Effects of population structure and cone production on outcrossing rates in Engelmann spruce and subalpine fir.

Abstract

In adjacent subpopulations in the Colorado Front Range, the overall multilocus outcrossing rate of 0.93 for Picea engelmannii was significantly higher than the outcrossing rate of 0.89 for Abies lasiocarpa. Outcrossing rates varied from 0.73-0.97 for spruce and 0.65-0.94 for fir when trees of each species were grouped according to age, size, spatial distribution, maternal heterozygosity, cone production and year of sampling. In both spruce and fir, trees with higher levels of male-cone production and/or more clumped spatial distribution had lower outcrossing rates. Temporal variation in outcrossing rates within subpopulations, examined only in spruce, was less than variation between subpopulations. Male-cone production was significantly correlated with tree size; highest outcrossing rates are expected on trees that are medium to large in size. While there is some temporal variation, patterns of male cone production and spatial distribution of individuals are the most important factors influencing outcrossing levels in these wind-pollinated forest trees. -from Author