Genetic Diversity And Population Structure Of Ottelia Ulvifolia In Zambia Using SSR Molecular Markers

Zambia,which has a complex river system,is considered one of Africa's affluent aquatic plant diversity areas and is regarded as the main distribution and speciation center of the Ottelia in Africa.It possesses an abundant and wide range of water bodies and five ecoregions that primarily represent the Freshwater Ecoregions of the World.However,the influence of river systems in shaping the population,genetic structure of aquatic species,remains poorly understood in the region.Ottelia ulvifolia Planch Walp.,is an endemic aquatic herb species that belongs to the genus Ottelia and family Hydrocharitaceae.It is widely distributed in tropical and sub-tropical Africa.This study was done to elucidate detailed information on the genetic diversity and population structure of O.ulvifolia in Zambia using Short Sequence Repeat(SSRs),while highlighting the barriers to gene flow among the river systems.The principal aims of the study were(1)to determine the genetic variation and population structure among populations;(2)to explore the historical gene flow among populations and groups of O.ulvifolia;(3)to assess the influence of river systems on the genetic differentiation of the various populations in Zambia Eighteen populations of O.ulvifolia;and(4)to assess the demographic history of O.ulvifolia in Africa.Our study sites were from three Freshwater Ecoregions extant in Zambia(Upper Zambezi Floodplain [UZF],Bangweulu-Mweru [BM],and Middle-Luangwa Zambezi [MLZ]).The 307 samples from 18 O.ulvifolia populations were genotyped using 10 polymorphic microsatellite loci.Multiple analyses were used to determine the genetic diversity while giving estimates of: observed heterozygosity,expected heterozygosity,number of alleles and number of effective alleles,allelic richness,and private alleles.Bayesian clustering,Principal Coordinate(PCo A),and unweighted pair group method with arithmetic mean(UPGMA)cluster analyses were used to show the relations among the present O.ulvifolia populations.We also performed the following analyses to assess the underlying patterns of genetic diversity;isolation by distance,recent bottlenecks,gene flow,and correlation.BARRIER program was used to test for genetic discontinuities among the river networks and basins.Lastly,we complemented the genetic data with ecological models during the Mid-Holocene and Last glacial maximum,to infer the refugial areas of O.ulvifolia,as well as project the species future habitat suitability.The findings of our research are summarized as below:(1)An overall high genetic variation(HE = 0.425,NT = 81,I = 0.713,Ar = 1.974)were observed using 10 polymorphic microsatellite loci.Biological characteristics,such as effective seed dispersal mechanisms(hydrochory),population size(N),longevity,and reproductive strategy-outcrossing nature(FIS=0.035),explain the high variations in genetic diversity in O.ulvifolia populations.(2)STRUCTURE,UPGMA tree,and PCo A analyses revealed two unambiguous genetic clusters(K = 2)AMOVA results showed a strong global differentiation of 73.70% within populations(FST = 0.263)and the Mantel test revealed slight evidence of range isolation(r = 0.130,P = 0.053).These results infer that limited long-distance pollen dispersal could cause diversity within the species.In addition,Factors such as sex would also influence breeding and pollination hence the divergence of the species.Higher differentiation noted in various populations revealed that O.ulvifolia is prone to fragmentation,despite being outcrossing,insect-pollinated,and perennial.The variations of flowering characteristics might also explain the present population structure.(3)Potential barriers to gene flow isolated at least three populations with relatively low gene flow in both Bangweulu-Mweru and Middle Lower Zambezi ecoregions.However,the overall number of migrants in each generation was relatively high(NM = 0.120-1.571).The intricate river systems,the absence of strong physical barriers,presence of extensive floodplains prone to perennial flooding during rainy seasons,and the connectivity of wetlands in the FEOWs in Zambia and could have resulted in gene flow among basins and significantly moderating the differentiation.(4)Species distribution modeling results revealed that O.ulvifolia was widespread through Africa with some high suitability in the northern and southern hemispheres.These results also highlighted species range contraction after the LGM(during the Mid-Holocene),with some potential refugia in the South-Central and Western Africa.In the future,there is a potential higher habitat suitability of O.ulvifolia than in the current.Overall,the study's findings support high levels of genetic diversity in O.ulvifolia and offer insights into this species population genetics and differentiation.In addition,our results reiterate that significantly isolated populations might have co-evolved separately as micro populations,hence the observed divergence within O.ulvifolia.Overall high gene flow among populations could be attributed to long-distance dispersal of seeds by insects and perennial floods in Zambia's floodplains.It is also probable that floral characteristics played a significant role in influencing and shaping the structure in O.ulvifolia.Zambia's composite river system and connection,however,allows for the connectivity of O.ulvifolia populations coupled with sufficient pollen and seed dispersers leading to high gene flow hence the moderate to low differentiation in the present study.Lastly,SDM results yielded evidence of glacial expansion in O.ulvifolia and suggested significantly high gene flow in tropical Africa.We,therefore,recommend attention be accorded to these isolated populations and keen probing to assess factors that might have led to speciation among O.ulvifolia,as well as their conservation and management.