Abstract
The family Carabidae is of particular interest not only due to its great specific diversity but also due to the geophilic nature of many of its members, which makes them good bioindicators of soil characteristics. The diversity of the epigean Carabidae is relatively well studied. However, there are no robust data on the presence of these beetles in hypogean habitats of non–karstic substrate and, therefore, without the development of caves. In the present study, we sampled the mesovoid shallow substratum (MSS) at various sites in the Sierra de Guadarrama National Park, with the aim of characterising the Carabidae hypogean fauna. Among many other organisms, we collected 12 species of Carabidae. Of these, despite being known from epigean/edaphic habitats, Leistus (Leistus) constrictus Schaufuss, 1862, Nebria (Nebria) vuillefroyi Chaudoir, 1866, Trechus (Trechus) schaufussi pandellei Putzeys, 1870, and Laemostenus (Eucryptotrichus) pinicola (Graells, 1851) are consistently reported from MSS habitats, albeit with certain differences as regards their occupation of subterranean spaces. The species from forest–dwelling (thermophilous) lineages, T. (T.) schaufussi pandellei and L. (E.) pinicola, presented a higher prevalence in subsoil cavities at lower altitudes, whereas those from orobiont (psychrophilic) lineages, L. (L.) constrictus and N. (N.) vuillefroyi, predominated in subsoils at higher altitudes. As regards the presence of these four species during their different life cycle stages, we found that N. (N.) vuillefroyi was present and abundant as both larval (in the three preimaginal stages) and imago stages, showing the most evident trend towards an hypogean lifestyle. In contrast, for the other three species, only one of the two stages showed a high presence on hypogean habitats. The facultative hypogean capabilities of N. (N.) vuillefroyi and L. (L.) constrictus calls into question the protected status conferred on both species when it was thought that they were exclusively epigean.
Highlights
The mesovoid shallow substratum (MSS) was discovered as a hypogean habitat in the 1980s (Juberthie et al, 1980, 1981; Uéno, 1980, 1981), and is probably one of the most extensive but least researched subterranean habitats on the planet
We collected a total of 12 Carabidae species in the MSS.These samples were unevenly represented: Carabus (Oreocarabus) guadarramus Laferté, 1847 [larva: 1, imagoes: 3]; Leistus (Leistus) constrictus Schaufuss, 1862 [L: 237, I: 32]; Nebria (Nebria) vuillefroyi Chaudoir, 1866 [L: 148, I: 203]; Nebria (Nebria) salina Fairmaire and Laboulbène, 1854 [I: 16]; Trechus (Trechus) quadristriatus (Schrank, 1781) [I: 1]; Trechus (Trechus) schaufussi pandellei Putzeys, 1870 [L: 1, I: 234]; Cryobius nemoralis nemoralis (Graells, 1851) [I: 1]; Steropus (Iberocorax) ghilianii (Putzeys, 1846) [I: 1]; Platyderus (Platyderus) varians Schaufuss, 1862 [I: 6]; Laemostenus (Eucryptotrichus) pinicola (Graells, 1851) [L: 14, I: 572]; Synuchus vivalis (Illiger, 1798) [I: 1]; and Cymindis (Cymindis) coadunata monticola Chevrolat, 1866 [I: 1]
Of the near 250 Carabidae species considered epigean and present in the Sierra de Guadarrama, only four, L. (L.) constrictus, N. (N.) vuillefroyi, T. (T.) schaufussi pandellei and L. (E.) pinicola, were systematically recovered in the sampled colluvial deposits. This suggests that penetrability and occupation of this habitat largely corresponds to the ecophysiological characteristics of the species, and that the MSS acts as a filter for the epigean Carabidae accessing hypogean environments
Summary
The mesovoid shallow substratum (MSS) was discovered as a hypogean habitat in the 1980s (Juberthie et al, 1980, 1981; Uéno, 1980, 1981), and is probably one of the most extensive but least researched subterranean habitats on the planet. As the MSS has a close association with the surface and soil horizons (Giachino and Vailati, 2010; Nitzu et al, 2014; Jiménez–Valverde et al, 2015), the ease with which organic matter enters the system is a substantial ecological difference from caves (Gers, 1998). This characteristic favours the presence of high densities of Arthropoda, many of them epigean or endogean, which encounter temporarily appropriate conditions in the MSS. Evolutionary and conservationist perspective, the MSS is a very important habitat that has remained unknown for a long time (Pipan et al, 2011; Ortuño et al, 2013; Jiménez–Valverde et al, 2015), partly due to the extreme difficulty in accessing and sampling its biocoenosis (Mammola et al, 2016)
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