Biology subjects

Marchan, D. F.

Publications and source records attributed to Marchan, D. F..

5 recordsLinked to original sources

bioRxiv2024

A can of worms: estimating the global number of earthworm species

Estimating the overall species number for a given taxon is a central issue in ecology and conservation biology. This is especially topical for soil organisms, which comprise most known species but whose taxonomy remains largely understudied. Here, we estimated the global number of earthworm species based on the Joppa approach, which models taxonomic effort over time to estimate the total number of known and as yet unknown species in a given taxa. Our Bayesian estimation of the Joppa model suggests a global diversity of the order of 30,000 species, suggesting that the 5,679 earthworm taxa already described only represent around 20% of the actual global species diversity. However, the uncertainty around this estimate is considerable due to severe undersampling and as the model cannot unambiguously decide whether we are describing few species because of a small pool of as yet unknown species, or because of a lack of taxonomic efficiency. Considering the current rate of new species description, we calculate that it would take at least 120 years to describe all the earthworm species existing on Earth, and we discuss thedifferent strategies that should be developed to facilitate and accelerate the discovery and naming of species new to science.

ecology↗

bioRxiv2024

The nunatak and tabula rasa hypotheses may be compatible: the European phylogeography of a riparian earthworm.

The tabula rasa hypothesis of postglacial immigration supports the notion that species now found in northern European areas must have been recently recolonized from historical refugia. Until the 1960s, however, there was almost complete consensus that disjunctions and endemism in the North Atlantic region of Europe could not be explained without in situ survival during glacial periods (the nunatak hypothesis). Although some earthworms can survive in permafrost and tolerate cold conditions, it is generally believed that most earthworms were eradicated from northern latitudes during the Last Glacial Maximum. To test which hypothesis explains the phylogeography of the riparian and parthenogenetic earthworm Eiseniella tetraedra, we collected 1,640 specimens from 19 different countries in Europe. We examined three molecular markers (COI, 16S and 28S) and their morphology. Eleven lineages were found, nested in five clades. Clade I was more prevalent in cold biogeographical regions such as the continental, the Atlantic or even the Arctic, while clade II was prevalent in Mediterranean regions. We investigated their potential niches through Species Distribution Models, which agreed with the distribution trends. The presence of restricted clades in the Iberian and Scandinavian peninsulas, as well as in Eastern Europe, suggests that these three regions served as refugia during the Last Glacial Maximum. Thus, both hypotheses were necessary to explain the actual distribution of this shore-dwelling earthworm.

zoology↗

bioRxiv2022

Environmental drivers of earthworm communities along an altitudinal gradient in the French Alps

The study of elevational diversity gradients is a central topic in biodiversity research. In this study, we tested for the effect of climate, resource quality and habitat heterogeneity on earthworm communities along an altitudinal gradient and around the treeline in the French Alps. Earthworm communities and environmental properties (i.e. climate, soil properties and vegetation structure and composition) were sampled in six altitudinal stages from 1400 to 2400 m. Results were analysed through multi-table factorial analyses and structural equation modelling. We found average density, biomass and species richness in the range of what is usually reported in comparable ecosystems. We found no monotonic decrease in species richness along the altitudinal gradient, which we explain by the species pool being dominated by taxa with high environmental tolerance and dispersal capacities. Instead, we highlighted the ecotone associated with the treeline as the primary driving factor of earthworm communities: at 1800-2000m altitude, communities were more abundant and diverse, and had a greater variability in body mass. This result was largely explained by the structure and composition of the vegetation, whereas soil and climate appeared to have only indirect effects. Therefore, the treeline effect on earthworm communities can be explained both by the effect of environmental heterogeneity and of trophic resource quality which increases at the ecotone level.

ecology↗

bioRxiv2019

Local adaptation fuels cryptic speciation in terrestrial annelids

Uncovering the genetic and evolutionary basis of cryptic speciation is a major focus of evolutionary biology. Next Generation Sequencing (NGS) allows the identification of genome-wide local adaptation signatures, but has rarely been applied to cryptic complexes - particularly in the soil milieu - as is the case with integrative taxonomy. The earthworm genus Carpetania, comprising six previously suggested putative cryptic lineages, is a promising model to study the evolutionary phenomena shaping cryptic speciation in soil-dwelling lineages. Genotyping-By-Sequencing (GBS) was used to provide genome-wide information about genetic variability between seventeen populations, and geometric morphometrics analyses of genital chaetae were performed to investigate unexplored cryptic morphological evolution. Genomic analyses revealed the existence of three cryptic species, with half of the previously-identified potential cryptic lineages clustering within them. Local adaptation was detected in more than 800 genes putatively involved in a plethora of biological functions (most notably reproduction, metabolism, immunological response and morphogenesis). Several genes with selection signatures showed shared mutations for each of the cryptic species, and genes under selection were enriched in functions related to regulation of transcription, including SNPs located in UTR regions. Finally, geometric morphometrics approaches partially confirmed the phylogenetic signal of relevant morphological characters such as genital chaetae. Our study therefore unveils that local adaptation and regulatory divergence are key evolutionary forces orchestrating genome evolution in soil fauna.

evolutionary biology↗

bioRxiv2019

Genome-informed integrative taxonomic description of three cryptic species in the earthworm genus Carpetania (Oligochaeta, Hormogastridae)

Research on cryptic species complexes has reached a consensus on the necessity of integrating multiple sources of evidence. Low-coverage genomic scan techniques like Genotyping-by-Sequencing (GBS) have proven useful to study these groups. Both integrative taxonomy and genome-wide single nucleotide polymorphism (SNP) data remain to be widely applied to earthworms, an animal group with widespread presence of cryptic diversity. The genus Carpetania (formerly the Hormogaster elisae species complex) was found to contain six deeply divergent genetic lineages and some inconspicuous morphological differentiation based in a handful of Sanger-sequenced markers. Marchan et al. (submitted) delimited three well supported species-level clades on the basis of a genomewide SNP dataset and geometric morphometric analyses, highlighting the necessity of a formal taxonomic description of these taxa. In this work, further analyses are applied to the SNP data and a thorough morphological study is performed in order to provide an integrative description of two new species and to redescribe Carpetania elisae. Species-specific SNPs are identified and used as diagnostic characters, and genome-wide and cytochrome oxidase C subunit 1 (COI) genetic distances are compared finding a strong correlation between them. The taxonomic description of these three cryptic species provides a useful tool to include them effectively in ecological studies and biodiversity conservation actions.

zoology↗