Speciation in cave-dwelling organisms

system for testing evolutionary and biogeographic hypotheses because of their isolation, simplicity of community structure and specialization. Adaptation to cave environments promotes the regression of functionless (unused) characters across a broad taxonomic range, in concert with evolutionary change in other morphological traits. Change typically involves the degeneration of eyes and loss of pigments, while at the same time appendices become elongated, intensification of sensory organs occurs, and life cycles become modified -a syndrome known as troglomorphy [1]. Modes of speciation and explanations for the geographic distributions of subterranean animals have both been debated (see for example [2,3]). Extrinsic environmental factors causing extinction of surface ancestors pre-adapted to the subterranean (such as glaciations or aridification) are suggested to be a mechanism forcing populations underground. is model is usually invoked in limestone cave systems of continental temperate regions. However, among tropical faunas, in which surface (epigean) taxa are often found co-occurring with subterranean sister taxa, active colonization of the subterranean habitat is suggested as a more plausible explanation [2]. Mirroring this debate, both the development of a topographic or ecological barrier resulting in the separation of a once continuously distributed ancestral population or species into separate populations (vicariance) and dispersal, have been discussed as contrasting factors shaping subterranean animal distributions. Vicariance is typically considered the dominant of these two processes, as subterranean species have very limited dispersal potential, particularly in ecologically unsuitable areas [4]. Testing hypotheses of origin and adaptation among subterranean taxa has been hindered by the inherent difficulties of sampling the rare and more elusive cave taxa and extensive morphological convergence caused by strong selection pressures imposed by the subterranean environment [4]. In recent years molecular phylogenies have been obtained for numerous taxonomic groups contain ing subterranean lineages, permitting rigorous comparisons of competing evolutionary hypotheses. In a study published in BMC Evolutionary Biology, Ribera et al. [5] have investigated the origin and evolution of a diverse lineage of subterranean beetles of the tribe Leptodirini (family Leiodidae) (Figure 1a), focusing on the distribution of this group in the western Mediter ranean. is study is one of the first in which the evolutionary history of a presumably monophyletic group composed of mostly subterranean species is examined using molecular data. Samples of a large number of species from genera occurring in the Iberian Peninsula plus representatives from Sardinia and the Carpathians are included in the study. DNA sequences totalling 4 kilobases from five mitochondrial and two nuclear DNA fragments were used to construct robust phylogenies using different methods and to quantify diversification patterns and times from molecular clock calibrations.