Diversity generally increases ecosystem productivity over short timescales. Over longer timescales, both ecological and evolutionary responses to new environments could alter productivity and diversity–productivity relationships. In turn, diversity might affect how component species adapt to new conditions. We tested these ideas by culturing artificial microbial communities containing between 1 and 12 species in three different environments for ∼60 generations. The relationship between community yields and diversity became steeper over time in one environment. This occurred despite a general tendency for the separate yields of isolates of constituent species to be lower at the end if they had evolved in a more diverse community. Statistical comparisons of community and species yields showed that species interactions had evolved to be less negative over time, especially in more diverse communities. Diversity and evolution therefore interacted to enhance community productivity in a new environment.

The effect of biodiversity on the ability of parasites to infect their host and cause disease (i.e. disease risk) is a major question in pathology, which is central to understand the emergence of infectious diseases, and to develop strategies for their management. Two hypotheses, which can be considered as extremes of a continuum, relate biodiversity to disease risk: One states that biodiversity is positively correlated with disease risk (Amplification Effect), and the second predicts a negative correlation between biodiversity and disease risk (Dilution Effect). Which of them applies better to different host-parasite systems is still a source of debate, due to limited experimental or empirical data. This is especially the case for viral diseases of plants. To address this subject, we have monitored for three years the prevalence of several viruses, and virus-associated symptoms, in populations of wild pepper (chiltepin) under different levels of human management. For each population, we also measured the habitat species diversity, host plant genetic diversity and host plant density. Results indicate that disease and infection risk increased with the level of human management, which was associated with decreased species diversity and host genetic diversity, and with increased host plant density. Importantly, species diversity of the habitat was the primary predictor of disease risk for wild chiltepin populations. This changed in managed populations where host genetic diversity was the primary predictor. Host density was generally a poorer predictor of disease and infection risk. These results support the dilution effect hypothesis, and underline the relevance of different ecological factors in determining disease/infection risk in host plant populations under different levels of anthropic influence. These results are relevant for managing plant diseases and for establishing conservation policies for endangered plant species. Biodiversity has been proposed as a major ecological factor determining disease prevalence. However, the relationship between biodiversity and disease risk remains underexplored. Few studies focus on host-virus systems and, particularly on plant viruses. To address this subject the prevalence of virus infection and disease symptoms was monitored in wild-pepper (chiltepin) populations under different levels of human management. For these populations, species diversity, host genetic diversity and host plant density were determined. Higher levels of human management resulted in increased disease and virus infection risk, which was associated with decreased habitat species diversity and host genetic diversity, and with increased host plant density. More specifically, for wild chiltepin populations, species diversity of the habitat was the primary predictor of disease risk; and host genetic diversity was the primary predictor in managed populations, with host density being generally a poorer predictor of disease risk. These results support a dilution effect of biodiversity on disease risk, and underline the relevance of different ecological factors in determining disease risk in wild and in human-managed habitats.

Barriers to microbial migrations can lead adaptive radiations and increased endemism. We propose that extreme unbalanced nutrient stoichiometry of essential nutrients can be a barrier to microbial immigration over geological timescales. At the oasis in the Cuatro Ciénegas Basin in Mexico, nutrient stoichiometric proportions are skewed given the low phosphorus availability in the ecosystem. We show that this endangered oasis can be a model for a lost world. The ancient niche of extreme unbalanced nutrient stoichiometry favoured survival of ancestral microorganisms. This extreme nutrient imbalance persisted due to environmental stability and low extinction rates, generating a diverse and unique bacterial community. Several endemic clades of Bacillus invaded the Cuatro Cienegas region in two geological times, the late Precambrian and the Jurassic. Other lineages of Bacillus, Clostridium and Bacteroidetes migrated into the basin in isolated events. Cuatro Ciénegas Basin conservation is vital to the understanding of early evolutionary and ecological processes.

The Cuatro Ciénegas Basin (CCB) has been identified as a center of endemism for many life-forms. Nearly half the bacterial species found in the spring systems have their closest relatives in the ocean. This raises the question of whether the high diversity observed today is the product of an adaptive radiation similar to that of the Galapagos Islands or whether the bacterial groups are “survivors” of an ancient sea, which would be of interest for astrobiology. To help answer this question, we focused on Firmicutes from Cuatro Ciénegas (mainly Bacillus and Exiguobacterium). We reconstructed the phylogenetic relationships of Firmicutes with 28 housekeeping genes and dated the resulting tree using geological events as calibration points. Our results show that marine Bacillus diverged from other Bacillus strains 838 Ma, while Bacillus from Cuatro Ciénegas have divergence dates that range from 770 to 202 Ma. The members of Exiguobacterium from the CCB conform to a much younger group that diverged from the Andes strain 60 Ma and from the one in Yellowstone 183 Ma. Therefore, the diversity of Firmicutes in Cuatro Ciénegas is not the product of a recent radiation but the product of the isolation of lineages from an ancient ocean. Hence, Cuatro Ciénegas is not a Galapagos Archipelago for bacteria but is more like an astrobiological “time machine” in which bacterial lineages survived in an oligotrophic environment that may be very similar to that of the Precambrian. Key Words: Firmicutes—Cuatro Ciénegas—Precambrian—Molecular dating—Western Interior Seaway. Astrobiology 12, 674–684.