Assortative mating and differential male mating success in an ash hybrid zone population

BACKGROUND: The structure and evolution of hybrid zones depend mainly on the relative importance of dispersal and local adaptation, and on the strength of assortative mating. Here, we study the influence of dispersal, temporal isolation, variability in phenotypic traits and parasite attacks on the male mating success of two parental species and hybrids by real-time pollen flow analysis. We focus on a hybrid zone population between the two closely related ash species Fraxinus excelsior L. (common ash) and F. angustifolia Vahl (narrow-leaved ash), which is composed of individuals of the two species and several hybrid types. This population is structured by flowering time: the F. excelsior individuals flower later than the F. angustifolia individuals, and the hybrid types flower in-between. Hybrids are scattered throughout the population, suggesting favorable conditions for their local adaptation. We estimate jointly the best-fitting dispersal kernel, the differences in male fecundity due to variation in phenotypic traits and level of parasite attack, and the strength of assortative mating due to differences in flowering phenology. In addition, we assess the effect of accounting for genotyping error on these estimations. RESULTS: We detected a very high pollen immigration rate and a fat-tailed dispersal kernel, counter-balanced by slight phenological assortative mating and short-distance pollen dispersal. Early intermediate flowering hybrids, which had the highest male mating success, showed optimal sex allocation and increased selfing rates. We detected asymmetry of gene flow, with early flowering trees participating more as pollen donors than late flowering trees. CONCLUSION: This study provides striking evidence that long-distance gene flow alone is not sufficient to counter-act the effects of assortative mating and selfing. Phenological assortative mating and short-distance dispersal can create temporal and spatial structuring that appears to maintain this hybrid population. The asymmetry of gene flow, with higher fertility and increased selfing, can potentially confer a selective advantage to early flowering hybrids in the zone. In the event of climate change, hybridization may provide a means for F. angustifolia to further extend its range at the expense of F. excelsior

Forest Management, Conflict and Social–Ecological Systems in a Changing World

Conflicts are ubiquitous in forest management because of several overlapping temporal and spatial issues (see examples in tropical and temperate areas [...

Data from: Ecological co-associations influence species’ responses to past climatic change: an example from a Sonoran Desert bark beetle

Ecologically interacting species may have phylogeographic histories that are shaped both by features of their abiotic landscape, and by biotic constraints imposed by their co-association. The Baja California peninsula provides an excellent opportunity to examine the influence of abiotic vs. biotic factors on patterns of diversity in plant-insect species. This is because past climatic and geological changes impacted the genetic structure of plants quite differently to that of co-distributed free-living animals (e.g., herpetofauna and small mammals). Thus, ‘plant-like’ patterns should be discernible in host-specific insect herbivores. Here we investigate the population history of a monophagous bark beetle, Araptus attenuatus, and consider drivers of phylogeographic patterns in light of previous work on its host plant, Euphorbia lomelii. Based on mitochondrial and nuclear markers, we found that the evolutionary history of A. attenuatus exhibits similarities to host plant that are attributable to both biotic and abiotic processes. Southward range expansion and recent colonization of continental Sonora peninsula appear to be unique to this taxon pair, and likely reflect influences of the host plant. On the other hand, abiotic factors with landscape-level influences on suites of co-distributed taxa, such as Plio- and Pleistocene-aged marine incursions in the region, also left genetic signatures in beetle populations. Superimposed on these similarities, bark beetle-specific patterns and processes were also evident. Taken together, this work illustrates that the evolutionary history of species-specific insect herbivores may represent a mosaic of influences, including—but not limited to—those imposed by the host plant

Trees on the move: using decision theory to compensate for climate change at the regional scale in forest social-ecological systems

The adaptation of social-ecological systems such as managed forests depends largely on decisions taken by forest managers who must choose among a wide range of possible futures to spread risks. We used robust decision theory to guide management decisions on the translocation of tree populations to compensate for climate change.We calibrated machine learning correlational models using tree height data collected from five common garden tests in France where Abies alba provenances from 11 European countries are planted. Resulting models were used to simulate tree height in the planting sites under current and 2050 climates (regional concentration pathway scenarios (RCPs) 2.6, 4.5, 6.0 and 8.5). Our results suggest an overall increase in tree height by 2050, but with large variation among the predictions depending on the provenance and the RCPs. We applied maximin, maximax and minimax decision rules to address outcomes under five uncertain states of the world represented by the four RCPs and the present climate (baseline). The maximin rule indicated that for 2050, the best translocation option for maximising tree height would be the use of provenances from Northwest France into all target zones. The maximax and minimax regret rules pointed out the same result for all target zones except for the ‘Les Chauvets’ trial, where the East provenance was selected. Our results show that decision theory can help management by reducing the number of options if most decision rules converge. Interestingly, the commonly suggested recommendation of using multiple provenances to mitigate long-term maladaptation risks or from ‘pre-adapted’ populations from the south was not supported by our approach

Differential patterns of morphological and molecular hybridization between Fraxinus excelsior L. and Fraxinus angustifolia Vahl (Oleaceae) in eastern and western France

International audienceWe examined large-scale patterns of morphology, genetic structure and ecological correlates of Fraxinus excelsior and the closely related species Fraxinus angustifolia in France, in order to determine the degree of hybridization between them. We sampled 24 populations in two putative hybrid zones (Loire and Saône), and five control populations of each species. We measured foliar characteristics of adult trees and used five nuclear microsatellites as molecular markers. Canonical discriminant analysis indicated that the two species differ in morphology, but that intermediate types are common in the Loire region but less frequent in the Saône region. Bayesian population assignment identified one F. angustifolia and two F. excelsior gene pools. Most Loire individuals clustered genetically with the F. angustifolia gene pool. In contrast, the Saône region presented individuals belonging mostly to F. excelsior pools, although the F. angustifolia type was frequent in certain populations. The lowest FST values were found between the Loire and F. angustifolia controls that also exhibited no significant isolation by distance. The proportion of the F. angustifolia gene pool in each locality was negatively correlated with winter temperatures, suggesting that a cold climate may be limiting. Hybridization is probably favoured by the intermediate climatic conditions in the Loire region that allow both species to occur, but is somewhat hampered by the harsher winters in the Saône area where morphological introgression has apparently not yet occurred

Environmental heterogeneity explains the genetic structure of Continental and Mediterranean populations of Fraxinus angustifolia Vahl.

Tree species with wide distributions often exhibit different levels of genetic structuring correlated to their environment. However, understanding how environmental heterogeneity influences genetic variation is difficult because the effects of gene flow, drift and selection are confounded. We investigated the genetic variation and its ecological correlates in a wind-pollinated Mediterranean tree species, Fraxinus angustifolia Vahl, within a recognised glacial refugium in Croatia. We sampled 11 populations from environmentally divergent habitats within the Continental and Mediterranean biogeographical regions. We combined genetic data analyses based on nuclear microsatellite loci, multivariate statistics on environmental data and ecological niche modelling (ENM). We identified a geographic structure with a high genetic diversity and low differentiation in the Continental region, which contrasted with the significantly lower genetic diversity and higher population divergence in the Mediterranean region. The positive and significant correlation between environmental and genetic distances after controlling for geographic distance suggests an important influence of ecological divergence of the sites in shaping genetic variation. The ENM provided support for niche differentiation between the populations from the Continental and Mediterranean regions, suggesting that contemporary populations may represent two divergent ecotypes. Ecotype differentiation was also supported by multivariate environmental and genetic distance analyses. Our results suggest that despite extensive gene flow in continental areas, long-term stability of heterogeneous environments have likely promoted genetic divergence of ashes in this region and can explain the present-day genetic variation patterns of these ancient populations

What sampling is needed for reliable estimations of genetic diversity in Fraxinus excelsior L. (Oleaceae)?

$\bullet$ Sample size is a critical issue for genetic diversity studies and conservation programs. However, sample size evaluation requires previous knowledge of allele frequencies estimated with precision and this is not often the case. $\bullet$ Here, we evaluated sample size requirements for accurate genetic diversity in adult trees and family arrays in a 12 ha plot of Fraxinus excelsior L. (Oleaceae) in a community forest in central France. Data consisted of 579 adult trees and 480 offspring from 24 families genotyped at four nuclear microsatellites. $\bullet$ Mean square errors (MSE) estimates performed on Monte Carlo simulations of resampled data indicated that several adult individuals ($>$ 300) are necessary for accurate measures of allele richness. However, expected heterozygosity requires smaller samples ($<$ 30). Seeds captured about 90% of adult allelic diversity requiring a sampling effort roughly 50% larger than that of adult trees (480 seeds vs. 300 adults) suggesting that seed sampling is heavily penalized for allele counts. Nevertheless, gene diversity of seeds was essentially identical to that of the adult population. $\bullet$ Extrapolation of these results to other ash tree populations appears feasible because of similar levels of diversity reported in the literature but it is not granted for species with significant selfing or high genetic structure.Quel échantillonnage pour des estimations fiables de la diversité génétique chez Fraxinus excelsior L. (Oleaceae)?. $\bullet$ La taille d'un échantillonnage est un paramètre difficile à estimer a priori pour les études de diversité génétique ainsi que pour les programmes de conservation. En général, l'évaluation de cette taille nécessite au préalable une connaissance fine des fréquences alléliques ce qui n'est pas toujours le cas. $\bullet$ Dans cette étude, nous avons évalué sur une parcelle de 12 ha de Fraxinus excelsior L. (Oleaceae), dans un forêt domaniale, la taille de l'échantillonnage nécessaire pour estimer de façon fiable la diversité génétique des arbres adultes ainsi que de leurs descendants. Un échantillon de 579 individus adultes et 480 graines issues de 24 arbres-mères ont été génotypés grâce à quatre marqueurs microsatellites nucléaires. $\bullet$ Des analyses d'erreurs quadratiques moyennes obtenues dans le cadre de simulations de type Monte Carlo indiquent que plus de 300 individus adultes sont nécessaires pour obtenir des mesures alléliques fiables. Par contre, l'hétérozygotie espérée est obtenue pour des échantillons plus petits ($<$ 30). Les graines capturent 90 % de la diversité allélique des adultes indiquant que l'échantillonnage des graines doit être deux fois celui des adultes pour obtenir la même information (480 graines vs. 300 adultes). Par ailleurs, la diversité génétique est identique pour les deux échantillonnages. $\bullet$ L'extrapolation de ces résultats à d'autres espèces de frêne est possible compte tenu des niveaux de diversité observés dans la littérature mais n'est pas garantie pour des espèces qui s'autofécondent et qui ont des populations très structurées génétiquement

Garrick_et_al_MolEcol_DRYAD

Garrick_et_al_MolEcol_DRYA

Raster file used for ecological niche modeling

Raster files used for ecological niche modeling File 1: 'araptus.curr.asc' Timescale: Present-day, class: RasterLaye, dimensions: 960, 720, 691200 (nrow, ncol, ncell), resolution: 0.008333, 0.008333 (x, y), extentL-115, -109.0002, 22, 29.99968 (xmin, xmax, ymin, ymax). File 2: 'araptus.lgm.asc' Timescale: Last Glacial Maximum, class: RasterLayer, dimensions: 960, 720, 691200 (nrow, ncol, ncell), resolution: 0.008333, 0.008333 (x, y), extent: -115, -109.0002, 22, 29.99968 (xmin, xmax, ymin, ymax