Do cryptic species of earthworms affect soil arthropods differently? The case of the Carpetania elisae complex in the center of the Iberian Peninsula

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In recent years, it has been discovered that the endemic earthworm Carpetania elisae (formerly Hormogaster elisae) consists of a complex of at least six cryptic species. Studying the relationships between these new cryptic species and other soil animal communities may be important to understand their functional role in the soil, and eventually to detect possible differences that may help in the delimitation of these species. We have studied the effects of two of these cryptic species (species I from El Molar [Ce1] and species II from El Tomillar [Ce2]) on soil microarthropod communities. Several laboratory experiments were performed with both cryptic species, in the soils of both localities inhabited by these earthworm species, to determine their effects on soil microarthropod communities. Both earthworm species grew quite well throughout the experiment in their original soil, but while Ce1 grew up well when cultivated in the opposite soil from El Tomillar, Ce2 cultivated in the soil from El Molar survived but did not grow. Ce1 from El Molar showed a clear negative effect on microarthropods from El Molar and El Tomillar, whereas Ce2 from El Tomillar had a clear negative effect on soil microarthropods from its original soil but not on the ones from the opposite soil of El Molar. This paper demonstrates differences of both cryptic species on their effects on soil community, which suggest that they may play different roles in the soil system. Several mechanisms likely involved on the effect of earthworms on soil arthropods are discussed, being the competition for organic matter the most probable one in the case of these endogeic earthworms.