Ancient origins determine global biogeography of hot and cold desert cyanobacteria

Factors governing large-scale spatio-temporal distribution of microorganisms remain unresolved, yet are pivotal to understanding ecosystem value and function. Molecular genetic analyses have focused on the influence of niche and neutral processes in determining spatial patterns without considering the temporal scale. Here, we use temporal phylogenetic analysis calibrated using microfossil data for a globally sampled desert cyanobacterium, Chroococcidiopsis, to investigate spatio-temporal patterns in microbial biogeography and evolution. Multilocus phylogenetic associations were dependent on contemporary climate with no evidence for distance-related patterns. Massively parallel pyrosequencing of environmental samples confirmed that Chroococcidiopsis variants were specific to either hot or cold deserts. Temporally scaled phylogenetic analyses showed no evidence of recent inter-regional gene flow, indicating populations have not shared common ancestry since before the formation of modern continents. These results indicate that global distribution of desert cyanobacteria has not resulted from widespread contemporary dispersal but is an ancient evolutionary legacy. This highlights the importance of considering temporal scales in microbial biogeography

Evidence of Weak Habitat Specialisation in Microscopic Animals

Macroecology and biogeography of microscopic organisms (any living organism smaller than 2 mm) are quickly developing into fruitful research areas. Microscopic organisms also offer the potential for testing predictions and models derived from observations on larger organisms due to the feasibility of performing lab and mesocosm experiments. However, more empirical knowledge on the similarities and differences between micro- and macro-organisms is needed to ascertain how much of the results obtained from the former can be generalised to the latter. One potential misconception, based mostly on anedoctal evidence rather than explicit tests, is that microscopic organisms may have wider ecological tolerance and a lower degree of habitat specialisation than large organisms. Here we explicitly test this hypothesis within the framework of metacommunity theory, by studying host specificify in the assemblages of bdelloid rotifers (animals about 350 µm in body length) living in different species of lichens in Sweden. Using several regression-based and ANOVA analyses and controlling for both spatial structure and the kind of substrate the lichen grow over (bark vs rock), we found evidence of significant but weak species-specific associations between bdelloids and lichens, a wide overlap in species composition between lichens, and wide ecological tolerance for most bdelloid species. This confirms that microscopic organisms such as bdelloids have a lower degree of habitat specialisation than larger organisms, although this happens in a complex scenario of ecological processes, where source-sink dynamics and geographic distances seem to have no effect on species composition at the analysed scale

Relationship of Geographic Distance, Depth, Temperature, and Viruses with Prokaryotic Communities in the Eastern Tropical Atlantic Ocean

The richness and biogeographical distribution pattern of bacterial and archaeal communities was assessed by terminal restriction fragment length polymorphism analysis of polymerase chain reaction-amplified fragments of the 16S rRNA gene at the surface (15-25 m depth), in the deep chlorophyll maximum layer (DCM; 50 m depth), and deep waters (75-1000 m depth) of the eastern tropical Atlantic Ocean. Additionally, prokaryotic and viral abundance and the frequency of infected prokaryotic cells (FIC) were determined along with physico-chemical parameters to identify factors influencing prokaryotic richness and biogeography. Viral abundance was highest in the DCM layer averaging 45.5 x 10(6) ml(-1), whereas in the mixed surface layer and in the waters below the DCM, average viral abundance was 11.3 x 10(6) and 4.3 x 10(6) ml(-1), respectively. The average estimate of FIC was 8.3% in the mixed surface layer and the DCM and 2.4% in deeper waters. FIC was positively related to prokaryotic and viral abundance and negatively to archaeal richness. There was no detectable effect of geographic distance (maximum distance between stations approximately 4600 km) or differences between water masses on bacterial and archaeal community composition. Bacterial communities showed a clear depth zonation, whereas changes in archaeal community composition were related to temperature and FIC. The results indicate that planktonic archaeal virus host systems are a dynamic component of marine ecosystems under natural conditions

Effects of environmental variation and spatial distance on Bacteria, Archaea and viruses in sub-polar and arctic waters

We investigated the influence of environmental parameters and spatial distance on bacterial, archaeal and viral community composition from 13 sites along a 3200-km long voyage from Halifax to Kugluktuk (Canada) through the Labrador Sea, Baffin Bay and the Arctic Archipelago. Variation partitioning was used to disentangle the effects of environmental parameters, spatial distance and spatially correlated environmental parameters on prokaryotic and viral communities. Viral and prokaryotic community composition were related in the Labrador Sea, but were independent of each other in Baffin Bay and the Arctic Archipelago. In oceans, the dominant dispersal mechanism for prokaryotes and viruses is the movement of water masses, thus, dispersal for both groups is passive and similar. Nevertheless, spatial distance explained 7–19% of the variation in viral community composition in the Arctic Archipelago, but was not a significant predictor of bacterial or archaeal community composition in either sampling area, suggesting a decoupling of the processes regulating community composition within these taxonomic groups. According to the metacommunity theory, patterns in bacterial and archaeal community composition suggest a role for species sorting, while patterns of virus community composition are consistent with species sorting in the Labrador Sea and suggest a potential role of mass effects in the Arctic Archipelago. Given that, a specific prokaryotic taxon may be infected by multiple viruses with high reproductive potential, our results suggest that viral community composition was subject to a high turnover relative to prokaryotic community composition in the Arctic Archipelago