Prokaryotic and Eukaryotic Community Structure in Field and Cultured Microbialites from the Alkaline Lake Alchichica (Mexico)

The geomicrobiology of crater lake microbialites remains largely unknown despite their evolutionary interest due to their resemblance to some Archaean analogs in the dominance of in situ carbonate precipitation over accretion. Here, we studied the diversity of archaea, bacteria and protists in microbialites of the alkaline Lake Alchichica from both field samples collected along a depth gradient (0–14 m depth) and long-term-maintained laboratory aquaria. Using small subunit (SSU) rRNA gene libraries and fingerprinting methods, we detected a wide diversity of bacteria and protists contrasting with a minor fraction of archaea. Oxygenic photosynthesizers were dominated by cyanobacteria, green algae and diatoms. Cyanobacterial diversity varied with depth, Oscillatoriales dominating shallow and intermediate microbialites and Pleurocapsales the deepest samples. The early-branching Gloeobacterales represented significant proportions in aquaria microbialites. Anoxygenic photosynthesizers were also diverse, comprising members of Alphaproteobacteria and Chloroflexi. Although photosynthetic microorganisms dominated in biomass, heterotrophic lineages were more diverse. We detected members of up to 21 bacterial phyla or candidate divisions, including lineages possibly involved in microbialite formation, such as sulfate-reducing Deltaproteobacteria but also Firmicutes and very diverse taxa likely able to degrade complex polymeric substances, such as Planctomycetales, Bacteroidetes and Verrucomicrobia. Heterotrophic eukaryotes were dominated by Fungi (including members of the basal Rozellida or Cryptomycota), Choanoflagellida, Nucleariida, Amoebozoa, Alveolata and Stramenopiles. The diversity and relative abundance of many eukaryotic lineages suggest an unforeseen role for protists in microbialite ecology. Many lineages from lake microbialites were successfully maintained in aquaria. Interestingly, the diversity detected in aquarium microbialites was higher than in field samples, possibly due to more stable and favorable laboratory conditions. The maintenance of highly diverse natural microbialites in laboratory aquaria holds promise to study the role of different metabolisms in the formation of these structures under controlled conditions

Forging Ahead By Land and By Sea: Archaeology and Paleoclimate Reconstruction in Madagascar

Madagascar is an exceptional example of island biogeography. Though a large island, Madagascar’s landmass is small relative to other places in the world with comparable levels of biodiversity, endemicity, and topographic and climatic variation. Moreover, the timing of Madagascar’s human colonization and the social-ecological trajectories that followed human arrival make the island a unique case study for understanding the dynamic relationship between humans, environment, and climate. These changes are most famously illustrated by the mass extinction of the island’s megafauna but also include a range of other developments. Given the chronological confluence of human arrival and dramatic transformations of island ecologies, one of the most important overarching questions for research on Madagascar is how best to understand the interconnections between human communities, the environment, and climate. In this review paper, we contribute to the well-established discussion of this complex question by highlighting the potential for new multidisciplinary research collaborations in the southwest part of the island. Specifically, we promote the comparison of paleoclimate indicators from securely dated archaeological and paleontological contexts with Western Indian Ocean climate records, as a productive way to improve the overall resolution of paleoclimate and paleoenvironmental reconstruction for the island. Given new archaeological findings that more than double the length of Madagascar’s human occupation, models of environmental transformation post-human arrival must be reassessed and allow for the possibility of slower and more varied rates of change. Improving the spatial and temporal resolution of paleoclimate reconstruction is critical in distinguishing anthropogenic and climate drivers of environmental change. It will also increase our capacity to leverage archaeological and paleoclimate research toward resolving modern challenges, such as environmental conservation and poverty alleviation