Rapid population differentiation in a mosaic environment

Abstract

SUMMARY1. Reciprocal transplants were made of pairs of contrasting populations of Ant hoxant hum odoratum collected from the Park Grass Experiment at Rothamsted.2. In most cases, plants survived longer, produced more tillers and produced more dry matter when transplanted into their native plots than when transplanted into ecologically contrasting plots.3. The average half-life of plants transplanted into contrasting plots was 8 months, that of plants in their native plots was about 2 years. 4. Selection coefficients against "alien" populations based on survival after 18 months ranged from O'09 to O77 with a mean value of O36. Similar coefficients of selection were calculated for tiller number and plant weight.5. The coefficients of selection on the various plots were correlated with both the yield of herbage on the plots and the vegetation height on the plots, this is discussed in relation to the observed pattern of differentiation of A. odoratum on the plots.6. We conclude that selection pressures acting upon A. odoratum in the mosaic of environments that occur on the Park Grass Experiment are large and sufficient to account for the morphological and physiological differences that have been observed between closely adjacent populations of A. odoratum on the plots.

Experimental evolution in Chlamydomonas II. Genetic variation in strongly contrasted environments

“…There is some evidence for a cost of adaptation from reciprocal transplant experiments, both in natural environments (Antonovics & Primack, 1982;van Tienderen, 1992) and in environments severely disturbed by human activity (Davies & Snaydon, 1976 Levene (1953), creates negative frequency-dependent selection that may retain genetic variance for site-specific fitness permanently in the population, although the conditions for stable genetic equilibrium are quite severe (Maynard Smith & Hoekstra, 1980;Via & Lande, 1985;Gillespie & Turelli, 1989). A less onerous hypothesis is that directional selection is less intense in heterogeneous environments, so that genetic variance, although eventually eliminated, declines more slowly than in comparable environments with uniform conditions of growth.…”

Evolution in Stressful Environments. I. Phenotypic Variability, Phenotypic Selection, and Response to Selection in Five Distinct Environmental Stresses

“…For longlived perennials, selection under environmental stress may lead to a metabolically more conservative phenotype characterized by reduced maximal growth rate, increased allo-cation to storage, and delayed reproduction, as envisioned by the triangle model (Grime 1977). Many perennial plant species or ecotypes characteristic of stressful environments have slower maximal growth rates than related taxa adapted to fertile environments (Clarkson 1967;Grime and Hunt 1975;Davies and Snaydon 1976;Veerkamp et al 1980;Chapin et al 1982;but see Shaw 1988;Wilson 1988;McGraw and Chapin 1989;Rice and Bazzaz 1989;Poorter and Remkes 1990;Chapin and Shaver 1996;Walters and Reich 1996). In contrast, when stress imposes selection on shorter-lived pioneer species, a stress avoidance strategy may evolve.…”

An assessment of the spaced-plant trial technique

“…The most likely cause of the differences between populations in response to sites was the large differences in soil pH (table 2); however, there was no evidence that the populations from plots with a history of liming (IL,42L,1OL) performed better on the calcareous soil at Churn, or that those from unlimed plots (1U, 42U, lOU) performed better on the acid soil at Branshill (table 7). Previous studies with dense plantings of individual populations in contrasting soils (Snaydon, 1970), and with reciprocal transplanting into swards on limed and unlimed plots (Davies and Snaydon, 1976), have shown that, under competitive conditions, each population performs better when grown on its native soil type. The absence of such differences in this study may be the result of the absence of competition, since competition has been shown to increase differences in performance between populations (Snaydon, 1962;Cook et al, 1972); this will be considered below.…”

“…This technique is now being increasingly used in studies of the ecological genetics of plant species (e.g., Davies and Snaydon, 1976;Turkington and Harper, 1979;Antonovics and Primack, 1982;Schmidt and Levin, 1985;McGraw, 1986).…”