Evolution of genomic diversity and sex at extreme environments: Fungal life under hypersaline Dead Sea stress

Abstract

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...

Adaptation and incipient sympatric speciation of Bacillus simplex under microclimatic contrast at “Evolution Canyons” I and II, Israel

“…Diversity is higher under European-like shady conditions. A positive correlation of genetic diversity with abiotic and biotic stresses has been widely documented (21,32,(44)(45)(46). B. simplex strains are strongly influenced by the soil specificities, which are undoubtedly caused by the interslope microclimatic differences and resulting divergent macrobiota (47).…”

Reproductive output of mosses under experimental warming on Fildes Peninsula, King George Island, maritime Antarctica

“…One possibility is that the mosses of Antarctica are under selective pressure to reproduce asexually rather than via sexual reproduction, perhaps because only a few phenotypes are adapted to such environments. Under such a scenario, sexual reproduction would not be adaptive under extreme stress and individuals that have evolved to favor asexual reproduction would be favored [33]. Alternatively, the abiotic conditions of Antarctica may limit sexual reproduction via short growing seasons, sporophyte mortality due to desiccation [67], sporophyte abortion after extreme conditions in winters or summers [26,67], and notably diurnal freeze-thaw cycles which may prevent gametangial initiation or maturation, fertilization, or sporophyte development [35].…”

Guanophilic Fungi of Mouse-Tailed Bats

“…Aspergillus niger produces many industrial important enzymes like amylase, amyloglucosidase, cellulases, glucoamylase, lactase, invertase, pectinase (Gautam et al, 2011). Aspergillus versicolor found in the guano of R. hardwickii was widely isolated from soil, indoor environments (Shelton et al, 2002;Engelhart et al, 2002;Amend et al, 2010;Anderson et al, 2011), various foods and hyper saline water (Kis-Papo et al 2003;Mbata, 2008) and also associated with many health issues of humans and animals (Perri et al, 2005;Baddley et al, 2009;Edmondson et al, 2009;Moreno and Arenas, 2010). It produces sterigmatocystin, a mycotoxin that is a precursor of aflatoxin B1 (Mills and Abramson, 1986;Tuomi et al, 2000;Nielsen, 2003;Veršilovskis and Saeger, 2010).…”