Genetic structure and mating system of Ammopiptanthus mongolicus (Leguminosae), an endangered shrub in north-western China

摘要

Ammopiptanthus mongolicus (Maxim.) Cheng f. is an endangered evergreen shrub endemic to the deserts of central Asia and is particularly important for the ecological-environmental stability of native habitats. We investigated the allozyme diversity of A. mongolicus seed populations and estimated the mating system of this species using progeny arrays assayed for polymorphic allozyme loci. The mating system analysis demonstrated that A. mongolicus has a mixed mating system with outcrossing rates of t(m) = 0.648-0.746, which are congruent with the floral biology of this species. An overall low level of allozyme variation was detected in A. mongolicus populations (mean H-e = 0.081, P = 20.1%). Using both STRUCTURE software and a neighbor-joining tree of the populations based on pairwise F-ST, genetic divergence was detected between populations from the Tengger Desert and from Ulan Buh Desert/Helan Mountain, which suggested that the populations in both regions may have originated from different refugia. Furthermore, the moderate level of genetic differentiation among populations (F-ST = 0.106) detected in the present study may result from a pre-existing population structure before habitat fragmentation. The mating system, natural selection and evolutionary history of A. mongolicus populations all play important roles in shaping the genetic structure of this species. The implications of the results of the present study for both in situ and ex situ conservation of the species are discussed.