Date of Award
Program or Major
Doctor of Philosophy
Anita S Klein
Mitochondrial and chloroplast haplotypes were identified in range-wide populations of white (Picea glauca), black (P. mariana ) and red spruce (P. rubens). The chloroplast genome exhibited more intraspecific variation than the mitochondrial genome. Red spruce displayed the most total chloroplast genetic diversity (H T = 0.52). Neighbor-joining analysis arranged the chloroplast haplotypes into three monophyletic groups that were nearly 100% species-specific. These results strongly refute a previously proposed progenitor/derivative relationship of black/red spruce. Red and black spruce were estimated to have diverged from their common ancestor ∼0.6--3.5 million years ago. Mitochondrial diversity detected in black spruce was attributed to interspecific hybridization, estimated to have taken place during the Holocene epoch (≥4000 years ago). White spruce mitochondrial haplotypes detected in multiple black spruce populations indicated that unidirectional introgressive hybridization has occurred between these two species. An east-west divide and opposing clines of chloroplast haplotypes in black spruce are consistent with leptokurtic dispersal out of either (1) a southeast glacial refugium of North America or (2) a small hypothetical northwestern refugium.
Some individual markers within cytoplasmic and nuclear genomes are species-specific. Some of these single nucleotide polymorphisms are appropriate to identify spruce macrofossils recovered from eastern North American lake cores. Since white, black and red spruce have differing climate tolerances, this would enable paleoclimatologists to track the migration routes of the individual spruce species during the last ice age and infer more precise climate estimates for eastern North America. Agarose gel electrophoresis, Southern blot and hybridization suggested that authentically ancient DNA survived in spruce macrofossils from 10--20,000 year old sediments of Browns Pond, Virginia.
A robust species phylogeny of the Picea is desirable to answer multiple questions about the history of the genus' biogeography. A phylogenetic study of sixteen North American and Eurasian Picea species was conducted utilizing DNA sequences of the chloroplast trnK intron and the mitochondrial nad1 intron 2. The topologies of inferred trees varied significantly, in particular to the placement of P. omorika, P. mexicana and P. glauca . Inter-species hybridization and introgression are discussed as possible reasons behind such incongruencies.
Germano-Presby, Joselle, "Nuclear and cytoplasmic genetic variation in Picea: DNA markers for evaluating past migration, introgression and evolutionary history" (2003). Doctoral Dissertations. 125.