Homogeneous Genetic Structure Research Articles

Shell Deformations in the Baltic Clam Macoma balthica from Southern Baltic Sea (the Gulf of Gdansk): Hypotheses on Environmental Effects

High-resolution digital photography and graphical image analyses systems have been used to define external morphometric characters of shell deformations in four populations of the Baltic clam Macoma balthica from the Gulf of Gdansk (southern Baltic Sea). The proposed shell deformation indices (SDI), which were based on the relationship of selected dimensions in the posterior and the anterior part of the shell, showed at least three morphological features that provide a distinctive diagnosis of "regular" and "deformed" clams: the presence of flexure on the posterior side (SDI1), elongated posterior region (SDI2), and shell growth (SDI3). The degree and prevalence of deformed clams varied locally over space. Increase in percentage contribution of aberrated shells with depth, corresponding to oxygen depletion profile in the Gulf, suggests low oxygen concentrations as the main agent exerting a deforming influence. The observed morphological aberrations developed with age (size) of a bivalve, suggesting a long-term effect of causal factors, and were accompanied by lightening shell weight, possibly due to decalcification of previously deposited calcareous material during anaerobic metabolism. It is hypothesized that hypoxic/anoxic conditions and a subsequent presence of hydrogen sulfide on a deep organic-rich sea bottom induce shell form alterations that enable the pumping of oxygenated water from above the anoxic layer. Such a morphological modification highlights the functional significance of shell deformations in protective response to the ambient low-oxygen concentrations. Sediment organotin concentrations fall within moderate to high contamination range and, therefore, may also have an adverse impact on the shell form. DNA analyses of the fragment of mitochondrial gene cytochrome oxidase I (COI, 393 base pairs) showed homogenous genetic structure of regular and deformed clams, indicating that shell deformations in M. balthica are primarily driven by acclimatization to the ambient environmental conditions.

Hyperinvasive genotypes of Neisseria meningitidis in France

Clinical isolates of Neisseria meningitidis from cases of meningococcal disease, collected between January 2000 and December 2004, were identified and typed at the French National Reference Centre. A representative subset of 546 isolates from among 2882 isolates was further genotyped by multilocus sequence typing to determine their genetic lineages (clonal complexes) and the degree of diversification among different clonal complexes. Representative isolates of the main clonal complexes were tested for their virulence in mice and for proapoptotic effects on human epithelial cells. High genetic diversity in some genetic lineages (ST-32 and ST-41/44) was correlated with heterogeneity in virulence in mice and proapoptotic effects on human epithelial cells. In contrast, the homogeneous genetic structure of isolates of the ST-11 clonal complex, regardless of their serogroup, correlated positively with a fatal outcome of the infection, increased virulence in mice and increased proapoptotic effects on human epithelial cells.

Population genetic structure of New Zealand's endemic corophiid amphipods: evidence for allopatric speciation

Allozyme electrophoresis was used to examine population genetic structure at inter- and intraspecific levels for the New Zealand endemic corophiid amphipods, Paracorophium lucasi and P. excavatum. Individuals were collected from estuarine and freshwater habitats from North, South and Chatham Islands. Analyses of genetic structure among interspecific populations indicated clear allelic differentiation between the two Paracorophium species (Nei's genetic distance, D = 1.62), as well as considerable intraspecific substructuring (D = 0.15–0.65). These levels of divergence are similar to interspecific levels for other amphipods and it is proposed that at least two groups from the P. lucasi complex and three from the P. excavatum complex correspond to sibling species. In most cases allopatry can account for the differentiation among the putative sibling species. For populations that share a common coastline we found low levels of differentiation and little or no correlation with geographical distance, suggesting that gene flow is adequate to maintain homogeneous population genetic structure. By contrast, populations on separate coastlines (i.e. isolated by land) showed moderate levels of geographical differentiation indicating restricted gene flow. The juxtaposition of population genetic and biogeographical data for Paracorophium in conjunction with the geological record infers past histories of glacial extirpation, and possible isolating effects of sea-level and landmass changes that have occurred throughout the Plio-Pleistocene. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 119–133.

Association between I/D, G14480C, A22982G Polymorphisms of Angiotesin I-Converting Enzyme Gene and Essential Hypertension in the Korean Population

Background and Objectives:The renin-angiotensin system (RAS) genes have been studied extensively as etiologic essential hypertension (EH) candidate genes in human populations worldwide. The angiotensin Iconverting enzyme (ACE) plays an important role in the RAS for the regulation of blood pressure. Recent reports on the association of ACE gene polymorphisms with EH and the related cardiovascular diseases have been controversial. Therefore, this study investigated the association of three polymorphisms (I/D, G14480C and A22982G) in the ACE gene with EH in Koreans. Subjects and Methods:This study recruited a sample population of 887 Koreans (comprising of 461 controls and 426 EH cases) from Cardiovascular Genome Center in Korea. The ACE gene polymorphisms were determined by a polymerase chain reaction and a SNP-IT assay. Results:The genotype and the allele frequencies of all three polymorphisms in the hypertensives and the normotensives not significantly different (p>0.05). In the female control group, there was a significant difference in SBP among the genotype with the I/D polymorphism (p<0.05). There was also an association between the ACE polymorphisms and the hypertensive male group with the total cholesterol level. Haplotype analysis showed that none of the haplotypes were significantly associated with hypertension. Conclusion:ACE polymorphisms do not appear to have any apparent association with essential hypertension in Koreans, who have a more homogeneous genetic structure than other ethnic groups. (Korean Circulation J 2004;34(12):1137-1147)

Beyond catchment considerations in the conservation of lotic biodiversity

Abstract The history of river conservation has largely focused on preservation of the physical and structural properties of lotic ecosystems in an attempt to ensure safe and potable water supplies for human consumption. Such strategies are increasingly being implemented at the catchment or basin scale. Although these reflect positive developments in the conceptualization of conservation issues pertaining to lotic systems and provide the logical economic, sociological and/or political units for management, we question whether they represent the appropriate scale for the protection of lotic biodiversity and biological processes. We argue that this requires considerations that extend beyond the protection of physical habitat to ensure protection of population processes. Although many species can be successfully conserved using the catchment as the basic management unit, many others cannot. We review evidence from genetic studies of aquatic populations to examine movement in relation to catchments, recognizing that organisms with poor dispersal characteristics during their life cycles exhibit a high degree of genetic structure, whilst organisms with robust dispersal characteristics typically exhibit a homogeneous genetic structure. Species with poor dispersal characteristics are more easily conserved at the catchment level, whereas those with high dispersal characteristics can only be safely conserved at bio‐regional supra‐catchment levels. Modern technological advances aimed at redistributing water from areas with perceived surpluses to those with perceived deficits (inter‐basin water transfers), demonstrated to transfer organisms between historically isolated catchments, pose a potential threat to the conservation of biodiversity by mixing genetically distinct populations and hence altering evolutionary processes and pathways. If our arguments hold, then it appears that conservation authorities need to reappraise the current dominant paradigm of the catchment as the basic unit for conservation and management, and incorporate broader, strategic landscape planning in water resource management. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Immunogenetic heterogeneity of multiple sclerosis in Sardinia.

Multiple sclerosis (MS) predisposition is thought to be influenced by a complex, yet unclear interaction of genetic and environmental factors. Studying ethnically selected populations may reduce genetic and environmental heterogeneities and help clarify the underlying mechanisms of MS susceptibility. Sardinians kept a homogeneous genetic structure and have among the highest MS frequency rates worldwide. Interestingly, MS in Sardinia is linked to otherwise rare HLA alleles. In this light, recent findings from epidemiological and immunogenetic studies of Sardinian MS are presented. Results confirm that, likely due to significant genetic differences at a microgeographic level, even in this homogeneous population MS is immunogenetically heterogeneous and tends to preferentially cluster in some more archaic areas of the island.

Population and subspecific genetic differentiation in the foxtail pine (Pinus balfouriana).

We performed an allozyme survey of genetic differentiation in Pinus balfouriana, a subalpine conifer endemic to California that is comprised of two allopatric subspecies, one in the Klamath Mountains and the other in the southern Sierra Nevada. Although the two subspecies are morphologically distinct and gene flow between them is virtually nonexistent, we observed much higher levels of differentiation among populations within a subspecies than between the two subspecies. Differentiation is particularly strong in the Klamath populations (multilocus FST = 0.242), which are small, isolated, and ecologically marginal. We attribute this strong differentiation to the mountain island effect, in which populations restricted to high elevations become isolated from each other on different mountains separated by unsuitable intervening habitat, with consequent reduced gene flow allowing populations to evolve independently. Populations of P. balfouriana in the Klamath region only exist scattered on the few highest ridges and peaks that rise above 2,000 m, which defines the lower limit of the species elevational distribution. This pattern of distribution has allowed genetic drift and allelic sorting through historical events to produce strong population-level differentiation, which was likely in place before the two subspecies were geographically separated. Because P. balfouriana occurs on both serpentine soils and nonserpentine soils in the Klamath Mountains, we tested for genetic differentiation between populations growing on serpentine versus nonserpentine soils and our results were equivocal. Our data, combined with several other studies of conifers, show that the mountain island effect can produce significant genetic differentiation in conifers whose life-history traits of widely dispersed pollen, long generation times, and high outcrossing rates would lead us to predict a more homogenous population genetic structure.

Homogeneous genetic structure ofmeganyctiphanes norvegica(euphausiacea) in the North-east Atlantic ocean, as interpreted fromallozymic variation

Abstract In order to elucidate the possible existence of genetically separated stocks of Meganyctiphanes norvegica in the north-east Atlantic Ocean, a population genetic analysis ofthe species was commenced. In particular we wanted to investigate how possible genetic cohesiveness between samples corresponds to the physical oceanographic structure in the region. An electrophoretic analysis of allele distributions at five enzyme loci identified in previous studies as being polymorphic was screened for variation between samples. 1 043 individuals from eight locations were studied and with the genetic resolution attained with a1lozymes on the loci studied, samples appear to represent a single panrnictic population.

日本近海に生息するイカナゴ個体群の遺転的分化

Genotypes at 10 enzyme loci were analyzed by horizontal starch gel electrophoresis for each of 11 populations of sand-lance Ammodytes personatus in Japan. Allele frequencies at each locus were calculated for each population. There were clear differences of allele frequencies at three loci (α-Gpdh, Me-2, Sod) between populations north of Iwate Prefecture and those south of Miyagi Prefecture. A cluster analysis based on genetic similarities calculated from allele fre-quencies at all 10 loci observed suggests that sand-lance among the Pacific coast of Japan are composed of two population groups; northern and southern groups. The boundary exsists be-tween Iwate and Miyagi Prefecture. Geographic distribution of these two groups is consistent with that of two groups previously described by morphological studies. Genetic distance between these groups falls within the values of intraspecific marine teleost populations. Comparison of genetic similarities and mean heterozygosities among populations suggests that the southern group has a smaller-scale genetic divergence and more homogeneous genetic structure than the northern group.