			Home About us Contact

Taxonomic Boundaries (taxonomic + boundary)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

GENE FLOW AND SPECIES DELIMITATION: A CASE STUDY OF TWO PINE SPECIES WITH OVERLAPPING DISTRIBUTIONS IN SOUTHEAST CHINA

EVOLUTION, Issue 8 2010
Yong Feng Zhou
Species delimitation detected by molecular markers is complicated by introgression and incomplete lineage sorting between species. Recent modeling suggests that fixed genetic differences between species are highly related to rates of intraspecific gene flow. However, it remains unclear whether such differences are due to high levels of intraspecific gene flow overriding the spread of introgressed alleles or favoring rapid lineage sorting between species. In pines, chloroplast (cp) and mitochondrial (mt) DNAs are normally paternally and maternally inherited, respectively, and thus their relative rates of intraspecific gene flow are expected to be high and low, respectively. In this study, we used two pine species with overlapping geographical distributions in southeast China, P. massoniana and P. hwangshanensis, as a model system to examine the association between organelle gene flow and variation within and between species. We found that cpDNA variation across these two pine species is more species specific than mtDNA variation and almost delimits taxonomic boundaries. The shared mt/cp DNA genetic variation between species shows no bias in regard to parapatric versus allopatric species' distributions. Our results therefore support the hypothesis that high intraspecific gene flow has accelerated cpDNA lineage sorting between these two pine species. [source]

Description and ultrastructure of araphid diatom species (Bacillariophyceae) morphologically similar to Pseudostaurosira elliptica (Schumann) Edlund et al.

PHYCOLOGICAL RESEARCH, Issue 2 2010
Eduardo A. Morales
SUMMARY Several populations identified and reported from North America and Mongolia under the names Fragilaria elliptica Schumann or Staurosira elliptica (Schumann) Williams et Round were analyzed in detail using light microscopy (LM) and scanning electron microscopy (SEM). The analysis yielded three variants that can not be ascribed to ,elliptica' of the type. Furthermore, two of the variants could not be related to published taxa and we describe them as new species, Staurosira ambigua sp. nov. and Staurosira dimorpha sp. nov. A third variant was identified as Pseudostaurosira trainorii Morales, a taxon originally reported from ponds and a river in the north-eastern USA. The combined LM and SEM analysis used here allowed for a more thorough circumscription of taxonomic boundaries among morphologically similar taxa and for better delimitation of their geographic distributions. A discussion of the taxonomy and ecology of these taxa based on literature and recent ecological data is presented. [source]

Tissue-dependent limited pleiotropy affects gene expression in barley

THE PLANT JOURNAL, Issue 2 2008
Elena Potokina
Summary Non-synonymous coding mutations in a gene change the resulting protein, no matter where it is expressed, but the effects of cis -regulatory mutations could be spatially or temporally limited , a phenomenon termed limited pleiotropy. Here, we report the genome-wide occurrence of limited pleiotropy of cis -regulatory mutations in barley (Hordeum vulgare L.) using Affymetrix analysis of 22 840 genes in a population of 139 doubled haploid lines derived from a cross between the cultivars Steptoe (St) and Morex (Mx). We identified robust cis -acting expression regulators that segregate as major genes in two successive ontogenetic stages: germinating embryo tissues and seedling leaves from the embryonic axis. We show that these polymorphisms may be consistent in both tissues or may cause a dramatic change in transcript abundance in one tissue but not in another. We also show that the parental allele that increases expression can vary with the tissue, suggesting nucleotide polymorphism in enhancer sequences. Because of the limited pleiotropy of cis -regulating mutations, the number of cis expression quantitative trait loci (cis -eQTLs) discovered by ,genetical genomics' is strongly affected by the particular tissue or developmental stage studied. Given that limited pleiotropy is a common feature of cis -regulatory mutations in barley, we predict that the phenomenon would be relevant to developmental and/or tissue-specific interactions across wide taxonomic boundaries in both plants and animals. [source]

Isolation and high genetic diversity in dwarf mountain toads (Capensibufo) from South Africa

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010
KRYSTAL A. TOLLEY
Traditional models of amphibian dispersal and gene flow point to low dispersal and high philopatry. In recent years, this traditional view has been challenged and it appears that no general model holds across taxa. Conservation of amphibians cannot be addressed on an over-arching scale, but must come on a case-by-case basis, especially for range-restricted species where information on gene flow and migration must be incorporated into conservation efforts. The only two members of the genus Capensibufo Grandison, 1980 (Anura: Bufonidae) are range restricted small bufonids, with distributions limited to montane areas in South Africa. Using a Bayesian analysis of two mitochondrial markers (16S and ND2), we examined the genetic patterns in Capensibufo rosei and Capensibufo tradouwi in order to understand both taxonomic and geographic boundaries. These species were not monophyletic, and demonstrate no clear taxonomic boundaries. Instead, the genus is extremely diverse genetically, with distinct lineages confined to isolated mountains that represent geographic boundaries. In addition, bioclimatic modelling using MAXENT and scenarios of climatic conditions at both the present and last glacial maximum suggest multiple bioclimatic and physical barriers to gene flow at present and in the past. We conclude that members of the genus have very low vagility, that current taxonomic boundaries are inadequate, and that strong geographic structuring has undoubtedly contributed to genetic diversity at the species level, rather than the population level. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 822,834. [source]