Ecological amplitude in relation to allozyme variation in Silene nutans at the western margin of its distribution

At the western border of its geographical range, Silene nutans (Caryophyllaceae) has evolved two groups of parapatric populations showing distinct allozyme patterns and apparently occurring on different bedrock types. This study tests the hypothesis that these groups represent edaphic ecotypes. With this in view, the ecological amplitude of 36 populations of Silene nutans from Belgium was investigated and their synecology specified using vegetation composition and soil parameters; Ellenberg indicator values were used for ecological interpretation of the vegetation analyses. The results provide evidence that allozyme and habitat variations are correlated, the two groups occurring on contrasting soil with distinct vegetation types. One group is restricted to alkaline soils and typically occurs in open calcareous grasslands, fringes and scrub. The other group is characterized by wider autecological and synecological ranges with a bimodal pH- distribution, occurring on two kinds of siliceous soils: (1) neutral soils, supporting vegetation with a high species richness comprising many mesophilous species, and (2) CaCO3 -free bedrocks characterized by acidophilous, species-poor, open dry grasslands and woodlands. It also appears that factors not related to soil chemistry, such as microclimate, are involved in the ecological specialization of the two ecotypes. It is argued that these ecotypes exemplify adaptive radiation and parapatric speciation at the margin of a species distribution area.FLWINinfo:eu-repo/semantics/publishe

A comparative study of allozyme variation of peripheral and central populations of Silene nutans L. (Caryophyllaceae) from Western Europe: implications for conservation

In Belgium, at the western border of its continental distribution range, the perennial herb S. nutans has evolved two parapatric ecotypes (calcicolous or silicicolous), which show contrasted allozyme, morphological and adaptive patterns, and isolating reproductive barriers. We examined allozyme variation in 21 populations close to Belgium (from France and Luxemburg) in relation to their peripheral or central geographical position, and investigated their genetic relationships with the Belgian ecotypes. Both peripheral and central populations showed high genetic variation. They were differentiated from each other, but not in relation to the substrate (calcareous or siliceous). The peripheral and central populations were related to the Belgian silicicolous and calcicolous ecotype, respectively. This suggests an ancient differentiation and different past histories for the Belgian ecotypes, and parapatric speciation processes. This study exemplifies the high evolutionary potential of populations at range peripheries and the need for considering them in conservation strategies.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Organisation de la variation génétique chez Silene nutans

info:eu-repo/semantics/publishe

Molecular basis of cold adaptation.

Cold-adapted, or psychrophilic, organisms are able to thrive at low temperatures in permanently cold environments, which in fact characterize the greatest proportion of our planet. Psychrophiles include both prokaryotic and eukaryotic organisms and thus represent a significant proportion of the living world. These organisms produce cold-evolved enzymes that are partially able to cope with the reduction in chemical reaction rates induced by low temperatures. As a rule, cold-active enzymes display a high catalytic efficiency, associated however, with a low thermal stability. In most cases, the adaptation to cold is achieved through a reduction in the activation energy that possibly originates from an increased flexibility of either a selected area or of the overall protein structure. This enhanced plasticity seems in turn to be induced by the weak thermal stability of psychrophilic enzymes. The adaptation strategies are beginning to be understood thanks to recent advances in the elucidation of the molecular characteristics of cold-adapted enzymes derived from X-ray crystallography, protein engineering and biophysical methods. Psychrophilic organisms and their enzymes have, in recent years, increasingly attracted the attention of the scientific community due to their peculiar properties that render them particularly useful in investigating the possible relationship existing between stability, flexibility and specific activity and as valuable tools for biotechnological purposes

Allozyme variation in relation to ecotypic differentiation and population size in marginal populations of Silene nutans

In Belgium, at the north-western margin of its geographical range, Silene nutans is a rare species, which has evolved a silicicolous (Si) and a calcicolous (Ca) ecotype, with contrasting morphometric traits. Genetic diversity and population genetic structure were examined for seven allozyme loci in 16 Si and 18 Ca populations (a total of 567 individuals). High genetic variation was found at both the ecotypic and population level, and no significant correlation was found between population size and any measure of genetic variation. The maintenance of high levels of genetic diversity in small, marginal populations might be explained by the perennial, long-lived life form and the outcrossing breeding system of the species. Additionally, low F(ST)-values suggested that efficient gene flow was occurring within both ecotypes. Genetic distance measures and cluster analysis using UPGMA on the distance matrix revealed that the populations were differentiated according to their ecotypic property in two distinct gene pools. It is argued that the congruence of allozymic and morphometric differentiation between edaphic races is unusual for an outcrossing species. This finding, together with previous observations of isolating mechanisms between ecotypes, strongly suggests that incipient speciation is occurring within Silene nutans at the margin of its geographical range.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/publishe