Chloroplast DNA polymorphisms in lodgepole and jack pines and their hybrids.

Abstract

Samples taken from throughout the ranges of distribution of lodgepole pine (Pinus contorta Dougl. ex. Loud.) and jack pine (Pinus banksiana Lamb.) were assayed for Sal I and Sst I chloroplast DNA restriction fragment variation. Although the chloroplast genome is often regarded as highly conserved, at least 2 distinct Sal I and 13 distinct Sst I restriction fragment banding patterns occur in these closely related species. None of the chloroplast DNA restriction fragment banding patterns observed in allopatric lodgepole pine was observed in allopatric populations of jack pine, and vice versa, even though the two species share an extensive zone of sympatry, and gene flow between the species has been reported for nuclear genes. However, several atypical Sst I restriction fragment banding patterns occur only in or near the zone of sympatry. Chloroplasts have been reported to be inherited maternally in the great majority of species studied; however, restriction fragment analyses indicated that chloroplasts are inherited paternally in controlled matings between lodgepole pine (Y) and jack pine (i).The chloroplast genome, which averages about 150 kilobase pairs (kbp) in size, encodes gene products that are involved in photosynthesis (1). It is inherited maternally in the great majority of species that have been studied, but biparental inheritance has been reported in at least 20 species (2, 3). Although studies of chloroplast DNA (cpDNA) have usually been based on one or a few samples per species, they have demonstrated that diversity among species is common and they have been informative phylogenetically (4-6). There have been few studies of intraspecific cpDNA polymorphisms. Although examples of intraspecific cpDNA polymorphisms have been reported (7-11), small sample sizes have been employed or the variants observed have been at low frequency; Consequently, little is known of the extent of intraspecific cpDNA diversity. In this paper we present evidence, from large samples, that lodgepole pine (Pinus contorta Dougl. ex. Loud.) and jack pine (Pinus banksiana Lamb.) differ in their Sal I and Sst I cpDNA phenotypes and that there are a large number of distinct Sst I restriction fragment variants throughout the wide allopatric distributional ranges ofboth species, as well as within a zone of sympatry in which the ranges of the two species overlap. We also present evidence that introgression of Sal I and Sst I variants is rare between the species and that cpDNA is inherited paternally in matings of P. contorta (9) with P. banksiana (d).MATERIALS AND METHODS Plant Materials. In total, 371 individuals were sampled, including 153 individuals of lodgepole pine from 63 populations in the allopatric (nonoverlapping) region, 115 individuals ofjack pine from 68 populations in the allopatric region, and 95 individuals from 16 populations in the zone of sympatry (Fig. 1); all four subspecies of P. contorta were represented in the sample of lodgepole pine. To maximize the number of populations represented, only a single indi...

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