Differential immunity as a factor influencing mussel hybrid zone structure

Interspecific hybridisation can alter fitness-related traits, including the response to pathogens, yet immunity is rarely investigated as a potential driver of hybrid zone dynamics, particularly in invertebrates. We investigated the immune response of mussels from a sympatric population at Croyde Bay, within the hybrid zone of Mytilus edulis and Mytilus galloprovincialis in Southwest England. The site is characterised by size-dependent variation in genotype frequencies, with a higher frequency of M. galloprovincialis alleles in large mussels, largely attributed to selective mortality in favour of the M. galloprovincialis genotype. To determine if differences in immune response may contribute to this size-dependent variation in genotype frequencies, we assessed the two pure species and their hybrids in their phagocytic abilities when subject to immune challenge as a measure of immunocompetence and measured the metabolic cost of mounting an antigen-stimulated immune response. Mussels identified as M. galloprovincialis had a greater immunocompetence response at a lower metabolic cost compared to mussels identified as M. edulis. Mussels identified as hybrids had intermediate values for both parameters, providing no evidence for heterosis but suggesting that increased susceptibility compared to M. galloprovincialis may be attributed to the M. edulis genotype. The results indicate phenotypic differences in the face of pathogenic infection, which may be a contributing factor to the differential mortality in favour of M. galloprovincialis, and the size-dependent variation in genotype frequencies associated with this contact zone. We propose that immunity may contribute to European mussel hybrid zone dynamics

Ectomycorrhizal fungal diversity decreases in Mediterranean pine forests adapted to recurrent fires

Fire is a major disturbance linked to the evolutionary history and climate of Mediterranean ecosystems, where the vegetation has evolved fire‐adaptive traits (e.g., serotiny in pines). In Mediterranean forests, mutualistic feedbacks between trees and ectomycorrhizal (ECM) fungi, essential for ecosystem dynamics, might be shaped by recurrent fires. We tested how the structure and function of ECM fungal communities of Pinus pinaster and Pinus halepensis vary among populations subjected to high and low fire recurrence in Mediterranean ecosystems, and analysed the relative contribution of environmental (climate, soil properties) and tree‐mediated (serotiny) factors. For both pines, local and regional ECM fungal diversity were lower in areas of high than low fire recurrence, although certain fungal species were favoured in the former. A general decline of ECM root‐tip enzymatic activity for P. pinaster was associated with high fire recurrence, but not for P. halepensis. Fire recurrence and fire‐related factors such as climate, soil properties or tree phenotype explained these results. In addition to the main influence of climate, the tree fire‐adaptive trait serotiny recovered a great portion of the variation in structure and function of ECM fungal communities associated with fire recurrence. Edaphic conditions (especially pH, tightly linked to bedrock type) were an important driver shaping ECM fungal communities, but mainly at the local scale and probably independently of the fire recurrence. Our results show that ECM fungal community shifts are associated with fire recurrence in fire‐prone dry Mediterranean forests, and reveal complex feedbacks among trees, mutualistic fungi and the surrounding environment in these ecosystems.This work was supported by the projects MyFUNCO (CGL2011-29585-C02-02) and PiroPheno (CGL2017-89751-R) founded by the Spanish Ministry for Economy and Competitiveness (MINECO), and by the LABoratoire d'EXcellence Arbre (LABEX Arbre). L.P.I. held a pre-doctoral fellowship awarded by MINECO. We also acknowledge three anonymous reviewers for their con-structive comments that greatly improved the quality of the manuscriptPeer reviewe

Fire recurrence effects over the structure and activity of ectomycorrhizal fungal communities in Mediterranean pine forests

Póster presentado en el congreso Ecology of soil Microorganisms, Microbes as Important Drivers of Soil Processes, celebrado en Praga, República Checa, del 29 de noviembre al 3 de diciembre de 2015Fire is an intrinsic factor of Mediterranean forest ecosystems, determinant of abiotic disturbance and organism¿s ecology. Wildfire recurrence and predicted increase associated with global change may particularly alter the fertility and microbial communities of soil. Symbiotic ectomycorrhizal (EM) fungi are main actors of forest soils, directly involved in the cycling of nutrients and the productivity of trees. We surveyed forests of two representative Mediterranean pines, Pinus pinaster Ait. (Ppi) and Pinus halepensis Mill. (Pha), to evaluate whether fire recurrence affected the structure and functioning of EM fungal communities. Ectomycorrhizal root tips of both pine species were collected in low and high fire recurrence forest sites, measured for enzymatic activities (EAs) involved in geochemistry cycles and nutrient mobilization, and fungal identification approached by high-throughput sequencing. Fire recurrence significantly altered the assemblage of EM fungi, while the community richness remained unaffected. EAs secreted by EM fungi highly diverged depending on the tree species, being generally greater in the rhizosphere of Pha compared with that of Ppi. High fire recurrence negatively impacted the activity of the Ppi ectomycorrhizas, whereas in the case of Pha, most EAs were unaffected. A general increase of laccase activity, involved in the oxidation of various substrates, such as phenols or lignin, was observed in recurrently burned areas. Fire recurrence effects might be explained through the divergent altered edaphic properties and specific fungal community composition of the forests studied, which could have relevant implications on decomposition rates, carbon storage, and availability of nutrients in soils, finally affecting the productivity of Mediterranean forest ecosystems. 247Peer Reviewe

Effect of sperm dosage transportation in stallions: Effect on sperm DNA fragmentation

Artificial insemination programs for horses usually involve ex vivo handling and transporting of sperm. The present experiment was designed to: (i) assess the effect of transportation on sperm DNA integrity at different time post semen collection, and (ii) evaluate if sperm DNA quality deteriorates rapidly beyond 24 h of cooled storage. After collection, the ejaculates were extended using INRA 96 and semen was prepared for prompt analysis (A0) or 24 h/48 h cooled-shipping (B24 and C48 respectively). Each sample was assessed for sperm DNA fragmentation index (SDFI) at time 0 and after incubation for 2, 6 and 24 h at 37 °C. There was very little difference in SDFI between freshly extended (A0) and 24 h/48 h cooled-transported semen samples (B24/C48) at time 0. After 2 h of incubation at 37 °C, there was an increase in SDFI ranging from 2.7% to 7.5% per hour in freshly extended semen samples (A0: 5.1 ± 1.5), while cooled-transported semen samples had a much greater increase in SDFI, ranging from 5.0% to 20.5% (B24: 14.7 ± 5.6) and from 8.2% to 26.8% (C48: 18.3 ± 7.2) respectively. There were not marked differences in the sperm DNA integrity between 24 and 48 h for transported samples, thus there is the possibility of desirable fertility with use of stallion sperm after 48 h of cooled storage.This research was supported with public funding from the Spanish Agency for International Cooperation and Development (AECID: AP/039620/11) and the Spanish Ministry of Economy and Competitiveness (MINECO: BFU-2013-44290-R)

Fire recurrence impacts the functioning and phylogenetic structure of fungal communities in Mediterranean pine forests

International audienc

Recent population decline and selection shape diversity of taxol-related genes

International audienceTaxanes are defensive metabolites produced by Taxus species (yews) and used in anticancer therapies. Despite their medical interest, patterns of natural diversity in taxane-related genes are unknown. We examined variation at five main genes of Taxus baccata in the Iberian Peninsula, a region where unique yew genetic resources are endangered. We looked at several gene features and applied complementary neutrality tests, including diversity / divergence tests, tests solely based on site frequency spectrum (SFS) and Zeng’s compound tests. To account for specific demography, microsatellite data were used to infer historical changes in population size based on an Approximate Bayesian Computation (ABC) approach. Polymorphism-divergence tests pointed to positive selection for genes TBT and TAT and balancing selection for DBAT. In addition, neutrality tests based on SFS found that while a recent reduction in population size may explain most statistics’ values, selection may still be in action in genes TBT and DBAT, at least in some populations. Molecular signatures on taxol genes suggest the action of frequent selective waves with different direction or intensity, possibly related to varying adaptive pressures produced by the host–enemy co-evolution on defence-related genes. Such natural selection processes may have produced taxane variants still undiscovered

Plant intraspecific variation modulates nutrient cycling through its below ground rhizospheric microbiome

Plant genetic variation, through its phenotypic display, can determine the composition of below ground microbial communities. Variation within a species is increasingly acknowledged to have substantial ecological consequences, particularly through trophic cascades. We hypothesized that the intraspecific genotypic variation of the tree host might impact the phylogenetic composition of its rhizospheric microbial communities, by favouring particular clades, that might be further reflected in ecosystem process rates. We tested whether the intraspecific genotypic variation of Pinus pinaster modulates nutrient cycling by determining the phylogenetic structure of its symbiotic ectomycorrhizal fungi and rhizospheric bacteria. We sequenced fungal and bacterial molecular markers and reconstructed phylogenies in the rhizosphere of P. pinaster trees belonging to three genotypic variants (Mediterranean, Atlantic, African) in three 45-year-old common garden experiments, and measured seven soil enzymatic activities. Local effects, based on differences in elevation and soil conditions across sites, were strong predictors of the ectomycorrhizal and bacterial communities thriving in tree's rhizosphere. Across-site variation also explained differences in phosphorus cycling. We detected, however, a significant effect of the plant genotype on the phylogenetic structure of the root-associated microbiota that was consistent across sites. The most productive Mediterranean plant genotype sheltered the most distinct root microbiome, with the dominant Basidiomycetes and Proteobacteria having a strong influence on the phylogenetic microbial community structure and associating with an enhanced hydrolysis of celluloses, hemicelluloses and chitin. Beneath the less productive Atlantic genotype, the less abundant Ascomycetes and up to thirteen bacterial phyla shaped the phylogenetic microbial structure, and predicted the rates of peptidase. Ectomycorrhizal fungi explained the activity of cellulases and protease, and bacteria that of hemicellulases and chitinase, suggesting functional complementarity. Synthesis. This is the first report using three-replicated long-term common gardens in mature forests to disentangle plant genotype- and site-specific drivers of the rhizospheric microbiome and its enzymatic potential. We concluded that intraspecific variation in primary producers leaves a phylogenetic signature in mutualists and decomposers that further modulate key steps in carbon and nitrogen cycles. These results emphasize the ecological relevance of plant intraspecific diversity in determining essential plant-soil feedbacks that control ecosystem productivity and performance

Data from: Wolbachia effects in natural populations of Chorthippus parallelus from the Pyrenean hybrid zone.

We evaluate for the first time the effect of Wolbachia infection, involving two different supergoups, on the structure and dynamics of the hybrid zone between two subspecies of Chorthippus parallelus (Orthoptera) in the Pyrenees. Wolbachia infection showed no effects on female fecundity or a slight increment in females infected by F supergroup although in the last case it has to be well-established. Cytoplasmic incompatibility (CI) is confirmed in crosses carried out in the field between individuals from a natural hybrid population. This CI, registered as the relative reduction in embryo production (sh), was of sh = 0.355 and sh = 0.286 in unidirectional crosses involving B and F supergroups, respectively. CI also occurred in bidirectional crosses (sh = 0.147) but with a weaker intensity. The transmission rates of the two Wolbachia strains (B and F) were estimated by the optimization of a theoretical model in order to reach the infection frequencies observed in certain population. To fit this scenario both supergroups should present transmission rates close to 1. Further, we have simulated the infection dynamics, and hence the capacity of Wolbachia to structure the population of the host insects, and to affect to reproduction and genetic introgression in the hybrid zone. This represents a first example of the influence of Wolbachia in an insect natural hybrid zone

Adaptive evolution of Mediterranean pines

Mediterranean pines represent an extremely heterogeneous assembly. Although they have evolved under similar environmental conditions, they diversified long ago, ca. 10. Mya, and present distinct biogeographic and demographic histories. Therefore, it is of special interest to understand whether and to what extent they have developed specific strategies of adaptive evolution through time and space. To explore evolutionary patterns, the Mediterranean pines' phylogeny was first reconstructed analyzing a new set of 21 low-copy nuclear genes with multilocus Bayesian tree reconstruction methods. Secondly, a phylogenetic approach was used to search for footprints of natural selection and to examine the evolution of multiple phenotypic traits. We identified two genes (involved in pines' defense and stress responses) that have likely played a role in the adaptation of Mediterranean pines to their environment. Moreover, few life-history traits showed historical or evolutionary adaptive convergence in Mediterranean lineages, while patterns of character evolution revealed various evolutionary trade-offs linking growth-development, reproduction and fire-related traits. Assessing the evolutionary path of important life-history traits, as well as the genomic basis of adaptive variation is central to understanding the past evolutionary success of Mediterranean pines and their future response to environmental changes. © 2013 Elsevier Inc

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experimental data from the crosses performe