Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations

There is accumulating evidence that individuals leave their natal area and select a breeding habitat non-randomly by relying upon information about their natal and future breeding environments. This variation in dispersal is not only based on external information (condition dependence) but also depends upon the internal state of individuals (phenotype dependence). As a consequence, not all dispersers are of the same quality or search for the same habitats. In addition, the individual's state is characterized by morphological, physiological or behavioural attributes that might themselves serve as a cue altering the habitat choice of conspecifics. These combined effects of internal and external information have the potential to generate complex movement patterns and could influence population dynamics and colonization processes. Here, we highlight three particular processes that link condition-dependent dispersal, phenotype-dependent dispersal and habitat choice strategies: (1) the relationship between the cause of departure and the dispersers' phenotype; (2) the relationship between the cause of departure and the settlement behaviour and (3) the concept of informed dispersal, where individuals gather and transfer information before and during their movements through the landscape. We review the empirical evidence for these processes with a special emphasis on vertebrate and arthropod model systems, and present case studies that have quantified the impacts of these processes on spatially structured population dynamics. We also discuss recent literature providing strong evidence that individual variation in dispersal has an important impact on both reinforcement and colonization success and therefore must be taken into account when predicting ecological responses to global warming and habitat fragmentation.     

Modelling population redistribution in a leaf beetle: an evaluation of alternative dispersal functions

1. Dispersal is a fundamental ecological process, so spatial models require realistic dispersal kernels. We compare five different forms for the dispersal kernel of the tansy beetle Chrysolina graminis moving between patches of its host-plant (tansy Tanacetum vulgare) in a riparian landscape. 2. Multi-patch mark-recapture data were collected every 2 weeks over 2 years within a large network of patches and from 2226 beetles. Dispersal was common (28.4% of 880 recaptures after a fortnight) and was more likely over longer intervals, out of small patches, for females and during flooding. Interpatch movement rates did not differ between years and exhibited no density dependence. Dispersal distances were similar for males and females, in both years and over all intervals, with a median dispersal distance of just 9.8 m, although a maximum of 856 m was recorded. 3. A model of dispersal, where patches competed for dispersers based on their size and distance from the beetle's source patch (scaled by the dispersal kernel) was fitted to the field data with a maximum likelihood procedure and each of five alternative kernels. The best fitting had relatively extended tails of long-distance dispersal, while Gaussian and negative exponential kernels performed worst. 4. The model suggests that females disperse more commonly than males and that both are strongly attracted to large patches but do not differ between years, which are consistent with the empirical results. Model-predicted emigration and immigration rates and dispersal phenologies match those observed, suggesting that the model captured the major drivers of tansy beetle dispersal. 5. Although negative exponential and Gaussian kernels are widely used for their simplicity, we suggest that these should not be the models of automatic choice, and that fat-tailed kernels with relatively higher proportions of long-distance dispersal may be more realistic.     

Colonization processes and the maintenance of genetic diversity: insights from a pioneer rainforest tree, Aucoumea klaineana

Despite recurrent episodes of range expansion and contraction, forest trees often harbour high genetic diversity. Studies of temperate forest trees suggest that prolonged juvenile phase and high pollen flow are the main factors limiting founder effects. Here, we studied the local colonization process of a pioneer rainforest tree in central Africa, Aucoumea klaineana. We identified 87% of parents among trees up to 20-25 years old and could thus compare direct parentage structure data with classical population genetics estimators. In this species, genetic diversity was maintained during colonization. The absence of founder effects was explained by (i) local random mating and (ii) local recruitment, as we showed that 75% of the trees in the close neighbourhood participated in the recruitment of new saplings. Long-distance pollen flow contributed little to genetic diversity: pollen and seed dispersal was mainly within stand (128 and 118 m, respectively). Spatial genetic structure was explained by aggregated seed dispersal rather than by mother-offspring proximity as assumed in classical isolation-by-distance models. Hence, A. klaineana presents a genetic diversity pattern typical of forest trees but does not follow the classical rules by which this diversity is generally achieved. We suggest that while high local genetic variability is of general importance to forest tree survival, the proximate mechanisms by which it is achieved may follow very different scenarios.     

Within-host competitive interactions as a mechanism for the maintenance of parasite diversity

Variation among parasite strains can affect the progression of disease or the effectiveness of treatment. What maintains parasite diversity? Here I argue that competition among parasites within the host is a major cause of variation among parasites. The competitive environment within the host can vary depending on the parasite genotypes present. For example, parasite strategies that target specific competitors, such as bacteriocins, are dependent on the presence and susceptibility of those competitors for success. Accordingly, which parasite traits are favoured by within-host selection can vary from host to host. Given the fluctuating fitness landscape across hosts, genotype by genotype (G×G) interactions among parasites should be prevalent. Moreover, selection should vary in a frequency-dependent manner, as attacking genotypes select for resistance and genotypes producing public goods select for cheaters. I review competitive coexistence theory with regard to parasites and highlight a few key examples where within-host competition promotes diversity. Finally, I discuss how within-host competition affects host health and our ability to successfully treat infectious diseases.     

The potential of plant viruses to promote genotypic diversity via genotype x environment interactions

Background and Aims

Genotype by environment (G × E) interactions are important for the long-term persistence of plant species in heterogeneous environments. It has often been suggested that disease is a key factor for the maintenance of genotypic diversity in plant populations. However, empirical evidence for this contention is scarce. Here virus infection is proposed as a possible candidate for maintaining genotypic diversity in their host plants.

Methods

The effects of White clover mosaic virus (WClMV) on the performance and development of different Trifolium repens genotypes were analysed and the G × E interactions were examined with respect to genotype-specific plant responses to WClMV infection. Thus, the environment is defined as the presence or absence of the virus.

Key Results

WClMV had a negative effect on plant performance as shown by a decrease in biomass and number of ramets. These effects of virus infection differ greatly among host genotypes, representing a strong G × E interaction. Moreover, the relative fitness and associated ranking of genotypes changed significantly between control and virus treatments. This shift in relative fitness among genotypes suggests the potential for WClMV to provoke differential selection on T. repens genotypes, which may lead to negative frequency-dependent selection in host populations.

Conclusions

The apparent G × E interaction and evident repercussions for relative fitness reported in this study stress the importance of viruses for ecological and evolutionary processes and suggest an important role for viruses in shaping population dynamics and micro-evolutionary processes.     

Landscape dynamics and evolution of colonizer syndromes: interactions between reproductive effortand dispersal in a metapopulation

The evolutionary consequences of changes in landscape dynamics for the evolution of life history syndromes are studied using a metapopulation model. We consider in turn the long-term effects of a change in the local disturbance rate, in the maximal local population persistence, in habitat productivity, and in habitat fragmentation. We examine the consequences of selective interactions between dispersal and reproductive effort by comparing the outcome of joint evolution to a situation where the species has lost the potential to evolve either its reproductive effort or its dispersal rate. We relax the classical assumption that any occupied site in the metapopulation reaches its carrying capacity immediately after recolonization. Our main conclusions are the following: (1) genetic diversity modifies the range of landscape parameters for which the metapopulation is viable, but it alters very little the qualitative evolutionary trends observed for each trait within this range. Although they are both part of a competition/colonization axis, reproductive effort and dispersal are not substitutable traits: their evolution reflects more directly the change in the landscape dynamics, than a selective interaction among them. (2) no general syndrome of covariation between reproductive effort and dispersal can be predicted: the pattern of association between the two traits depends on the type of change in landscape dynamics and on the saturation level. We review empirical evidence on colonizer syndromes and suggest lines for further empirical work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evolution and ecology meet molecular genetics: adaptive phenotypic plasticity in two isolated Negev desert populations of Acacia raddiana at either end of a rainfall gradient

Background and Aims

The ecological, evolutionary and genetic bases of population differentiation in a variable environment are often related to the selection pressures that plants experience. We compared differences in several growth- and defence-related traits in two isolated populations of Acacia raddiana trees from sites at either end of an extreme environmental gradient in the Negev desert.

Methods

We used random amplified polymorphic DNA (RAPD) to determine the molecular differences between populations. We grew plants under two levels of water, three levels of nutrients and three levels of herbivory to test for phenotypic plasticity and adaptive phenotypic plasticity.

Key Results

The RAPD analyses showed that these populations are highly genetically differentiated. Phenotypic plasticity in various morphological traits in A. raddiana was related to patterns of population genetic differentiation between the two study sites. Although we did not test for maternal effects in these long-lived trees, significant genotype × environment (G × E) interactions in some of these traits indicated that such plasticity may be adaptive.

Conclusions

The main selection pressure in this desert environment, perhaps unsurprisingly, is water. Increased water availability resulted in greater growth in the southern population, which normally receives far less rain than the northern population. Even under the conditions that we defined as low water and/or nutrients, the performance of the seedlings from the southern population was significantly better, perhaps reflecting selection for these traits. Consistent with previous studies of this genus, there was no evidence of trade-offs between physical and chemical defences and plant growth parameters in this study. Rather, there appeared to be positive correlations between plant size and defence parameters. The great variation in several traits in both populations may result in a diverse potential for responding to selection pressures in different environments.     

Between migration load and evolutionary rescue: dispersal,adaptation and the response of spatially structured populations to environmental change

The evolutionary potential of populations is mainly determined by population size and available genetic variance. However, the adaptability of spatially structured populations may also be affected by dispersal: positively by spreading beneficial mutations across sub-populations, but negatively by moving locally adapted alleles between demes. We develop an individual-based, two-patch, allelic model to investigate the balance between these opposing effects on a population''s evolutionary response to rapid climate change. Individual fitness is controlled by two polygenic traits coding for local adaptation either to the environment or to climate. Under conditions of selection that favour the evolution of a generalist phenotype (i.e. weak divergent selection between patches) dispersal has an overall positive effect on the persistence of the population. However, when selection favours locally adapted specialists, the beneficial effects of dispersal outweigh the associated increase in maladaptation for a narrow range of parameter space only (intermediate selection strength and low linkage among loci), where the spread of beneficial climate alleles is not strongly hampered by selection against non-specialists. Given that local selection across heterogeneous and fragmented landscapes is common, the complex effect of dispersal that we describe will play an important role in determining the evolutionary dynamics of many species under rapidly changing climate.     

The ecological genetics of introduced populations of the giant toad, Bufo marinus (Amphibia: Anura): dispersal and neighbourhood size

The pattern of colonization of the Moreton Bay region in southeast Queensland, Australia, by the giant toad, Bufo marinus , is described. Estimates are made of the rates of colonization in this and other regions. The mean values obtained range from 2.5 km/year in the south to 15.1 km/year in the north. The analysis suggests that colonization has been discontinuous in many areas, probably as a result of occasional, long-distance transportation of toads by humans. The variation in colonization rate is related in a predictable way to variation in environmental factors such as temperature and topography. In areas where discontinuities are least likely, colonization rates are used to estimate rates of continuous dispersal. These are combined with estimates of population density, sex ratios and offspring number variance to obtain estimates of genetic neighbourhood size. These are much greater than estimates of the effective size of B. marinus populations determined from gene frequency variances. The reasons for and implications of this discrepancy are discussed.     

Early establishment and dispersal of the weevil, Mogulones cruciger (Coleoptera: Curculionidae) for biological control of houndstongue (Cynoglossum officinale) in British Columbia, Canada

First released in Canada in 1997 to control the invasive rangeland weed, houndstongue (Cynoglossum officinale), the European root weevil, Mogulones cruciger, is showing early potential as a successful biocontrol agent. Out of 22 experimental releases in southeastern British Columbia, Canada, 100% established, regardless of initial release size (range 100-400). These founding populations persisted beyond 2 years, and quickly dispersed through a treed and variable landscape to colonise new houndstongue patches surrounding the original release patches. Within 3 years, the weevil had moved 1.42 km. Both initial, within-patch and later, between-patch dispersal followed a similar pattern, with M. cruciger adults and/or their feeding/oviposition damage being more concentrated nearest the original points of release and declining with distance. Within-patch, this pattern of distribution and also the rate of spread of weevils were similar regardless of initial release size; suggesting density-independence in dispersal behaviour at this scale. Closer investigation of the sequence of invasion at a larger spatial scale suggested that the weevil arrived at, colonized and increased in number on the closest host patches first. Three years post release, both distance from release patch and the number of M. cruciger released, were significant predictors of the amount of feeding/oviposition damage, and presumably weevil population size, within newly colonized houndstongue patches surrounding the original releases. These data, and the finding that more weevils were retrieved from patches where higher numbers of weevils were released in the previous year (i.e., 300 or 400 vs 100 or 200), suggest that release number and placement of releases within a landscape can be manipulated for effective houndstongue control.     

Towards a functional-structural plant model of cut-rose: simulation of light environment, light absorption, photosynthesis and interference with the plant structure

Background and Aims

The production system of cut-rose (Rosa × hybrida) involves a complex combination of plant material, management practice and environment. Plant structure is determined by bud break and shoot development while having an effect on local light climate. The aim of the present study is to cover selected aspects of the cut-rose system using functional–structural plant modelling (FSPM), in order to better understand processes contributing to produce quality and quantity.

Methods

The model describes the production system in three dimensions, including a virtual greenhouse environment with the crop, light sources (diffuse and direct sun light and lamps) and photosynthetically active radiation (PAR) sensors. The crop model is designed as a multiscaled FSPM with plant organs (axillary buds, leaves, internodes, flowers) as basic units, and local light interception and photosynthesis within each leaf. A Monte-Carlo light model was used to compute the local light climate for leaf photosynthesis, the latter described using a biochemical rate model.

Key Results

The model was able to reproduce PAR measurements taken at different canopy positions, different times of the day and different light regimes. Simulated incident and absorbed PAR as well as net assimilation rate in upright and bent shoots showed characteristic spatial and diurnal dynamics for different common cultivation scenarios.

Conclusions

The model of cut-rose presented allowed the creation of a range of initial structures thanks to interactive rules for pruning, cutting and bending. These static structures can be regarded as departure points for the dynamic simulation of production of flower canes. Furthermore, the model was able to predict local (per leaf) light absorption and photosynthesis. It can be used to investigate the physiology of ornamental plants, and provide support for the decisions of growers and consultants.     

APOE Modulates the Correlation Between Triglycerides,Cholesterol, and CHD Through Pleiotropy,and Gene-by-Gene Interactions

Relationship loci (rQTL) exist when the correlation between multiple traits varies by genotype. rQTL often occur due to gene-by-gene (G × G) or gene-by-environmental interactions, making them a powerful tool for detecting G × G. Here we present an empirical analysis of apolipoprotein E (APOE) with respect to lipid traits and incident CHD leading to the discovery of loci that interact with APOE to affect these traits. We found that the relationship between total cholesterol (TC) and triglycerides (ln TG) varies by APOE isoform genotype in African-American (AA) and European-American (EA) populations. The e2 allele is associated with strong correlation between ln TG and TC while the e4 allele leads to little or no correlation. This led to a priori hypotheses that APOE genotypes affect the relationship of TC and/or ln TG with incident CHD. We found that APOE*TC was significant (P = 0.016) for AA but not EA while APOE*ln TG was significant for EA (P = 0.027) but not AA. In both cases, e2e2 and e2e3 had strong relationships between TC and ln TG with CHD while e2e4 and e4e4 results in little or no relationship between TC and ln TG with CHD. Using ARIC GWAS data, scans for loci that significantly interact with APOE produced four loci for African Americans (one CHD, one TC, and two HDL). These interactions contribute to the rQTL pattern. rQTL are a powerful tool to identify loci that modify the relationship between risk factors and disease and substantially increase statistical power for detecting G × G.     

Psychotherapies for depression: a network meta‐analysis covering efficacy,acceptability and long‐term outcomes of all main treatment types

The effects of psychotherapies for depression have been examined in several hundreds of randomized trials, but no recent network meta‐analysis (NMA) has integrated the results of these studies. We conducted an NMA of trials comparing cognitive behavioural, interpersonal, psychodynamic, problem‐solving, behavioural activation, life‐review and “third wave” therapies and non‐directive supportive counseling with each other and with care‐as‐usual, waiting list and pill placebo control conditions. Response (50% reduction in symptoms) was the primary outcome, but we also assessed remission, standardized mean difference, and acceptability (all‐cause dropout rate). Random‐effects pairwise and network meta‐analyses were conducted on 331 randomized trials with 34,285 patients. All therapies were more efficacious than care‐as‐usual and waiting list control conditions, and all therapies – except non‐directive supportive counseling and psychodynamic therapy – were more efficacious than pill placebo. Standardized mean differences compared with care‐as‐usual ranged from –0.81 for life‐review therapy to –0.32 for non‐directive supportive counseling. Individual psychotherapies did not differ significantly from each other, with the only exception of non‐directive supportive counseling, which was less efficacious than all other therapies. The results were similar when only studies with low risk of bias were included. Most therapies still had significant effects at 12‐month follow‐up compared to care‐as‐usual, and problem‐solving therapy was found to have a somewhat higher long‐term efficacy than some other therapies. No consistent differences in acceptability were found. Our conclusion is that the most important types of psychotherapy are efficacious and acceptable in the acute treatment of adult depression, with few significant differences between them. Patient preference and availability of each treatment type may play a larger role in the choice between types of psychotherapy, although it is possible that a more detailed characterization of patients with a diagnosis of depression may lead to a more precise matching between individual patients and individual psychotherapies.     

Dynamics of polyploid formation and establishment in the allotetraploid rock fern Asplenium majoricum

Background and Aims

Successful establishment of newly formed polyploid species depends on several interlinked genetic and ecological factors. These include genetic diversity within and among individuals, chromosome behaviour and fertility, novel phenotypes resulting from novel genomic make-up and expression, intercytotypic and interspecific competition, and adaptation to distinct habitats. The allotetraploid rock fern Asplenium majoricum is known from one small population in Valencia, Spain, and several larger populations on the Balearic island of Majorca. In Valencia, it occurs sympatrically with its diploid parents, A. fontanum subsp. fontanum and A. petrarchae subsp. bivalens, and their diploid hybrid A. × protomajoricum. This highly unusual situation allowed the study of polyploid genetic diversity and its relationship to the formation and establishment of nascent polyploid lineages.

Methods

Genetic variation for isozyme and chloroplast DNA markers was determined for A. majoricum and A. × protomajoricum sampled thoroughly from known sites in Majorca and Valencia. Results were compared with variation determined previously for the diploid parent taxa.

Key Results

A highly dynamic system with recurring diploid hybrid and allotetraploid formation was discovered. High diversity in the small Valencian A. majoricum population indicates multiple de novo origins from diverse parental genotypes, but most of these lineages become extinct without becoming established. The populations on Majorca most probably represent colonization(s) from Valencia rather than an in situ origin. Low genetic diversity suggests that this colonization may have occurred only once.

Conclusions

There is a striking contrast in success of establishment of the Majorcan and Valencian populations of A. majoricum. Chance founding of populations in a habitat where neither A. fontanum subsp. fontanum nor A. petrarchae subsp. bivalens occurs appears to have been a key factor enabling the establishment of A. majoricum on Majorca. Successful establishment of this polyploid is probably dependent on geographic isolation from diploid progenitor competition.     

Isoform identification, recombinant production and characterization of the allergen lipid transfer protein 1 from pear (Pyr c 3)

Non-specific lipid transfer proteins belonging to LTP1 family represent the most important allergens for non pollen-related allergies to Rosaceae fruits in the Mediterranean area. Peach LTP1 (Pru p 3) is a major allergen and is considered the prototypic allergenic LTP. On the contrary, pear allergy without pollinosis seems to be under-reported when compared to other Rosaceae fruits suggesting that the as-yet-uncharacterized pear LTP1 (Pyr c 3) has in vivo a low allergenicity. We report here on the identification of four cDNAs encoding for LTP1 in pear fruits. The two isoforms exhibiting amino acid sequences most similar to those of peach and apple homologues were obtained as recombinant proteins. Such isoforms exhibited CD spectra and lipid binding ability typical of LTP1 family. Moreover, pear LTP1 mRNA was mainly found in the peel, as previously shown for other Rosaceae fruits. By means of IgE ELISA assays a considerable immunoreactivity of these proteins to LTP-sensitive patient sera was detected, even though allergic reactions after ingestion of pear were not reported in the clinical history of the patients. Finally, the abundance of LTP1 in protein extracts from pear peel, in which LTP1 from Rosaceae fruits is mainly confined, was estimated to be much lower as compared to peach peel. Our data suggest that the two isoforms of pear LTP1 characterized in this study possess biochemical features and IgE-binding ability similar to allergenic LTPs. Their low concentrations in pear might be the cause of the low frequency of LTP-mediated pear allergy.     

Activation of the Ghrelin Receptor is Described by a Privileged Collective Motion: A Model for Constitutive and Agonist-induced Activation of a Sub-class A G-Protein Coupled Receptor (GPCR)

Three homology models of the human ghrelin receptor (GHS-R1a) have been generated from the available X-ray structures of rhodopsin (RHO model), opsin (OPS model) and beta-2 adrenergic receptor (B2 model). The latter was used as a starting point for combined molecular dynamics simulation (MDS) and full atom normal modes analysis (NMA). A low-frequency normal mode (mode 16) perfectly reproduced the intracellular motions observed between B2 and RHO models; in the opposite direction along the same mode, the generated structures are closer to the OPS model, suggesting a direct link with GHS-R1a activation. This was in agreement with motions of the seven transmembranous segments, increase of the solvent accessibility of the 140-ERY-142 sequence, and flip of the Trp276 (C WLP) residue, some features related to GPCRs activation. According to our model, His280 was proposed to stabilize Trp276 in the active state; this was verified by site-directed mutagenesis and biochemical characterization of the resulting H280A and H280S mutants, which were fully functional but sharing an important decrease of their basal activities. Docking performed with short ghrelin derivatives Gly-Ser-Ser _[octa]-Phe-NH ₂ and Gly-Ser-Ser _[octa]-Phe-Leu-NH ₂ allowed the identification of a robust position of these peptides in the active site of the receptor. This model was refined by MDS and validated by docking experiments performed on a set of 55 ghrelin receptor ligands based on the 1,2,4- triazole scaffold. Finally, NMA performed on the obtained peptide-receptor complex suggested stabilization of the Trp276 residue and of the whole receptor in the active state, preventing the motion observed along mode 16 computed for the unbound receptor. Our results show that NMA offers a powerful approach to study the conformational diversity and the activation mechanism of GPCRs.     

Structural and phylogenetic comparison of napsin genes: The duplication,loss of function and human-specific pseudogenization of napsin B

Aspartic proteinases form a widely distributed protein superfamily, including cathepsin D, cathepsin E, pepsins, renin, BACE and napsin. Human napsin genes are located on human chromosome 19q13, which comprises napsin A and napsin B. Napsin B has been annotated as a pseudogene because it lacks an in-frame stop codon; its nascent chains are cotranslationally degraded. Until recently, there have been no studies concerning the molecular evolution of the napsin protein family in the human genome. In the present study, we investigated the evolution and gene organization of the napsin protein family. Napsin B orthologs are primarily distributed in primates, while napsin A orthologs are the only napsin genes in other species. The corresponding regions of napsin B in the available sequences from primate species contain an in-frame stop codon at a position equivalent to that of human napsin A. In addition, a rare single-nucleotide polymorphism (SNP) that creates a proper stop codon in human napsin B was identified using HapMap populations. Recombinant protein expression and three-dimensional comparative modeling revealed that napsin B exhibits residual activity toward synthetic aspartic protease substrates compared with napsin A, presumably through a napsin B-specific Arg287 residue. Thus, napsin B was duplicated from napsin A during the early stages of primate evolution, and the subsequent loss of napsin B function during primate evolution reflected ongoing human-specific napsin B pseudogenization.     

Biotechnological advances on Penicillin G acylase: Pharmaceutical implications,unique expression mechanism and production strategies

In light of unrestricted use of first-generation penicillins, these antibiotics are now superseded by their semisynthetic counterparts for augmented antibiosis. Traditional penicillin chemistry involves the use of hazardous chemicals and harsh reaction conditions for the production of semisynthetic derivatives and, therefore, is being displaced by the biosynthetic platform using enzymatic transformations. Penicillin G acylase (PGA) is one of the most relevant and widely used biocatalysts for the industrial production of β-lactam semisynthetic antibiotics. Accordingly, considerable genetic and biochemical engineering strategies have been devoted towards PGA applications. This article provides a state-of-the-art review in recent biotechnological advances associated with PGA, particularly in the production technologies with an emphasis on using the Escherichia coli expression platform.