Genetic diversity and population structure of Ottelia ulvifolia (Hydrocharitaceae) from three freshwater ecoregions in Zambia

Abstract

As vital components of freshwater ecosystems, river systems directly boost the dispersal and gene flow of aquatic species. However, various river systems might also increase the potential for isolation of these species and their genetic differentiation. In Africa, the roles of river systems in shaping the genetic diversity and structures of aquatic species are still poorly studied. In order to assess the influence of river systems in freshwater ecoregions on the genetic variation of Ottelia ulvifolia, we genotyped 307 individuals of 18 populations from Bangweulu-Mweru, Middle Zambezi-Luangwa, and Upper Zambezi Floodplain ecoregions in Zambia using ten microsatellite markers. Our results revealed an overall high genetic diversity (HE = 0.475) and high gene flow (Nm > 1) among the three ecoregions. Notably, a relatively higher diversity (HE = 0.485; I = 0.836) was detected in Bangweulu-Mweru compared to those other ecoregions, which could be contributed by frequent river capture events in the area. STRUCTURE, TESS, PCoA, and NJ analyses identified two distinct clusters that were further divided into five sub-clusters, three in bisexual populations and two in the unisexual populations, respectively. The lower genetic differentiation among 18 populations (Fst = 0.258) in the present study could be attributed to the frequent hybridization among populations via insect pollination and water-mediated seed dispersal. A significant positive correlation between Jost’s D/(1-Jost’s D) and geographic distance among populations (r = 0.142, P = 0.050) indicated deviation for mutation-drift equilibrium. The current findings, however, do not support the hypothesis that variations within ecoregions drive the genetic variation and population structure of O. ulvifolia in Zambia. Lastly, habitat specialization and floral characteristics are examples of behavioral factors that may promote a genetic difference in O. ulvifolia. Our study provides general knowledge of the genetic variation of O. ulvifolia in tropical Africa and indicates a possible regional alteration of various macrophyte dispersal mechanisms at a vast geographic scale, therefore encouraging the need for further research on the genus.