Measurement of gene flow in Lupinus texensis

Abstract

Gene flow, the movement or dispersal of genes within or among populations, is a crucial factor in determining the structure and cohesiveness of species and populations. Spatial restriction of gene flow can lead to non-random mating and to subdivision of a population into genetic neighbourhoods. On the other hand, extensive gene flow over large geographical areas can overshadow the influence of selection, leading to genetic similarity among populations and increased uniformity within a species. The extent and magnitude of actual gene flow are thus relevant to a broad range of disciplines. While the central role of gene flow is widely recognised, actual measurements of gene flow in either plants or animals are few. In plants gene flow can occur via seed or pollen dispersal. Levels of gene flow due to pollen dispersal have usually been inferred, either by marking pollen with a chemical or radioactive label for wind pollinated species or by determining the distribution of pollinator foraging flight distances for insect-pollinated species. Measurements of gene flow via pollen movement in plants have been limited to studies of a few agricultural species, where the minimum separation distance required to isolate stocks genetically was of interest^1,2. Here I report the measurement of the pollen component of gene flow in the insect-pollinated species, Lupinus texensis, compare the actual gene flow distribution with the distribution inferred from pollinator flight movements, and finally, determine the genetic neighbourhood size of this species from the pollen and seed dispersal distributions. Actual gene flow via pollen is found to be greater than would be inferred from pollinator movement alone. Gene flow and neighbourhood size are nevertheless very restricted.