Sergei Volis

Abstract:  A joint demographic and population genetics stage‐based model for a subdivided population was applied to Gentiana pneumonanthe, an early successional perennial herb, at a regional (metapopulation) scale. We used numerical simulations to determine the optimal frequency of habitat disturbance (sod cutting) and the intensity of gene flow among populations of G. pneumonanthe to manage both population viability and genetic diversity in this species. The simulations showed that even small populations that initially had near‐equal allele frequencies could, if managed properly through sod cutting every 6 to 7 years, sustain their high genetic variation over the long run without gene flow. The more the allele frequencies in the small populations are skewed, however, the higher the probability that in the absence of gene flow, some alleles will be lost and within‐population genetic variation will decrease even under proper management. This implies that although local population dynamics should be the major target for management, regional dynamics become important when habitat fragmentation and decreased population size lead to the loss of local genetic diversity. The recommended strategy to improve genetic composition of small populations is the introduction of seeds or seedlings of nonlocal origin.

Plasticity of the phenotypic architecture of wild barley, Hordeum spontaneum, was studied in response to water and nutrient stress. Direct and indirect selection on several vegetative and reproductive traits was estimated and path analysis used to reveal how regulating pathways via maternal investment differed between environments. Vegetative traits displayed differential regulating effect on fitness across experimental environments: (1) increase in size was selected for under optimal conditions and under water stress, but not under nutrient stress; (2) allocation to root biomass was selected for under optimal conditions, but it had no effect under nutrient stress and was strongly selected against when water was limiting; (3) delayed onset of reproduction was selected under nutrient limitation whereas earlier onset was selected under water stress. The regulating effect of reproductive traits on final reproductive output also differed across treatments, operating either at the ‘early’ stage of plant development through varying the number of initiated spikelets per spike (no stress and water stress treatment) or at the ‘late’ developmental stage adjusting the fertile spikelet weight (no stress and nutrient stress treatment). Reproductive output was regulated via seed abortion under no stress and water stress treatments. Although the underlying mechanism of the regulation through abortion has yet to be discovered, the specific mechanism of abortion under water stress appears to be different from that under optimal conditions. Our results demonstrate that not only is the character architecture in wild barley plastic and sensitive to changing availability of water and nutrients, but the regulating mechanism of maternal investment is also environmentally sensitive.

Populations of wild barley, H. spontaneum Koch., were collected in two countries, Israel and Turkmenistan, in environments representing two similar sharp clines of aridity. This allowed us to use the same criteria to define species core and periphery in two regions. Plants from 10 Israeli and 19 Turkmenian populations were grown in a field trial with three water treatments and compared for amount and structure of variation in phenological and morphological traits. Extent of variation was similar in populations at species border (periphery by aridity criterion) or at species border and near it (by habitat), and in populations inhabiting favorable environments away from the border (core). In contrast, two regions (Israel and Turkmenistan) exhibited different amount of variation in phenotypic traits. Israeli populations were more diverse than Turkmenian populations in all except one phenotypic traits and the variation was differently structured among regionally specific core and periphery. While Turkmenian core and periphery defined by either criterion did not differ for all except one trait, corresponding Israeli populations exhibited opposite patterns of variation for trait complexes. Israeli core (Mediterranean) populations were twice as variable than peripheral (desert) populations in parameters of reproductive growth (stem, spike and awn length) and grain filling (spikelet weight) and half as variable in the length of flag and penultimate leaves and onset of reproduction. Possible modes of regionally specific natural selection as a cause of regional/local variation in phenotypic triats are discussed.

Reciprocal introduction of seeds and seedlings was used to test for local adaptation and to identify a set of co-adapted traits of Mediterranean and desert ecotypes of wild barley Hordeum spontaneum. Evidence for local adaptation was found in seedling introductions into intact environments and from ecotype colonization success in the first generation after seed dispersal. Estimates of fitness were obtained at particular stages of the life cycle (seed, seedling and adult). Experiments that manipulated the environment (vegetation removal, different plant density) demonstrated the intensity and direction of natural selection in different life history episodes, but there was no strong evidence for local adaptation under these circumstances. The observed genetically determined differences between Mediterranean and desert ecotypes can be summarized as the following: reproductive output was higher in desert plants, with smaller seeds than in Mediterranean plants. There was a higher competitive ability of Mediterranean than desert plants. Plants of desert origin had significant reductions in yield when grown in mixed stands with Mediterranean plants; no such effect was observed for plants of Mediterranean origin. Seed germination and seedling survival was lower in seeds of desert origin. This was due to both: genetically determined higher dormancy of desert seeds and a trade-off between no. of seeds and their size (directly related to seed/seedling vigour).

Populations of wild barley, Hordeum spontaneum Koch, were collected in two distinct climatic regions, desert and Mediterranean. Plants from five desert and five Mediterranean populations were compared and contrasted for extent and structure of phenotypic variation. These same 10 and one other population from each region were analyzed for allozyme variation. In a field trial of phenotypic diversity, two phenological and 14 morphological traits were examined. Study of allozyme variation was performed using eight enzyme systems encoding for 13 loci. Plants from the desert and Mediterranean regions were significantly different in seven of 16 phenotypic traits, exhibited a high (30%) interregional component of phenotypic variation, and showed a high degree of segregation on a principal component scattergram indicating ecotypic differentiation. Mediterranean populations were twice as variable as desert populations in reproductive growth parameters (stem and spike length) and grain filling (spikelet weight), but half as variable for onset of reproduction. The extent and structure of phenotypic and allozyme variation did not match. The Mediterranean and desert populations did not differ in amount of allozyme variation as estimated by mean number of alleles per locus, effective number of alleles, polymorphism, and gene diversity (n(a), n(e), P, and H(e)), did not segregate on the basis of population genetic distances, and exhibited a low proportion of interregion allozyme diversity (2%). No effect of selection on allozyme distribution was detected. Our results suggest that the adaptation of plants originating from desert and Mediterranean environments is reflected in phenotypic but not in allozyme variation.