BGN 23: Fitness in wild barley from two opposing slopes of a Mediterranean microsite at Mount Carmel, Israel

Fitness in wild barley from two opposing slopes of a Mediterranean microsite at Mount Carmel, Israel.

B. Lavie, V. Stow, T. Krugman, A. Beiles and E. Nevo
Institute of Evolution, University of Haifa, Mt. Carmel, Haifa 31905, Israel.


We tested in wild barley, Hordeum spontaneum, the hypothesis that individuals were locally adapted to microclimatic conditions. Genetic differentiation at the allozymic levels was reported for wild barley, Hordeum spontaneum (Nevo et al., 1981, 1983, 1986), according to soil type, topography and microclimate diversity. Genetic diversity, divergence and adaptations in H. spontaneum was reviewed by Nevo (1992) at local, regional and global scales. Here we report on fitness tests of H. spontaneum from two opposing slopes at Nahal Oren, Mt. Carmel, Israel.

Spike-samples of H. spontaneum were collected in May 1991 on each slope (S and N) from the upper, middle and lower levels, i.e., from 6 sites. The distances between collection sites on each slope were from 20 to 50 meters. From the N-slope, 67 genotypes were collected from top to bottom: 30, 28, and 9, respectively; and from the S-slope 68 genotypes: 30, 14 and 24, respectively. The spikes were stored in a cold room until sowing in November 1991. From each genotype two seeds were sown, one in each type of alternative plots at the Institute of Evolution, Mt. Carmel, Haifa. One plot was exposed to the sun, simulating the conditions on the S-slope. An alternative plot was shaded by a 30% net (i.e., penetration of only 30% of the light) representing conditions on the N-slope. The seeds were sown randomly with a 15 cm distance between plants.

Winter 1991 was very unusually snowy in Mt. Carmel. Consequently, most seeds did not reach maturity. From the N-slope, 61 of 134 seeds yielded spikes and from the S-slope 56 of 136. Originally, the experimental design was pairwise, but due to the high mortality, only 20 pairs from the N-slope and 10 pairs from the S-slope developed to maturity. Thus, we analyzed the data as independent samples. In April, 4 months after the sowing time, each spike was developmentally ranked and the plant was marked by the mean rank of its spikes (Table 1A). In May, all spikes were collected and a yield index expressed by the number of spikes per plant was calculated, representing fitness (Table 1B).

In spite of the low number of maturing plants, we observed the expected trends: All subpopulations developed faster in the sun (p < 0.03 by sign test) but this trend is emphasized more by the S-slope plants whose development in the shade was slower than those from N origin. The average yield (by number of spikes) for the N-slope plants was higher in the shade, while for the S-slope plants the average was higher in the sun. These results were statistically significant only for the upper site S-subpopulation. In this subpopulation, 8 genotypes reached maturity in both sun and shade and all had a higher number of spikes in the sun (p = 0.0039, sign test). Considering all the 10 paired genotypes on the S-slope, 9 genotypes had a higher number of spikes in the sun (p < 0.0l, Wilcoxon sign-rank test). We also compared the frequency of the high yielding plants. The middle N-slope subpopulation did not show the expected trend of higher spike average in the shade, but there were 3 plants with more than 10 spikes per plant in the shade versus none in the sun. On the N-slope as a whole, there were 4 high yielding plants in the shade versus none in the sun (t(57) = 2.1824, p < 0.05, Beiley test for proportions).

The mean for the S-slope genotypes showed a better yield than the N-slope genotypes in both shade and sun, but the difference was greater in the sun, and was significant (t(60) = 3.234 p < 0.001).

These preliminary results in H. spontaneum, of both phenotypic and genotypic adaptations to the drastic microenvironmental divergence at the Mount Carmel Nahal Oren gorge suggest that genetic adaptations to xeric and mesic conditions, respectively, have evolved in wild barley in a microsite, strongly diverging microclimatically due to higher radiation stress on the S-facing slope, which is warmer, drier and environmentally more fluctuating.

Acknowledgement.

We thank Leon Blaustein for commenting on the manuscript. This study was supported by the Israeli Discount Bank Chair of Evolutionary Biology, and the Ancell-Teicher Research Foundation for Genetics and Molecular Evolution, established by Florence and Theodore Baumritter of New York.

Table 1. Comparison of developmental stage (A) and number of spikes (B) between plants growing in shady and in sunny conditions, originating from 6 subpopulations of Hordeum spontanaeum from two opposing slopes (north facing (N) and south facing (S)) at Nahal Oren, Mt. Carmel, Israel. Number of plants tested appear in parenthesis.

References:

Nevo, E., A.H.D. Brown, D. Zohary, N. Storch and A. Beiles. 1981. Microgeographic edaphic differentiation in allozyme polymorphisms of wild barley (Hordeum spontaneum, Poaceae). Pl. Syst. Evol. 138:287-292.

Nevo, E., A. Beiles, N. Storch, H. Doll and B. Andersen. 1983. Microgeographic edaphic differentiation in hordein polymorphisms of wild barley. Theor. Appl. Genet. 64:123-132.

Nevo, E., A. Beiles, D. Kaplan, E.M. Golenberg, L. Olsvig-Whittaker and Z. Naveh. 1986. Natural selection of allozyme polymorphisms: A microsite test revealing ecological genetic differentiation in wild barley. Evolution 40:13-20.

Nevo, E. 1992. Origin, evolution, population genetics and resources for breeding of wild barley, Hordeum spontaneum, in the Fertile Crescent. pp. 19-43. In: Barley: genetics, molecular biology and biotechnology, P. Shewry (ed.) C.A.B. International.


table of contents | BGN main index