Find research datasets worth reusing

Data from: The temporal dimension in individual-based plant pollination networks

The pollination success of animal-pollinated plants depends on the temporal coupling between flowering schedules and pollinator availability. Within a population, individual plants exhibiting disparate flowering schedules will be exposed to different pollinators when the latter exhibit temporal turnover. The temporal overlap between individual plants and pollinators will result in a turnover of interactions, which can be analyzed through a network approach. We have explored the temporal dynamics of individual-based plant networks resulting from pairwise similarities in pollinator composition. During two flowering seasons, we surveyed the phenology and pollinator fauna of the individual plants from a population of Erysimum mediohispanicum (Brassicaceae). We analyzed the topology of these networks by means of their modularity, clustering, and core–periphery structure. These metrics are related to network functional properties such as cohesion, transitivity and centralization respectively. Afterwards, we analyzed the influence of each pollinator functional group on network topology. We found that network topology varied widely over time as a consequence of the differences in plant phenology and the idiosyncratic and contextual effect of pollinators. When integrating all temporary networks, the network became cohesive (non modular), transitive (locally clusterized), and centralized (core–periphery topology). These topologies could entail important consequences for plant reproduction. Our results highlight the importance of considering the entire flowering season and the necessity of making comprehensive temporal sampling when trying to build reliable interaction networks.

opencc-zeroDec 2011View details →

Data from: Social learners require process information to outperform individual learners

Humans exhibit a rich and complex material culture with no equivalent in animals. Also, social learning, a crucial requirement for culture, is particularly developed in humans and provides a means to accumulate knowledge over time and to develop advanced technologies. However, the type of social learning required for the evolution of this complex material culture is still debated. Here, using a complex and opaque virtual task, the efficiency of individual learning and two types of social learning (product-copying and process-copying) were compared. We found that (1) individuals from process-copying groups outperformed individuals from product-copying groups or individual learners, whereas access to product information was not a sufficient condition for providing an advantage to social learners compared to individual learners; (2) social learning did not seem to affect the exploration of the fitness landscape; (3) social learning led to strong within-group convergence and also to between-group convergence and (4) individuals used widely variable social learning strategies. The implications of these results for cumulative culture evolution are discussed.

Data from: Individual ant workers show self-control

Often, the first option is not the best. Self-control can allow humans and animals to improve resource intake under such conditions. Self-control in animals is often investigated using intertemporal choice tasks—choosing a smaller reward immediately or a larger reward after a delay. However, intertemporal choice tasks may underestimate self-control, as test subjects may not fully understand the task. Vertebrates show much greater apparent self-control in more natural foraging contexts and spatial discounting tasks than in intertemporal choice tasks. However, little is still known about self-control in invertebrates. Here, we investigate self-control in the black garden ant Lasius niger. We confront individual workers with a spatial discounting task, offering a high-quality reward far from the nest and a poor-quality reward closer to the nest. Most ants (69%) successfully ignored the closer, poorer reward in favour of the further, better one. However, when both the far and the close rewards were of the same quality, most ants (83%) chose the closer feeder, indicating that the ants were indeed exercising self-control, as opposed to a fixation on an already known food source.

opencc-zeroDec 2013View details →

Data from: Heterogeneity in individual quality and reproductive trade-offs within species

Interspecifically, a reasonable body of evidence supports a trade-off between offspring size and number. However, at the intraspecific level, a whole manner of phenotypic correlations between offspring size and number are observed. These correlations may be predicted when heterogeneity in resource availability, or quality, is considered. Making the assumption that maternal size is a proxy for resource availability, we meta-analytically quantified four phenotypic reproductive correlations within numerous species: (1) maternal size and offspring size, (2) maternal size and offspring number, (3) offspring number and offspring size, and (4) offspring number and offspring size after controlling for maternal size. Within species, maternal size showed a positive correlation with both offspring size and number. Despite this consistency, no correlation between offspring size and number was found. After controlling for maternal size, however, offspring size and number showed a significant negative correlation. A phylogenetic component of our analysis accounted for little heterogeneity in the data, suggesting that our findings show remarkable consistency across taxa. Overall, our results support an observable phenotypic trade-off between offspring size and number. However, this analysis also highlights the importance of considering quality when examining trade-offs, a task that is not always straightforward as quality is context dependant.

opencc-zeroDec 2013View details →

Data from: Individual recognition through olfactory - auditory matching in lemurs

Individual recognition can be facilitated by creating representations of familiar individuals, whereby information from signals in multiple sensory modalities become linked. Many vertebrate species use auditory–visual matching to recognize familiar conspecifics and heterospecifics, but we currently do not know whether representations of familiar individuals incorporate information from other modalities. Ring-tailed lemurs (Lemur catta) are highly visual, but also communicate via scents and vocalizations. To investigate the role of olfactory signals in multisensory recognition, we tested whether lemurs can recognize familiar individuals through matching scents and vocalizations. We presented lemurs with female scents that were paired with the contact call either of the female whose scent was presented or of another familiar female from the same social group. When the scent and the vocalization came from the same individual versus from different individuals, females showed greater interest in the scents, and males showed greater interest in both the scents and the vocalizations, suggesting that lemurs can recognize familiar females via olfactory–auditory matching. Because identity signals in lemur scents and vocalizations are produced by different effectors and often encountered at different times (uncoupled in space and time), this matching suggests lemurs form multisensory representations through a newly recognized sensory integration underlying individual recognition.

Data from: A comparative approach to cooperative transport in ants: individual persistence correlates with group coordination

When groups of ants work together to carry large objects—called cooperative transport—they must form consensus on a travel direction. In many species, groups are unsuccessful at this decision, and deadlock. In other collective decisions, including nest-site selection in honeybees, individuals' enthusiasm or recruitment intensity for a given option affects the selection process. A similar mechanism may be important during cooperative transport in ants and may account for coordination differences among species. Results from theoretical models suggest that individuals' persistence—their reluctance to give up or change their preferred direction—may promote coordination. More persistent individuals formed more successful groups in a theoretical context. As an empirical test of this hypothesis, I examined cooperative transport in four ant species that differ substantially in their group-level coordination, from exceedingly coordinated to rarely successful. I focused on the beginning of transport, evaluating groups' transitions from uncoordinated to successful. I measured two types of persistence at the individual level—total engagement effort and local engagement time—and I measured group coordination for each species. In one species, I also manipulated persistence by adding a force equivalent to infinitely persistent ants to the existing transport groups. Species with more persistent individuals succeeded more often and formed more coordinated transport groups, with more direct paths. Furthermore, adding two infinitely persistent ants to the existing groups seemed to moderately increase their path directness. These results support the hypothesis that high individual persistence promotes group coordination during cooperative transport, and this study informs the mechanisms of emergent coordination.

opencc-zeroDec 2017View details →

Data from: The influence of environmental gradients on individual behaviour: individual plasticity is consistent across risk and temperature gradients

1. The expression of individual behaviour as a function of environmental variation (behavioural plasticity) is recognised as a means for animals to modify their phenotypes in response to changing conditions. Plasticity has been studied extensively in recent years, leading to an accumulation of evidence for behavioural plasticity within natural populations. 2. Despite the recent attention given to studying individual variation in behavioural plasticity, there is still a lack of consensus regarding its causes and constraints. One pressing question related to this is whether individual plasticity carries over across temporal and environmental gradients. That is, are some individuals more plastic (responsive) than others in general? 3. Here, we examined the influence of temporal and environmental gradients on individual behavioural responses in a marine gastropod, Littoraria irrorata. We measured individual boldness repeatedly over time and in response to tidal cycle (high vs low an index of risk) and daily temperature fluctuations (known to affect metabolism), in a controlled field experiment. 4. On average, boldness increased from high to low tide and with increasing temperature but decreased marginally over time. Individuals also differed in their responses to variation in tide and temperature, but not over time. Those that were relatively bold at high tide (when predation risk is greater) were similarly bold at low tide, whereas shy individuals became much more 'bold' at low tide. Most notably, individuals that were more responsive to tide (and thus risk) were also more responsive to temperature changes, meaning that plasticity was correlated across contexts (r = 0.57) and that bolder individuals were least plastic overall. 5. This study provides a rare and possibly first example of consistency of individual behavioural plasticity across contexts, suggesting underlying physiology as a common mechanism, and raises the possibility of correlational selection on plasticity.

opencc-zeroDec 2011View details →

Data from: Shape analysis of symmetric structures: quantifying variation among individuals and asymmetry

Morphometric studies often consider parts with internal left-right symmetry, for instance, the vertebrate skull. This type of symmetry is called object symmetry and is distinguished from matching symmetry, in which two separate structures exist as mirror images of each other, one on each body side. We explain a method for partitioning the total shape variation of landmark configurations with object symmetry into components of symmetric variation among individuals and asymmetry. This method is based on the Procrustes superimposition of the original and a reflected copy of each landmark configuration and is compatible with the two-factor ANOVA model customary in studies of fluctuating asymmetry. We show a fully multivariate framework for testing the effects in the two-factor model with MANOVA statistics, which also applies to shapes with matching symmetry. We apply the new methods in a small case study of pharyngeal jaws of the Neotropical cichlid fish Amphilophus citrinellus. The analysis revealed that the symmetric component of variation in the pharyngeal jaws is dominated by the contrast between two alternative trophic morphs in this species and that there is subtle but statistically significant directional asymmetry. Finally, we provide some general recommendations for morphometric studies of symmetric shapes.

Data from: Combining noninvasive genetics and a new mammalian sex-linked marker provides new tools to investigate population size, structure and individual behaviour: an application to bats

Monitoring wild populations is crucial for their effective management. Noninvasive genetic methods provide robust data from individual free-ranging animals, which can be used in capture-mark-recapture (CMR) models to estimate demographic parameters without capturing or disturbing them. However, sex- and status-specific behaviour, which may lead to differences in detection probabilities, is rarely considered in monitoring. Here, we investigated population size, sex ratio, sex- and status-related behaviour in 19 Rhinolophus hipposideros maternity colonies (Northern France) with a noninvasive genetic CMR approach (using faeces) combined with parentage assignments. The use of the DDX3X/Y-Mam sexual marker designed in this study, which shows inter- and intra-chromosomal length polymorphism across placental mammals, together with 8 polymorphic microsatellite markers, produced high quality genetic data with limited genotyping errors and allowed us to reliably distinguish different categories of individuals (males, reproductive and non-reproductive females) and to estimate population sizes. We showed that visual counts represent well adult female numbers and that population composition in maternity colonies changes dynamically during the summer. Before parturition, colonies mainly harbour pregnant and non-pregnant females with a few visiting males whereas after parturition, colonies are mainly composed of mothers and their offspring with a few visiting non-mothers and males. Our approach gives deeper insight into sex- and status-specific behaviour, a prerequisite for understanding population dynamics and developing effective monitoring and management strategies. Provided sufficient samples can be obtained, this approach can be readily applied to a wide range of species.

Data from: Intra-individual polymorphism in chloroplasts from NGS data: where does it come from and how to handle it?

Next generation sequencing allows access to a large quantity of genomic data. In plants, several studies used whole chloroplast genome sequences for inferring phylogeography or phylogeny. Even though the chloroplast is a haploid organelle, NGS plastome data identified a non negligible number of intra-individual polymorphic SNPs. Such observations could have several causes such as sequencing errors, the presence of heteroplasmy or transfer of chloroplast sequences in the nuclear and mitochondrial genomes. The occurrence of allelic diversity has practical important impacts on the identification of diversity, the analysis of the chloroplast data and beyond that, significant evolutionary questions. In this study, we show that the observed intra-individual polymorphism of chloroplast sequence data is probably the result of plastid DNA transferred into the mitochondrial and/or the nuclear genomes. We further assess nine different bioinformatics pipelines' error rates for SNP and genotypes calling using SNPs identified in Sanger sequencing. Specific pipelines are adequate to deal with this issue, optimizing both specificity and sensitivity. Our results will allow a proper use of whole chloroplast NGS sequence and will allow a better handling of NGS chloroplast sequence diversity.

Data from: Individual aggression, but not winner-loser effects, predicts social rank in male domestic fowl

Many factors can affect the probability for an individual to obtain a high social rank, including size, weaponry, and behavioral attributes such as aggression. Recent experiences of winning or losing can also affect the chances of winning future contests, commonly referred to as "winner–loser effects". Individuals often differ in behavior in a consistent way, including in aggression, thereby showing differences in personality. However, the relative importance of recent experience and aspects of personality in determining rank, as well as the extent to which winning or losing affects aggression, has rarely been studied. Here, we investigate these questions using male domestic fowl. We matched males for body size, comb size, and aggression in pair-wise duels to: 1) study the effect of contest outcome on aggression and 2) compare the effect of individual aggression and contest experience on future social status in small groups. We found that aggression was a highly repeatable personality trait and that aggression increased after winning and decreased after losing. Nevertheless, such winner–loser effects were not enough to increase the odds of becoming dominant in a small group. Instead, aggressiveness measured prior to a contest experience best predicted future rank. Boldness and exploration did not predict rank and of the 2, only boldness was positively correlated with aggressiveness. We conclude that for male domestic fowl in contests among phenotypically matched contestants, aggressiveness is more important for obtaining high rank than winner–loser effects, or other aspects of personality.

Data from: Estimation of individual growth trajectories when repeated measures are missing

Individuals in a population vary in their growth due to hidden and observed factors such as age, genetics, environment, disease, and carryover effects from past environments. Because size affects fitness, growth trajectories scale up to affect population dynamics. However, it can be difficult to estimate growth in data from wild populations with missing observations and observation error. Previous work has shown that linear mixed models (LMMs) underestimate hidden individual heterogeneity when over 25% of repeated measures are missing. Here we demonstrate a flexible and robust way to model growth trajectories. We show that state-space models (SSMs), fit using R package growmod, are far less biased than LMMs when fit to simulated datasets with missing repeated measures and observation error. This method is much faster than MCMC methods, allowing more models to be tested in a shorter time. For the scenarios we simulated, SSMs gave estimates with little bias when up to 87.5 % of repeated measures were missing. We use this method to quantify growth of Soay sheep, using data from a long-term mark-recapture study, and demonstrate that growth decreased with age, population density, weather conditions, and when individuals are reproductive. The method improves our ability to quantify how growth varies among individuals in response to their attributes and the environments they experience, with particular relevance for wild populations.

Data from: Individual behaviour mediates effects of warming on movement across a fragmented landscape

Global warming and habitat fragmentation impose dramatic and potentially interactive impacts on ecosystems. Warming induces shifts in species' distributions as they track temperature changes, but this can be hindered in fragmented landscapes. Corridors connecting habitat patches might ameliorate the combined effects of fragmentation and global warming. Using novel automated tracking methods, the movement of woodlice (Oniscus asellus) ranging in body size from 15·3 to 108·6 mg was quantified across a temperature range from 15 to 25 °C as they moved around an experimental fragmented landscape. We used confirmatory path analysis to test causal effects of temperature and body size on individual movement and corridor crossing rates between two habitat patches. Results showed that woodlice behaved differently in corridors than patches by moving, on average, faster and more often. This is congruent with natural systems where corridors generally provide lower quality habitat than patches. Although metabolic theory suggests positive scaling of movement with body temperature (up to a peak) and body size, we found that corridor crossing rate was (i) not directly affected by body size and (ii) negatively influenced by temperature, possibly due to its indirect effects via humidity. Our path model revealed that metabolic scaling could only explain temperature effects on maximum body velocity, but decision-based behaviour explained most variation in corridor crossing rates. This led to direct and indirect effects of temperature and size on individual movement between habitat patches. Our findings suggest that increasing mean global temperatures, coupled with increasing habitat fragmentation, could have synergistic negative impacts on populations through a combination of physiological and behavioural factors that mediate individual responses to temperature and fragmentation.

Data from: Individual size inequality links forest diversity and above-ground biomass

1. Despite the mounting evidence for positive diversity–productivity relationships found in controlled experiments, diversity effects on productivity in natural systems remain hotly debated. Understanding the multivariate links between diversity and productivity in natural systems, in particular natural forests that host the majority of terrestrial biodiversity and provide essential services for humanity, remains a critical challenge for ecologists. 2. We analyzed data from 448 plots of varying tree species diversity, stand ages, and local nutrient availability in Canada's boreal forest (52°30' – 55°24' N latitude and 102°36' – 108° W longitude). We used structural equation models to link multivariate relationships between above-ground biomass, tree species diversity, stand age, and soil nutrient availability. 3. Above-ground biomass increased with diversity indirectly via increasing tree size inequality, and increased with stand age and was higher on sites of medium soil nutrient regime directly as well as indirectly via increased tree size inequality. 4. Synthesis. Our results demonstrate positive diversity effects on above-ground biomass in natural forests of diverse forest ages and soil resource availability. Furthermore, we show that tree size inequality acts as a mechanism for the positive diversity effects on above-ground biomass, and as a mechanism in regulating above-ground biomass and species diversity simultaneously via interactions among individuals in natural forests.

Data from: Altered fronto-temporal functional connectivity in individuals at ultra-high-risk of developing psychosis

Background: The superior temporal gyrus (STG) is one of the key regions implicated in psychosis, given that abnormalities in this region are associated with an increased risk of conversion from an at-risk mental state to psychosis. However, inconsistent results regarding the functional connectivity strength of the STG have been reported, and the regional heterogeneous characteristics of the STG should be considered. Methods: To investigate the distinctive functional connection of each subregion in the STG, we parcellated the STG of each hemisphere into three regions: the planum temporale, Heschl's gyrus, and planum polare. Resting-state functional magnetic resonance imaging was obtained from 22 first-episode psychosis (FEP) patients, 41 individuals at ultra-high-risk for psychosis (UHR), and 47 demographically matched healthy controls. Results: Significant group differences (in seed-based connectivity) were demonstrated in the left planum temporale and from both the right and left Heschl's gyrus seeds. From the left planum temporale seed, the FEP and UHR groups exhibited increased connectivity to the bilateral dorsolateral prefrontal cortex. In contrast, the FEP and UHR groups demonstrated decreased connectivity from the bilateral Heschl's gyrus seeds to the dorsal anterior cingulate cortex. The enhanced connectivity between the left planum temporale and right dorsolateral prefrontal cortex was positively correlated with positive symptom severity in individuals at UHR (r = .34, p = .03). Conclusions: These findings corroborate the fronto-temporal connectivity disruption hypothesis in schizophrenia by providing evidence supporting the altered fronto-temporal intrinsic functional connection at earlier stages of psychosis. Our data indicate that subregion-specific aberrant fronto-temporal interactions exist in the STG at the early stage of psychosis, thus suggesting that these aberrancies are the neural underpinning of proneness to psychosis.

opencc-zeroDec 2017View details →

Data from: Context-dependency and anthropogenic effects on individual plant-frugivore networks

Anthropogenic activities, such as grazing by domestic animals, are considered drivers of environmental changes that may influence the structure of interaction networks. The study of individual-based networks allows testing how species-level interaction patterns emerge from the pooled interaction modes of individuals within populations. Exponential random graph models (ERGMs) examine the global structure of networks by allowing the inclusion of specific node (i.e. interacting partners) properties as explanatory covariates. Here we assessed the structure of individual plant-frugivore interaction networks and the ecological variables that influence the mode of interactions under different land-use (grazed vs ungrazed protected areas). We quantified the number of visits, the number of fruits removed per visit and the interaction strength of mammal frugivore species at each individual tree. Additionally we quantified ecological variables at the individual, microhabitat, neighborhood and habitat scales that generated interaction network structure under the different land uses. Individual plant-frugivore networks were significantly modular in both land uses but the number of modules was higher in the grazed areas. We found interaction networks for grazed and ungrazed lands were structured by phenotypic traits of individual trees, by the microhabitat beneath the tree canopy and were affected by habitat modifications of anthropogenic origin. The neighborhood surrounding each individual plant influenced plant-frugivore interactions only at the grazed-land trees. We conclude that anthropogenic land uses influence the topological patterns of plant-frugivore networks and the frugivore visitation to trees through modification of both habitat complexity and the ecological traits underlying interactions between individual plants and frugivore species.

opencc-zeroDec 2017View details →

Data from: Do larger individuals cope with resource fluctuations better? An artificial selection approach

Size determines the rate at which organisms acquire and use resources but it is unclear what size should be favoured under unpredictable resource regimes. Some theories claim smaller organisms can grow faster following a resource pulse, whereas others argue larger species can accumulate more resources and maintain growth for longer periods between resource pulses. Testing these theories has relied on interspecific comparisons, which tend to confound body size with other life-history traits. As a more direct approach, we used 280 generations of artificial selection to evolve a 10-fold difference in mean body size between small- and large-selected phytoplankton lineages of the green microalga Dunaliella tertiolecta, while controlling for biotic and abiotic variables. We then quantified how body size affected the ability of this species to grow at nutrient-replete conditions and following periods of nitrogen or phosphorous deprivation. Overall, smaller cells showed slower growth, lower storage capacity and poorer recovery from phosphorous depletion, as predicted by the "fasting endurance hypothesis". However, recovery from nitrogen limitation was independent of size – a finding unanticipated by current theories. Phytoplankton species are responsible for much of the global carbon fixation and projected trends of cell size decline could reduce primary productivity by lowering the ability of a cell to store resources.

opencc-zeroNov 2019View details →

Data from: Using quantum dots as pollen labels to track the fates of individual pollen grains

1. Despite a long history of significant advances in understanding natural selection and evolution, the field of plant reproductive biology has largely studied plant mating without directly tracking pollen movement due to a lack of suitable pollen-tracking methods. 2. Here, we develop and test a novel pollen-tracking technique using quantum dots as pollen-grain labels. Quantum dots are semiconductor nanocrystals that are so small, they behave like atoms. When exposed to UV light, they emit extremely bright light in both visible and infrared wavelengths We tested the suitability of non-toxic CuInSexS2-x/ZnS (core/shell) quantum dots with oleic acid ligands as pollen-grain labels.Using a micropipette, we dispensed quantum dots dissolved in hexane in minute volumes (0.15–0.5 µl) directly onto dehisced anthers of four different plant species from four different families [Wachendorfia paniculata (Haemodoraceae), Sparaxis villosa (Iridaceae), Arctotheca calendula (Asteraceae), Oxalis purpurea (Oxalidaceae)]. 3. After application, the hexane solvent evaporated immediately, leaving behind quantum dots that remained attached to pollen grains of the four different plant species even after agitation in a polar solvent. This suggests a lipophilic interaction between oleic-acid ligands on quantum dots, and pollenkitt surrounding pollen grains. We also showed that most pollen grains within anthers of the same four plant species were labelled with quantum dots after applying a volume of quantum-dot solution sufficient to cover an individual anther. To test whether quantum-dot pollen-labels influenced pollen transport, we conducted pollen transfer trials (one donor, ten sequential recipients) on S. villosa using captively-reared honey bees to ensure bees were free of external pollen prior to experiments. We found no difference in pollen transport to recipients from donor flowers with labelled or unlabelled pollen grains. 4. We demonstrate that quantum dots can be used as pollen labels allowing subsequent tracking of pollen fates. This method is relatively inexpensive (<$500 for equipment and ca. $0.02 per labelled anther thereafter) and can be simply and directly applied to anthers of most flowers in the lab and field. The ability to track pollen grain movement in situ, may help to address an historically neglected aspect of plant reproductive ecology and evolution.

opencc-zeroDec 2015View details →

Data from: Genetic diversity confers colony-level benefits due to individual immunity

Several costs and benefits arise as a consequence of eusociality and group-living. With increasing group size, spread of disease among nest-mates poses selective pressure on both individual immunity and group-level mechanisms of disease resistance (social immunity). Another factor known to influence colony-level expression of disease is intracolony genetic diversity, which in honeybees (Apis mellifera) is a direct function of the number of mates of the queen. Colonies headed by queens with higher mating numbers have less variable infections of decreased intensity, though the underlying mechanisms remain unclear. By pathogen-challenging larvae in vitro, we decoupled larval immune response from mechanisms of social immunity. Our results show that baseline immunity and degree of immune response do not vary with genetic diversity. However, intracolony variance in antimicrobial peptide production after pathogen challenge decreases with increasing genetic diversity. This reduction in variability of the larval immune response could drive the mitigation of disease observed in genetically diverse colonies.

Data from: Hybridization between two cryptic filamentous brown seaweeds along the shore: analysing pre- and post-zygotic barriers in populations of individuals with varying ploidy levels

We aimed to study the importance of hybridization between two cryptic species of the genus Ectocarpus, a group of filamentous algae with haploid-diploid life cycles that include the principal genetic model organism for the brown algae. In haploid-diploid species, the genetic structure of the two phases of the life cycle can be analysed separately in natural populations. Such life cycles provide a unique opportunity to estimate the frequency of hybrid genotypes in diploid sporophytes and meiotic recombinant genotypes in haploid gametophytes allowing the effects of reproductive barriers preventing fertilization or preventing meiosis to be untangle. The level of hybridization between E. siliculosus and E. crouaniorum was quantified along the European coast. Clonal cultures (568 diploid, 336 haploid) isolated from field samples were genotyped using cytoplasmic and nuclear markers to estimate the frequency of hybrid genotypes in diploids and recombinant haploids. We identified admixed individuals using microsatellite loci, classical assignment methods and a newly developed Bayesian method (XPloidAssignment), which allows the analysis of populations that exhibit variations in ploidy level. Over all populations, the level of hybridization was estimated at 8.7%. Hybrids were exclusively observed in sympatric populations. More than 98% of hybrids were diploids (40% of which showed signs of aneuploidy) with a high frequency of rare alleles. The near absence of haploid recombinant hybrids demonstrates that the reproductive barriers are mostly post-zygotic and suggests that abnormal chromosome segregation during meiosis following hybridisation of species with different genome sizes could be a major cause of interspecific incompatibility in this system.