Dolores Trigo

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.

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.

Appearances can be deceptive: different diversification patterns within a group of Mediterranean earthworms (Oligochaeta, Hormogastridae)

Many recent studies on invertebrates have shown how morphology not always captures the true diversity of taxa, with cryptic speciation often being discussed in this context. Here, we show how diversification patterns can be very different in two clades of closely related earthworms in the genus Hormogaster stressing the risk of using nonspecific substitution rate values across taxa. On the one hand, the Hormogaster elisae species complex, endemic to the central Iberian Peninsula, shows morphological stasis. On the other hand, a clade of Hormogaster from the NE Iberian Peninsula shows an enormous morphological variability, with 15 described morphospecies. The H. elisae complex, however, evolves faster genetically, and this could be explained by the harsher environmental conditions to which it is confined—as detected in this study, that is, sandier and slightly poorer soils with lower pH values than those of the other species in the family. These extreme conditions could be at the same time limiting morphological evolution and thus be responsible for the observed morphological stasis in this clade. Contrarily, Hormogaster species from the NE Iberian Peninsula, although still inhabiting harsher milieu than other earthworm groups, have had the opportunity to evolve into a greater morphological disparity. An attempt to delimit species within this group following the recently proposed general mixed Yule‐coalescent method showed a higher number of entities than expected under the morphospecies concept, most probably due to the low vagility of these animals, which considerably limits gene flow between distant conspecific populations, but also because of the decoupling between morphological and genetic evolution in the H. elisae complex.

Activity of glycolytic enzymes in the gut of Hormogaster elisae (Oligochaeta, Hormogastridae).

Abstract The glycolytic enzymatic activities in the gut of the endogeic earthworm Hormogaster elisae from El Molar (Madrid, Spain) were studied in order to determine its digestive capacity and to assess its alimentary regime. Most endogeic earthworms have weak enzymatic complement and they usually establish mutualistic relationships with soil microflora to digest some organic compounds. Therefore, the intestinal wall tissues were cultured in vitro to assess the origin of the glycolytic enzymes found in the gut and enzymatic activities were measured in both cultured tissues and culture media. H. elisae had a wide but not very strong enzyme complement, since all substrates were degraded but most of them at a low rate. This species cannot produce cellulase and mannanase, so for the digestion of these substrates it probably uses the digestive enzymatic capabilities of the ingested microflora.

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.

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.

Biogeographical divisions of continental Portugal as regards earthworm fauna

Abstract Biogeographical provinces have been defined for the earthworm fauna of continental Portugal by subjecting data obtained at 100 sites distributed among 23 zones to correspondence analysis and dendritic clustering so as to detect faunistically similar groups of zones. Various measures of species importance and interspecific association were calculated in order to characterize the provinces so detected. On the basis of our findings and the existing literature, ve propose that Galicia and Northern Portugal be included in a Galaico‐Lusitanian Province characterized by the joint dominance of A. caliginosa and the three typical species D. madeirensis, D. taedra and A. olivtirae, which are accompanied by other, more widely distributed species; and that continental Portugal south of he River Mondego be considered an Atlantic Province character‐zed by the dominance ofA. caliginosa, A. rosea and the ≪A. molleri≫: omplex species, and by the absence of the three typical Northern species and all species of the...

Earthworms of continental Portugal. Relationships with soil factors

Abstract The relationships between the 13 most common species of Por tuguese earthworms and 20 soil characteristics have been investi gated by analysis of ecological profiles, correspondence analysis and canonical correlation. Two groups emerged: one comprising basi cally the epigeic species Allolobophora oliveirae, Dendrobaena madeiren‐sis, Dendrobaena octaedra and Eisenia eiseni, which tend to prefer organic acid soils with little calcium or magnesium and large quan tities of aluminium in the exchange complex, and the other made up of the endogeic species Allolobophora caliginosa, Allolobophora mol‐leri, Allolobophora rosea and Allolobophora chlorotica, which exhibit the opposite tendencies.

Growth in the laboratory of Hormogaster elisae (Oligochaeta, Hormogastridae)

Studies of the growth, at room temperature, of 32 individuals of Hormogaster elisae have been carried out under laboratory conditions between February 1993 and September 1995. The individuals were obtained from cocoons collected at El Molar (Madrid, Spain) and cultured until emergence. Data obtained from the 32 individuals suggest a gradual growth, whereas a selective study of individuals belonging to the same age group (emerging within a 3-month period) reveals the existence of growth periods during the colder months alternating periods of no growth during the hottest months. A comparison between the common time period for which data exist for the coetaneous groups reveals that there is a parallel growth pattern independent of time of hatching and weight of individuals. # 1998 Elsevier Science B.V.