Effect of Population Size and Mutation Rate on the Evolution of RNA Sequences on an Adaptive Landscape Determined by RNA Folding.

The dynamics of populations evolving on an adaptive landscape depends on multiple factors, including the structure of the landscape, the rate of mutations, and effective population size. Existing theoretical work often makes ad hoc and simplifying assumptions about landscape structure, whereas experimental work can vary important parameters only to a limited extent. We here overcome some of these limitations by simulating the adaptive evolution of RNA molecules, whose fitness is determined by the thermodynamics of RNA secondary structure folding. We study the influence of mutation rates and population sizes on final mean population fitness, on the substitution rates of mutations, and on population diversity. We show that evolutionary dynamics cannot be understood as a function of mutation rate µ, population size N, or population mutation rate Nµ alone. For example, at a given mutation rate, clonal interference prevents the fixation of beneficial mutations as population size increases, but larger populations still arrive at a higher mean fitness. In addition, at the highest population mutation rates we study, mean final fitness increases with population size, because small populations are driven to low fitness by the relatively higher incidence of mutations they experience. Our observations show that mutation rate and population size can interact in complex ways to influence the adaptive dynamics of a population on a biophysically motivated fitness landscape

Floristic characteristics of the Hyrcanian submountain forests (case study: Ata-Kuh forest)

Ata-Kuh forest, a preserved area within Hyrcanian relict forests, with an area of 700 ha is located in north of Iran. Based on floristic studies from 2011 through 2012, 194 vascular plant species were identified belonging to 143 genera and 66 families. Among our samples, 24 taxa were endemic to Hyrcanian area. The largest families in the area were Rosaceae (10.3 %), Poaceae (9.7 %), Asteraceae (6.7 %), Fabaceae (5.6 %) and Lamiaceae (5.1 %). The genera represented by the greatest number of species were Rubus (8 species), Carex (7 species), Viola and Euphorbia (each with four species). Classification based on life form indicated that geophytes comprise the largest proportion of the plants in the studied area. From the chorological point of view, the largest proportion of the flora belonged to the Euro-Siberian elements (60 taxa, 31.1%). In this study, a comparison was performed between our results and other studies on the northern Iranian forests with respect to life forms and phytochoria. Psilotum nodum is reported here again from a new locality in North Iran, indicating the old Tertiary history of this forest