Genetic divergence and analysis of the relationships between species of Mosla(Labiatae)
ZHOU Shi Liang (Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China)
Seven species were recognized in Mosla in China. M. pauciflora (C. Y. Wu) C. Y. Wu et H. W. Li is an allotetraploid (2n=36), while the other six species are diploids (2n=18). Cluster analysis based on allozyme data from 28 loci of 15 enzyme systems reveals that the six diploid species formed three species pairs. M. cavaleriei Lévl. is closely related to M. dianthera (Buch. Ham. ex Roxb.) Maxim., M. chinensis and M.hangchouensis Matsuda are sibling species, and M. scabra (Thunb.) C. Y. Wu et H. W. Li is allied to M. soochouensis. Although M. cavaleriei and M. dianthera are close relatives, considerable genetic divergence has been detected between them. One third of alleles are unique to either of them, and 28.6% of their loci have different alleles fixed. The average genetic identity (I) between populations of these two species is 0.770, and the average genetic distance (D) is 0.261. M. scabra and M. soochouensis are the least divergent species pair (I=0.979, D=0.025). No completely divergent locus was detected, and the percentages of unique alleles are 11.1% to M. scabra and 16.7% to M. soochouensis. This finding indicates that a high level of genetic differentiation is unnecessarily a prerequisite of speciation. A moderate divergence is detected between M. chinensis and M. hangchouensis (I=0.899, D=0.107, and 7.1% of completely diverged loci) yet the latter harbors four times as many unique alleles (45.1%) as the former does( 11.8% ). Compared to the genetic divergence between M. scabra and M. soochouensis, M. dianthera and M. hangchouensis and may well been undergoing active speciation have the high genetic distance between populations (0.034 and 0.026 respectively).