Population structure, genic diversity, and morphological variation in <i>Pinus</i><i>contorta</i> Dougl.

Abstract

Lodgepole pine (Pinuscontorta Dougl.) occupies a large and ecologically diverse range in western North America. The species is generally recognized as consisting of four subspecies, three of which are widespread and the fourth endemic to the north coast of California. Geographic isolation of subspecies is nearly complete although gene flow may occur in certain instances. Moderate heterozygosity estimates (0.10–0.14) and low standard errors of the estimate (0.02–0.04) were obtained for all populations of lodgepole pine and are comparable with other recent studies of conifers that based estimates on 20 or more loci. The distribution of allozyme variation indicates that very little population differentiation has occurred. Approximately 91% of the allozyme variability resides within populations, with 3 and 6% distributed among subspecies and among populations, respectively. The extent of population differentiation is far less than that observed for many herbaceous plants but similar to reports for other conifers. In contrast, a large proportion of morphometric variation in lodgepole pine cone and seed traits is distributed among subspecies (38%) and among populations within subspecies (19%). This may be attributed to the effects of strong selective pressures acting on important reproductive structures and to the conventional methodology for analyzing morphometric variation. The present study confirms, with minor exceptions, an earlier taxonomic treatment of lodgepole pine. Notably, the assignment of lodgepole pine in the Cascade Range of southern Oregon to ssp. murrayana is probably inappropriate. While morphological data suggest a close affinity to ssp. murrayana, allozyme data suggest that populations in this area should be assigned to ssp. latifolia.