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We have found that genomic diversity is generally positively correlated with abiotic and biotic stress levels (1-3). However, beyond a high-threshold level of stress, the diversity declines to a few adapted genotypes. The Dead Sea is the harshest planetary hypersaline environment (340 g⅐liter ؊1 total dissolved salts, Ϸ10 times sea water). Hence, the Dead Sea is an excellent natural laboratory for testing the ''rise and fall'' pattern of genetic diversity with stress proposed in this article. Here, we examined genomic diversity of the ascomycete fungus Aspergillus versicolor from saline, nonsaline, and hypersaline Dead Sea environments. We screened the coding and noncoding genomes of A. versicolor isolates by using >600 AFLP (amplified fragment length polymorphism) markers (equal to loci). Genomic diversity was positively correlated with stress, culminating in the Dead Sea surface but dropped drastically in 50-to 280-m-deep seawater. The genomic diversity pattern paralleled the pattern of sexual reproduction of fungal species across the same southward gradient of increasing stress in Israel. This parallel may suggest that diversity and sex are intertwined intimately according to the rise and fall pattern and adaptively selected by natural selection in fungal genome evolution. Future large-scale verification in micromycetes will define further the trajectories of diversity and sex in the rise and fall pattern. G enomic diversity in nature across all forms of life at global, regional, and local scales has been investigated widely since 1975 at the Institute of Evolution at the University of Haifa (Haifa, Israel) (1-4). The major problem investigated was how much of the genomic diversity in nature is adaptive. Our results indicated that genomic diversity is positively correlated with, and partially predictable by, ecological diversity and environmental stress (3). Theoretically, spatial and temporal ecological variation is of prime importance in maintaining genomic diversity in nature. Even in small isolated populations, genomic diversity is influenced strongly by natural selection, including diversifying, balancing, cyclical, and purifying selective regimes, interacting with but ultimately overriding the effects of mutation, migration, and stochasticity (3). The genomic era dramatically reinforced insights into genomic diversity as a factor in the twin evolutionary processes of adaptation and speciation. Molecular methods such as amplified fragment length polymorphism (AFLP) (5) can screen diversity effectively in both coding and noncoding regions of individuals and populations, making DNA-based studies excellent monitors of evolution. Here, we examined in filamentous fungi the relation between increasing ecological salinity stress and genome diversity from mild to extreme stress, culminating in the extreme hypersaline Dead Sea.The Dead Sea, located in the Syrian-African Rift Valley between Israel and Jordan, is a unique ecological theater. Its waters are hypersaline (340 g⅐liter Ϫ1 total dissolved salts) and domi...

The Dead Sea is one of the most hypersaline habitats on Earth. The fungus Eurotium rubrum (Eurotiomycetes) is among the few species able to survive there. Here we highlight its adaptive strategies, based on genome analysis and transcriptome profiling. The 26.2 Mb genome of E. rubrum shows, for example, gains in gene families related to stress response and losses with regard to transport processes. Transcriptome analyses under different salt growth conditions revealed, among other things differentially expressed genes encoding ion and metabolite transporters. Our findings suggest that long-term adaptation to salinity requires cellular and metabolic responses that differ from short-term osmotic stress signalling. The transcriptional response indicates that halophilic E. rubrum actively counteracts the salinity stress. Many of its genes encode for proteins with a significantly higher proportion of acidic amino acid residues. This trait is characteristic of the halophilic prokaryotes as well, supporting the theory of convergent evolution under extreme hypersaline stress.