Biology subjects

Pontier, O.

Publications and source records attributed to Pontier, O..

3 recordsLinked to original sources

bioRxiv2025

Single-cell phylogenomics identifies major groups of marine eugregarine parasites (Apicomplexa)

Gregarines are a large group of apicomplexan parasites that infect a wide range of invertebrate hosts, including diverse and speciose groups, such as annelids and arthropods. Marine eugregarines represent the majority of gregarine diversity, but remain poorly understood, especially their deepest phylogenetic relationships. To expand knowledge of marine eugregarine diversity and their evolutionary history, we surveyed marine invertebrates, with a particular focus on annelids, across multiple locations in British Columbia, Canada. From this effort, we obtained high-quality, single-cell transcriptomes from 20 different species of marine eugregarines, including nine previously described species and 11 novel ones, which more than doubles the amount of phylogenomic data for the group. These data, which comprehensively represent the known diversity of marine gregarines in annelid hosts, allowed us to construct an expanded phylogenetic tree based on small subunit ribosomal DNA sequences and a phylogenomic tree inferred from 142 proteins and 44,802 amino acid sequences. Our analyses identified five "superfamily-level" groups of marine eugregarines infecting annelid hosts: The Ancoroidea, Lecudinoidea, Loxomorphoidea n. superfam., Paralecudinoidea n. superfam., and Belladinoidea n. superfam., with the latter three newly established in this study. These findings contribute to ongoing efforts to build a robust molecular phylogenetic framework for gregarine diversity and refine gregarine classification, supporting the recognition of 11 eugregarine superfamilies. However, some of the deepest evolutionary relationships among these superfamilies remain unresolved, highlighting the need for expanded taxon sampling to better capture the true diversity of eugregarine parasites.

microbiology↗

bioRxiv2025

Consumer resilience suppresses the recovery of overgrazed ecosystems

O_LIMany heterotroph species perish when faced with severe food limitation, others can persist, adapt, and thrive. Sea urchins are emblematic of this paradox: they can overgraze kelp forests to form barren habitats, but can then survive for decades in these nutritionally depauperate seascapes. Understanding the mechanisms enabling persistence under starvation, and rapid recovery when food returns, provides insight into how consumer resilience shapes ecosystem dynamics. C_LIO_LIWe quantified how food abundance, quality, deprivation, and reintroduction influence bioenergetic performance in the red sea urchin (Mesocentrotus franciscanus), integrating field observations of kelp forest and barren populations with a controlled feeding experiment. We measured respiration, feeding rates, gonadal growth, and fatty acid biomarkers to test how habitat history and diet jointly govern metabolic plasticity and nutrient assimilation. C_LIO_LIResting metabolic rates (RMR) were nearly twofold higher in kelp forest urchins than barrens conspecifics, yet feeding rates were equivalent across habitats, indicating that metabolic depression does not constrain food intake. Reciprocal shifts emerged in the experiment: starvation reduced RMR and lipid reserves in kelp forest urchins, while feeding elevated both traits in barrens urchins to levels comparable with kelp forest conspecifics. These results demonstrate rapid physiological compensation in response to both food deprivation and reintroduction. C_LIO_LIDiet quality strongly modulated performance. Urchins fed nutritionally poor monospecific diets consumed more biomass and calories than those on diverse, polyunsaturated fatty acid (PUFA)-rich diets, but did so with markedly lower efficiency of conversion to gonadal tissue. Fatty acid assimilation revealed that starvation elevated bacterial and biofilm biomarkers in tissues, whereas algal diets enriched essential PUFA profiles, particularly when diets were diverse. These results highlight that both quantity and quality of food influence consumer recovery trajectories, with nutritional geometry shaping efficiency of energy and nutrient use. C_LIO_LITogether, our findings show that M. franciscanus exhibits pronounced metabolic resilience, allowing persistence in barren habitats and rapid reactivation of grazing and reproduction when food becomes available. This work links nutritional ecology to ecosystem feedbacks by showing how compensatory feeding and metabolic flexibility enable consumers to maintain pressure on primary producers, thereby influencing the stability, hysteresis, and recovery of degraded ecosystems. C_LI

ecology↗

bioRxiv2024

A blueprint for national assessments of the blue carbon capacity of kelp forests applied to Canadas coastline

Kelp forests offer substantial carbon fixation, with the potential to contribute to natural climate solutions (NCS). However, to be included in national NCS inventories, governments must first quantify the kelp-derived carbon stocks and fluxes leading to carbon sequestration. Here, we present a blueprint for assessing the national carbon sequestration capacity of kelp forests in which data synthesis and Bayesian hierarchical modelling enable estimates of kelp forest carbon production, storage, and export capacity from limited data. Applying this blueprint to Canadas extensive coastline, we find kelp forests store an estimated 1.4 Tg C in short-term biomass and produce 3.1 Tg C yr-1 with modest carbon fluxes to the deep ocean. Arctic kelps had the highest carbon stocks and production capacity, while Pacific kelps had greater carbon fluxes overall due to their higher productivity and export rates. Our transparent, reproducible blueprint represents an important step towards accurate carbon accounting for kelp forests.

ecology↗