Spatial structure of AFLP genetic diversity of remnant populations of Metasequoia glyptostroboides (Taxodiaceae)

Abstract

The Tertiary relic species, Metasequoia glyptostroboides, is naturally distributed in a narrowly restricted area bordering Hubei, Hunan Provinces and Chongqing City in central China. The genetic background of its overall genetic diversity and population structure is prerequisite for formulating an efficient conservation program and effective practice in management of remnant populations. The spatial structure of gene frequencies of M. glyptostroboides remnant populations in its original habitat was investigated using AFLP markers followed by spatial autocorrelation analysis. A total of 39 individuals were sampled from remnant populations and subjected to spatial autocorrelation analysis in two approaches of equal gene frequency correlograms with five classes and equal distance interval correlograms with ten classes, respectively. Of 46 polymorphic bands generated by six selective primer-pairs, 27 polymorphic bands with frequencies ranging from 25% to 75% were then used to calculate Moran's I spatial autocorrelation coefficient. The result revealed a lack of spatial structure of genetic variation existing in the remnant population of M. glyptostroboides, indicating that genetic variations of the most polymorphic loci were randomly distributed, strongly supported by insignificant Moran's I coefficients. However, lump, depression or double cline structures of the genetic variation were found in a few AFLP markers with significant Moran's I in several distance classes. The distance interval 4-8 km is probably a sufficient barrier to gene flow, as evidenced by Moran's I coefficients showing negative correlations within this distance class. In addition, remnant individuals were not absent in distance classes from 12 to 28 km, suggesting that the habitat of the remnant populations had been disturbed since humans moved in and subsequent agricultural activities occurred. Apparently, habitat fragmentation resulted in an island distribution and genetic drift had occurred even before M. glyptostroboides was rediscovered in 1941. Based on the results of the present study combined with the lower genetic diversity previously detected in the remnant populations, possible mechanisms causing the endangerment of M. glyptostroboides are discussed and a conservation strategy for M. glyptostroboides remnant populations is proposed. The results provide valuable information for formulating future in situ and ex situ conservation programs of this relic species.