Natural hybridization between Engelmann and blue spruce in southwestern Colorado: Genetic evidence from RFLP analysis of mitochondrial and chloroplast DNA

Engelmann spruce (Picea engelmannii) and blue spruce (P. pungens) are two western spruce species that are morphologically very similar and usually separated by differences in elevation. Occasionally, the two species are found in parapatry where they may hybridize. There were 4 main objectives of this research. (1) Determine the inheritance of mitochondrial DNA (mtDNA) in Picea, (2) investigate the stability of the mechanism that controls inheritance of mtDNA in Picea, (3) ascertain the suitability of Restriction Fragment Length Polymorphism (RFLP) analysis, using mtDNA and chloroplast DNA (cpDNA) probes, as a technique for identifying natural hybrids, and (4) investigate a putative hybrid zone between Engelmann and blue spruce in the Scotch Creek drainage of southwestern Colorado.; RFLP analysis of total DNA from foliage samples of Serbian, white spruce and fifteen interspecific hybrids representing 5 separate crosses, including reciprocals, was used to demonstrate the maternal inheritance of mtDNA in Picea. Maternal inheritance was indicated in all hybrids for nine diagnostic enzyme/probe combinations (AvaI, BamHI, ClaI, EcoRI, or ScaI/ATPase{dollar}alpha{dollar} and ClaI, EcoRI, ScaI, or PstI/COXII) and no paternal or non-parental bands were detected. Thus, the mechanism that controls the inheritance of mitochondria in Picea is functional even in wide interspecific crosses.; The next series of experiments utilized mtDNA and cpDNA probes and RFLP analysis to differentiate 14 of 14 artificial Engelmann X blue spruce F{dollar}sb1{dollar} hybrids from their parents. This was possible due to the uniparental inheritance of organelles in Picea, which dictates that mitochondria are maternally inherited while chloroplasts are paternally inherited, and the unilateral crossing incompatibility between Engelmann and blue spruce where hybrids are successful only when Engelmann spruce is the female parent. Finally, the same enzyme/probe combinations (BamHI/COXII and ClaI/P16) used above, plus two new combinations (AvaI/ATPase{dollar}alpha{dollar} and SmaI/P3) were used in the investigation of a putative hybrid zone which resulted in the discovery of four naturally occurring interspecific hybrids (one of which was heteroplasmic) and a potential introgressant. A fire disturbance model for the Scotch Creek drainage is presented that allows for the continued integrity of the two species despite high levels of natural hybridization and introgression.