“Evolution

 Canyon”

The Bacillus simplex evolution under environmental stress

Here, I introduce the “Evolution Canyon” model project (EC), and I briefly summarize the results.

1) The "Evolution Canyon" model project

The “Evolution Canyon” is a east-west facing canyon with microclimatically strongly divergent slopes, despite their proximity. The microclimatic heterogeneity results from the slope orientation to the sun: The SFS (red) is always facing the sun, the NFS (blue) is mostly in the shade.

The great advantage of this situation for evolutionary research in natural habitats: Living beings can migrate easily between the slopes, this, however, is ultimately linked to a strong microclimatic habitate change, i.e. to an exposure to natural selection. The question is: Will the pressure of natural selection result in adaptation and, subsequently, in speciation?

References

Edaphic interslope and valley bottom differences at “Evolution Canyon”, Lower Nahal Oren, Mount Carmel, Israel. Nevo, E., Travleev, A.P., Belova, N.A., Tsatskin, A., Pavlicek, T., Kulik, A.F. et al. (1998). Catena 33: 241-254.

Microclimatic interslope differences underlying biodiversity contrasts in “Evolution Canyonr”, Mt. Carmel, Israel. Pavlicek, T., Sharon, D., Kravchenko, V., Saaroni, H., and Nevo, E. (2003). Isr. J Eart Sci 52: 1-9.

Asian, African and European biota meet at “Evolution Canyon” Israel: Local tests of global biodiversity and genetic diversity patterns. Nevo, E. (1995). Proc R Soc Lond [Biol ] 262: 149-155.

Molecular evolution and ecological stress at global, regional and local scales: The Israeli perspective. Nevo, E. (1998). Journal of Experimental Zoology 282: 95-119.

Evolution of genome-phenome diversity under environmental stress. Nevo, E. (2001). Proc Natl Acad Sci U S A 98: 6233-6240.

2) Basic results from EC

In long-term research projects of the “Evolution Canyons” the intraspecific interslope divergence was compared in many species across life including a procaryotic bacterium,  eukaryotic lower and higher plants, fungi and animals. In general, a higher intraspecific genetic diversity was observed in the more stressful SFS (Nevo, 2001). Heritable mutation rate levels in the fungus Sordaria fimicola were higher on the stressful SFS than on the milder NFS (Lamb et al., 1998). Mate choice was highly different between Drosophila melanogaster flies from the NFS and SFS (Korol et al., 2000). The higher copy number of BARE-1 retrotransposons in the wild barley Hordeum spontaneum on the SFS was correlated with adaptive selection in order to cope better with aridity stress (Kalendar et al., 2000). The duplications of the gene cluster for circadian rhythms of the strains living on the SFS of the cyanobacterium Nostoc linckia was discussed as adaptation to the more stressful environment of the SFS slopes (Dvornyk et al., 2001). In summary, there is evidence for the differential evolution of living beings in the more stressful SFS in comparison to their intraspecific counterparts in the milder NFS, indicating incipient speciation processes (Nevo, 2001).

References

Evolution of genome-phenome diversity under environmental stress . Nevo, E. (2001). Proc Natl Acad Sci USA 98, 6233-40.

Inherited and environmentally induced differences in mutation frequencies between wild strains of Sordaria fimicola from “Evolution Canyon”. Lamb, B. C., Saleem, M., Scott, W., Thapa, N. & Nevo, E. (1998). Genetics 149, 87-99.

Genome evolution of wild barley (Hordeum spontaneum) by BARE-1 retrotransposon dynamics in response to sharp microclimatic divergence. Kalendar, R., Tanskanen, J., Immonen, S., Nevo, E. & Schulman, A. H. (2000). Proc Natl Acad Sci U S A 97, 6603-7.

Nonrandom mating in Drosophila melanogaster laboratory populations derived from closely adjacent ecologically contrasting slopes at “Evolution Canyon”. Korol, A., Rashkovetsky, E., Iliadi, K., Michalak, P., Ronin, Y. & Nevo, E. (2000). Proc Natl Acad Sci U S A 97, 12637-42.

Long-term microclimatic stress causes rapid adaptive radiation of kaiABC clock gene family in a cyanobacterium, Nostoc linckia, from “Evolution Canyons” I and II, Israel. Dvornyk, V., Vinogradova, O. & Nevo, E. (2002). Proc Natl Acad Sci U S A 99, 2082-7.

3) Bacillus simplex evolution in EC

We studied approximately 1000 isolates of Bacillus simplex from “Evolution Canyon” I and II. These two canyons are separated by approximately 40 km, but are very similar in their structure.

The questions were:
- Would the genetic structure be related rather to the habitate type, or to the geographical distance?
- How would natural selection shape the genetic structure?
- Would adaptive patterns be visible?

First, we found that the habitate type strongly influenced the genetic divergence of the population. The impact of geographical distance was far less (Sikorski & Nevo, 2005). The results suggest some influence of migration, but this is strongly overridden by natural selection.

Second, we found that natural selection resulted in evolutionary-phylogenetic lineages that are specifically abundant on either slope type, i.e. that are most probably adapted to the specific environmental conditions (Sikorski & Nevo, 2005). We found 2 genomic lineages, that each split into (several) African-like and European-like lineages. In genomic lineage 1 we found nested structures that suggest a switch of habitat type during the phylogenetic genealogy.

Third, we found differences in potentially adaptive phenotypes. The UV-C survival was substantually increased in the African-like lineages of genomic lineage 1. Also, differences in the mutation rates between Afrikan-like and European-like strains were observed (Sikorski & Nevo, 2005).

What are further adaptive phenotypes that could have aided in the evolutionary and slope-specific divergence of lineages? Here are some examples.
- Adaptation to difference in slope temperature.
- Adaptation to the differential nutrient supply.
- What is the role of plasmids in the population?
- What is the role of phages in the population?
- Bacilli may produce bacteriocins. Could bacteriocins as a biological warfare have been influential?

Reference

Adaptation and incipient sympatric speciation of Bacillus simplex under microclimatic contrast at “Evolution Canyons” I and II, Israel. Sikorski, J., and Nevo, E. (2005). Proc Natl Acad Sci USA 102: 15924-15929.