A novel vein graft model: adaptation to differential flow environments

Accelerated intimal hyperplasia in response to altered flow environment is critical to the process of vein bypass graft failure. Lack of a reproducible animal model for dissecting the mechanisms of vein graft (VG) remodeling has limited progress toward solving this clinically significant problem. Combining a cuffed anastomotic technique with other surgical manipulations, we developed a well-defined, more robust method for studying hemodynamic factors in VG arterialization. VG with fistula placement, complete occlusion, or partial distal branch ligation (DBL) was performed in the carotid artery of 56 rabbits. Extensive hemodynamic and physiological analyses were performed to define the hemodynamic forces and histological adaptations of the wall at 1-28 days. Anastomotic time averaged 12 min, with 100% patency of bilateral grafts and unilateral grafts plus no adjunct or delayed fistula. Bilateral VG-DBL resulted in an immediate disparity in wall shear (0.8 +/- 0.1 vs. 12.4 +/- 1.1 dyn/cm2, ligated vs. contralateral graft). Grafts exposed to low shear stress responded primarily through enhanced intimal thickening (231 +/- 35 vs. 36 +/- 18 microm, low vs. high shear). High-shear-stress grafts adapted through enhanced outward remodeling, with a 24% increase in lumen diameter at 28 days (3.0 +/- 0.1 vs. 3.7 +/- 0.2 mm, low vs. high shear). We have taken advantage of the cuffed anastomotic technique and combined it with a bilateral VG-DBL model to dissect the impact of hemodynamic forces on VG arterialization. This novel model offers a robust, clinically relevant, statistically powerful small animal model for evaluation of high- and low-shear-regulated VG remodeling.     

Reproductive strategy of insects as adaptation to temporally varying environments

Diversity of oviposition curve observed in 125 insects was analysed using the ratio of the length of period for development to that for reproduction. On the basis of this empirical data, two extreme reproductive patterns were selected: prolonged reproduction with early maturity and concentrated reproduction with late maturity. Population growth of the species with each reproductive pattern was calculated usingLeslie Matrix under some simulated fluctuating environments where the length of time during which the environments change is short compared with the time required to stabilize age structure. These simulation studies show that there is an optimal ratio of the length of period for development to that for reproduction in achieving high population densities and this ratio varies depending on the favorableness of environment for reproductive success: as the environmental favorableness decreases, the optimal ratio becomes larger.     

Genomic insights into adaptation to high-altitude environments

Elucidating the molecular genetic basis of adaptive traits is a central goal of evolutionary genetics. The cold, hypoxic conditions of high-altitude habitats impose severe metabolic demands on endothermic vertebrates, and understanding how high-altitude endotherms cope with the combined effects of hypoxia and cold can provide important insights into the process of adaptive evolution. The physiological responses to high-altitude stress have been the subject of over a century of research, and recent advances in genomic technologies have opened up exciting opportunities to explore the molecular genetic basis of adaptive physiological traits. Here, we review recent literature on the use of genomic approaches to study adaptation to high-altitude hypoxia in terrestrial vertebrates, and explore opportunities provided by newly developed technologies to address unanswered questions in high-altitude adaptation at a genomic scale.     

The strategy of Na+ compartmentation and growth of Atriplex centralasiatica in adaptation to saline environments

In this study, we investigated the adaptation strategy employed by Atriplex centralasiatica Iljin in response to high salinity. When grown in high saline environments (100–200 mM NaCl), A. centralasiatica plants were larger and more succulent. This increased growth and water uptake was correlated with a large and specific cellular accumulation of sodium, demonstrating that in A. centralasiatica Na⁺ is beneficial rather than toxic. More than 95% of Na⁺ absorbed by salt-treated A. centralasiatica plants accumulated in shoots, especially in leaves; approximately 98% of Na⁺ that accumulated in leaves was localized in leaf protoplasts, a situation that was responsible for the decreased photosynthetic rate observed with increasing salt concentration. Because of the greater leaf area per plant found under saline conditions, no reduction in biomass of individual plants was observed. Measurements on isolated tonoplast-enriched membrane vesicles derived from the leaves of A. centralasiatica revealed increased V-H⁺-ATPase hydrolytic activity and V-H⁺-ATPase proton pump activity in salt-treated leaves compared with controls. These results suggest that, as an adaptation to saline environments, A. centralasiatica can efficiently sequester Na⁺ into vacuoles, thereby increasing leaf area to maintain its CO₂ assimilation capabilities.     

A method for the enumeration of Aeromonas bacteriophage in aquatic environments

K.P. FLINT. 1996. Bacteriophage were isolated against type strains and environmental isolates of Aeromonas hydrophila, Aeromonas sobria and Aeromonas caviae . A most probable number method for estimating the number of bacteriophage in a water sample was devised and tested using some of these isolates. The maximum number of bacteriophage against all three type strains were found in water from below a sewage effluent outfall. This corresponds to the increased numbers of each species of bacterium also found in this water sample. High numbers of bacteriophage against Aer. hydrophila were also found in the lake sample examined. Bacteriophage against Aer. caviae were rare in water samples other than those contaminated with sewage effluent.     

Consequences of host adaptation for performance of vesicular stomatitis virus in novel thermal environments

Although it is widely assumed that the selective advantage of niche specialization drives species biodiversity, some theory suggests that generalists are favored over specialists when environments change unexpectedly. But this idea is rarely tested empirically, and its relevance is unknown for microparasites such as RNA viruses. Due to their small genome sizes pleiotropy is not uncommon in RNA viruses. Therefore, the genetic architectures underlying generalist traits may be indirectly molded by selection to better prepare generalist organisms for growth in new environments. Previously, vesicular stomatitis viruses were evolved to specialize on a single host, or to generalize on multiple hosts. Here we test whether virus generalists arising in the context of host adaptation also perform differently than specialists when viruses grow at novel temperatures. We compared thermal reaction norms of performance, within and among groups of viral specialists and generalists. Results showed that host adaptation was consequential for some fitness traits at novel temperatures due to modification of pleiotropic viral genes. Contrary to theoretical predictions, host generalists were selectively disadvantaged at extreme cool and warm environments. Multi-host adaptation may compromise the evolved thermostability of viral proteins, creating a cost of host generalization when viruses replicate at extreme temperatures.     

The genetics of adaptation to novel environments: selection on germination timing in Arabidopsis thaliana

When studying selection during adaptation to novel environments, researchers have often paid little attention to an organism’s earliest developmental stages. Despite this lack of attention, early life history traits may be under strong selection during colonization, as the expression of adaptive phenotypes at later points is contingent upon early survival. Moreover, the timing of early developmental transitions can constrain the timing of later transitions, with potentially large effects on fitness. In this issue, Huang et al. (2010) underscore the importance of early life history traits in the adaptation of Arabidopsis thaliana to old‐field sites in North America. Using a new population of mapped recombinant inbred lines, the authors examined germination timing and total lifetime fitness of A. thaliana while varying site latitude, dispersal season, and maternal photoperiod. Huang et al. (2010) discovered several Quantitative Trait Loci (QTL) with large effects on fitness that colocalized with QTL for field germination timing and seed dormancy—demonstrating that fitness is genetically associated with these early life history traits, and that these loci are likely under strong selection during adaptation to novel environments. In the epistatic interactions of some loci, recombinant genotypes outperformed parental genotypes, supporting the potentially adaptive role of recombination. This study provides elegant evidence that traits expressed early in an organism’s development can play an important role during adaptive evolution.     

Mammalian keratin associated proteins (KRTAPs) subgenomes: disentangling hair diversity and adaptation to terrestrial and aquatic environments

Background

Adaptation of mammals to terrestrial life was facilitated by the unique vertebrate trait of body hair, which occurs in a range of morphological patterns. Keratin associated proteins (KRTAPs), the major structural hair shaft proteins, are largely responsible for hair variation.

Results

We exhaustively characterized the KRTAP gene family in 22 mammalian genomes, confirming the existence of 30 KRTAP subfamilies evolving at different rates with varying degrees of diversification and homogenization. Within the two major classes of KRTAPs, the high cysteine (HS) subfamily experienced strong concerted evolution, high rates of gene conversion/recombination and high GC content. In contrast, high glycine-tyrosine (HGT) KRTAPs showed evidence of positive selection and low rates of gene conversion/recombination. Species with more hair and of higher complexity tended to have more KRATP genes (gene expansion). The sloth, with long and coarse hair, had the most KRTAP genes (175 with 141 being intact). By contrast, the “hairless” dolphin had 35 KRTAPs and the highest pseudogenization rate (74% relative to the 19% mammalian average). Unique hair-related phenotypes, such as scales (armadillo) and spines (hedgehog), were correlated with changes in KRTAPs. Gene expression variation probably also influences hair diversification patterns, for example human have an identical KRTAP repertoire as apes, but much less hair.

Conclusions

We hypothesize that differences in KRTAP gene repertoire and gene expression, together with distinct rates of gene conversion/recombination, pseudogenization and positive selection, are likely responsible for micro and macro-phenotypic hair diversification among mammals in response to adaptations to ecological pressures.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-779) contains supplementary material, which is available to authorized users.     

Extremophiles and their adaptation to hot environments.

Water-containing terrestrial, subterranean and submarine high temperature areas harbor a variety of hyperthermophilic bacteria and archaea which are able to grow optimally above 80 degrees C. Hyperthermophiles are adapted to hot environments by their physiological and nutritional requirements. As a consequence, cell components like proteins, nucleic acids and membranes have to be stable and even function best at temperatures around 100 degrees C. The chemolithoautotrophic archaeon Pyrolobus fumarii is able to grow at 113 degrees C and, therefore, represents the upper temperature border of life. For the first time, (vegetative) cultures of Pyrolobus and Pyrodictium are able to survive autoclaving.     

Genome biology of a novel lineage of planctomycetes widespread in anoxic aquatic environments

Anaerobic strains affiliated with a novel order‐level lineage of the Phycisphaerae class were retrieved from the suboxic zone of a hypersaline cyanobacterial mat and anoxic sediments of solar salterns. Genome sequences of five isolates were obtained and compared with metagenome‐assembled genomes representing related uncultured bacteria from various anoxic aquatic environments. Gene content surveys suggest a strictly fermentative saccharolytic metabolism for members of this lineage, which could be confirmed by the phenotypic characterization of isolates. Genetic analyses indicate that the retrieved isolates do not have a canonical origin of DNA replication, but initiate chromosome replication at alternative sites possibly leading to an accelerated evolution. Further potential factors driving evolution and speciation within this clade include genome reduction by metabolic specialization and rearrangements of the genome by mobile genetic elements, which have a high prevalence in strains from hypersaline sediments and mats. Based on genetic and phenotypic data a distinct group of strictly anaerobic heterotrophic planctomycetes within the Phycisphaerae class could be assigned to a novel order that is represented by the proposed genus Sedimentisphaera gen. nov. comprising two novel species, S. salicampi gen. nov., sp. nov. and S. cyanobacteriorum gen. nov., sp. nov.     

Action spectra for photosynthetic adaptation in Scenedesmus obliquus

Photosynthetic adaptation of the unicellular green alga Scenedemus obliquus to different light conditions was investigated with respect to chlorophyll synthesis. Cultures were grown under white light (20 W · m^–2) from fluorescent lamps and were then transferred and subjected to the actual adaptation regime which consisted of a 24-h irradiation by different fluence rates and wavelengths. Fluence rate-response curves for chlorophyll synthesis were measured between 4 · 10^–2 and 1 · 10² W · m^–2. In white light from incandescent lamps, in blue and red light the fluence rate-response curves for chlorophyll (Chl) a and also for Chl b were bell-shaped. In red light the threshold was about the same as under blue light. The maximal amounts of Chl a and b were about twofold increased under blue light relative to the values obtained with red light. Action spectra for the stimulation of chlorophyll synthesis (Chl a + Chl b) as well as those for the separate chlorophylls showed two maxima near 450 and 500 nm. However, the action spectrum for Chl b synthesis demonstrated a considerably higher value in the 450-nm peak. Experiments with the photosynthesis inhibitor 3-(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU) indicated that photosynthetic energy supply supported the photostimulation of chlorophyll synthesis. The action spectra indicate the cooperation of two photoreceptors. The 460-nm peak is attributed to the typical blue-light receptor, being more active in Chl b formation. The peak at 500 nm may represent carotenoproteins acting as an accessory pigment system.Abbreviations PCV packed cell volume - Chl total amount of chlorophyll - Chl a, b chlorophyll a, b - DCMU 3-(3,4-dichlorphenyl)-1,1-dimethylurea This project was supported by the Deutsche Forschungsgemeinschaft. We thank Ms. K. Bölte for technical assistance.     

Photosynthetic adaptation ofSolanum dulcamara L. to sun and shade environments. III. Characterization of genotypes with differing photosynthetic performance

Summary Clone mal9, a genotype ofSolanum dulcamara L. having photosynthetic characteristics similar to previously hypothesized shade ecotypes, is compared to five other genotypes having photosynthetic characteristics similar to previously hypothesized sun ecotypes. The primary differences are a 35% reduction in total leaf conductance and a 15% reduction in leaf chlorophyll content in mal9. Both factors contribute to a 44% reduction in lightsaturated photosynthetic rate in mal9. In relation to the 5 other genotypes, mal9 appears to be poorly adapted for growth in the normal range of natural habitats.     

The evolution of viviparity in holocene islands: ecological adaptation versus phylogenetic descent along the transition from aquatic to terrestrial environments

Species that contain populations with different reproductive modes offer excellent opportunities to study the transition between such strategies. Salamandra salamandra (Linnaeus, 1758) is one of two species within the Salamandra – Lyciasalamandra clade which displays two reproductive modes simultaneously. Along the S. salamandra distribution, the common reproductive mode is ovoviviparity although the species also has viviparous populations in the northern Iberian Peninsula. The occurrence of viviparity has recently been reported in two small offshore island populations on the Atlantic coast (NW Iberia), which originated after the last glacial period (8000–9000 years ago). In this paper, we analysed ovoviviparous, hybrid and viviparous populations (inland and mainland) from 17 localities across the northern Iberian Peninsula using two mitochondrial markers (Cyt b and COI , c . 1100 bp). Phylogenetic and phylogeographic analyses highly support that viviparity arose as an evolutionary novelty in the S. salamandra island populations and that viviparous populations are therefore not monophyletic. The recent insularity of Atlantic island populations leads us to conclude that the transition from ovoviviparity to viviparity can happen in a very short-time span. Additionally, to determine the likely source of this evolutionary transition, we discuss how ecological pressures could have an effect on the maintenance of the ovoviviparous reproductive mode. Hence, taking into account the results of this study, we propose the consideration of the island populations as an evolutionary unit for conservation purposes.     

Arginine deiminase system and bacterial adaptation to acid environments

The arginine deiminase system in a variety of streptococci and in Pseudomonas aeruginosa was found to be unusually acid tolerant in that arginolysis occurred at pH values well below the minima for growth and glycolysis. The acid tolerance of the system allowed bacteria to survive potentially lethal acidification through production of ammonia to raise the environmental pH value.     

Aquatic zooremediation: deploying animals to remediate contaminated aquatic environments

The ability of animals to act in a bioremediative capacity is not widely known. Animals are rarely considered for bioremediation initiatives owing to ethical or human health concerns. Nonetheless, specific examples in the literature reveal that some animal species are effective remediators of heavy metals, microbial contaminants, hydrocarbons, nutrients and persistent organic pollutants, particularly in an aquatic environment. Recent examples include deploying pearl oysters to remove metals and nutrients from aquatic ecosystems and the harvest of fish to remove polychlorinated biphenyls (PCBs) from the Baltic. It is probable that many animal taxa will possess attributes amenable to bioremediation. We introduce zoological equivalents of the definitions used in phytoremediation literature (zooextraction, zootransformation, zoostabilization and animal hyperaccumulation), to serve as useful benchmarks in the evaluation of candidate animal species for zooremediation initiatives, and propose that recognition of the concept of zooremediation would act to stimulate discussion and future research in this area.