Gene flow, spatial patterns and seed-collection zones

Abstract

Models of gene flow, selection and demography were employed to determine the minimum limits and amplitudes of seed-collection and seed-transfer zones in forest trees, using loblolly pine ( Pinus taeda L.) and white spruce ( Picea glauca (Moench.) Voss.) as examples. Seed-collection zones were defined in terms of spatial patterns for polygenic (growth) characters. Fora given character, the boundaries of a seed-collection zone were found to be determined by interactions among gene flow, selection strength and genetic variation for that character at a specific age. For example, the width of a seed-collection zone for 5-year-old trees of loblolly pine was found to be larger if it was based on diameter rather than height growth. Conversely, the width of these zones differed between 5- and 15-year-old trees for either diameter or height growth. A similar trend was evident for white spruce. The average minimum width of seed-collection zones for loblolly pine and white spruce varied from 324 to 400 m. These results are consistent with many reports on gene flow, selection and differentiation in natural populations of forest trees. Seed-transfer zones should be based on the amount of genetic variation in the adaptive traits of each population representing a seed-collection zone. The adaptive amplitudes of populations from various seed-collection zones on a large geographical scale must be determined on the basis of the homeostatic properties specific to each population.