155 research outputs found
Adaptation to enemy shifts: rapid resistance evolution to local Vibrio spp. in invasive Pacific oysters
One hypothesis for the success of invasive species is reduced pathogen burden, resulting from a release from infections or high immunological fitness of invaders. Despite strong selection exerted on the host, the evolutionary response of invaders to newly acquired pathogens has rarely been considered. The two independent and genetically distinct invasions of the Pacific oyster Crassostrea gigas into the North Sea represent an ideal model system to study fast evolutionary responses of invasive populations. By exposing both invasion sources to ubiquitous and phylogenetically diverse pathogens (Vibrio spp.), we demonstrate that within a few generations hosts adapted to newly encountered pathogen communities. However, local adaptation only became apparent in selective environments, i.e. at elevated temperatures reflecting patterns of disease outbreaks in natural populations. Resistance against sympatric and allopatric Vibrio spp. strains was dominantly inherited in crosses between both invasion sources, resulting in an overall higher resistance of admixed individuals than pure lines. Therefore, we suggest that a simple genetic resistance mechanism of the host is matched to a common virulence mechanism shared by local Vibrio strains. This combination might have facilitated a fast evolutionary response that can explain another dimension of why invasive species can be so successful in newly invaded ranges
Marine turf of an invasive alga expels lugworms from the lower shore
Bare sandy flats at and below low tide level of the Wadden Sea (eastern North Sea, European Atlantic) were observed in 2020 to have been invaded by an introduced grass-like alga, Vaucheria cf. velutina (Xanthophyceae). A dense algal turf accumulated and stabilized mud, where resident seniors of the lugworm Arenicola marina had reworked rippled sand. Algae and worms were incompatible. Initially, rising patches with algal turf alternated with bare pits where lugworms crowded. Their bioturbation inhibited young algae, while the felt of established algal rhizoids clogged feeding funnels of worm bur- rows. Eventually, a mosaic pattern of competitors gave way to a coherent algal turf without lugworms. Concomitantly, a rich small-sized benthic fauna took advantage of the novel algal turf. This exotic Vaucheria may have the potential for drastically altering the ecological web at the lower shore
Genomic and Transcriptomic Differentiation of Independent Invasions of the Pacific Oyster Crassostrea gigas
Upon colonizing new habitats, invasive species face a series of new selection
pressures as a result of changing abiotic conditions and novel biotic interactions with
native species. These new selection pressures can be accommodated by different
mechanisms that act on different levels and across different time scales: (1) By changing
transcriptomic profiles, species can react by plasticity within individual physiological
limitations. (2) Invasive populations can adapt by fixing beneficial genetic variants in
response to the newly encountered selection pressures. Here, we compare the genomic
and transcriptomic landscapes of two independent invasions of the Pacific Oyster
(Crassostrea gigas) into the North Sea. In detail, we combine ddRAD sequencing
on the genomic level with RNAseq on the transcriptomic level to reveal outlier loci
(SNPs) indicative of adaptation, as well as transcriptomic profiles from a translocation
experiment to show immediate physiological reactions between two populations
characterizing the two independent invasions. Generally, we found low physical
congruence between differentially regulated genes and outlier loci, indicating that
different genes are involved on the different time scales. Functionally matching outlier loci
and differentially expressed genes were however found for spliceosomal modification of
mRNA and particularly for transposon activation, indicating that these variation creating
processes might be connected across eco-physiological and evolutionary time scales.
By contrasting and identifying functional congruence between population outlier loci and
population specific transcriptomic profiles, we can thus reveal a glimpse at the traits and
processes characterizing specific mechanisms involved in successful invasions
Complex adaptive responses during antagonistic coevolution between Tribolium castaneum and its natural parasite Nosema whitei revealed by multiple fitness components
Background: Host-parasite coevolution can lead to local adaptation of either parasite or host if there is specificity (GxG interactions) and asymmetric evolutionary potential between host and parasite. This has been demonstrated both experimentally and in field studies, but a substantial proportion of studies fail to detect such clear-cut patterns. One explanation for this is that adaptation can be masked by counter-adaptation by the antagonist. Additionally, genetic architecture underlying the interaction is often highly complex thus preventing specific adaptive responses. Here, we have employed a reciprocal cross-infection experiment to unravel the adaptive responses of two components of fitness affecting both parties with different complexities of the underlying genetic architecture (i.e. mortality and spore load). Furthermore, our experimental coevolution of hosts (Tribolium castaneum) and parasites (Nosema whitei) included paired replicates of naive hosts from identical genetic backgrounds to allow separation between host-and parasite-specific responses.
Results: In hosts, coevolution led to higher resistance and altered resistance profiles compared to paired control lines. Host genotype x parasite genotype interactions (G(H) x G(P)) were observed for spore load (the trait of lower genetic complexity), but not for mortality. Overall parasite performance correlated with resistance of its matching host coevolution background reflecting a directional and unspecific response to strength of selection during coevolution. Despite high selective pressures exerted by the obligatory killing parasite, and host-and parasite-specific mortality profiles, no general pattern of local adaptation was observed, but one case of parasite maladaptation was consistently observed on both coevolved and control host populations. In addition, the use of replicate control host populations in the assay revealed one case of host maladaptation and one case of parasite adaptation that was masked by host counter-adaptation, suggesting the presence of complex and probably dynamically changing fitness landscapes.
Conclusions: Our results demonstrate that the use of replicate naive populations can be a useful tool to differentiate between host and parasite adaptation in complex and dynamic fitness landscapes. The absence of clear local adaptation patterns during coevolution with a sexual host showing a complex genetic architecture for resistance suggests that directional selection for generality may be more important attributes of host-parasite coevolution than commonly assumed
Persistence, seasonal dynamics and pathogenic potential of Vibrio communities from pacific oyster hemolymph
Bacteria of the genus Vibrio occur at a continuum from free-living to symbiotic life forms, including opportunists and pathogens, that can contribute to severe diseases, for instance summer mortality events of Pacific oysters Crassostrea gigas. While most studies focused on Vibrio isolated from moribund oysters during mortality outbreaks, investigations of the Vibrio community in healthy oysters are rare. Therefore, we characterized the persistence, diversity, seasonal dynamics, and pathogenicity of the Vibrio community isolated from healthy Pacific oysters. In a reciprocal transplant experiment we repeatedly sampled hemolymph from adult Pacific oysters to differentiate population from site-specific effects during six months of in situ incubation in the field. We characterized virulence phenotypes and genomic diversity based on multilocus sequence typing in a total of 70 Vibrio strains. Based on controlled infection experiments we could show that strains with the ability to colonize healthy adult oysters can also have the potential to induce high mortality rates on larvae. Diversity and abundance of Vibrio varied significantly over time with highest values during and after spawning season. Vibrio communities from transplanted and stationary oysters converged over time, indicating that communities were not population specific, but rather assemble from the surrounding environment forming communities, some of which can persist over longer period
Mortality selection during the 2003 European heat wave in three-spined sticklebacks: effects of parasites and MHC genotype
<p>Abstract</p> <p>Background</p> <p>Ecological interaction strength may increase under environmental stress including temperature. How such stress enhances and interacts with parasite selection is almost unknown. We studied the importance of resistance genes of the major histocompatibility complex (MHC) class II in 14 families of three-spined sticklebacks <it>Gasterosteus aculeatus </it>exposed to their natural macroparasites in field enclosures in the extreme summer of 2003.</p> <p>Results</p> <p>After a mass die-off during the 2003-European heat wave killing 78% of 277 experimental fish, we found strong differences in survival among and within families. In families with higher average parasite load fewer individuals survived. Multivariate analysis revealed that the composition of the infecting parasite fauna was family specific. Within families, individuals with an intermediate number of MHC class IIB sequence variants survived best and had the lowest parasite load among survivors, suggesting a direct functional link between MHC diversity and fitness. The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important.</p> <p>Conclusion</p> <p>The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003. Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.</p
Antagonistic experimental coevolution with a parasite increases host recombination frequency
Background: One of the big remaining challenges in evolutionary biology is to understand the evolution and maintenance of meiotic recombination. As recombination breaks down successful genotypes, it should be selected for only under very limited conditions. Yet, recombination is very common and phylogenetically widespread. The Red Queen Hypothesis is one of the most prominent hypotheses for the adaptive value of recombination and sexual reproduction. The Red Queen Hypothesis predicts an advantage of recombination for hosts that are coevolving with their parasites. We tested predictions of the hypothesis with experimental coevolution using the red flour beetle, Tribolium castaneum, and its microsporidian parasite, Nosema whitei.
Results: By measuring recombination directly in the individuals under selection, we found that recombination in the host population was increased after 11 generations of coevolution. Detailed insights into genotypic and phenotypic changes occurring during the coevolution experiment furthermore helped us to reconstruct the coevolutionary dynamics that were associated with this increase in recombination frequency. As coevolved lines maintained higher genetic diversity than control lines, and because there was no evidence for heterozygote advantage or for a plastic response of recombination to infection, the observed increase in recombination most likely represented an adaptive host response under Red Queen dynamics.
Conclusions: This study provides direct, experimental evidence for an increase in recombination frequency under host-parasite coevolution in an obligatory outcrossing species. Combined with earlier results, the Red Queen process is the most likely explanation for this observation
FicD genes in invertebrates: A tale of transposons, pathogenic and integrated viruses
: Many gene families are shared across the tree of life between distantly related species because of horizontal gene transfers (HGTs). However, the frequency of HGTs varies strongly between gene families and biotic realms suggesting differential selection pressures and functional bias. One gene family with a wide distribution are FIC-domain containing enzymes (FicDs). FicDs catalyze AMPylation, a post-translational protein modification consisting in the addition of adenosine monophosphate to accessible residues of target proteins. Beside the well-known conservation of FicDs in deuterostomes, we report the presence of a conserved FicD gene ortholog in a large number of protostomes and microbial eukaryotes. We also reported additional FicD gene copies in the genomes of some rotifers, parasitic worms and bivalves. A few dsDNA viruses of these invertebrates, including White spot syndrome virus, Cherax quadricarinatus iridovirus, Ostreid herpesvirus-1 and the beetle nudivirus, carry copies of FicDs, with phylogenetic analysis suggesting a common origin of these FicD copies and the duplicated FicDs of their invertebrate hosts. HGTs and gene duplications possibly mediated by endogenous viruses or genetic mobile elements seem to have contributed to the transfer of AMPylation ability from bacteria and eukaryotes to pathogenic viruses, where this pathway could have been hijacked to promote viral infection
Dual transcriptomics reveals co-evolutionary mechanisms of intestinal parasite infections in blue mussels Mytilus edulis
On theoretical grounds, antagonistic co-evolution between hosts and their parasites should be a widespread phenomenon but only received little empirical support sofar. Consequently, the underlying molecular mechanisms and evolutionary stepsremain elusive, especially in nonmodel systems. Here, we utilized the natural history of invasive parasites to document the molecular underpinnings of co-evolutionary trajectories. We applied a dual-species transcriptomics approach to experimental cross-infections of blue mussel <i>Mytilus edulis</i> hosts and their invasive parasitic copepods <i>Mytilicola intestinalis</i> from two invasion fronts in the Wadden Sea. We identified differentially regulated genes from an experimental infection contrast for hosts (infected vs. control) and a sympatry contrast (sympatric vs. allopatric combinations)for both hosts and parasites. The damage incurred by <i>Mytilicola</i> infection and the following immune response of the host were mainly reflected in cell division processes,wound healing, apoptosis and the production of reactive oxygen species(ROS). Furthermore, the functional coupling of host and parasite sympatry contrasts revealed the concerted regulation of chitin digestion by a Chitotriosidase 1 homologin hosts with several cuticle proteins in the parasite. Together with the coupled regulation of ROS producers and antagonists, these genes represent candidates that mediate the different evolutionary trajectories within the parasiteâs invasion. The hostâparasite combination-specific coupling of these effector mechanisms suggests that underlying recognition mechanisms create specificity and local adaptation. In this way, our study demonstrates the use of invasive speciesâ natural history to elucidate molecular mechanisms of hostâparasite co-evolution in the wild
Biological invasions and hostâparasite coevolution: different coevolutionary trajectories along separate parasite invasion fronts
Hostâparasite coevolution has rarely been observed in natural systems. Its study often relies on microparasitic infections introducing a potential bias in the estimation of the evolutionary change of host and parasite traits. Using biological invasions as a tool to study hostâparasite coevolution in nature can overcome these biases. We demonstrate this with a cross-infection experiment in the invasive macroparasite <i>Mytilicola intestinalis</i> and its bivalve host, the blue mussel <i>Mytilus edulis</i>. The invasion history of the parasite is well known for the southeastern North Sea and is characterised by two separate invasion fronts that reached opposite ends of the Wadden Sea (i.e. Texel, The Netherlands and Sylt, Germany) in a similar time frame. The speciesâ natural history thus makes this invasion an ideal natural experiment to study hostâparasite coevolution in nature. We infected hosts from Texel, Sylt and Kiel (Baltic Sea, where the parasite is absent) with parasites from Texel and Sylt, to form sympatric, allopatric and naĂŻve infestation combinations, respectively. We measured infection rate, host condition and parasite growth to show that sympatric hostâparasite combinations diverged in terms of pre- and post-infection traits within <100 generations since their introduction. Texel parasites were more infective and more efficient at exploiting the hostâs resources. Hosts on Texel, on the other hand, evolved resistance to infection, whereas hosts on Sylt may have evolved tolerance. This illustrates that different coevolutionary trajectories can evolve along separate invasion fronts of the parasite, highlighting the use of biological invasions in studies of hostâparasite coevolution in nature
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