Adaptive Features (adaptive + feature)

Distribution by Scientific Domains

Selected Abstracts

Influence of temperature and salinity on the germination of Lotus creticus (L.) from the arid land of Tunisia

Mokhtar Rejili
Abstract Effects of salinity, temperature and their interactions on the rate and final percentage of germination were evaluated for two populations (Msarref, Oued dkouk) of the invasive glycophyte Lotus creticus Linné, grown under arid environmental conditions of the Tunisia. Seeds that were not treated with NaCl germinated well in a wide range of temperatures. For both populations, maximum germination occurred in distilled water at 25°C and lowest germination for all salinities was at 35°C. Germination was substantially delayed and significantly reduced with an increase in NaCl to levels above 300 mm. Compared to the Oued dkouk population, final germination and germination rate of the Msarref population was completely inhibited at 300 mm NaCl. The interactive effect of temperature and NaCl concentration on final germination and germination rate was significant (P < 0.01), indicating that the germination response to salinity depended on temperature. The inhibition of Oued dkouk population seed germination at high salt concentration was mostly due to osmotic effects while ionic effects were noted at Msarref population. The germination behaviour of the Oued dkouk population would therefore imply adaptive mechanisms to saline environments, while in the Msarref population such mechanisms seem to be absent. Since seed germination is more sensitive to salinity stress than the growth of established plants, the greater tolerance to salinity of Oued dkouk population would be an adaptive feature of this population to saline environment. Résumé L'effet de l'interaction de la salinité et de la température sur la germination de deux populations (Msarref et Oued Dkouk) du lotier de crête (Lotus creticus L.), glycophyte poussant dans des conditions environnementales arides en Tunisie, est étudié. Chez les deux populations, le taux de germination le plus élevé est obtenu à 25°C et le plus faible à 35°C. A 300 mm de NaCl, la germination de la population d'Oued Dkouk est ralentie alors que celle de Msarref est complètement inhibée. L'effet de l'interaction de deux stress est hautement significatif (P < 0,01). Il semble, ainsi, que l'effet de chacun de deux stress est intensifié par l'autre. Cependant, les deux populations montrent un comportement halophytique différent. L'inhibition de la germination, par la salinité, chez Oued Dkouk est due à un effet osmotique alors que chez Mserref, il est ionique. Il en résulte que la population de oued Dkouk présente une capacité adaptative à l'aridité plus importante que celle observée chez la population Msarref. [source]

The evolution of human fatness and susceptibility to obesity: an ethological approach

Jonathan C. K. Wells
ABSTRACT Human susceptibility to obesity is an unusual phenomenon amongst animals. An evolutionary analysis, identifying factors favouring the capacity for fat deposition, may aid in the development of preventive public health strategies. This article considers the proximate causes, ontogeny, fitness value and evolutionary history of human fat deposition. Proximate causes include diet composition, physical activity level, feeding behaviour, endocrine and genetic factors, psychological traits, and exposure to broader environmental factors. Fat deposition peaks during late gestation and early infancy, and again during adolescence in females. As in other species, human fat stores not only buffer malnutrition, but also regulate reproduction and immune function, and are subject to sexual selection. Nevertheless, our characteristic ontogenetic pattern of fat deposition, along with relatively high fatness in adulthood, contrasts with the phenotype of other mammals occupying the tropical savannah environment in which hominids evolved. The increased value of energy stores in our species can be attributed to factors increasing either uncertainty in energy availability, or vulnerability to that uncertainty. Early hominid evolution was characterised by adaptation to a more seasonal environment, when selection would have favoured general thriftiness. The evolution of the large expensive brain in the genus Homo then favoured increased energy stores in the reproducing female, and in the offspring in early life. More recently, the introduction of agriculture has had three significant effects: exposure to regular famine; adaptation to a variety of local niches favouring population-specific adaptations; and the development of social hierarchies which predispose to differential exposure to environmental pressures. Thus, humans have persistently encountered greater energy stress than that experienced by their closest living relatives during recent evolution. The capacity to accumulate fat has therefore been a major adaptive feature of our species, but is now increasingly maladaptive in the modern environment where fluctuations in energy supply have been minimised, and productivity is dependent on mechanisation rather than physical effort. Alterations to the obesogenic environment are predicted to play a key role in reducing the prevalence of obesity. [source]

Approaches to prokaryotic biodiversity: a population genetics perspective

Francisco Rodríguez-Valera
Summary The study of prokaryotic diversity has blossomed during the last 10,15 years as a result of the introduction of molecular identification, mostly based on direct 16S rRNA gene polymerase chain reaction (PCR) amplification and sequencing from natural samples. A large amount of information exists about the diversity of this specific gene. However, data from the field of bacterial population genetics and genomics make questionable the value of information regarding just one gene. Even if we accept 16S rRNA genes as useful for species identification, intraspecific variation in bacteria is so high that species catalogues are often of little value. The gene pools represented by an operational species are yet impossible to predict. On the other hand, adaptive features in prokaryotes are often coded in gene clusters (genomic islands) that can be cloned directly from the environment, sequenced and even expressed in a surrogate host. Thus, the study of the environmental genome or metagenome appears as an alternative that could eventually lead to a more realistic understanding of prokaryotic biodiversity, provide biotechnology with new tools and maybe even contribute to develop a model of prokaryotic evolution. [source]

The adaptive phenotype of cortical thymic epithelial cells

Thomas Boehm
Abstract Epithelial cells in the thymus are required for positive and negative selection of developing thymocytes. Although medullary epithelial cells play a major role in negative selection owing to their facility of expressing peripheral self-antigens, the adaptive features of cortical epithelial cells are largely unknown. A paper in this issue of the European Journal of Immunology shows that the putative serine protease Prss16 affects positive selection of a subset of CD4+ T cells. A survey of chordate genomes indicates that the Prss16 gene emerged in vertebrates as a paralogue of evolutionarily older members of the serine carboxypeptidase 28 family; thus, Prss16 is not associated with the appearance of the adaptive immune system and the thymus in jawed vertebrates. Nevertheless, it appears that Prss16 has later evolved as an essential contributor to the MHC class II peptide/ligand repertoire. [source]

Genetic interactions between marine finfish species in European aquaculture and wild conspecifics

The principal species of marine aquaculture in Europe are Atlantic salmon (Salmo salar), sea bass (Dicentrarchus labrax) and sea bream (Sparus auratus). For Atlantic salmon and sea bass, a substantial part of total genetic variation is partitioned at the geographical population level. In the case of sea bream, gene flow across the Azores/Mediterranean scale appears to be extensive and population structuring is not detected. For Atlantic salmon and sea bass, natural population structure is at risk from genetic interaction with escaped aquaculture conspecifics. The locally adaptive features of populations are at risk from interbreeding with non-local aquaculture fish. Wild populations, generally, are at risk from interactions with aquaculture fish that have been subject to artificial selection or domestication. Atlantic salmon is the main European aquaculture species and its population genetics and ecology have been well-studied. A general case regarding genetic interactions can be based on the information available for salmon and extended to cover other species, in the appropriate context. A generalized flow chart for interactions is presented. Salmon escape from aquaculture at all life stages, and some survive to breed among wild salmon. Reproductive fitness in the escaped fish is lower than in native, wild fish because of behavioural deficiencies at spawning. However, as the number of salmon in aquaculture greatly exceeds the number of wild fish, even small fractional rates of escape may result in the local presence of large numbers, and high frequencies, of escaped fish. At present, policy and legislation in relation to minimizing genetic interactions between wild and aquaculture fish is best developed for Atlantic salmon, through the recommendations of the Oslo Agreement developed by the North Atlantic Salmon Conservation Organization and subsequent agreements on their implementation. In future, the potential use of genetically modified fish in aquaculture will make additional policy development necessary. Improved containment is recommended as the key to minimizing the numbers and therefore the effects of escaped fish. Emergency recovery procedures are recommended as a back-up measure in the case of containment failure. Reproductive sterility is recommended as a future key to eliminating the genetic potential of escaped fish. The maintenance of robust populations of wild fish is recommended as a key to minimizing the effects of escaped fish on wild populations. [source]

Analysis of learners' navigational behaviour and their learning styles in an online course

S. Graf
Abstract Providing adaptive features and personalized support by considering students' learning styles in computer-assisted learning systems has high potential in making learning easier for students in terms of reducing their efforts or increasing their performance. In this study, the navigational behaviour of students in an online course within a learning management system was investigated, looking at how students with different learning styles prefer to use and learn in such a course. As a result, several differences in the students' navigation patterns were identified. These findings have several implications for improving adaptivity. First, they showed that students with different learning styles use different strategies to learn and navigate through the course, which can be seen as another argument for providing adaptivity. Second, the findings provided information for extending the adaptive functionality in typical learning management systems. Third, the information about differences in navigational behaviour can contribute towards automatic detection of learning styles, helping in making student modeling approaches more accurate. [source]

Ultrastructure of cyst shell and underlying membranes of three strains of the brine shrimp Artemia (Branchiopoda: Anostraca) from South India

V. Sugumar
Abstract The cyst of Artemia has shell and membranous coverings over the embryo. The membranous coverings have special adaptive features to allow the physical changes accompanying repeated hydration and dehydration cycles that might occur and adversely influence postembryonic development. Whole and slices of cryptobiotic cysts were processed for electron microscopy to study the internal details and to compare the morphological architecture of three Artemia strains of South India. Surface topography of scanning electron microscopic (SEM) studies revealed distinct button shaped structures on the cyst of Puthalam strain. Transmission electron microscopic (TEM) studies of the cysts displayed the conventional pattern of anostracan crustaceans with outer cortex and alveolar layer, cuticular membranes, and the cytoplasmic inclusions namely nucleus, yolk droplets, lipoid bodies, and mitochondria. The prominent wavy outer cortex layer of Puthalam cysts corroborates the results of SEM studies. Microsc. Res. Tech. © 2006 Wiley-Liss, Inc. [source]

Simple evolutionary pathways to complex proteins

Michael Lynch
Abstract A recent paper in this journal has challenged the idea that complex adaptive features of proteins can be explained by known molecular, genetic, and evolutionary mechanisms. It is shown here that the conclusions of this prior work are an artifact of unwarranted biological assumptions, inappropriate mathematical modeling, and faulty logic. Numerous simple pathways exist by which adaptive multi-residue functions can evolve on time scales of a million years (or much less) in populations of only moderate size. Thus, the classical evolutionary trajectory of descent with modification is adequate to explain the diversification of protein functions. [source]

The role of wood anatomy in phylogeny reconstruction of Ericales

CLADISTICS, Issue 3 2007
Frederic Lens
The systematic significance of wood anatomical characters within Ericales is evaluated using separate and combined parsimony analyses including 23 wood characters and 3945 informative molecular characters. Analyses of wood features alone result in poorly resolved and conflicting topologies. However, when pedomorphic character states are coded as inapplicable, the combined bootstrap topology results in an increase of resolution and support at most deeper nodes compared with the molecular analyses. This suggests that phylogenetic information from the limited number of morphological characters is not completely swamped by an overwhelming amount of molecular data. Based on the morphology of vessels and fibers, and the distribution of axial parenchyma, two major wood types can be distinguished within Ericales: (i) a "primitive" type, nearly identical to the wood structure in the more basal outgroup Cornales, which is likely to have persisted in one major clade, and (ii) a "derived" type that must have evolved in at least two separate evolutionary lines. The occurrence of the first type is strongly correlated with shrubs to small trees growing in cold temperate or tropical montane regions, while the second type is common in tall trees of tropical lowlands. This favors the inclusion of ecologically adaptive features in phylogeny reconstruction. © The Willi Hennig Society 2006. [source]