Chloroplast DNA diversity among trees, populations and species in the California closed-cone pines (Pinus radiata, Pinus muricata and Pinus attenuata)

Abstract

The amount, distribution and mutational nature of chloroplast DNA polymorphisms were studied via analysis of restriction fragment length polymorphisms in three closely related species of conifers, the California closed-cone pines-knobcone pine: Pinus attenuata Lemm.; bishop pine: Pinus muricata D. Don; and Monterey pine: Pinus radiata D. Don. Genomic DNA from 384 trees representing 19 populations were digested with 9-20 restriction enzymes and probed with cloned cpDNA fragments from Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] that comprise 82% chloroplast genome. Up to 313 restriction sites were surveyed, and 25 of these were observed to be polymorphic among or within species. Differences among species accounted for the majority of genetic (haplotypic) diversity observed [Gst = 84(+/- 13)%]; nucleotide diversity among species was estimated to be 0.3(+/- 0.1)%. Knobcone pine and Monterey pine displayed almost no genetic variation within or among populations. Bishop pine also showed little variability within populations, but did display strong population differences [Gst = 87(+/- 8)%] that were a result of three distinct geographic groups. Mean nucleotide diversity within populations was 0.003(+/- 0.002)%; intrapopulation polymorphisms were found in only five populations. This pattern of genetic variation contrasts strongly with findings from study of nuclear genes (allozymes) in the group, where most genetic diversity resides within populations rather than among populations or species. Regions of the genome subject to frequent length mutations were identified; estimates of subdivision based on length variant frequencies in one region differed strikingly from those based on site mutations or allozymes. Two trees were identified with a major chloroplast DNA inversion that closely resembled one documented between Pinus and Pseudotsuga.