Darío J. Díaz Cosín

Cryptic speciation of hormogastrid earthworms revealed by mitochondrial and nuclear data.

Species delimitation of earthworms has been difficult to determine with certainty due to their structural simplicity. We sequenced fragments of COI, 16S, t-RNAs and 28S for 202 Hormogastridae individuals from the central Iberian Peninsula and three outgroup taxa. A morphological constancy was found but a high genetic diversity suggests the presence of five cryptic allopatric species. Results showed a pattern of isolation by distance and a positive but weak correlation between some soil properties (coarse sand and total loam content) and genetic distances, which indicates that these populations may have been shaped genetically but not morphologically, by the environment.

Understanding the biogeography of a group of earthworms in the Mediterranean basin—The phylogenetic puzzle of Hormogastridae (Clitellata: Oligochaeta)

Traditional earthworm taxonomy is hindered due to their anatomical simplicity and the plasticity of the characteristics often used for diagnosing species. Making phylogenetic inferences based on these characters is more than difficult. In this study we use molecular tools to unravel the phylogeny of the clitellate family Hormogastridae. The family includes species of large to mid-sized earthworms distributed almost exclusively in the western Mediterranean region where they play an important ecological role. We analyzed individuals from 46 locations spanning the Iberian Peninsula to Corsica and Sardinia, representing the four described genera in the family and 20 species. Molecular markers include mitochondrial regions of the cytochrome c oxidase subunit I gene (COI), 16S rRNA and tRNAs for Leu, Ala, and Ser, two nuclear ribosomal genes (nearly complete 18S rRNA and a fragment of 28S rRNA) and two nuclear protein-encoding genes (histones H3 and H4). Analyses of the data using different approaches corroborates monophyly of Hormogastridae, but the genus Hormogaster is paraphyletic and Hormogaster pretiosa appears polyphyletic, stressing the need for taxonomic revisionary work in the family. The genus Vignysa could represent an early offshoot in the family, although the relationships with other genera are uncertain. The genus Hemigastrodrilus is related to the Hormogaster elisae complex and both are found in the Atlantic drainage of the Iberian Peninsula and France. From a biogeographic perspective Corsica and Sardinia include members of two separate hormogastrid lineages. The species located in Corsica and Northern Sardinia are related to Vignysa, whereas Hormogaster pretiosa pretiosa, from Southern Sardinia, is closely related to the Hormogaster species from the NE Iberian Peninsula. A molecular dating of the tree using the separation of the Sardinian microplate as a calibration point (at 33 MY) and assuming a model of vicariance indicates that the diversification of Hormogastridae may be ancient, ranging from 97 to 67 Ma.

Annual dynamics of the earthworm Hormogaster elisae (Oligochaeta, Hormogastridae) in central Spain

Abstract A population of an endogeic earthworm Hormogaster elisae (Oligochaeta, Hormogastridae) from the area known as El Molar (Madrid, Spain) was studied by sampling over 12 months. Annual rainfall in the area is low, amounting only to 411 mm. Rainfall is distributed irregularly with two rainy periods alternating with two dry ones. The H. elisae population varies according to rainfall and increases during wet periods. Individuals of all developmental stages are present throughout the year and two recruitment periods can be distinguished during the rainy periods. The presence of mature individuals of H. elisae is high throughout most of the year. This fact together with other characteristics of the species suggests that H. elisae portrays a K type reproductive strategy. H. elisae population moves within the soil profile according to its humidity contents, with the population present near surface soil during humid months and in deeper soil during dry months.

Heavy metals and earthworms on the border of a road next to Santiago (Galicia, northwest of Spain). Initial results

Abstract The concentration of some heavy metals in the soil and earthworms existing on the border of a road next to the city of Santiago de Compostela was investigated. Three points which were at 3, 15 and 30 m from the border of the road were sampled in February, May and November 1988. In June, the traffic was diverted as a consequence of a rectification in the road. Heavy metals were determined by atomic absorption spectrophotometry. Interspecific differences were observed among the five studied species Allolobophora caliginosa (Savigny, 1826), A. rosea (Savigny, 1826), Dendrobaena madeirensis (Michaelsen, 1891), D. octaedra (Savigny, 1826) and Lumbricus friendi (Cognetti, 1904). Four metals were studied, copper, lead, cadmium and zinc. Cadmium and zinc were concentrated, copper and lead were accumulated by earthworms.

Reproduction of Earthworms: Sexual Selection and Parthenogenesis

Earthworms are generally cross-fertilization hermaphrodites, but up to 40% of the species can be parthenogenetic. In simultaneous hermaphrodites, a trade-off between male and female sexual functions is expected because the two sexes share limited resources from the same individual. In this chapter, several issues regarding sexual selection such as the role of spermathecae, copulatory behavior, allohormone injection, or adjustment of the donated sperm volume are reviewed. Parthenogenesis is present in some families as Lumbricidae, but is lacking in others. Parthenogenetic reproduction in earthworms is generally automictic and thelytokous, although apomixis and pseudogamy have been occasionally described. This kind of reproduction is poorly understood due to some background limitations such as the species concept in parthenogens or its possible origin, which are discussed in this chapter.

New light into the hormogastrid riddle: morphological and molecular description of Hormogaster joseantonioi sp. n. (Annelida, Clitellata, Hormogastridae)

Abstract The earthworm family Hormogastridae shows a remarkable disjunction in its distribution in the Iberian Peninsula, with the Hormogaster elisae species complex isolated from the rest of the species. Hormogaster joseantonioi sp. n., a new species found in the intermediate area between the main ranges (in Teruel, Aragón), was described following the integrative approach, as it is suitable for earthworms due to their highly homoplasic morphology. The phylogenetic analysis of the molecular markers placed the new species as a sister taxon to H. elisae, thus showing the colonizing lineage of Central Iberian Peninsula could have originated near the H. joseantonioi sp. n. current range. External morphological characters revealed some degree of overlap with previously described species, but internal characters presented configurations/states unknown from other members of the family. These traits make the new species a key piece to understand the evolution of Hormogastridae.

Horizontal distribution of an earthworm community at El Molar, Madrid (Spain)

The earthworm community in El Molar (Madrid) is studied, and its distribution patterns and relation with some soil factors are described by using geostatistic and multivariate tools. Six species were found, Hormogaster elisae, Allolobophora rosea and Allolobophora caliginosa being the three most abundant ones. These speciesexhibited a clumped distribution. The most dominant species, H. elisae, was distributed in patches of an average size of 45m in spring and more than 100m inautumn. A. rosea was aggregated in patches of an average size of 22m and A. caliginosa formed patches of an average size of 38 m. There seemed to be a positive correlation between the abundance of H. elisae and the percentage of total and coarse sands, as well as a negative correlation with clay, nitrogen, carbon and coarse loams contents, opposite to what was observed for A. rosea.

Compilation of morphological and molecular data, a necessity for taxonomy: The case of Hormogaster abbatissae sp. n. (Annelida, Clitellata, Hormogastridae)

Conflict among data sources can be frequent in evolutionary biology, especially in cases where one character set poses limitations to resolution. Earthworm taxonomy, for example, remains a challenge because of the limited number of morphological characters taxonomically valuable. An explanation to this may be morphological convergence due to adaptation to a homogeneous habitat, resulting in high degrees of homoplasy. This sometimes impedes clear morphological diagnosis of species. Combination of morphology with molecular techniques has recently aided taxonomy in many groups difficult to delimit morphologically. Here we apply an integrative approach by combining morphological and molecular data, including also some ecological features, to describe a new earthworm species in the family Hormogastridae, Hormogaster abbatissaesp. n., collected in Sant Joan de les Abadesses (Girona, Spain). Its anatomical and morphological characters are discussed in relation to the most similar Hormogastridae species, which are not the closest species in a phylogenetic analysis of molecular data. Species delimitation using the GMYC method and genetic divergences with the closest species are also considered. The information supplied by the morphological and molecular sources is contradictory, and thus we discuss issues with species delimitation in other similar situations. Decisions should be based on a profound knowledge of the morphology of the studied group but results from molecular analyses should also be considered.

Interactions of Hormogaster elisae (Oligochaeta, Hormogastridae) with other earthworm species from Redueña (Madrid, Spain)

Abstract Variations in density and community structure have been observed in an earthworm community comprising Hormogaster elisae, Allolobophora rosea and A. caliginosa trapezoides has been found in Reduena (Madrid, Spain) which could reflect competition. In order to study the possible negative interactions between H. elisae and A. rosea, and H. elisae and A. caliginosa, survival, growth rate and cocoon production in monospecific (controls) and polyspecific microcosms were compared. No evidence of competition between H. elisae and A. rosea was detected, since no significant differences in the variables studied were found between monospecific and polyspecific cultures. In contrast, H. elisae and A. caliginosa showed negative interactions. The growth rate of H. elisae decreased in the presence of A. caliginosa, and A. caliginosa produced less cocoons in polyspecific than in monospecific microcosms.

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.