BackgroundA key question in evolutionary biology is the relationship between species traits and their habitats. Caves offer an ideal model to test the adjustment of species to their surrounding temperature, as they provide homogeneous and simple environments. We compared two species living under different thermal conditions within a lineage of Pyrenean beetles highly modified for the subterranean life since the Miocene. One, Troglocharinus fonti, is found in caves at 4-11°C in the ancestral Pyrenean range. The second, T. ferreri, inhabits the coastal area of Catalonia since the early Pliocene, and lives at 14-16°C.ResultsWe found no differences in their short term upper thermal limit (ca. 50°C), similar to that of most organisms, or their lower thermal limit (ca. -2.5°C), higher than for most temperate insects and suggesting the absence of cryoprotectants. In longer term tests (7 days) survival between 6-20°C was almost 100% for both species plus two outgroups of the same lineage, but all four died between 23-25°C, without significant differences between them.ConclusionsOur results suggest that species in this lineage have lost some of the thermoregulatory mechanisms common in temperate insects, as their inferred default tolerance range is larger than the thermal variation experienced through their whole evolutionary history.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0288-2) contains supplementary material, which is available to authorized users.

Aim To investigate the possibility of range expansion and diversification within the subterranean environment in a genus of troglobiont beetles of the family Leiodidae (Troglocharinus), which have a disjunct distribution between the Pyrenees and the Catalonian coast. Location North‐eastern Iberian Peninsula. Methods We sequenced 4 kb of five mitochondrial and two nuclear genes of 50 specimens of 12 of the 18 species of Troglocharinus, plus several outgroups. We reconstructed a phylogeny using Bayesian inference and maximum likelihood, estimated divergence times using Bayesian probabilities and an a priori evolutionary rate, compared the diversification of the main clades within the genus, and reconstructed their ancestral distribution using maximum likelihood. Results We found strong support for the monophyly of Troglocharinus and the clades in each of the geographical areas, which diverged in the early Pliocene. The coastal clade was further divided into geographically well‐defined lineages, separated by Quaternary deposits. The origin of the coastal clade was a single colonization in the early Pliocene from the central Pyrenees. The diversification of the Pyrenean clade followed a constant rate, while the diversification rate of the coastal clade significantly decreased through the Plio‐Pleistocene transition. Main conclusions Troglocharinus expanded its range from its ancestral area in the central Pyrenees to the coast of Catalonia and subsequently diversified, probably within the subterranean environment. Our favoured scenario is a stepping‐stone migration, with possibly short‐distance dispersals through the surface, along the eastern margin of the north‐eastern Ebro basin. The range expansion took place in a narrow temporal window with favourable conditions between the early Pliocene and the onset of the Mediterranean climate by the mid‐Pliocene. Surface dispersal was probably severely limited afterwards, as shown by the fragmentation of the coastal lineage.

One of the main challenges in ecology, biogeography and evolution is to understand and predict how species may respond to environmental changes. Here we focus on the deep subterranean environment, a system that minimizes most of the typical uncertainties of studies on epigean (surface) environments. Caves are relatively homogeneous habitats with nearly constant environmental conditions and simplified biological communities, allowing to control for biotic interactions. Thus, this particular system could be considered a natural habitat whose environmental conditions are similar to what can be reproduced in a laboratory, being an ideal model system for ecological, biogeographical and evolutionary studies. Subterranean species may potentially be used to assess the capability to persist in situ in a global change scenario, as they cannot accommodate to drastic changing conditions by behavioural plasticity, microhabitat use or by migrating to distant, more suitable areas, something frequent in epigean environments. In order to provide accurate predictions of the response of the subterranean biodiversity to climate change, we encourage evolutionary biologist, biogeographers and conservation biologist to work in this interesting ecosystem.