Conservation genetics and evolutionary history of Gleditsia caspica: Inferences from allozyme diversity in populations from Azerbaijan

摘要

Gleditsia caspica is an endemic tree species found in the endangered lowland Hyrcanian forests near the Caspian Sea in southeastern Azerbaijan and northwestern Iran. Phylogenetic analyses show that G. caspica is a derivative of G. japonica, a widely distributed species of eastern Asia. Using allozyme markers to investigate genetic diversity within two populations from Azerbaijan, we discovered that a population from a protected nature reserve was composed largely of first-generation hybrids between G. caspica and G. triacanthos, which is native to eastern North America but is planted as an ornamental shade tree in Azerbaijan. Hybrids exhibited higher levels of self-fertilization and lower seed production than either parental species. In the second population, composed of pure G. caspica, 11 of 31 loci scored were polymorphic, the average number of alleles per locus was 1.39, and gene diversity was 0.105. All diversity estimates were substantially lower than those we obtained from a small sample of G. japonica from South Korea and than estimates from more extensive samples of South Korean G. japonica and North American G. triacanthos published by other workers. We conclude that (i) in addition to ongoing threats from habitat conversion and fragmentation, G. caspica may also be threatened in Azerbaijan by hybridization with G. triacanthos; and (ii) low variability in G. caspica populations is most likely not a consequence of recent habitat loss and reductions in population size, but instead reflects a long history of range contraction and endemism following isolation from G. japonica during the Pliocene or Pleistocene.