Adaptive Differentiation Of Invasive Gambusia Affinis In Mainland China

An adaptive trait is one phenotypic trait that helps an individual better interact with their environment.It occurs due to the evolutionary pressures of natural selection,and it will enable or enhance the probability of surviving and reproducing in organisms.Once introduced into a new environment,an invasive species will face a variety of novel environmental factors that likely act as selection factors promoting adaptive differentiation in multivariate phenotypic traits,which should be attributed to phenotypic plasticity and/or local adaptation.Gambusia(Poey,1854)is a large genus of fish in family Poeciliidae,order Cyprinodontiformes,class Actinopterygii.Gambusia,native species of Southern United States and Mexico,contains over 40 species,most of which are principally found in freshwater habitats,though some species may also be found in brackish or saltwater habitats.Nine Gambusia species are listed as Vulnerable in the IUCN Red List.Gambusia species are often called topminnows refers more specifically to two species,Gambusia affinis(Baird & Giard,1853)and G.holbrooki(Giard,1859).Mosquitofish were first introduced into mainland China in 1920 s for reducing mosquitoes and mosquito-borne diseases(e.g.malaria and dengue fever).After more than 90 years of diffusion distribution,it is ubiquitous occurrence in Southern China.Even so,it still lacks of molecular evidence for which species was introduced.Yet,we know little about the route of transmission and distribution of mosquitofish,or their invasive ability for future range expansion in mainland China.In addition,we currently have a poor understanding of the evolutionary mechanisms by which organisms successfully colonize new environments and expand their range.This thesis was designed and conducted in the light of problems above.Firstly,I investigated the distribution of invasive mosquitofish in mainland China,and used combined molecular information(based on phylogenetic analyses of sequence variation of the mitochondrial cytochrome bgene)and morphometric data(dorsal and anal fin ray counts)to confirm the species of mosquitofish in mainland China.Secondly,I assessed genetic diversity and genetic structure on ten populations of invasive G.affinis in mainland China using fifteen microsatellite markers.Thirdly,I investigated phenotypic divergence in multiple traits,including body size,life history traits and morphological variations,in G.affinis along climatic gradients.Then,I explored the geographic and temporal variations in multiple paternity of mosquitofish based on eight highly polymorphic microsatellite loci,while considering potential effects of both environmental factors and life-history traits.Lastly,I acquired most of the functional genes in G.affinis and explored genetic markers using RNA-seq.The main results in this thesis are as follows:1.Invasive mosquitofish in mainland China is confirmed as only one species,G.affinis.G.affinis is ubiquitous occurrence in Southern China,while some populations may also be found in Northern China(e.g.Baoding).2.Totally,the genetic diversity of G.affinis populations is abundant,while that of Beihai,Xiamen and Chaozhou populations showed a bit lower than other populations from higher latitudes.These ten studied populations could be divided into two genetically distinct clusters.Three populations located in the Yangtze river delta,namely Nanjing,Hangzhou and Huzhou,formed a distinct cluster;while the other seven populations formed the other cluster.The diffusion process of G.affinis in mainland China seems to be gradual translocation in a stepping-stone-like fashion.In addition,genetic drift had made its contributions to genetic differentiation between G.affinis populations.3.Female G.affinis tends to have a bigger body size in higher latitude,altitude and more coastal areas,vice versa.In stable environments,such as lower latitude,higher altitude and more coastal areas,females produced less but bigger embryos,which had greater competitiveness.In fluctuant environments,however,females produced more but smaller embryos,which had greater evolutionary flexibility.Body shape divergence in G.affinis follows patterns observed for life-history diversification,with enlarged abdominal cavities,anteriorly positioned pectoral fins,smaller heads and shorter caudal peduncle in fluctuant environments(i.e.,higher latitudes,lower altitudes and more inland areas),vice versa.In line with reproductive strategy in females,males had higher reproductive invests at lower altitude and higher latitude areas.The body size,life-histories and morphological variations along climatic gradients in G.affinis indicates temperature regimes and environmental stability are two important factors in driving phenotypic variations among populations.4.Multiple paternity is widespread in populations of invasive mosquitofish.Both G.affinis and G.holbrooki benefits a lot from this reproductive strategy,such as improves evolutionary flexibility of a population by increasing genetic diversity of offspring.Multiple paternity varies with reproductive invests and also climatic factors.The observed patterns of geographic and temporal variations in multiple paternity were caused by female-mediated processes and shaped by both natural selection and sexual selection.Coincident with life-history stragegy,mosquitofish had higher level of multiple paternity per clutch towards the north.The occurrence of multiple paternity always accompanied by reproductive skew,which should be attributed to postcopulatory sexual selection(e.g.sperm competition and cryptic female choice).5.A total of 152,036 unigenes with a mean length of 2,262 bp were obtained using RNAseq.Among these unigenes,111,502(73.33%)were successful annoted.A total of 81,722 microsatellite loci were detected from these unigenes.The number of detected single nucleotide polymorphism(SNP)loci in each hepatic cDNA library ranged from 63,014 to 88,627.The Ka/Ks ratios calculated from these SNP loci were less than one in all populations,indicating ongoing purifying selection on functional genes in G.affinis from these populations.In summary,this thesis mainly focused on the adaptive differentiation in life-history,morphology and reproductive stragegy in invasive G.affinis.Throughout of the thesis,I identified the invasive mosquitofish in mainland China as G.affinis,then acquired the genetic diversity and structure of these invasion populations.Moreover,the thesis obtained large number of functional genes and genetic markers in G.affinis,laid a basis for further exploring the molecular mechanisms of adaptive evolution in G.affinis.Additionally,this thesis will deepen public understand of invasive mosquitofish,provides information for biological resources conservation,control and prevention of the invasive G.affinis.