Institut des Sciences de l'Evolution de Montpellier

Recent studies of marine sediments adjacent to the Parnaíba Basin, in northeastern Brazil, have been used for continental paleoenvironmental reconstructions of the glacial epoch. As the largest basin entirely located within the Northeast region, it spans a critical transition zone between the Cerrado and Caatinga biomes. To characterize the modern pollen rain within this ecotone, we analyzed 41 surface sediment samples and compared the pollen assemblages with published botanical surveys. First, pollen assemblages were characterized using three diagrams: vegetation type, geographical location, and depositional environment. The basin presents a unique mixed signature combining Cerrado elements (e.g., Astronium- type , Tapirira- type) with Caatinga taxa ( Mimosa -type). Spatially, the Upper and Lower sectors exhibited high heterogeneity, contrasting with arboreal consistency in the Mid-Parnaíba. Distinct hydrological markers also emerged: Cyperaceae was strictly linked to lacustrine environments, whereas Mauritia indicated permanently flooded soils within gallery forests and palm swamps. Landscape analysis subsequently confirmed that Arboreal Pollen (AP) frequencies accurately track woody cover, while Borreria -type and Poaceae serve as robust proxies for landscape openness. Multivariate analyses refined these patterns: Cluster Analysis identified six specific floristic groups ( Tapirira-Astronium , mixed, Melastomataceae-Combretaceae, Borreria-Aspidosperma , mixed woody-herbaceous, and Mimosa- type assemblages), while Redundancy Analysis (RDA) identified Mean Annual Temperature (MAT) as a significant environmental driver within the explained variance. Critically, comparison with paleoecological records reveals a sharp floristic shift from cooler, humid glacial periods to the current warmer climate, marked by the scarcity of montane taxa. This study establishes a crucial baseline for interpreting fossil records and understanding ecosystem dynamics in this transition zone. • Modern pollen rain reflects vegetation patterns along the Parnaíba River gradient. • Cerrado, Caatinga, and transitional zones show distinct pollen assemblages. • Analyses reveal floristic structure influenced by edaphoclimatic gradients. • Pollen assemblages are more related to local conditions than spatial location. • Anthropization and distinct grasslands strongly influence pollen assemblages.

Understanding the extent to which the species composition of a community can be explained by pairwise interactions is a long-standing question in ecology. Recent observations have revealed that stable microbial communities contain a high number of species that cannot coexist in pairs, providing new empirical elements to explore this question from a fresh perspective. Here, using species-rich models of ecological communities with pairwise interactions alone, we show that emergent coexistence arises naturally in an extent that is consistent with empirical observations. Interestingly, this phenomenon does not require additional mechanisms like intransitive or higher-order interactions; rather, coexistence can arise from the dense networks of indirect effects. As diversity increases, we show that indirect effects can become so intricate that pairwise interactions decouple from community composition, revealing a fundamental limit to reductionist explanations of coexistence. Our findings provide the theoretical foundations to understand how simple pairwise interactions can lead to emergent coexistence patterns in ecological communities.

This study investigates the modern distribution, diversity, composition, and extreme preservation challenges of shallow-water benthic foraminifera along the nearshore marine mud flats of French Guiana. This coastal environment is overwhelmingly controlled by the vast, high-flux discharge of sediment and organic matter (OM) from the Amazon River system, creating a highly stressed habitat for calcifying organisms. Quantitative analysis reveals a severely constrained and moderately diverse fauna. The community structure is heavily skewed towards extremely small species (e.g., Ammonia, Elphidium), and a few robust calcareous taxa (e.g., Eponides). The dominance of stress-tolerant genera is consistent with a highly turbid, high-organic, and potentially low-oxygen environment.The primary finding is the exceptionally poor preservation of calcareous foraminiferal shells, acting as a powerful taphonomic filter. This dissolution is a direct consequence of the extremely high rates of OM decomposition within the muddy sediments. Microbial breakdown (remineralization) of the abundant Amazon-derived OM rapidly consumes oxygen and generates large quantities of carbon dioxide (CO2). This CO2 increases the concentration of carbonic acid (H2CO3) in the sediment pore waters, leading to a significant pH decrease. The resulting undersaturation (Ω < 1) with respect to CaCO3 minerals (calcite and aragonite) triggers the rapid chemical dissolution of the foraminiferal tests. The poor buffering capacity of the fine-grained, terrigenous muds exacerbates this effect. In addition to the completely preserved foraminifera, almost all samples contain an impressive number of hardened, brown molds (ˈSteinkerneˈ) that capture the original shape of the foraminifera's chamber arrangement, as well as the space once occupied by the living cell. Here, the original calcium carbonate shell is dissolved by acidic waters over time. What remains is a three-dimensional "negative" of the shell's interior.The sedimentary environment of the French Guiana mud flats represents an end-member environment where near-complete post-mortem dissolution of the calcareous fraction severely biases the fossil record and acts as an effective taphonomic filter. The observed foraminiferal census, dominated by Ammonia, Elphidium and a very few robust taxa, therefore represents a highly-biased reflection of the original living community. This has significant implications for paleoenvironmental reconstructions based on foraminifera in similar high-organic-flux, tropical deltaic systems, highlighting the need to account for dissolution-driven loss of the calcareous fraction.

Why populations persist in active volcanic zones poses a fundamental challenge to risk perception models. We propose that perceptual advantages wherein tangible and intangible benefits filtered through local worldviews underpin this resilience. Through a thematic analysis of an open-ended question/answer study of communities in Mount Semeru, Indonesia, we identify six core frameworks of perceptual advantages. Analysis of Multiple Response Categorical Variable (MRCV) reveals that residents of high-risk zones cognitively amplify bio-cultural and livelihood benefits, showing significantly higher odds of emphasizing BIRTH/FAMILY (lineage/kin ties, birthright, and deep social networks that create an intergenerational connection to the land) and ECONOMIC (livelihood opportunities, including agriculture and volcano-driven tourism) advantages, while safe-zone residents prioritize ambient CLIMATE-related benefits (a preferred quality of life attributed to the region’s cool, fresh air and superior air quality). Crucially, the influence of gender is context-dependent, as significant disparities in perception vanish within the high-risk zone. In this environment, the shared experience of chronic volcanic threat supersedes gender distinction to foster a "community of fate". Within this collective, a shared risk-benefit calculus and a unified identity override individual perspectives. These findings demonstrate that persistence in hazardous environments reflects an active cognitive recalibration of risk and benefit, necessitating disaster policies that integrate these perceptual realities.

Conodont elements are components of the feeding apparatus of extinct early jawless vertebrates named conodonts. The shape of these tooth-like elements has been explored through different approaches to test whether their morphological changes through time were related to trophic ecology, environmental pressure or ontogeny. Several morphometric analyses have previously been performed on the 2D outline of P1 elements belonging to the conodont genus Palmatolepis from the Upper Devonian (381–360 Ma) of the Montagne Noire (France). These analyses showed a general decrease in breadth of P1 elements, which was interpreted as a long-term response to a change in available food resources and/or a possible change in the trophic position of this conodont. In contrast, analyses of calcium stable isotopes ratio have shown that no changes occurred in δ44/42Ca through time, suggesting that Palmatolepis did not change its trophic position despite the mentioned change in element morphology. To further investigate changes in Palmatolepis morphology through time, 3D topographic analyses were performed on Palmatolepis P1 elements spanning the Famennian. The results of this analysis highlight the first evidence of a sharpness increase over time in this genus. This covariation between the platform reduction and the increase in blade sharpness through time suggests morphofunctional changes allowing a more efficient processing of their prey. Moreover, allometric changes in Palmatolepis gracilis, the latest representative of the Palmatolepis genus, bring new insights into the palaeoecology of this species.

Abstract Understanding how reproductive isolation (RI) evolves in the context of gene flow is central to explaining how new species arise. Theory predicts that the accumulation of barrier loci is shaped by the interplay between divergent selection, recombination, and genomic architecture, yet empirical tests spanning multiple stages of divergence at the intraspecific level remain rare. The pea aphid complex, comprising multiple sympatric biotypes specialised on different legume hosts and spanning a continuum of RI, provides an exceptional opportunity to examine how ecological adaptation drives reproductive isolation under ongoing gene flow. Using whole-genome sequencing data from 13 sympatric European biotypes, we constructed a dense, reference-genome anchored picture of the divergence continuum that controls for genetic background and recombination landscape. Joint patterns of genetic differentiation, absolute divergence and genetic diversity, as well as recombination and introgression rates, reveal a consistent signature of divergence with gene flow and allow robust identification of barrier loci. Across the divergence gradient, RI is highly polygenic, yet barrier loci are clustered and enriched in low-recombination regions and large chromosomal rearrangements, which promote strong linkage disequilibrium and coupling among barrier effects. While genome-wide F ST and the number of barrier loci gradually accumulate as divergence increases, the dynamics of differentiation within barrier loci show stepwise increases consistent with theoretical “tipping points” in the accumulation of RI. Barrier loci are enriched in salivary effector, detoxification and chemosensory genes, highlighting their central role in host plant specialisation and RI. These candidate genes are dynamically recruited at different stages of divergence, and some of them are shared among independent biotype comparisons, suggesting generic functional determinants of host plant specialisation and reproductive isolation acquired via parallel evolution or introgression. Our study provides a comprehensive view of the genomic architecture and evolutionary dynamics underlying speciation with gene flow, illustrating how tightly linked, polygenic architectures can facilitate adaptation and diversification in natural populations.

Spreading epidemics can foster the rapid emergence of novel parasite variants. Similar to range expansions, parasites at the front of an epidemic wave may evolve traits facilitating their spatial spread. Typically, higher transmissibility and virulence are expected to evolve at the epidemic front, but predictions change if virulence reduces dispersal of infected hosts. We investigated the feedbacks between epidemiology and evolution in interconnected microcosms of the ciliate Paramecium caudatum and its bacterial parasite Holospora undulata. First, two long-term treatments mimicked the moving front of epidemic waves, with and without the natural dispersal of infected hosts. Phenotypic trait assays revealed an eco-to-evo feedback: wave-front parasites (i.e., travelling with infected hosts) were less virulent and interfered less with host dispersal, but also showed higher infectivity, compared to parasites from the control treatment. Whole-genome resequencing corroborated phenotypic divergence, but the genetic targets of selection remain unknown. Second, measurement of the spread of evolved parasites in linear landscapes demonstrated an evo-to-eco feedback: wave-front parasites produced stronger infection outbreaks and faster spreading epidemic waves than did evolution-control parasites. A simulation model assessed the relative importance of the different parasite traits in determining infectious spread over a broad parameter range. It suggests that, if dispersal is generally low, higher infectivity alone can produce the observed differences in epidemic spread speed. Our study illustrates how the need to travel with the host shapes eco-evolutionary feedbacks at parasite invasion fronts, and it highlights the importance of considering concomitant evolutionary change when predicting epidemic speed.