Molecular tools applied to study the evolution and adaptation of springtails to the extreme Antarctic terrestrial ecosystem

Collembola (=springtails) is one of the most abundant, widespread and ancient lineages of basal hexapods. During their long evolutionary history, springtails have adapted to most damp environments on Earth, including those of South Pole. Antarctic springtails are endemic to the frozen Continent and among the few invertebrate taxa adapted to its strictly terrestrial ecosystem. These species have evolved when Antarctica was still linked to the Gondwanaland at lower latitudes and have adapted and survived to the cooling, isolation and southwards migration of the landmass. Antarctic springtails’ habitats are restricted to the few coastal areas, seasonally ice-free and accounting for less than the 0.5% of the entire continental area and off-shore islands. The niche fragmentation, together with springtails poor dispersal capability (due to the primary absence of wings), entail a severe degree of isolation among populations, with very low levels of gene flow. The Antarctic springtail species composition is limited without overlap among the two main Antarctic bioregions (i.e., the maritime and the continental Antarctica), with Friesea antarctica being the only species found both in the Antarctic Peninsula and Victoria Land (continental Antarctica). The high levels of endemism and fragmentation among populations, as well as the low invertebrate biodiversity and the complex and delicate array of physiological adaptation these species evolved, make Antarctic taxa particularly susceptible to anthropogenic climate changes, that we are all experiencing since the second industrial revolution in the XIXth century. In this respect, studying the molecular mechanisms underlying springtail adaptation to such a harsh environment, as well as the genetic structure of the populations and the way in which specimens may have been and can be influenced by the Antarctic terrestrial environment, may greatly assist the development of adequate and biogeographically-specific (thus, effective) conservational plans. In order to address these issues, different studies have been carried out during the current PhD project. A genetics of population study was performed to investigate the genetic structure of the Antarctic springtail species Cryptopygus terranovus. As previously observed in other Antarctic species (i.e, F. antarctica), high levels of genetic divergence were detected, with very few haplotypes shared among populations nearly suggesting the absence of gene flow, as well as the presence of cryptic species. One way to address this issue is the integration of morphological, molecular and biogeographic data to assess whether the detection of cryptic species is due to an ongoing phylogenetic niche conservatism process or to overlooked morphological differences. In this respect, an integrative taxonomic analysis has been carried out on the Antarctic springtail F. antarctica. Nuclear and mitochondrial markers were used in bioinformatic analyses of species delimitation. Although applied tools rely on different algorithms and biological assumptions, and the chosen molecular markers are generally subject to different evolutionary pressures, the results obtained in this study would suggest that at least two more species may be hidden within the F. antarctica complex. Specimens from the same localities were also morphologically re-described so that new species could be possibly established. These analyses would suggest an even higher species richness of the Antarctic terrestrial ecosystem, that should be taken into account when developing conservational plans. Our ability to safeguard Antarctica relies also on our in-depth understanding of the terrestrial ecosystem functioning and dynamics. In this perspective, an initial descriptive analysis of the microbial communities associated to four Antarctic springtail species was performed (specifically on: Cryptopygus antarcticus antarcticus and F. antarctica from the Antarctic Peninsula and C. terranovus and F. antarctica collected along Victoria Land). The results obtained are in line with previous studies on Collembola microbiomes. In addition, the occurrence of particularly interesting OTUs, such as those of the genera Streptomyces and Bacillus, was, to my knowledge, firstly detected among springtails and may break new grounds for biotechnology development, especially starting from such an unspoiled ecosystem, like the Antarctic one. Finally, the mitochondrial genomes from 13 springtail species, both living at low and high latitudes, have been applied to maximum likelihood analyses of positive selection in order to investigate whether or not the organelle chromosome may have been involved in Antarctic springtails adaptation to such an extreme environment. The results pointed out that some mitochondrial genes involved in the oxidative phosphorylation process may have been under positive selection, thus suggesting the development of additional thermoregulatory mechanism within the mitochondrion, complementary to the well-known cold hardiness strategies.