Cytoplasmic DNA variation in and genetic delimitation of Abies nephrolepis and Abies holophylla in northeastern China

It has recently been hypothesized that genetic markers experiencing high rates of gene flow would be better suited to differentiate closely related species. We tested this hypothesis by examining genetic variation 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 (Trautv.) Maxim. and Abies holophylla Maxim., with overlapping distributions in northeastern 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 was 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.