Search

The capacity to forecast the effects of climate change on biodiversity largely relies on identifying traits capturing mechanistic relationships with the environment through standardized field experiments distributed across relevant spatial scales. The effects of short-term experimental manipulations on local communities may overlap with regional climate gradients that have been operating during longer time periods. However, to the best of our knowledge, there are no studies simultaneously assessing such long-term macroecological drivers with local climate manipulations. We analysed this issue with springtails (Class Collembola), one of the dominant soil fauna groups, in a standardized climate manipulation experiment conducted across six European countries encompassing broad climate gradients. We combined community data (near 20K specimens classified into 102 species) with 22 eco-morphological traits and reconstructed their phylogenetic relationships to track the evolution of adaptations to live at different soil depths, which is key to cope with desiccation. We then applied joint species distribution models to investigate the combined effect of the regional aridity gradient with the local experimental treatment (drought and warming) over the assembly of springtail communities and tested for significant trait–environment relationships mediating their community-level responses. Our results show (1) a convergent evolution in all three major collembolan lineages of species adapted to inhabit at different soil strata; (2) a clear signature of aridity selecting traits of more epigeic species at a biogeographical scale and (3) the association of short-term experimental drought with traits related to more euedaphic life-forms. The hemiedaphic condition would be the plesiomorphic state for Collembola while the adaptations for an epigeic life would have been secondarily gained. Epigeic springtails are not only more resistant to drought, but also have a higher dispersal capacity that allows them to seek more favourable micro-habitats after experiencing drier conditions. The observed relative edaphization of the springtail communities after short-term experimental drought may thus be a transient community response. The disparity between macroecological trends and fast community-level responses after climate manipulations highlights the need of simultaneously assessing long-term and short-term drivers at broad spatial scales to adequately interpret trait–environment relationships and better forecast biodiversity responses to climate change. Read the free Plain Language Summary for this article on the Journal blog.

Many ecological and evolutionary studies require to quantify the degree of adaptation of subterranean species to caves or other subterranean systems. In 1962, Kenneth A. Christiansen (1924–2017) coined the term “troglomorphism” to illustrate the process of subterranean adaptation and the suite of adaptive traits of organisms (“troglomorphic traits” or “troglomorphies”) (Christiansen 1962). Although this term was proposed in a paper published in French, “troglomorphism” and its derivatives (e.g. “troglobiomorphism”) became widely adopted jargon in subterranean biology. Yet, after decades of work and countless discussions around the subtle meanings of the term, there is still no consensus on how to best quantify troglomorphism in a simple operational way to support eco-evolutionary research. In a recent interview, Boris Sket made the excellent point that “nothing [makes] sense in speleobiology without a comparison of cave animals with the 'normal' epigean ones” (Lučić 2021). Building on this idea, we contend that one could quantify troglomorphism on a continuous scale within a given group of organisms (e.g., family or genus) as the functional distance of each species to the phylogenetically closest surface species or the “average” surface species (depending on whether phylogenetic information is available or not). We illustrate this approach using subterranean spiders in the genus Troglohyphantes, a well-studied group for which both a phylogeny and functional traits are available (Isaia et al. 2017, Mammola et al. 2020). We tested two approaches: i) quantifying adaptation as the morphological distance of each species to the phylogenetically closest surface-dwelling relative; ii) using a kernel density n-dimensional hypervolume (sensu Blonder et al. 2014) to construct the morphospace occupied by all surface-dwelling species of Troglohyphantes, and quantifying the degree of adaptation of subterranean species as their distance from the centroid of this “average” surface species. To test the effectiveness of these alternative methods, we compare how functional distance varies in relation the habitat occupied by each species (deep caves vs cave entrances vs interstitial habitats) and its range size. We suggest our approach could be applied to any group of subterranean organisms for which a surface relative is known, allowing to explore a range of questions on the degree to which the specialization of a given community relates to local environmental conditions, interspecific interactions, and more.

The true stress-true strain curves of 11 Australian spider species from the Entelegynae lineage were tensile tested and classified based on the values of the alignment parameter, α*, in the framework of the Spider Silk Standardization Initiative (S3I). The application of the S3I methodology allowed the determination of the alignment parameter in all cases, and were found to range between α* = 0.03 and α* = 0.65. These data, in combination with previous results on other species included in the Initiative, were exploited to illustrate the potential of this approach by testing two simple hypotheses on the distribution of the alignment parameter throughout the lineage: (1) whether a uniform distribution may be compatible with the values obtained from the studied species, and (2) whether any trend may be established between the distribution of the α* parameter and phylogeny. In this regard, the lowest values of the α* parameter are found in some representatives of the Araneidae group, and larger values seem to be found as the evolutionary distance from this group increases. However, a significant number of outliers to this apparent general trend in terms of the values of the α* parameter are described.

Caves put strong constraints on organisms living there, which results in acquisition of variety of troglomorphic traits, most obvious ones being depigmentation and degradation of visual system (Christiansen 2012). Cave habitats are considered fragmented, and the animals living there face limited connectivity between potential habitats (Barr 1967, Bregović and Zagmajster 2016, Trontelj 2018). Additionally, once adapted to underground conditions, cave-dwellers are thought to be unable to use the surface for dispersal, thus demonstrating population dynamics similar to those of the species found in islands (Barr and Holsinger 1985). We compared the population genetic structure of several cave spider species with different biology and ecology from different caves in the Dinarides. Namely, depigmented and anophthalmic Dysderidae species which were never collected outside caves, and several species from the genus Troglohyphantes, which exhibit different levels of troglomorphisms and dependency on cave habitat (some, like T. excavatus and T. kordunlikanus, can be occasionally found in surface habitats). Additionally, Dysderidae are wandering active hunters, while all Troglohyphantes species spin webs. In our study, we applied a hybridization-capture approach, i.e., HyRAD (Suchan et al. 2016) to extract and capture DNA from historical samples. We compared the population genetic structures among the species, and studied isolation by distance, and identified contrasted genetic structures related to the biology and ecology of each species. We identified a deeper population structuring and more pronounced patterns of isolation by distance in the highly troglomorphic species compared to the less troglomorphic ones. Species that can occasionally be found in surface habitats showed less structured populations compatible with higher dispersal ability. Additionally, we detected several common breaks in gene flow for most studied species, some of which can be explained by geographic and geologic features.

Because of their ability for aerial dispersal using silk and preference for open habitats, many wolf spiders are formidable colonisers. Pioneering arachnologists were already aware of the large and colourful wolf spiders in the Madeira archipelago, currently included in the genus