Rapid population differentrtion in a mosaic environment

Abstract

Populations of the grass species Ant/zoxanthum odoratum were collected at intervals across two boundaries between contrasting plots of the Park Grass Experiment, Rothamsted. One boundary (8L/9L) had been in existence for 112 years, and the other (1L/1U) for 60 years. Environmental conditions at both boundaries changed to almost the maximum extent within 05 m. There were significant differences in height, yield, flowering date, and other morphological attributes between populations collected only 0 1 m apart at each boundary, when grown in spaced plant trials. The sharpest differences occurred between populations collected close to the boundary. The patterns of variation of morphological attributes across one boundary(8L/9L) closely followed the patterns of environmental conditions and vegetation, which were relatively simple. The patterns of variation of morphological attributes across the other boundary (1L/1U) were not simply related to the patterns of environmental conditions or vegetation, which were complex. Reverse dines (Ford, 1971) occurred for several attributes, especially at the 1 L/1 U boundary.At both boundaries, the population collected at the boundary flowered 4-6 days earlier than adjacent populations. There appeared to be partial reproductive isolation between these populations and adjacent populations. Most attributes were highly heritable. Population samples collected in situ as seed were closely similar to population samples collected as tillers. The similarities were greatest for populations collected furthest from the boundary. Comparisons of populations grown from seed and tifier collections indicated that gene flow was greatest 02 m downwind of the boundary, but rapidly declines to a small level at 2 m. © 1976 The Genetical Society of Great Britain. All rights reserved.