Population genetics of the cycad Encephalartos barteri ssp. barteri (Zamiaceae) in Benin with notes on leaflet morphology and implications for conservation

Abstract

Encephalartos barteri ssp. barteri (Zamiaceae) is a cycad endemic to Benin, Nigeria, Ghana and Togo. The species is considered as vulnerable in its area of distribution. In the present study, we analysed the patterns of leaflet morphological variation and the genetic variability within and among five populations sampled in Benin, between 7 degrees 34' and 10 degrees 20'N. Leaflet morphology showed significant variation among populations. The differences observed among populations were not correlated with geographic distances. Sixteen Random Amplified Polymorphic DNA (RAPD) primers with a total of 133 scorable bands (82.7% polymorphic) were tested. Three primers generating 32 consistently and well-amplified bands were used to characterise the 150 individuals sampled. High levels of genetic diversity were observed (P = 93.75%, H-E = 0.297 at the species level, and P = 75%, H-E = 0.228 at the population level). Two population-specific bands with high frequencies were found. There was also evidence of high differentiation among populations (G(ST) = 0.2313, Phi(ST) = 0.3236, p < 0.001). Cluster analysis corroborated the previous results and mainly grouped the individuals and populations according to their geographic origin. Current patterns of morphological and genetic variation in E. barteri ssp. barteri appear to reflect interactions amongst a range of factors namely, past climate changes, phenotypic plasticity, local adaptation, geographic isolation and limited seed dispersal/pollen transfer. Conservation strategies are discussed: urgent actions need to be taken to protect the populations (Gangamou and Doh) not having any legal protection status but containing unique genetic variants, and community-based nursery management should be envisaged. Finally, given the ongoing decline of the habitat of the species and the continued removal of individuals from the wild it is recommended that the IUCN Red List category for this species should be changed from vulnerable to endangered.