Contrasting patterns of genetic diversity in two tropical pines: Pinus kesiya (Royle ex Gordon) and P. merkusii (Jungh et De Vriese)

Alfred E. Szmidt, Xiao-Ru Wang, and Suchitra Changtragoon

Theoretical and Applied Genetics (1996) 92: 436-441.

For reprint, send email to: Alfred E. Szmidt

Abstract

We studied allozyme and chloroplast (cp) DNA variation in natural populations of Pinus kesiya and P. merkusii from Thailand and Vietnam. The results showed striking differences between the two species in the amount and distribution of allozyme variation. Pinus kesiya harboured relatively much allozyme variation and showed weak interpopulational differentiation. In contrast, P. merkusii had very low intrapopulational variability but high level of interpopulational differentiation. The average Nei's genetic distance separating the two species was exceptionally high (0.701) taking into account their close taxonomic placement in the same subsection Sylvestres. The constructed phylogenetic trees revealed very early divergence of P. kesiya and P. merkusii. The present analysis of cpDNA variation also confirmed dissimilar character of these two species and was compatible with other evidence indicating outstanding position of P. merkusii as compared to other Asian members of the subsection Sylvestres. Analysis of cpDNA variation in sympatric populations of P. kesiya and P. merkusii revealed that they are pure representatives of the species in question. This result indicates that despite overlapping distribution P. kesiya and P. merkusii do not hybridise in nature. We suggest that distinct character of P. merkusii is a result of an early separation from other Eurasian pines. Despite spatial proximity, P. kesiya and P. merkusii are held apart by strong reproductive barriers. The low genetic variability of P. merkusii may be explained by previous bottlenecks, reduced gene flow among populations and an inbreeding due to small population size and asynchronous flowering.

Key words: Pinus, allozymes, genetic variation, evolution, migration

by Alfred E. Szmidt