Contribution to the knowledge of the genus Boucheona (Oligochaeta, Hormogastridae) in France with a newly described species and a redescribed species.

Hormogastrid earthworms are found in the diversity hotspot of the Franco-Iberian domain, together with the better-known family Lumbricidae. Integrative systematics (the combination of morphological, molecular and ecological data) have increased our knowledge of the diversity and evolutionary history of these earthworms, highlighting unresolved taxonomic conflicts. One example of a species group in need of integrative taxonomic revision is the genus Boucheona in France. In this work, we analyzed their diversity using previously published data together with additional data obtained from recently sampled localities. Molecular data including DNA barcodes and additional markers enabled us to reconstruct Bayesian and time-calibrated phylogenies to discuss the evolutionary relationships among the different taxa, and to propose hypotheses regarding their biogeographical history. Based on our results, four species of Boucheona are present in Southern France, including two new taxa. Morphological distinctness and molecular phylogenetics results supported the status of four populations as the newly described Boucheona corbierensis sp. nov., as well as the status of "Hormogaster pretiosa var. nigra" as an independent species, redescribed as Boucheona tenebrae sp. nov. These results provide a new perspective of the importance of the genus Boucheona in southern France, as the possible evolutionary origin of a clade of giant anecic earthworms with unknown (but probably remarkable) impact on ecosystem functioning across their range.

Evaluating the Conservation Status of a North-Western Iberian Earthworm (Compostelandrilus cyaneus) with Insight into Its Genetic Diversity and Ecological Preferences.

In spite of the high conservation value of soil fauna, the evaluation of their conservation status has usually been neglected. This is more evident for earthworms, one of the most important ecosystem service providers in temperate habitats but rarely the subject of conservation research. These studies have not been developed in Western Europe, which comprises high diversity and several early-branching, relic genera. One potentially menaced representative of this fauna is Compostelandrilus cyaneus; this risk can be assessed by implementing potential distribution modeling and genetic diversity monitoring to their known populations. Genetic barcoding was performed in representatives of four populations (three of them newly sampled) in order to estimate genetic diversity and population genetics parameters. Ensemble species distribution models were built by combining several algorithms and using the five more relevant bioclimatic and soil variables as predictors. A large amount of genetic diversity was found in a small area of less than 20 km2, with populations located in less managed, better-preserved habitats showing higher genetic variability than populations isolated from natural habitats and surrounded by anthropic habitats. Potential distribution appears to be strongly restricted at a regional scale, and suitable habitats within the extent of occurrence appear fragmented and relatively limited. In addition, the main variables determining the ecological niche of C. cyaneus suggests a vulnerability to climate change and increasing soil compaction. Based on this knowledge, this species was assessed as Critically Endangered following the IUCN Red List of Threatened Species criteria, and some potential conservation actions are suggested.

How to thrive in unstable environments: Gene expression profile of a riparian earthworm under abiotic stress.

Nowadays, extreme weather events caused by climate change are becoming more frequent. This leads to the occurrence of extreme habitats to which species must adapt. This challenge becomes crucial for species living in unstable environments, such as the riparian earthworm Eiseniella tetraedra. Its cosmopolitan distribution exposes it to various environmental changes, such as freezing in subarctic regions or droughts in Mediterranean areas. Transcriptional changes under cold and desiccation conditions could therefore shed light on the adaptive mechanisms of this species. An experiment was performed for each condition. In the cold experiment, the temperature was lowered to -14 °C ± 2 °C (compared to 8 °C for control samples), and in the desiccation treatment, humidity was lowered from 60% to 15%. Comparisons of gene expression levels between earthworms under freezing conditions and control earthworms revealed a total of 84 differentially expressed genes and comparisons between the desiccation experiment and the control yielded 163 differentially expressed genes. However, no common responses were found between the two treatments. The results suggest that E. tetraedra can acclimate to low temperatures due to the upregulation of genes involved in glucose accumulation. However, downregulation of the respiratory chain suggests that this earthworm does not tolerate freezing conditions. Under desiccation conditions, genes involved in cell protection from apoptosis and DNA repair were upregulated. In contrast, lipid metabolism was downregulated, presumably to conserve resources by reducing the rate at which they are consumed.

Systematic revision of Gatesona (Crassiclitellata, Lumbricidae), an endemic earthworm genus from the Massif Central (France).

The Massif Central in France could potentially harbor numerous ancient endemic lineages owing to its long history of continuous geological stability. Several endemic earthworm species inhabit the area, with Allolobophora (Gatesona) chaetophora, Helodrilus (Acystodrilus) and Avelona ligra showing hints of a common evolutionary origin. However, the phylogenetic relationships and taxonomic status of the species remain to be studied through integrative molecular and morphological methods. To this end, eight species including most of the known species and subspecies of All. (Gatesona), Helodrilus (Acystodrilus) musicus, and Avelona ligra were sequenced for a set of five molecular markers. The species were grouped on the basis of the molecular findings in a phylogenetic framework. All. (Gatesona) was included within the same clade as Helodrilus (Acystodrilus) and Avelona, separated from Allolobophora sensu stricto, supporting its status as a good genus. Branch lengths and average pairwise genetic distances suggested the subspecies of All. (Gatesona) chaetophora examined should be considered species-level taxa. Thus, a generic diagnosis for Gatesona stat. nov. is provided, along with redescriptions of Gatesona chaetophora comb. nov., Gatesona rutena comb. nov. stat. nov., Gatesona lablacherensis comb. nov. stat. nov. and Gatesona serninensis comb. nov. stat. nov. The study findings highlight the need for further sampling of earthworm diversity in the Massif Central (and Southern France), in addition to an increased focus on the Eastern European species of Helodrilus.

Insights into the diversity of Hormogastridae (Annelida, Oligochaeta) with descriptions of six new species.

The earthworm family Hormogastridae is a relatively diverse group in the Western Mediterranean basin. Since 1887, around thirty species have been described and assigned to four genera. However, from 2010 on, molecular, ecological and morphological studies have questioned the validity of those genera. Meanwhile, new species were discovered and assigned to them, pending a formal systematic revision; such a revision has been performed recently by integrating all the existing sources of information. The resulting classification consists of nine genera, including four newly erected ones. This revised systematic background is used in the current work as a base for the description of six new hormogastrid species: Diazcosinia sacrarium Marchán, Fernández, Díaz Cosín Novo, sp. nov., Boucheona martae Marchán, Fernández Díaz Cosín, sp. nov., Boucheona rosae Marchán, Díaz Cosín Novo, sp. nov., Norana emiliae Marchán, Fernández, Díaz Cosín Novo, sp. nov., Norana xylocerasi Marchán, Fernández, Díaz Cosín Novo, sp. nov., and Norana beatrizae Marchán, Fernández, Díaz Cosín Novo, sp. nov. Norana is a new replacement name for the preoccupied Nora Marchán, Fernández, Díaz Cosín Novo, 2018. Likewise, Xanina is proposed to replace the preoccupied Xana Díaz Cosín, Briones Trigo, 1989. We provide an overview of the currently known diversity of the different genera, and we further propose common names in several languages for some of the species of Hormogastridae.

Pinpointing cryptic borders: Fine-scale phylogeography and genetic landscape analysis of the Hormogaster elisae complex (Oligochaeta, Hormogastridae).

Spatial and temporal aspects of the evolution of cryptic species complexes have received less attention than species delimitation within them. The phylogeography of the cryptic complex Hormogaster elisae (Oligochaeta, Hormogastridae) lacks knowledge on several aspects, including the small-scale distribution of its lineages or the palaeogeographic context of their diversification. To shed light on these topics, a dense specimen collection was performed in the center of the Iberian Peninsula - resulting in 28 new H. elisae collecting points, some of them as close as 760m from each other- for a higher resolution of the distribution of the cryptic lineages and the relationships between the populations. Seven molecular regions were amplified: mitochondrial subunit 1 of cytochrome c oxidase (COI), 16S rRNA and tRNA Leu, Ala, and Ser (16S t-RNAs), one nuclear ribosomal gene (a fragment of 28S rRNA) and one nuclear protein-encoding gene (histone H3) in order to infer their phylogenetic relationships. Different representation methods of the pairwise divergence in the cytochrome oxidase I sequence (heatmap and genetic landscape graphs) were used to visualize the genetic structure of H. elisae. A nested approach sensu Mairal et al. (2015) (connecting the evolutionary rates of two datasets of different taxonomic coverage) was used to obtain one approximation to a time-calibrated phylogenetic tree based on external Clitellata fossils and a wide molecular dataset. Our results indicate that limited active dispersal ability and ecological or biotic barriers could explain the isolation of the different cryptic lineages, which never co-occur. Rare events of long distance dispersal through hydrochory appear as one of the possible causes of range expansion.

Phylogenomic analyses of a Mediterranean earthworm family (Annelida: Hormogastridae).

Earthworm taxonomy and evolutionary biology remain a challenge because of their scarce distinct morphological characters of taxonomic value, the morphological convergence by adaptation to the uniformity of the soil where they inhabit, and their high plasticity when challenged with stressful or new environmental conditions. Here we present a phylogenomic study of the family Hormogastridae, representing also the first piece of work of this type within earthworms. We included seven transcriptomes of the group representing the main lineages as previously-described, analysed in a final matrix that includes twelve earthworms and eleven outgroups. While there is a high degree of gene conflict in the generated trees that obscure some of the internal relationships, the origin of the family is well resolved: the hormogastrid Hemigastrodrilus appears as the most ancestral group, followed by the ailoscolecid Ailoscolex, therefore rejecting the validity of the family Ailoscolecidae. Our results place the origin of hormogastrids in Southern France, as previously hypothesised.

Diversification patterns in cosmopolitan earthworms: similar mode but different tempo.

Comparative phylogeography of widespread species that span the same geographic areas can elucidate the influence of historical events on current patterns of biodiversity, identify patterns of co-vicariance, and therefore aid the understanding of general evolutionary processes. Soil-dwelling animals present characteristics that make them suitable for testing the effect of the palaeogeographical events on their distribution and diversification, such as their low vagility and population structure. In this study, we shed light on the spatial lineage diversification and cladogenesis of two widely-distributed cosmopolitan and invasive earthworms (Aporrectodea rosea and A. trapezoides) in their putative ancestral area of origin, the Western Palearctic, and a few populations in North America. Molecular analyses were conducted on mitochondrial and nuclear markers from 220 (A. rosea) and 198 (A. trapezoides) individuals collected in 56 and 57 localities, respectively. We compared the lineage diversification pattern, genetic variability and cladogenesis in both species. Our findings showed that both species underwent a similar diversification from the Western Mediterranean plates to (i) Northern Europe and (ii) the Iberian Peninsula, establishing their two main lineages. Their diversification was in concordance with the main palaeogeographical events in the Iberian Peninsula and Western Mediterranean, followed by a later colonization of North America from individuals derived exclusively from the Eurosiberian lineage. Their diversification occurred at different times, with the diversification of A. rosea being potentially more ancient. Cladogenesis in both species seems to have been modelled only by the Mediterranean plate shifts, ignoring historical climatic oscillations such as the Messinian salinity crisis. Their high genetic variability, strong population structure, lack of gene flow and stepping-stone-like cladogenesis suggest the existence of different cryptic lineages. Our results may indicate a recurrent event in invasive earthworms within their ancestral distribution areas in the Western Palearctic.