles or population subdivision.     

Genetic variability in a captive herd of Speke's gazelle (Gazella spekei)

A captive herd of Speke' gazelle was screened for genetic variability at 28 enzyme-coding loci, the nuclear ribosomal DNA (rDNA), and the mitochondrial DNA (mtDNA). There is one variable restriction site out of 52 in the rDNA and three variable sites out of 41 in the mtDNA. This amount of mitochondrial diversity is low for a mammal, but is about the maximum to be expected given that the entire herd is derived from three females. However, 14% of the enzymecoding loci were polymorphic, a figure typical for mammals. Hence, despite the fact that the herd was founded by one male and three females, much genetic variation is still present. It is therefore important to continue breeding programs designed to maintain genetic diversity. MtDNA is maternally inherited, so tracing back from the current animals through females allowed us to infer that each founding female had a distinct mtDNA haplotype. Hence, the founding females could not have shared the same mother. The nuclear variability could also be traced back through the pedigrees to the founders. One female was found to have contributed none of the assayed genetic variability to the current herd. “Gene drop” simulations of the herd indicated that this was the only founder for which much genetic variability had already been lost because of breeding decisions made during the early history of the herd. This illustrates the importance of implementing breeding programs designed to preserve genetic variability as soon as possible.     

Factors of intraspecific variability in ammonites,the example of Gassendiceras alpinum (d’Orbigny, 1850) (Hemihoplitidae,Upper Barremian)

The homogeneity of a large sample of Gassendiceras alpinum is tested statistically. The quantitative analysis did not reject the null hypothesis and the homogeneity of the sample is accepted. As a result, the different taxa used in the literature (G. alpinum, “Barrancyloceras barremense”, Leroyiceras mascarellii and Spinocrioceras sauvanae) all fall into the variability of a single species, although some doubt subsist for L. dolloi. Taxonomically, by the priority principle the only name that should be used is G. alpinum. The results and other examples about the intraspecific variability confirm the importance of the Westermann's laws in ammonites, but they show that there are other important sources of covariation. In Gassendiceras the variability is tripolar (both the classic robust-slender poles of the Westermann's laws plus a third morphological pole with thick section and not so robust ornamentation), which implies that the intraspecific variability is not always uniform or consistent from one group to another, or in any case do not necessarily respond to the same factors in equivalent proportions. Heterochronies, erasing of the ornamentation and uncoiling of the heteromorph ammonites are also considered as factors of the intraspecific variability.     

Intraspecific heterogeneity in the mini-exon gene localization of Leishmania (Viannia) panamensis and Leishmania (Viannia) guyanensis from Colombia

Intraspecific heterogeneity was demonstrated in the mini-exon gene localization from Leishmania (Viannia) panamensis and L. (Viannia) guyanensis. Different karyotypes were detected in human isolates circulating in endemic areas of Colombia. The presence of mini-exon gene sequences on chromosomes of different sizes, ranging from 370 to 800 kb in L. (V.) panamensis and from 500 to 800 kb in L. (V.) guyanensis, was observed and was neither strain nor species specific. In some cases, hybridization with 2 chromosomes in the same strain was observed. The variability of chromosomal localization of mini-exon gene sequences of these 2 species highlights the genetic variability of the Viannia subgenus and the potential utility of the mini-exon gene as a molecular epidemiologic marker.     

Intraspecific Variability of the Shape of the Lower Third Premolar in Ochotona hyperborea (Pallas 1811)

Biology Bulletin - The shape variability of the chewing surface of the third lower premolar (p3) was analyzed in modern members of the Northern Pika (Ochotona hyperborea). The variability in the...     

Nitrogen in the Pyrenean lakes (Spain)

Lakes in the Pyrenees show a broad variability in nitrogen content and in the distribution of its different oxidation forms, which has no direct relation with any single physiographical, chemical or trophic feature of the lakes. Concentration of bound nitrogen in rain is low compared with other European mountains, but the annual load lies in the middle range. Seasonal and local variation in the composition of rainwater mainly depends on the geographical origin of the storms. Catchment and in-lake processes introduce further variability: NH₄ ⁺, which is at similar concentration to NO₃ ^- in the rain, is quickly oxidized or adsorbed in the catchment; aquatic macrophytes can either reduce mean NO₃ ^- concentration in lake water (Ranunculo-Potametum) or greatly increase it in sediment pore water (Isoetes); NO₂ ^- depends on pH; decomposition of particulate nitrogen in sediments changes with depth; lakes act as traps for dissolved inorganic nitrogen; changes in dissolved organic nitrogen suggest high microbial activities even in cold waters; melting period introduces most of the seasonal variability. Institute of High-Mountain Research, University of Barcelona     

Enzyme polymorphisms in the fire ant,Solenopsis invicta (hymenoptera: formicidae)

A survey of allozyme variability in the fire ant, Solenopsis invicta Buren, was conducted using samples collected throughout the species' range in North America. A substantial amount of variability was found, although heterozygosity estimates were considerably less than estimates for diploid non-hymenopterous species. The presence of this variability raises the possibility of multiple introductions of this ant to North America. Although based on a limited sample, our data indicate no differences in variability between individuals from monogynous and polygynous populations or between individuals from the Mobile, Alabama area (presumed point of introduction) and outside the area. Individuals from polygynous colonies shared all detected alleles with individuals from monogynous colonies indicating the lack of long-term reproductive isolation between the two types of populations.     

Hybridization in Acacia nilotica (Mimosoideae) complex

The variability in the Acacia nilotica complex is explained in terms of hybridization between A. nilotica subsp. indica and A. nilotica subsp. hemispherica . This is substantiated by the study of phenolic constituents, pollen fertility and intra-plant fruit variability. The hybrid populations may backcross with A. nilotica subsp. indica and A. nilotica subsp. hemispherica producing plants similar to A. nilotica subsp. adstringens and A. nilotica subsp. subalata respectively. The role of humans in directly and indirectly distributing the seeds of hybrid plants over vast areas and in creating the disturbed habitats suitable for plants of hybrid origin is discussed. Phenolic constituents of A. nilotica subsp. hemispherica and A. nilotica subsp. leiocarpa are shown to be distinctive. Probable hybridization between A. nilotica subsp. indica and A. nilotica subsp. cupressiformis is also discussed.     

Genetic variability in the diapause response of the burnet moth Zygaena trifolii (Lepidoptera: Zygaenidae)

A high degree of phenotypic variability was observed in the diapause response of the burnet moth Zygaena trifolii. In this study, we show that the observed variability is partly based on genetic differences between individuals. In a selection experiment, the larval instar at which diapause occurs was changed within six generations. Diapause instars were dependent on the time of pre-diapause development of larvae, which varied considerably between larvae. A heritability analysis indicates that a part of the variability in development time is based on additive genetic variance. The maintenance of genetic variability in the development time and the diapause response of Z. trifolii is discussed in the context of spatially and temporally changing selection pressures.     

Genetic control of organogenesis in cotyledons of sunflower (Helianthus annuus)

Genetic variability for regeneration ability was evaluated by studying direct organogenesis from cotyledons of thirteen genotypes including three cytoplasmic male sterile, three maintenor, three restorer inbred lines, and four F1 hybrids obtained by crosses between some of these inbred lines. The experimental design was a complete randomized block with three replications. A high genetic variability for organogenesis parameters between genotypes was observed in this study. Evidence of cytoplasmic effect and nucleo-cytoplasmic interaction for some of regeneration parameters was observed. The data also showed the importance of additive genetic control for organogenesis parameters in most genotypes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genic homozygosity in an ancient reptile (Alligator mississippiensis)

Proteins assayed electrophoretically showed variation at only three of 49 presumed genetic loci in alligators from southwestern Louisiana. Average heterozygosity per individual was 0.021±0.012; proportion of polymorphic loci was 0.06. Data on the history, structure, and ecology of this alligator population are consistent with natural selection as the primary factor accounting for this low genetic variability. However, neither a historic population bottleneck nor some genetic mechanism limiting variability can be dismissed as a possible factor.The study was supported by NSF Grant BMS 73-0125 to H.C.D.