Cytoplasmic DNA Variation In And Genetic Delimitation Of Abies Nephrolepis And A. Holophylla

Delimiting species is important in the context of understanding many evolutionary mechanisms and processes. Recent empirical studies suggest that genetic variations experiencing high rates of gene flow are more effective to diagnose the closely related conifer species than those experiencing low rates of gene flow, in part because high rates of intraspecific gene flow can prevent introgression. In Abies, chloroplast (cp) and mitochondrial (mt) DNAs are normally paternally and maternally inherited, respectively, and thus their relative rates of intraspecific gene flow are expected to be high and low, respectively. In this study, we tested the hypothesis by examining genetic variations in the chloroplast (cp) DNA (trnS-trnG and trnL-trnF) and mitochondrial (mt) DNA(nad5 intron 4 and nad7 intron 1) of two fir species, Abies nephrolepis and A. holophylla, with overlapping distributions in northeast China. Two mitotypes were identified; one was common to both species, whereas the other occurred only in A. holophylla. However, four chlorotypes were identified, clustered into two species-specific groups exhibiting distinct mutations; species delimitation using these generated genetic variants congruent with those obtained by morphological delimitation. Our findings supported the hypotheses that cpDNA, with its high rates of gene flow, is more useful than mtDNA for species delimitation in fir trees. In addition, the low intraspecific diversity observed for both species may result from their repeated range retractions and expansions in response to climatic oscillations in the history.