Impact Of Fire On Genetic Diversity And Structure Of Morella Salicifolia In Mount Rungwe Nature Forest Reserve,Mbeya,Tanzania

Fire history dates back to the Silurian period when terrestrial plants came into existence and plays an important role in shaping ecosystems worldwide.The impacts of fire on biodiversity,ranging from community and species levels to entire ecosystems,have been studied extensively.However,the impact of fire on genetic diversity and structure which are crucial components of biodiversity in forest ecosystems for providing adaptation abilities in response to disturbances,still remain under investigated.Presently,Tanzania has experienced a rapid increase in incidences of wildfires.However,limited studies have investigated the impact on ecosystems and little has been done on the effect on genetic diversity in plant species.This study investigated the impact of fire on genetic diversity,covering most burned areas to the natural dense forest,in Mount Rungwe Nature Forest Reserve(MRNFR)which has been reported as the leading in fire incidences in Tanzania.Morella salicifolia has been recorded as a fire tolerant species in most mountain ecosystems experiencing fire in Tanzania and is common in MRNFR,thus chosen for this study.The study was achieved based on two major goals;(1)development of microsatellite markers for M salicifolia and(2)application of the developed markers to estimate the levels of genetic diversity of populations exposed to different fire frequencies.Sampling was designed into five experimental sites,each with varying number of populations,categorized as high fire frequency(Bukanda&Ilundo sites),moderate fire frequency(Ndengasombyo&Kabwe sites)and unburnt dense forest(Kasemba).In total,288 samples representing 17 populations were genotyped using eight newly developed microsatellites.Genetic diversity parameters were estimated using GenAlEx version 6.5 software.In addition,all samples were subjected to Bayesian STRUCTURE and dendrogram genetic clustering techniques to infer the links among the populations.Finally,contemporary migration and evidence of recent population bottleneck estimates were calculated.Initially,30 microsatellites were screened for both amplification success and polymorphism tests among different populations of M salicifolia.Eight microsatellites exhibited stable amplifications and high polymorphism thus ideal for estimating genetic diversity in different populations.The results revealed high genetic diversity(Mean He=0.655)indicating that fire might not necessarily lead to genetic erosion in M.salicifolia.Compared among the five sites,it was observed that the highest genetic diversity was in Bukanda(He=0.696),Ilundo(He-0.66),Ndengasombyo(0.66),Kabwe(0.64)while Kasemba recorded the lowest genetic diversity(He=0.62).The increase in genetic diversity in fire-prone areas indicate that the species might have evolved different alleles as response to fire.Both STRUCTURE and UPGMA clustered the 17 populations into three genetic clusters,with Cluster 1 being more noticeable in populations exposed to high fire frequency(populations 1-5)while clusters 2 and 3 were admixed in both slightly burned and unburned populations.This supports the influence of fire on genetic structuring in M salicifolia.Population bottleneck revealed no bottleneck event in the three sites using Two-Phase Mutation Model equilibrium and a normal L-shaped distribution of allele frequencies,indicating that the sites have not experienced any recent bottleneck.Contemporary migration estimates revealed high migration from Ndengasombyo to Kasemba(0.3172)and limited exchange of genes between Bukanda and the other sites,thus the distinctiveness of Bukanda.Successful formulation of management strategies in fire-prone mountains of Tanzania is undoubtfully an uphill task and requires insights from a combination of both genetic and ecological data.According to the results of this study,frequently burned area displayed higher genetic variation compared to the other areas.In addition,all the 17 populations were grouped into three major clusters depending on the three different fire frequencies.These results conclude that;(1)fire plays a role in influencing genetic diversity but does cause genetic erosion,(2)fire can lead to genetic structuring in the long-term and(3)fire might play a part in fragmentation based on the observed low gene exchange between frequently burned site and other sites.This study provides baseline data for the design of conservation approaches.