Ecosystèmes, Biodiversité, Evolution

Abstract Many simultaneous hermaphrodites use selfing for reproductive assurance only when outcrossing opportunities are limited, owing to inbreeding depression in selfed progeny. However, scenarios that enforce substantial selfing (such as during recolonisation) can rapidly select for a high selfing propensity, a shift in mating system that is expected to eliminate both inbreeding depression and the delayed reproductive onset under selfing that is typically associated with it. We tested these predictions in the flatworm Macrostomum hystrix , using a line derived from an outcrossing population that had been subjected to enforced selfing for multiple generations followed by several years of relaxed selection. As predicted, isolated individual forced to self and individuals with constant partner access (i.e. outcrossing opportunities) did not differ in reproductive onset nor in inbreeding depression estimated through offspring survival. However, a third treatment group that provided intermittent partner access (to allow outcrossing but minimise potential competition effects) showed a different pattern: no inbreeding depression in offspring but a substantially accelerated reproductive onset. Whilst our results thus support the effective purging of inbreeding depression and increased selfing propensity under enforced selfing, we suggest that cues of an unstable social or physical environment nevertheless exert a major influence on reproductive timing.

Across the planet, angiosperm diversification has been shaped by palaeoclimates and biotic interactions, particularly with pollinators, leaving signatures in the angiosperm age structure. Regional floras represent biased samples of this global diversification shaped by dispersal, extinction and environmental filtering, yet it remains unclear whether floristic age structure reflects pollination strategies or their interaction with palaeoclimates. We constructed a 97% resolved phylogeny of all 1,178 angiosperms in the Netherlands and characterized age structure of eight pollination syndromes by standardized epoch-specific lineage diversities (stELDs) quantifying the proportional increase in lineages per 10-Myr interval. Overall, stELDs peaked under the coldest intervals and were lowest for intermediate-temperature intervals (geological age alone had no effect). This age structure was strongest in wind-pollinated species. Resolving insect pollination into six syndromes revealed strong heterogeneity: lepidoptera-pollination was most strongly associated with warmest palaeotemperatures, bumblebee and wasp-pollination under intermediate temperatures, and fly, lepidoptera and beetle-pollination under coldest temperatures. Paleotemperature signatures correlated positively with contemporary seasonal flowering temperatures, indicating conserved thermal niches across ecological and macroevolutionary timescales. We suggest that temperate floras reflect both recent cold-house diversification of wind- and certain insect-pollinated lineages and earlier warm-house radiations of lineages pollinated by older insect clades. Phylogenetic age structures permit detecting such patterns.

This study describes morphologically and molecularly a new species, Gammarus ariegiensis sp. nov. from the Pyrenean Mountains in southern France. The new species is characterized by the lack of calceoli on the second antenna, the presence of long setae on anterior margin of merus and carpus of pereopod 5–7, endopodite of uropod 3 between 0.4 and 0.5 times the exopodite. A full description of the new species and information about its distribution is given in this paper together with molecular data (COI and 28S genes) corroborating the morphological delimitation of the new species.

Abstract In the sub-Antarctic, where food webs are relatively simple and species richness is low, the introduction of predators can be devastating, as native prey may lack sufficient defences and native predators may be less competitive. Merizodus soledadinus Guerin-Meneville, 1930 is a predatory carabid beetle that has been introduced to two sub-Antarctic islands. This ground beetle is known to threaten native insect populations; however, the full extent of its impacts in its introduced ranges is unknown because of its poorly described dietary breadth. As invasive predator impacts depend strongly on their dietary preferences and behaviour, we performed experiments to study the responses of this beetle to olfactory cues and sub-Antarctic diet. We studied the responses of M. soledadinus to olfactory cues to understand whether this species relies on odour to locate prey or different habitats, but we found no significantly different responses to different stimuli. We found that M. soledadinus attacked and consumed mostly juvenile forms of invertebrates from diverse phylogenetic lineages, indicating that many native species may be at risk from this predator and that attack by multiple individuals increased their success with hunting difficult prey. Our findings reveal that M. soledadinus has a wide dietary breadth, which has probably contributed to its successful establishment in multiple novel communities. We discuss the implications of our results for the ecology and conservation of terrestrial macroinvertebrate communities in its colonized range, where limited options exist to prevent further spread of this invader.

The study of phylogeography has transitioned from mitochondrial haplotypes to genome-wide analyses, borrowing from population genomics methods along the way. Whole-genome sequencing allows the study of both mitochondrial and nuclear DNA and provides the density of markers to investigate recombination along the genome. This level of resolution could unravel complex histories of admixture between lineages, which are commonly observed in species evolving in recently deglaciated habitats. In this study, we sequenced 1120 Arctic Char genomes from 33 populations across Canada and Greenland to characterise patterns of genetic variation and diversity, and how they are shaped by hybridisation between the Arctic and Atlantic glacial lineages. Mitochondrial genomes across the study area were predominantly of Arctic origin, except in Greenland, where we observed some Atlantic descent. Through admixture analyses and demographic inferences on nuclear markers, we identified that all Canadian populations under the 66th parallel showed introgression from the Atlantic lineage, leading to higher genetic diversity. By scanning the genome using local principal component analyses, we identified putative large low-recombining haploblocks as local ancestry tracts from either lineage. Since haplotypes might retain different signatures of postglacial histories by sheltering sequences from recombination, we attempted to infer origins of recolonisation using whole genomes vs. ancestry tracts for the Arctic lineage. Despite limitations, we unveiled clues suggesting a complex postglacial history in Arctic Char. Overall, our study demonstrates that, even at low depth, making the most of whole-genome sequencing by analysing several genomic compartments provides a versatile and powerful way to address phylogeographic dynamics.

Veterinary antibiotics, widely used in agriculture, are emerging contaminants with significant implications for water quality and ecosystem health. This study investigates the presence and heritage of antibiotics and other pollutants in groundwater within the Naizin watershed (~5 km²) in Brittany (western France), a region marked by intensive agricultural activity. Field measurements revealed the occurrence of veterinary antibiotics in surface water and groundwater, alongside other pollutants. Additionally, CFCs and SF6 gas tracers provided groundwater age estimates ranging from 20 to 30 years, suggesting potential long-term heritage effects. A particle-tracking approach using HydroModPy, a calibrated MODFLOW-coupled groundwater flow model, was implemented to complement this study. Hydraulic conductivity and porosity, determined from hydrological characterization and calibration of the watershed, were incorporated to estimate residence times. The simulated groundwater residence times closely matched those inferred from tracer data, strengthening the linkage between field measurements and model outputs. These results highlight the persistence of pollutants such as antibiotics and underscore the need for integrated field and modelling approaches to assess contaminant load and transport  in agricultural catchments. This study offers critical insights into the interactions between anthropogenic activities, pollutant dynamics, and groundwater quality, providing a foundation for improved water resource management and pollution mitigation strategies.