Plasticity is a locally adapted trait with consequences for ecological dynamics in novel environments

Phenotypic plasticity is predicted to evolve in more variable environments, conferring an advantage on individual lifetime fitness. It is less clear what the potential consequences of that plasticity will have on ecological population dynamics. Here, we use an invertebrate model system to examine the effects of environmental variation (resource availability) on the evolution of phenotypic plasticity in two life history traits—age and size at maturation—in long‐running, experimental density‐dependent environments. Specifically, we then explore the feedback from evolution of life history plasticity to subsequent ecological dynamics in novel conditions. Plasticity in both traits initially declined in all microcosm environments, but then evolved increased plasticity for age‐at‐maturation, significantly so in more environmentally variable environments. We also demonstrate how plasticity affects ecological dynamics by creating founder populations of different plastic phenotypes into new microcosms that had either familiar or novel environments. Populations originating from periodically variable environments that had evolved greatest plasticity had lowest variability in population size when introduced to novel environments than those from constant or random environments. This suggests that while plasticity may be costly it can confer benefits by reducing the likelihood that offspring will experience low survival through competitive bottlenecks in variable environments. In this study, we demonstrate how plasticity evolves in response to environmental variation and can alter population dynamics—demonstrating an eco‐evolutionary feedback loop in a complex animal moderated by plasticity in growth.     

Estimating the heritability of female lifetime fecundity in a locally adapted Drosophila melanogaster population

The heritability of genome‐wide fitness that is expected in finite populations is poorly understood, both theoretically and empirically, despite its relevance to many fundamental concepts in evolutionary biology. In this study, we used two independent methods of estimating the heritability of lifetime female fecundity (the predominant female fitness component in this population) in a large, outbred population of Drosophila melanogaster that had adapted to the laboratory environment for over 400 generations. Despite strong directional selection on adult female fecundity, we uncovered high heritability for this trait that cannot be explained by antagonistic pleiotropy with juvenile fitness. The evolutionary significance of this high heritability of lifetime fecundity is discussed.     

Parasite-host fitness trade-offs change with parasite identity: genotype-specific interactions in a plant-pathogen system

Simultaneous effects of host and parasite in determining quantitative traits of infection have long been neglected in theoretical and experimental investigations of host-parasite coevolution with the notable exception of gene-for-gene resistance studies. A cross-infection experiment, using five lines of the plant Arabidopsis thaliana and two strains of its oomycete pathogen Hyaloperonospora parasitica, revealed that three traits traditionally considered those of the parasite (number of infected leaves, transmission success, and time until 50% transmission), differed among specific combinations of host and parasite lines, being determined by the two protagonists of the infection. However, the two parasite strains did not differ significantly for most measured phenotypic traits of the infection. Globally, transmission increased with increasing virulence among the different host-parasite combinations, as assumed by most models of evolution of virulence. Surprisingly, however, there was no general relationship between parasite and host fitness, estimated respectively as transmission and seed production. Only one of the two strains showed the expected significant negative genetic correlation between these two variables. Our results thus highlight the importance of taking into account both host and parasite genetic variation because their interaction can lead to unexpected evolutionary outcomes.     

Limited evolutionary rescue of locally adapted populations facing climate change

Dispersal is a key determinant of a population''s evolutionary potential. It facilitates the propagation of beneficial alleles throughout the distributional range of spatially outspread populations and increases the speed of adaptation. However, when habitat is heterogeneous and individuals are locally adapted, dispersal may, at the same time, reduce fitness through increasing maladaptation. Here, we use a spatially explicit, allelic simulation model to quantify how these equivocal effects of dispersal affect a population''s evolutionary response to changing climate. Individuals carry a diploid set of chromosomes, with alleles coding for adaptation to non-climatic environmental conditions and climatic conditions, respectively. Our model results demonstrate that the interplay between gene flow and habitat heterogeneity may decrease effective dispersal and population size to such an extent that substantially reduces the likelihood of evolutionary rescue. Importantly, even when evolutionary rescue saves a population from extinction, its spatial range following climate change may be strongly narrowed, that is, the rescue is only partial. These findings emphasize that neglecting the impact of non-climatic, local adaptation might lead to a considerable overestimation of a population''s evolvability under rapid environmental change.     

Colonization of new host plant individuals by locally adapted thrips

This study considered the dispersal and subsequent reproduction of Apterothrips aptens a wingless, folivorous thrips species that is divided into local populations, each adapted to its individual host plant We placed host plants with no thrips into the field and observed the rate at which thrips colonized these plants Colonization events were rare, on average each pot received 1 47 immigrants during the year Immature thrips were found associated with 64 59c of these events, indicating that reproduction had occurred Colonization was most likely to occur during the summer Most colonists walked onto the new host and airborne movements were very rare Plants that were located far from near neighbors were less likely to be colonized although the size of nearby source populations did not influence the rate of colonization
These results suggest that limited movement is associated with division of this population into isolated demes Limited movement appeared to be more important as a barner to successful colonization than was demographic success following arrival at a new host plant     

Modeling a version of the good-genes hypothesis: female choice of locally adapted males

In addition to other potential causes, immigration into locally adapted populations has been suggested to maintain the genetic variance in fitness that is necessary for the good-genes hypothesis. Using population-genetic simulations, the present contribution shows that co-occurring local adaptation and migration can maintain genetic variance in fitness. In combination with an effect of local adaptation on condition and condition-dependent sexual signaling, such a scenario therefore enables the evolution and maintenance of female choice for locally adapted males. The simulations show that this mechanism can also work when choice is costly, and that the potential benefit is similar to that in other good-genes mechanisms. As a consequence of female choice in favor of locally adapted males, differentiation between populations can be expected to increase due to the decreased effective gene flow between populations. Based on such effects, choice of locally adapted males has the potential to play an important role in speciation and adaptive radiation.     

Resistance of a rodent malaria parasite to a thymidylate synthase inhibitor induces an apoptotic parasite death and imposes a huge cost of fitness

Background

The greatest impediment to effective malaria control is drug resistance in Plasmodium falciparum, and thus understanding how resistance impacts on the parasite''s fitness and pathogenicity may aid in malaria control strategy.

Methodology/Principal Findings

To generate resistance, P. berghei NK65 was subjected to 5-fluoroorotate (FOA, an inhibitor of thymidylate synthase, TS) pressure in mice. After 15 generations of drug pressure, the 2% DT (the delay time for proliferation of parasites to 2% parasitaemia, relative to untreated wild-type controls) reduced from 8 days to 4, equalling the controls. Drug sensitivity studies confirmed that FOA-resistance was stable. During serial passaging in the absence of drug, resistant parasite maintained low growth rates (parasitaemia, 15.5%±2.9, 7 dpi) relative to the wild-type (45.6%±8.4), translating into resistance cost of fitness of 66.0%. The resistant parasite showed an apoptosis-like death, as confirmed by light and transmission electron microscopy and corroborated by oligonucleosomal DNA fragmentation.

Conclusions/Significance

The resistant parasite was less fit than the wild-type, which implies that in the absence of drug pressure in the field, the wild-type alleles may expand and allow drugs withdrawn due to resistance to be reintroduced. FOA resistance led to depleted dTTP pools, causing thymineless parasite death via apoptosis. This supports the tenet that unicellular eukaryotes, like metazoans, also undergo apoptosis. This is the first report where resistance to a chemical stimulus and not the stimulus itself is shown to induce apoptosis in a unicellular parasite. This finding is relevant in cancer therapy, since thymineless cell death induced by resistance to TS-inhibitors can further be optimized via inhibition of pyrimidine salvage enzymes, thus providing a synergistic impact. We conclude that since apoptosis is a process that can be pharmacologically modulated, the parasite''s apoptotic machinery may be exploited as a novel drug target in malaria and other protozoan diseases of medical importance.     

Validation of a microsatellite panel for parentage testing of locally adapted and commercial goats in Brazil

Brazilian goats are generally kept in small herds and extensive rearing systems, mainly in the northeastern region of the country. Despite production improvement in recent years, the lack of pedigree control has affected genetic progress. This study aimed to validate a panel of 16 microsatellites for parentage testing in locally adapted and commercial goats breeds raised in Brazil, as well as to compare its efficiency with the panel recommended by the Brazilian Ministry of Agriculture, Livestock and Supplies (MAPA) in 2004. The number of alleles and expected heterozygosity (He) per marker ranged from four to 18, and from 0.051 to 0.831, respectively. Using all markers, 100% of parentage cases of the validation dataset were resolved with a strict confidence level of 95%. The 16 microsatellites panel showed adequate exclusion power (99.99%) and identity accuracy (99.99%). Suggestions for improvement of the marker panel endorsed by MAPA are provided.     

Unexpected benefit of a social parasite for a key fitness component of its ant host

Numerous invertebrates inhabit social insect colonies, including the hoverfly genus Microdon, whose larvae typically live as brood predators. Formica lemani ant colonies apparently endure Microdon mutabilis infections over several years, despite losing a considerable fraction of young, and may even produce more gynes. We present a model for resource allocation within polygynous ant colonies, which assumes that whether an ant larva switches development into a worker or a gyne depends on the quantity of food received randomly from workers. Accordingly, Microdon predation promotes gyne development by increasing resource availability for surviving broods. Several model predictions are supported by empirical data. (i) Uninfected colonies seldom produce gynes. (ii) Infected colonies experience a short-lived peak in gyne production leading to a bimodal distribution in gyne production. (iii) Low brood : worker ratio is the critical mechanism controlling gyne production. (iv) Brood : worker ratio reduction must be substantial for increased gyne production to become noticeable.     

Genotype-specific interactions and the trade-off between host and parasite fitness

Background  

Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete Hyaloperonospora arabidopsis (= parasitica), a natural pathogen of the Brassicaceae Arabidopsis thaliana.     

Inference of parasite local adaptation using two different fitness components

Estimating parasite fitness is central to studies aiming to understand parasite evolution. Theoretical models generally use the basic reproductive rate R(0) to express fitness, yet it is very difficult to quantify R(0) empirically and experimental studies often use fitness components such as infection intensity or infectivity as substitutes. These surrogate measures may be biased in several ways. We assessed local adaptation of the microsporidium Ordospora colligata to its host, the crustacean Daphnia magna using two different parasite fitness components: infection persistence over several host generations in experimental populations and infection intensity in individual hosts. We argue that infection persistence is a close estimator of R(0), whereas infection intensity measures only a component of it. Both measures show a pattern that is consistent with parasite local adaptation and they correlate positively. However, several inconsistencies between them suggest that infection intensity may at times provide an inadequate estimate of parasite fitness.     

Nosema bombi: A pollinator parasite with detrimental fitness effects

Nosema bombi is an obligate intracellular parasite that infects different bumblebee species at a substantial, though variable, rate. To date its pathology and impact on host fitness are not well understood. We performed a laboratory experiment investigating the pathology and fitness effects of this parasite on the bumblebee Bombus terrestris. We experimentally infected one group of colonies with N. bombi spores at the start of the worker production, while a second uninfected group of colonies served as controls. During colony development we collected live workers for dissections to measure infection intensities. In parallel, we measured several life history traits, to investigate costs to the host. We succeeded in infecting 11 of 16 experimental colonies. When infection occurred at an early stage of colony development, virtually all individuals were infected, with spores being found in a number of tissues, and the functional fitness of males and young queens was reduced to zero. Further, the survival of workers from infected colonies and infected males were reduced. With such severe effects, N. bombi appears to decrease its opportunities for transmission to the next host generation.     

Effects of natural enemies on relative fitness of Heliothis virescens genotypes adapted and not adapted to resistant host plants

We investigated the potential of two natural enemies of Heliothis virescens (F.) (Noctuidae) to affect its rate of adaptation to tobacco containing Bacillus thuringiensis Berliner toxin. Larval fitness of two laboratory strains of H. virescens, one adapted to B. thuringiensis toxin and one not adapted, was compared on toxic and nontoxic plants, in the presence of the parasitoid Campoletis sonorensis (Cameron) (Ichneumonidae) or the entomopathogenic fungus Nomuraea rileyi (Farlow) Samson. By exposing larvae to plants and enemies for no more than 24 h, we focussed on the behavioral rather than physiological component of their interaction with toxic plants and natural enemies. Parasitism of H. virescens larvae by C. sonorensis during exposure periods of 1–4 h was lower on toxic plants than nontoxic plants and was lower for nonadapted larvae than for toxin-adapted larvae. Decreased larval feeding damage on toxic versus nontoxic plants, and by nonadapted versus adapted larvae, may explain differences in parasitism, because C. sonorensis locates host larvae using cues from damaged plants. Effects of plant toxicity and larval strain on H. virescens survival were numerically consistent with effects on parasitism, but they were not statistically significant. When mean larval survival is used to estimate fitness of the nonadapted genotype relative to the toxin-adapted genotype, we find that C. sonorensis is expected to delay adaptation to toxic plants. Percent infection by N. rileyi of H. virescens larvae exposed to fungus-treated plants for 24 h was greater when plants were toxic, and was greater for nonadapted larvae than toxin-adapted larvae. There were corresponding decreases in larval survival on toxic compared to nontoxic plants, and of nonadapted compared to adapted larvae. Interaction of effects of plant line and larval strain on survival was significant in the presence of fungus, but not in the absence of fungus, which indicates that the effect of toxic plants on the relative fitness of toxin-adapted and nonadapted larvae was mediated by fungus. As in the interaction with C. sonorensis, behavior of larvae on plants may explain differences in susceptibility to N. rileyi. Because nonadapted larvae moved more than toxin-adapted larvae on toxic plants, nonadapted larvae may have been more likely to encounter a lethal dose of conidia. In contrast with C. sonorensis, N. rileyi, which decreased the fitness of the nonadapted genotype relative to the adapted genotype, is expected to accelerate adaptation to toxic plants.     

When a virus is not a parasite: the beneficial effects of prophages on bacterial fitness

Most organisms on the planet have viruses that infect them. Viral infection may lead to cell death, or to a symbiotic relationship where the genomes of both virus and host replicate together. In the symbiotic state, both virus and cell potentially experience increased fitness as a result of the other. The viruses that infect bacteria, called bacteriophages (or phages), well exemplify the symbiotic relationships that can develop between viruses and their host. In this review, we will discuss the many ways that prophages, which are phage genomes integrated into the genomes of their hosts, influence bacterial behavior and virulence.     

Ecological strategies and fitness tradeoffs inEscherichia coli mutants adapted to prolonged starvation

Many bacteria in nature are nutritionally deprived, and there has been heightened interest during the past decade in the properties of these bacteria. We subjected five populations ofEscherichia coli to prolonged starvation in a minimal salts medium, during which time the density of viable cells declined by several orders of magnitude. From each one, we isolated a surviving clone that showed some heritable difference in colony morphology. We then characterized these mutants in two ecologically relevant respects. First, we determined the nature of their selective advantage, if any, during prolonged starvation. (i) Three of the five mutants had significantly lower net death rate when progenitor and mutant clones were starved separately. (ii) Three mutants showed a significant reduction in death rate in mixed culture that was frequency dependent and manifest when the mutant clone was initially rare. This pattern suggests that these mutants fed on some byproduct of progenitor cells (living or dead). (iii) Two mutants caused the death rate of their progenitors to increase significantly relative to the rate measured in the absence of the mutant. This pattern suggests that these mutants had become allelopathic to their progenitors. Thus, three distinct ecological adaptations to prolonged starvation are evident. No advantage was detected for one mutant, whereas two mutants exhibited multiple advantages. Second, we asked whether the starvation-selected mutants were as fit in growth-supporting conditions as their progenitors. All five mutants were inferior to their progenitor during competition in fresh medium. Evidently, there is an evolutionary tradeoff between performance under growth and starvation conditions.     

Seasonal influence on semen traits and freezability from locally adapted Curraleiro bulls

Studies were conducted to characterize the effect of season of the year on testicular morphology, fresh and frozen/thawed semen quality from Curraleiro (Pé-duro) bulls in the Brazilian Central west region. Five adult, healthy bulls underwent an andrological examination and semen collection using an electroejaculator, once a month for a year. Fresh and thawed semen were evaluated for progressive sperm motility and sperm vigor, sperm morphology and acrosomal integrity. Testicular length and volume were less (P<0.05) in April than in the other months of the year. For fresh semen, the ejaculate in April had less volume and sperm concentration (P<0.05), while sperm vigor was less (P<0.05) in June, increasing in January and February. With the frozen/thawed semen, the proportion of sperm was greater (P<0.05) in April to July, decreasing from October to December. Semen collected in December had the greatest (P<0.05) proportion of major defects while that collected in February/March had the highest proportion of minor defects. The proportion of live intact sperm reduced progressively from December to April/May. The marginal influence of the time of the year on testicular biometry and fresh semen in Curraleiro bulls shows the adaptation of this breed to the environmental conditions in the region. Thus, reproduction with natural mating should be successful at any time of year. For frozen semen collection for conservation programs, the best time of year is from June to September.     

Landscape genomic approach to detect selection signatures in locally adapted Brazilian swine genetic groups

Samples of 191 animals from 18 different Brazilian locally adapted swine genetic groups were genotyped using Illumina Porcine SNP60 BeadChip in order to identify selection signatures related to the monthly variation of Brazilian environmental variables. Using BayeScan software, 71 SNP markers were identified as F_ST outliers and 60 genotypes (58 markers) were found by Samβada software in 371 logistic models correlated with 112 environmental variables. Five markers were identified in both methods, with a Kappa value of 0.073 (95% CI: 0.011–0.134). The frequency of these markers indicated a clear north–south country division that reflects Brazilian environmental differences in temperature, solar radiation, and precipitation. Global spatial territory correlation for environmental variables corroborates this finding (average Moran's I = 0.89, range from 0.55 to 0.97). The distribution of alleles over the territory was not strongly correlated with the breed/genetic groups. These results are congruent with previous mtDNA studies and should be used to direct germplasm collection for the National gene bank.