bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adaptation to environmental stress: a rare or frequent driver of speciation?
Authors: LEXER C. , FAY M. F. 
Published: March 2006

AbstractRecent results of evolutionary genomics and other research programmes indicate an important role for environment‐dependent selection in speciation, but the conceptual frameworks of speciation genetics and environmental stress physiology have not been fully integrated. Only a small number of model systems have been established for cross‐disciplinary studies of this type in animals and plants. In these taxa (e.g.DrosophilaandArabidopsis/Arabis), studies of the mechanistic basis of various stress responses are increasingly combined with attempts to understand their evolutionary consequences. Our understanding of the role of environmental stress in speciation would benefit from studies of a larger variety of taxa. We pinpoint areas for future study and predict that in many taxa ‘broad’ hybrid zones maintained by ecological selection will be valuable venues for addressing the link between environmental stress, adaptation, and speciation.
Can cytoplasmic incompatibility inducingWolbachiapromote the evolution of mate preferences?
Authors: CHAMPION DE CRESPIGNY F. E. , BUTLIN R. K. , WEDELL N. 
Published: March 2006

AbstractThe maternally inherited bacterium,Wolbachia pipientis, manipulates host reproduction by rendering uninfected females reproductively incompatible with infected males (cytoplasmic incompatibility, CI). Hosts may evolve mechanisms, such as mate preferences, to avoid fitness costs ofWolbachiainfection. Despite the potential importance of mate choice forWolbachiapopulation dynamics, this possibility remains largely unexplored. Here we model the spread of an allele encoding female mate preference for uninfected males alongside the spread of CI inducingWolbachia. Mate preferences can evolve but the spread of the preference allele depends on factors associated with bothWolbachiainfection and the preference allele itself. Incomplete maternal transmission ofWolbachia, fitness costs and low CI, improve the spread of the preference allele and impact on the population dynamics ofWolbachia. In addition, mate preferences are found in infected individuals. These results have important consequences for the fate ofWolbachiaand studies addressing mate preferences in infected populations.
Cell‐mediated immunity predicts the probability of local recruitment in nestling blue tits
Authors: CICHOŃ M. , DUBIEC A. 
Published: March 2006

AbstractWe investigated whether the variation in T‐cell‐mediated immune function of blue tit nestlings affected their fledgling success and the probability of local survival. We studied the relationship between immune function and survival under two rearing conditions: control, unmanipulated, and experimentally enlarged broods. Brood enlargement had negative effects on nestling immune response. Immune response was positively related to fledgling success and it predicted the probability of local recruitment. However, the relationship between immune response and the probability of recruitment was significantly positive only among control broods and nonsignificant among enlarged broods. The effect of immune response on the recruitment probability was not affected by variation in body mass. Our study suggests that selection for immune responsiveness seems to be weak or even absent under unfavourable rearing conditions as simulated by brood size enlargement. Therefore, year‐to‐year environmental variation and environmental heterogeneity may constrain evolution towards higher immune responsiveness.
One tool, many uses: precopulatory sexual selection on genital morphology inAquarius remigis
Authors: BERTIN A. , FAIRBAIRN D. J. 
Published: March 2006

AbstractWhile congruent evidence indicates that sexual selection is the most likely selective force explaining the rapid divergence of male genital morphology in insects, the mechanisms involved in this process remain unclear. In particular, little attention has been paid to precopulatory sexual selection. We examine sexual selection for mating success on male genital components in six populations ofAquarius remigis, a water strider characterized by unique genital morphology. Multivariate selection analysis confirms previous findings that precopulatory sexual selection favours longer external genitalia, and provides new evidence that this selection acts independently on external genital components. In contrast, the size of the major internal genital sclerite is not correlated with mating success. Thus, precopulatory sexual selection acts strongly on the size of the external genitalia, but not on the intromittent organ itself. These results highlight the multiple functions of genital organs and the importance of both precopulatory and post‐copulatory sexual selection in shaping the remarkable diversity of male genitalia in insects.
Sex, mutation and fitness: asymmetric costs and routes to recovery through compensatory evolution
Authors: PISCHEDDA A. , CHIPPINDALE A. 
Published: March 2006

AbstractA wild‐type population of Drosophila melanogaster was used to assess the impact of a known deleterious mutation, nub1, when it had (1) evolved for up to 180 generations with the mutation or (2) recently had the same mutant allele introgressed into it. Relative to this benchmark, we observed much stronger initial fitness depression in males (−74%) than in females (−38%) and also relatively greater fitness recovery by evolved males (+55%) than females (+17%). Experimental assays revealed amelioration in both juvenile and adult fitness and suggested that the greater relative recovery of male fitness was from gains through sexual selection. These evolutionary changes in male fertility depended on pairing with their coevolved mates for both mate choice and post‐copulatory components of sexual selection. Without replication at the population level, these results are used to motivate a general hypothesis rather than definitively test it: Differences in reproductive optima may generally skew mutational effects towards the more strongly sexually‐selected sex due to genic capture and condition dependence.
Phenotypic plasticity of host–parasite interactions in response to the route of infection
Authors: VIZOSO D. B. , EBERT D. 
Published: March 2006

AbstractThe microsporidium Octosporea bayeri can infect its host, the planktonic crustacean Daphnia magna, vertically and horizontally. The two routes differ greatly in the way the parasite leaves the harbouring host (transmission) and in the way it enters a new, susceptible host (infection). Infections resulting from each route may thus vary in the way they affect host and parasite life‐histories and, subsequently, host and parasite fitness. We conducted a life‐table experiment to compare D. magna infected with O. bayeri either horizontally or vertically, using three different parasite isolates. Both the infection route and the parasite isolate had significant effects on host life‐history. Hosts matured at different ages depending on the parasite isolate, and at a size that varied with infection route. The frequency of host sterility and the host's life‐time reproductive success were affected by both the infection route and the parasite isolate. The infection route also affected parasite life‐history. The production of parasite spores was much higher in vertically than in horizontally infected hosts. We found a trade‐off between the production of spores (the parasite's horizontal fitness component) and the production of infected host offspring (the parasite's vertical fitness component). This study shows that hosts and parasites can react plastically to different routes of infection, suggesting that ecological factors that may influence the relative importance of horizontal and vertical transmission can shape the evolution of host and parasite life histories, and, consequently, the evolution of virulence.
The biological limitations of transcriptomics in elucidating stress and stress responses
Authors: FEDER M. E. , WALSER J.‐C. 
Published: March 2006

AbstractGlobal analysis of mRNA abundance via genomic arrays (i.e. transcriptomics or transcriptional profiling) is one approach to finding the genes that matter to organisms undergoing environmental stress. In evolutionary analyses of stress, mRNA abundance is often invoked as a proxy for the protein activity that may underlie variation in fitness. To provoke discussion of the utility and sensible application of this valuable approach, this manuscript examines the adequacy of mRNA abundance as a proxy for protein activity, fitness and stress. Published work to date suggests that mRNA abundance typically provides little information on protein activity and fitness and cannot substitute for detailed functional and ecological analyses of candidate genes. While the transcriptional profile can be an exquisitely sensitive indicator of stress, simpler indicators will often suffice. In view of this outcome, transcriptomics should undergo careful cost‐benefit analysis before investigators deploy it in studies of stress responses and their evolution.
Correlated responses to selection for stress resistance and longevity in a laboratory population of Drosophila melanogaster
Authors: BUBLIY O. A. , LOESCHCKE V. 
Published: March 2006

AbstractLaboratory studies on Drosophila have revealed that resistance to one environmental stress often correlates with resistance to other stresses. There is also evidence on genetic correlations between stress resistance, longevity and other fitness‐related traits. The present work investigates these associations using artificial selection in Drosophila melanogaster. Adult flies were selected for increased survival after severe cold, heat, desiccation and starvation stresses as well as increased heat‐knockdown time and lifespan (CS, HS, DS, SS, KS and LS line sets, respectively). The number of selection generations was 11 for LS, 27 for SS and 21 for other lines, with selection intensity being around 0.80. For each set of lines, the five stress‐resistance parameters mentioned above as well as longevity (in a nonstressful environment) were estimated. In addition, preadult developmental time, early age productivity and thorax length were examined in all lines reared under nonstressful conditions. Comparing the selection lines with unselected control revealed clear‐cut direct selection responses for the stress‐resistance traits. Starvation resistance increased as correlated response in all sets of selection lines, with the exception of HS. Positive correlated responses were also found for survival after cold shock (HS and DS) and heat shock (KS and DS). With regard to values of resistance across different stress assays, the HS and KS lines were most similar. The resistance values of the SS lines were close to those of the LS lines and tended to be the lowest among all selection lines. Developmental time was extended in the SS and KS lines, whereas the LS lines showed a reduction in thorax length. The results indicate a possibility of different multiple‐stress‐resistance mechanisms for the examined traits and fitness costs associated with stress resistance and longevity.
Habitat dependent associations between parasitism and fluctuating asymmetry among endemic stickleback populations
Authors: BERGSTROM C. A. , REIMCHEN T. E. 
Published: March 2006

AbstractInconsistencies in the relationship between fluctuating asymmetry (FA) and fitness may be due to selection acting on the degree of trait asymmetry that differs among populations or among traits. We assessed relationships between parasite susceptibility and fluctuating asymmetry in the number of bony lateral plates among 83 populations of freshwaterGasterosteus aculeatus(three spined stickleback) and among lateral plate positions that vary in the selection they experience for symmetry. The correlation between FA and parasite infection was highly variable among samples. Excess of infected asymmetricG. aculeatusincreased significantly as the robustness of structural predator defences decreased. This effect was found for one parasite species only (Eustrongylidessp.) and was slightly stronger in females. In addition, there was a trend for there to be an excess of infected females asymmetric in those lateral plates positions that did not experience selection for their symmetry, although the trend only approached significance. These results suggest that selection for trait symmetry can obscure relationships between fitness and individual‐wide developmental stability, providing one possible explanation for some of the heterogeneity in FA/fitness relationships seen in the literature. These results are also consistent with previous reports showing that ecological segregation between symmetric and asymmetricG. aculeatusand between sexes can alter the FA/fitness relationship.
Spatial scale of local adaptation in a plant‐pathogen metapopulation
Authors: LAINE A.‐L. 
Published: March 2006

AbstractThe rate and scale of gene flow can strongly affect patterns of local adaptation in host–parasite interactions. I used data on regional pathogen occurrence to infer the scale of pathogen dispersal and to identify pathogen metapopulations in the interaction betweenPlantago lanceolataand its specialist phytopathogen,Podosphaera plantaginis. Frequent extinctions and colonizations were recorded in the metapopulations, suggesting substantial gene flow at this spatial scale. The level of pathogen local adaptation was assessed in a laboratory inoculation experiment at three different scales: in sympatric host populations, in sympatric host metapopulations and in allopatric host metapopulations. I found evidence for adaptation to sympatric host populations, as well as evidence indicating that local adaptation may extend to the scale of the sympatric host metapopulation. There was also variation among the metapopulations in the degree of pathogen local adaptation. This may be explained by regional differences in the rate of migration.
Seasonality and the dynamics of infectious diseases
Authors: Altizer Sonia , Dobson Andrew , Hosseini Parviez , Hudson Peter , Pascual Mercedes , Rohani Pejman 
Published: March 2006

AbstractSeasonal variations in temperature, rainfall and resource availability are ubiquitous and can exert strong pressures on population dynamics. Infectious diseases provide some of the best‐studied examples of the role of seasonality in shaping population fluctuations. In this paper, we review examples from human and wildlife disease systems to illustrate the challenges inherent in understanding the mechanisms and impacts of seasonal environmental drivers. Empirical evidence points to several biologically distinct mechanisms by which seasonality can impact host–pathogen interactions, including seasonal changes in host social behaviour and contact rates, variation in encounters with infective stages in the environment, annual pulses of host births and deaths and changes in host immune defences. Mathematical models and field observations show that the strength and mechanisms of seasonality can alter the spread and persistence of infectious diseases, and that population‐level responses can range from simple annual cycles to more complex multiyear fluctuations. From an applied perspective, understanding the timing and causes of seasonality offers important insights into how parasite–host systems operate, how and when parasite control measures should be applied, and how disease risks will respond to anthropogenic climate change and altered patterns of seasonality. Finally, by focusing on well‐studied examples of infectious diseases, we hope to highlight general insights that are relevant to other ecological interactions.
Annual cycles of solar insolation predict spawning times of Caribbean corals
Authors: Van Woesik R. , Lacharmoise F. , Köksal S. 
Published: March 2006

AbstractSeasonal increases in sea surface temperature (SST) have long been considered the trigger for mass spawning events in reef corals. We critically examined the relationship between SST and the spawning activity of broadcasting corals in the tropical western Atlantic (Caribbean). This meta‐analysis examined 12 species of broadcasting corals at 25 sites spanning 22 degrees of latitude (10°–32° N) from Venezuela to Bermuda in the Atlantic Ocean from 1986 to 2004. Sigmoidal logit regression models were used to examine the relationship between the release of reef‐coral gametes and the environmental variables SST and solar insolation defined as (1) the cumulative response 7–10 months prior to spawning (integral); (2) the rate of change at the time of spawning (derivative); and (3) the average for the month of spawning. The Quasi–Newton method was used to estimate the maximum likelihood of the response function. We demonstrate that the recent history and rate of change in temperature correlate poorly with the timing of spawning, while the average temperature during the month of spawning was significant (with all corals releasing gametes 28–30 °C, except Montastraea annularis, which released gametes at 27–30 °C). In contrast, the rate of change and the cumulative response of solar insolation cycles was a better predictor of gamete release, but solar insolation intensity at the time of spawning was not. These models have important implications for predicting coral reproductive cycles in all oceans, and for examining other marine phototrophic systems beyond corals.
Early onset of secondary extinctions in ecological communities following the loss of top predators
Authors: Borrvall Charlotte , Ebenman Bo 
Published: March 2006

AbstractThe large vulnerability of top predators to human‐induced disturbances on ecosystems is a matter of growing concern. Because top predators often exert strong influence on their prey populations their extinction can have far‐reaching consequences for the structure and functioning of ecosystems. It has, for example, been observed that the local loss of a predator can trigger a cascade of secondary extinctions. However, the time lags involved in such secondary extinctions remain unexplored. Here we show that the loss of a top predator leads to a significantly earlier onset of secondary extinctions in model communities than does the loss of a species from other trophic levels. Moreover, in most cases time to secondary extinction increases with increasing species richness. If local secondary extinctions occur early they are less likely to be balanced by immigration of species from local communities nearby. The implications of these results for community persistence and conservation priorities are discussed.
Testing the role of parasites in driving the cyclic population dynamics of a gamebird
Authors: Redpath Stephen M. , Mougeot François , Leckie Fiona M. , Elston David A. , Hudson Peter J. 
Published: March 2006

AbstractThe role of parasites in regulating populations has been the subject of debate. We tested whether parasites caused population cycles in red grouse by manipulating parasite intensities in four, paired 1 km2 study areas during cyclic population declines over 4 years. Parasite reductions led to (1) larger grouse broods, (2) higher population densities in both autumn and spring, (3) reduced autumn population declines in one of two regions, and (4) reduced spring declines, but only in the first year. We infer that a single trophic interaction between a parasite and its host does not explain cyclic dynamics in spring breeding density in this species, although it contributed to the start of a cyclic decline. Another process was operating to drive the populations down. Together with our other results these findings emphasize that both trophic and intrinsic processes may act within populations to cause unstable dynamics.
Biological control agents elevate hantavirus by subsidizing deer mouse populations
Authors: Pearson Dean E. , Callaway Ragan M. 
Published: March 2006

AbstractBiological control of exotic invasive plants using exotic insects is practiced under the assumption that biological control agents are safe if they do not directly attack non‐target species. We tested this assumption by evaluating the potential for two host‐specific biological control agents (Urophora spp.), widely established in North America for spotted knapweed (Centaurea maculosa) control, to indirectly elevate Sin Nombre hantavirus by providing food subsidies to populations of deer mice (Peromyscus maniculatus), the primary reservoir for the virus. We show that seropositive deer mice (mice testing positive for hantavirus) were over three times more abundant in the presence of the biocontrol food subsidy. Elevating densities of seropositive mice may increase risk of hantavirus infection in humans and significantly alter hantavirus ecology. Host specificity alone does not ensure safe biological control. To minimize indirect risks to non‐target species, biological control agents must suppress pest populations enough to reduce their own numbers.
Likelihood Inference for a Class of Latent Markov Models under Linear Hypotheses on the Transition Probabilities
Authors: Bartolucci Francesco 
Published: March 2006

SummaryFor a class of latent Markov models for discrete variables having a longitudinal structure, we introduce an approach for formulating and testing linear hypotheses on the transition probabilities of the latent process. For the maximum likelihood estimation of a latent Markov model under hypotheses of this type, we outline an EM algorithm that is based on well-known recursions in the hidden Markov literature. We also show that, under certain assumptions, the asymptotic null distribution of the likelihood ratio statistic for testing a linear hypothesis on the transition probabilities of a latent Markov model, against a less stringent linear hypothesis on the transition probabilities of the same model, is of χ¯2 type. As a particular case, we derive the asymptotic distribution of the likelihood ratio statistic between a latent class model and its latent Markov version, which may be used to test the hypothesis of absence of transition between latent states. The approach is illustrated through a series of simulations and two applications, the first of which is based on educational testing data that have been collected within the National Assessment of Educational Progress 1996, and the second on data, concerning the use of marijuana, which have been collected within the National Youth Survey 1976–1980.
Mean-Squared Error Estimation in Transformed Fay–Herriot Models
Authors: Slud Eric V. , Maiti Tapabrata 
Published: March 2006

SummaryThe problem of accurately estimating the mean-squared error of small area estimators within a Fay–Herriot normal error model is studied theoretically in the common setting where the model is fitted to a logarithmically transformed response variable. For bias-corrected empirical best linear unbiased predictor small area point estimators, mean-squared error formulae and estimators are provided, with biases of smaller order than the reciprocal of the number of small areas. The performance of these mean-squared error estimators is illustrated by a simulation study and a real data example relating to the county level estimation of child poverty rates in the US Census Bureau's on-going ‘Small area income and poverty estimation’ project.