Biological variation in Trichinella species and genotypes

At present, the genus Trichinella comprises seven species of which five have encapsulated muscle larvae (T. spiralis, T. nativa, T. britovi, T. nelsoni and T. murrelli) and two do not (T. pseudospiralis and T. papuae) plus three genotypes of non-specific status (T6, T8 and T9). The diagnostic characteristics of these species are based on biological, biochemical and genetic criteria. Of biological significance is variation observed among species and isolates in parameters such as infectivity and immunogenicity. Infectivity of Trichinella species or isolates is determined, among other considerations, by the immune status of the host in response to species- or isolate-specific antigens. Common and particular antigens determine the extent of protective responses against homologous or heterologous challenge. The kinetics of isotype, cytokine and inflammatory responses against T. spiralis infections are isolate-dependent. Trichinella spiralis and T. pseudospiralis induce different dose-dependent T-cell polarizations in the early host response, with T. spiralis initially preferentially promoting Th1-type responses before switching to Th2 and T. pseudospiralis driving Th2-type responses from the outset.     

Observations on gymnoascaceae. VIII. A new species of arthroderma

Summary A new species ofArthroderma, A. tuberculatum, is described and illustrated. This new species is represented by two strains isolated from feathers of a robin and from an owl pellet. AlthoughA. tuberculatum is similar to the only other known species of the genus,A. curreyi, with regard to the characteristics of the perfect stage, the two species may easily be distinguished by virtue of the accessory spore forms.Arthroderma curreyi forms small aleuriospores whileA. tuberculatum produces large, tuberculate aleuriospores. The morphological development of the ascocarp is presented along with other diagnostic characteristics. Asci are formed through the intervention of croziers.     

Intraspecific variation and species coexistence

We use a two-species model of plant competition to explore the effect of intraspecific variation on community dynamics. The competitive ability ("performance") of each individual is assigned by an independent random draw from a species-specific probability distribution. If the density of individuals competing for open space is high (e.g., because fecundity is high), species with high maximum (or large variance in) performance are favored, while if density is low, species with high typical (e.g., mean) performance are favored. If there is an interspecific mean-variance performance trade-off, stable coexistence can occur across a limited range of intermediate densities, but the stabilizing effect of this trade-off appears to be weak. In the absence of this trade-off, one species is superior. In this case, intraspecific variation can blur interspecific differences (i.e., shift the dynamics toward what would be expected in the neutral case), but the strength of this effect diminishes as competitor density increases. If density is sufficiently high, the inferior species is driven to extinction just as rapidly as in the case where there is no overlap in performance between species. Intraspecific variation can facilitate coexistence, but this may be relatively unimportant in maintaining diversity in most real communities.     

Molecular variation in Leymus species and populations

Icelandic populations of European lymegrass [Leymus arenarius (L.) Hochst.] were examined using amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) of the major ribosomal genes (18S-5.8S-26S rDNA), in comparison with Alaskan populations of its closely related species L. mollis (Trin.) Pilger. The AFLP profiles emerged as two distinct entities, clearly separating the two species, and based on species-specific bands it was simple to distinguish these two morphologically similar species. The rDNA-RFLPs also differentiated the species. Within species, the Icelandic L. arenarius was more homogeneous than the Alaskan L. mollis, and its variation was dispersed over geographically different populations, suggesting a common gene pool. The variation among the Alaskan L. mollis was more extensive and its interrupted pattern may be the result of gene introgression at subspecies level. Within a 40-year-old population of L. mollis established in Iceland from Alaskan material, the molecular profiles separated old and new genotypes. Both AFLP and rDNA revealed the new genotypes to be extremely similar. This rapid change in allele frequency is thought to be the result of adaptation to a new environment.     

AFLP variation in 25 Avena species

Current molecular characterization of ex situ plant germplasm has placed more emphasis on cultivated gene pools and less on exotic gene pools representing wild relative species. This study attempted to characterize a selected set of germplasm accessions representing various Avena species with the hope to establish a reference set of exotic oat germplasm for oat breeding and research. The amplified fragment length polymorphism (AFLP) technique was applied to screen 163 accessions of 25 Avena species with diverse geographic origins. For each accession, 413 AFLP polymorphic bands detected by five AFLP primer pairs were scored. The frequencies of polymorphic bands ranged from 0.006 to 0.994 and averaged 0.468. Analysis of molecular variance revealed 59.5% of the total AFLP variation resided among 25 oat species, 45.9% among six assessed sections of the genus, 36.1% among three existing ploidy levels, and 50.8% among eight defined genome types. All the species were clustered together according to their ploidy levels. The C genome diploids appeared to be the most distinct, followed by the Ac genome diploid A. canariensis. The Ac genome seemed to be the oldest in all the A genomes, followed by the As, Al and Ad genomes. The AC genome tetraploids were more related to the ACD genome hexaploids than the AB genome tetraploids. Analysis of AFLP similarity suggested that the AC genome tetraploid A. maroccana was likely derived from the Cp genome diploid A. eriantha and the As genome diploid A. wiestii, and might be the progenitor of the ACD genome hexaploids. These AFLP patterns are significant for our understanding of the evolutionary pathways of Avena species and genomes, for establishing reference sets of exotic oat germplasm, and for exploring new exotic sources of genes for oat improvement.     

Genome size variation and species diversity in salamanders

Salamanders (Urodela) have among the largest vertebrate genomes, ranging in size from 10 to 120 pg. Although changes in genome size often occur randomly and in the absence of selection pressure, nonrandom patterns of genome size variation are evident among specific vertebrate lineages. Several reports suggest a relationship between species richness and genome size, but the exact nature of that relationship remains unclear both within and across different taxonomic groups. Here, we report (a) a negative relationship between haploid genome size (C‐value) and species richness at the family taxonomic level in salamander clades; (b) a correlation of C‐value and species richness with clade crown age but not with diversification rates; (c) strong associations between C‐value and both geographic area and climatic‐niche rate. Finally, we report a relationship between C‐value diversity and species diversity at both the family‐ and genus‐level clades in urodeles.     

Song variation in an avian ring species

Abstract.— Divergence of mating signals can occur rapidly and be of prime importance in causing reproductive isolation and speciation. A ring species, in which two reproductively isolated taxa are connected by a chain of intergrading populations, provides a rare opportunity to use spatial variation to reconstruct the history of divergence. I use geographic variation in the song of a likely ring species, the greenish warbler ( Phylloscopus trochiloides ) to reconstruct the microevolutionary steps that occurred during divergence of a trait that is often important in speciation in birds. Populations of a western Siberian ( P. t. viridanus ) and an eastern Siberian ( P. t. plumbeitarsus ) form of the greenish warbler meet, but do not interbreed in central Siberia; these forms are connected by a chain of interbreeding populations extending in a ring to the south around the treeless Tibetan Plateau. I show that: (1) song structure differs greatly between the two Siberian forms, which share the same habitat; (2) song structure changes gradually around the ring; (3) singing behavior is relatively simple in the Himalayas, but becomes increasingly complex to the north, both to the west and east of the Tibetan Plateau; and (4) song varies along independent axes of complexity in the western and eastern south-north clines. By comparing geographic variation in singing behavior and ecological variables, I distinguish among possible causes of song divergence, including selection based on the acoustic environment, stochastic effects of sexual selection, and selection for species recognition. I suggest that parallel south-to-north ecological gradients have caused a greater intensity of sexual selection on song in northern populations and that the stochastic effects of sexual selection have led to divergence in song structure.     

Chemical variation and the species concept in lichenized ascomycetes

Differences in secondary metabolites produced by lichens are not always genetically based, and even if genetically based may represent only a one gene difference. Taxonomic decision involving secondary metabolism should be based on the degree of difference demonstrated between biosynthetic pathways, not on the individual products. No taxonomic status should be accorded to entities which differ only in products from a single biosynthetic pathway, but varietal status should be given to those which have different biosynthetic pathways. Species status is justified if chemistry is correlated with morphological or proven physiological difference, or if more than one major biosynthetic system is involved. While ecological and biogeographic differences point to the likelihood of differences being found, if no differences can be demonstrated which in themselves justify taxonomic separation, then features ought not be allowed to influence the taxonomic decision.     

Metric variation and species recognition in the fossil record

One of the first and most important tasks of the paleontologist is classifying specimens into species. Species recognition commonly involves sorting specimens on the basis of qualitative and quantitative similarities and differences. Often, however, variation in simple metric characters like tooth size or jaw length plays an important role in debates about whether a sample comprises a single species or more than one morphologically similar species. For example, Simpson, Roe, and Lewontin 1 suggested that a fossil sample showing a coefficient of variation greater than 10.0 was likely to comprise more than one species. Well‐known controversies over species recognition in which metric sample variation has been important have simmered for years, focusing on hominids, hominoids, and other extinct primates. Some of these have been resolved; others have not. For example, Pilbeam and Zwell 2 convincingly demonstrated multiple species among South African hominids by showing that metric tooth size variation was too great to be reasonably interpreted as sexual dimorphism. But metric variation continues to play a role in debates about whether Australopithecus afarensis 3 , 4 and Homo habilis 5 - 9 each comprise a single species or two or more separate species. Similarly, there has been steady debate about the number of species present in African Proconsul. Some favor an interpretation of a single extremely dimorphic species, 10 - 12 while others favor an interpretation of two or more species. 13     

Population and species variation of minisatellite DNA in Plantago

Three Plantago species were surveyed for within- and between-population variation at DNA sequences detected with the M13 minisatellite probe. The levels and patterns of variation detected by this probe correspond to those expected from the mating systems of the species. The highly-selfing species P. major has a relatively low variability of minisatellite sequences within populations and considerable differentiation between populations. The outcrossing species P. lanceolata exhibits higher minisatellite variability within populations and moderate differentiation between populations. P. coronopus, with a mixed mating system, has levels of variation intermediate between P. major and P. lanceolata. The levels of variation within and between populations corresponds, in general, to the levels of allozyme variation determined in an earlier study. Mating system and population structure appear to have a major influence on M13-detected fragment variation.     

Chloroplast DNA variation in pearl millet and related species

The evolution of specific regions of the chloroplast genome was studied in five grass species in the genus Pennisetum, including pearl millet, and one species from a related genus (Cenchrus). Three different regions of the chloroplast DNA were investigated. The first region included a 12-kilobase pair (kbp) EcoRI fragment containing the 23S, 16S and 5S ribosomal RNA genes, which is part of a larger duplicated region of reverse orientation. The second region was contained in a 21-kbp Sa/I fragment, which spans the short single-copy sequence separating the two reverse repeat structures and which overlaps the duplicated copies of the 12-kbp Eco RI fragment. The third region was a 6-kbp EcoRI fragment located in the large single-copy region of the chloroplast genome. Together these regions account for slightly less than 25% of the chloroplast genome. Each of these DNA fragments was cloned and used as hybridization probes to determine the distribution of homologous DNA fragments generated by various restriction endonuclease digests.—A survey of 12 geographically diverse collections of pearl millet showed no indication of chloroplast DNA sequence polymorphism, despite moderate levels of nuclear-encoded enzyme polymorphism. Interspecific and intergeneric differences were found for restriction endonuclease sites in both the small and the large single-copy regions of the chloroplast genome. The reverse repeat structure showed identical restriction site distributions in all materials surveyed. These results suggest that the reverse repeat region is differentially conserved during the evolution of the chloroplast genome.     

Mitochondrial DNA variation in pearl millet and related species

Summary Mitochondrial DNA (mtDNA) restriction endonuclease fragment patterns and patterns of mtDNA hybridized by mitochondrial gene probes were used to study phylogenetic relationships of seven Pennisetum species, including five P. americanum (pearl millet) ecotypes and a reference species from the distantly related genus, Panicum. The restriction patterns of the pearl millet ecotypes were uniform with the exception of the ecotype collected in Ethiopia. The probe hybridization method revealed more variability, with both the Rhodesian and Ethiopian ecotypes differing from the others and from each other. Considerable restriction pattern polymorphism was noted among different species of Pennisetum, and Panicum. Significant relationships were noted of Pennisetum polystachyon to P. pedicellatum and of P. purpureum to P. squamulatum using the restriction pattern method. In addition to those relationships, the hybridization method showed relationships of pearl millet to P. purpureum and to P. squamulatum. The relationships noted between species by the hybridization method agreed more closely to the cytological data than those indicated by the restriction pattern method. Therefore, the hybridization method appeared to be the preferred method for studying species relationships. The mitochondrial genome size of pearl millet was calculated to be 407 kb and the mitochondrial genome sizes of other Pennisetum species ranged from 341 to 486 kb.Florida Agricultural Experiment Station Journal Series No. 8485.     

Recombination rate variation in closely related species

Despite their importance to successful meiosis and various evolutionary processes, meiotic recombination rates sometimes vary within species or between closely related species. For example, humans and chimpanzees share virtually no recombination hotspot locations in the surveyed portion of the genomes. However, conservation of recombination rates between closely related species has also been documented, raising an apparent contradiction. Here, we evaluate how and why conflicting patterns of recombination rate conservation and divergence may be observed, with particular emphasis on features that affect recombination, and the scale and method with which recombination is surveyed. Additionally, we review recent studies identifying features influencing fine-scale and broad-scale recombination patterns and informing how quickly recombination rates evolve, how changes in recombination impact selection and evolution in natural populations, and more broadly, which forces influence genome evolution.     

Biological variation of Vanilla planifolia leaf metabolome

The metabolomic analysis of Vanilla planifolia leaves collected at different developmental stages was carried out using ¹H-nuclear magnetic resonance (NMR) spectroscopy and multivariate data analysis in order to evaluate their variation. Ontogenic changes of the metabolome were considered since leaves of different ages were collected at two different times of the day and in two different seasons. Principal component analysis (PCA) and partial least square modeling discriminate analysis (PLS-DA) of ¹H NMR data provided a clear separation according to leaf age, time of the day and season of collection. Young leaves were found to have higher levels of glucose, bis[4-(β-d-glucopyranosyloxy)-benzyl]-2-isopropyltartrate (glucoside A) and bis[4-(β-d-glucopyranosyloxy)-benzyl]-2-(2-butyl)-tartrate (glucoside B), whereas older leaves had more sucrose, acetic acid, homocitric acid and malic acid. Results obtained from PLS-DA analysis showed that leaves collected in March 2008 had higher levels of glucosides A and B as compared to those collected in August 2007. However, the relative standard deviation (RSD) exhibited by the individual values of glucosides A and B showed that those compounds vary more according to their developmental stage (50%) than to the time of day or the season in which they were collected (19%). Although morphological variations of the V. planifolia accessions were observed, no clear separation of the accessions was determined from the analysis of the NMR spectra. The results obtained in this study, show that this method based on the use of ¹H NMR spectroscopy in combination with multivariate analysis has a great potential for further applications in the study of vanilla leaf metabolome.     

Biological variation of rabbit chondrocyte 5'nucleotidase

The activity of 5'nucleotidase was investigated in rabbit chondrocytes. Studies of chondrocytes in organ culture and intact cells revealed that ecto-5'nucleotidase activity varies with the age of the animal. Specific activities of 0.29, 0.62, 1.97, and 1.39 mumole/hr/10(6) cells were observed in intact cells from 3-week-, 3-month-, 6-month-, and 2-year-old animals. Specific activities of 15.5, 33.1, 80.3, and 39.5 mumole/hr/mg protein, respectively, were observed when the enzyme protein was solubilized from disrupted cells with the detergent octyl-beta-D-glucopyranoside. Membrane-bound nonspecific neutral phosphatase activity did not vary with age. Activity of 5'nucleotidase was observed on all chondrocytes using a histochemical staining technique. Kinetic properties of the enzyme from animals of different ages were investigated. No differences were noted in apparent Km value for AMP (23 microM), pH optima (7.3), substrate competition studies, and effects of MgCl2 or CaCl2. These data demonstrate a biological variation in rabbit chondrocyte 5'nucleotidase activity with age. The variation of activity represents an apparent increase in the amount of enzyme protein rather than an alteration in kinetic properties.     

Genetic variation and recombination in Penicillium miczynskii and Eupenicillium species

Reproduction in the genus Penicillium is thought to be completely asexual. Sexual reproduction, as occurs in the related genus Eupenicillium, is thought to provide evolutionary benefits because it allows for new combinations of alleles and therefore increases the amount of variation within the species. This hypothesis was tested using inter-simple sequence repeats (ISSRs) to assess the amount of intraspecific and intra-population variation within Penicillium miczynskii and the closely related Eupenicillium shearii. The data for both genera were also used to test for clonal reproduction against the null hypothesis of panmixis, using measures of genotypic diversity, linkage disequilibrium and phylogenetic tree length. The ISSR fingerprints indicated that the 70 Eupenicillium strains actually included two distinct species, Eupenicillium shearii and Eupenicillium tropicum sp. nov., each represented by populations in both Costa Rica and India. While none of the species or populations were found to be randomly recombining, the relative strength of the clonal component differed among the species. Penicillium miczynskii had the smallest clonal component, with the highest genotypic diversity, lowest Index of Association, 40 % of alleles non-randomly associated, and phylogenetic tree length closer to that of recombined data sets than to the minimum possible. Eupenicillium tropicum showed nearly complete clonal reproduction with the lowest genotypic diversity and 100 % of alleles non-randomly associated in both populations. On the other hand, it also had the greatest amount of intraspecific variation, with as little as 38 % similarity among strains. The results indicate that Penicilliumspecies may, on rare occasion, genetically recombine; the regular occurrence of meiosis in the life cycle of Eupenicilliumspecies does not facilitate recombination; and the greatest amount of genetic variation was not associated with recombination, but with clonal propagation.     

The local introduction of strongly interacting species and the loss of geographic variation in species and species interactions

Species introductions into nearby communities may seem innocuous, however, these introductions, like long-distance introductions (e.g. trans- and intercontinental), can cause extinctions and alter the evolutionary trajectories of remaining community members. These 'local introductions' can also more cryptically homogenize formerly distinct populations within a species. We focus on several characteristics and the potential consequences of local introductions. First, local introductions are commonly successful because the species being introduced is compatible with existing abiotic and biotic conditions; many nearby communities differ because of historical factors and the absence of certain species is simply the result of barriers to dispersal. Moreover, the species with which they interact most strongly (e.g. prey) may have, for example, lost defences making the establishment even more likely. The loss or absence of defences is especially likely when the absent species is a strongly interacting species, which we argue often includes mammals in terrestrial communities. Second, the effects of the introduction may be difficult to detect because the community is likely to converge onto nearby communities that naturally have the introduced species (hence the perceived innocuousness). This homogenization of formerly distinct populations eliminates the geographic diversity of species interactions and the geographic potential for speciation, and reduces regional species diversity. We illustrate these ideas by focusing on the introduction of tree squirrels into formerly squirrel-less forest patches. Such introductions have eliminated incipient species of crossbills (Loxia spp.) co-evolving in arms races with conifers and will likely have considerable impacts on community structure and ecosystem processes.