Biology subjects

Merciere, A.

Publications and source records attributed to Merciere, A..

5 recordsLinked to original sources

bioRxiv2026

Host genetics structure prokaryotic and Symbiodiniaceae assemblages and their co-variation in sympatric fire coral species

Host-symbiont specificity and environmental filtering are important constraints on holobiont structure and resilience. Yet, resolving the extent of these constraints requires moving beyond species-level resolution, as intraspecific host genetic diversity can further modulate symbiotic associations in ways that remain poorly understood. Here, we resolved host genetic identity at the subspecies level to disentangle drivers of symbiotic plasticity in three sympatric fire coral species (Millepora cf. exaesa, M. tenera, and M. cf. platyphylla) across three adjacent but environmentally distinct habitats on Reunion Island (inner and outer reef flats, reef slope,). Symbiont assemblages were primarily structured by host species and genotypes, with a stronger genetic influence on Symbiodiniaceae than on prokaryotic assemblages, while habitat played a significant but secondary role. Symbiodiniaceae communities were dominated by Symbiodinium A16 and A3 radiations, showing marked specificity across species and habitats. All Millepora species consistently associated with the Spirochaetaceae, Kiloniellaceae and Desulfobacteraceae bacterial families across all habitats, suggesting evolutionarily maintained core associations. Both symbiotic compartments shifted across every habitat in host-specific ways, demonstrating microbiome plasticity to local environmental conditions. Integration of symbiont sequence data (ITS2 and 16S) further revealed genotype-specific co-variation patterns, with some genotypes maintaining stable and co-varying symbionts across clones, while others exhibited greater plasticity. Together, our results indicate that fire coral holobionts acquire symbionts from locally available pools based primarily on their specific genetic compatibility. This study sheds light on how fine-scale host identity and environment jointly shape unique host-symbiont associations contributing to the ecological success of these sympatric coral species.

ecology↗

bioRxiv2026

ASYNCHRONOUS TROPHIC NICHE SHIFTS AMONG INVERTEBRATE-FEEDING FISHES ACROSS A CORAL COVER GRADIENT

Unraveling the links between habitat structure, resource availability and the trophic niche is key to anticipate the effects of global change on ecosystems. On coral reefs, recurrent coral bleaching and increasing anthropogenic pressures have led to rapid losses of structural complexity, with implications for food web dynamics. Invertebrate-feeding fishes are one of the most diverse guilds, and benthic invertebrate communities may be reshuffled by coral loss. Ecological theory suggests that, within the same guild, species respond to habitat and resource change in synchrony, resulting in less partitioning and more functional redundancy at the community level. However, whether the trophic niches of invertivorous reef fishes shift across a gradient of reef condition remains undocumented. Here, we combine otolithometry, gut content metabarcoding, and stable isotope analysis to investigate the performance and trophic plasticity and synchrony of six invertivorous fishes from French Polynesia across various states of coral cover. Most species exhibited distinct niche breath in high versus low cover sites. However, the direction and magnitude of trophic niche differences between high and low coral cover sites varied among species, indicating asynchronous differences in trophic niche breadth across the guild. Our findings reveal that habitat loss may not result in one universal response, even within the same guild. Rather, reef invertivores may have asynchronous trophic differentiation, allowing the maintenance of interspecific coexistence even on degraded reefs. Together, these findings suggest that asynchronous trophic responses may contribute to the resilience of coral reef food webs and help sustain biodiversity under habitat degradation.

ecology↗

bioRxiv2026

Ubiquitous trophic niche partitioning drives species coexistence and biomass on coral reefs

Coral reefs support an extraordinary diversity and biomass of fishes. However, whether species coexist through fine-scale niche partitioning, and whether this impacts ecosystem functioning, remain unresolved. We combined DNA metabarcoding and stable isotope analysis to reconstruct a high-resolution food web and quantify the trophic niches of 2,060 reef fishes across 261 species. We observed extreme trophic partitioning: species pairs diverged by a median of 93% (DNA metabarcoding) and 86% (stable isotopes), consistently overlapping far less than expected by chance. Further, communities with greater trophic complementarity supported higher standing-stock biomass, particularly at high species richness. Our results confirm limiting similarity and trophic complementarity as the driving forces of coexistence and ecosystem functioning in the ocean's most diverse ecological community.

ecology↗

bioRxiv2023

Algal symbioses with fire corals demonstrate host genotype specificity and niche adaptation at subspecies resolution

Corals share an intimate relationship with photosynthetic dinoflagellates that contribute to the biology of the emerging metaorganism. While many coral-algal associations exhibit high host fidelity, the extent of this specificity under environmental change remains to be fully understood and is a prerequisite to forecasting the adaptive potential of this obligate symbiosis. Here, we disentangled the contribution of host genotype and environment on governing coral-algae associations by working at subspecies resolution. We used fine-scale genotyping of algal symbionts from 198 fire coral colonies (Millepora cf. platyphylla) that map to ten distinct sexually produced clonal host genotypes across three environmentally distinct reef habitats. Based on microalgal ITS2 genotyping, we show that algal-host specificity extends down to the Symbiodiniaceae subspecies level in a natural reef environment. Closely related Symbiodinium (A7)-dominated algal assemblages almost perfectly mapped to fire coral host genotype. Furthermore, identification of host genotype- and habitat-specific Symbiodinium alga suggest the presence of algal phenotypic diversity even at this taxonomic resolution (i.e., within Symbiodinium A7), which may aid environmental niche adaptation of the metaorganism. Our results suggest that the here-identified Millepora-Symbiodinium associations are co-evolved to match their prevailing environment. Thus, despite the presence of rarer host generalist Cladocopium algae, scope for environmentally induced modification of the cnidarian-algal association is likely constrained by host genotype.

evolutionary biology↗

bioRxiv2018

Dispersal limitations of early life stages and sibling aggregations in a broadcasting Millepora hydrocoral, as revealed by parentage analysis

Dispersal is a critical process for the persistence and productivity of marine populations. For many reef species, there is increasing evidence that local demography and self-recruitment have major consequences on their genetic diversity and adaptation to environmental change. Yet empirical data of dispersal patterns in reef-building species remain scarce. Here, we document the first genetic estimates of local dispersal and self-recruitment in a broadcasting reef-builder, the hydrocoral Millepora platyphylla. Using microsatellite markers, we gathered genotypic information from 3160 georeferenced colonies collected over 9000 m2 of reef in three adjacent habitats in Moorea, French Polynesia; the mid slope, upper slope and back reef. Our parentage analysis revealed a predominance of self-recruitment with 58% of sexual propagules produced locally. Sexual propagules often settled at less than 10 meters from their parents and dispersal events decrease with increasing geographic distance. Limited dispersal among adjacent habitats via cross-reef transport was also detected. Sibship analysis showed that both full and half siblings recruit together on the reef, resulting in sibling aggregations. The identification of local families revealed discrepancies between dispersal patterns of sexual and asexual propagules. Self-recruits are dispersed with along-reef currents and settled in alignment with the location of their parents, while the dispersal of asexual fragments is heavily influenced by wave-driven cross-reef currents. Our findings highlight the importance of self-recruitment together with clonality in stabilising population dynamics, as it can enhance local sustainability and resilience to disturbance, but also raise uncertainties on the widely accepted high dispersal ability of broadcasting reef species.

ecology↗