Using Climatic Niche And Chloroplast Genome To Investigate The Adaptive Evolution Of Annonaceae

Under the background of global climate change,the rising temperature of land surface and the frequent extreme weather events affect the growth of plants,and consequently affect their survival,extinction and geographic change.Especially for tropical plants,with relatively narrow tolerance range to climate change,may face higher risks.Climatic niche is the climatic range that plants could live in,which represents the tolerance of species to climate,can be used to predict plant's response to futural climate change.Using phylogenetic comparative analysis method,and linking climatic niche with phylogenetic tree,it could be explained and analyzed for the climatic niche evolution,as well as the interrelationship between it and species diversification,to provide data support for describing adaptive evolution of plants.Annonaceae is the most species-abundant family in basal angiosperms order Magnoliales.It is widely distributed in tropics and is an important component of tropical forests.Thus,Annonaceae can be used as an indicator to explore the climatic adaptation and evolution of tropical plants,while few studies focused on its climatic niche characteristics,evolutionary patterns,and their relationship to diversification.In addition,most phylogenetic studies of Annonaceae are based on a few plastid DNA markers or DNA barcodes,and only 6 complete chloroplast genomes have been published,which leads to a lack of understanding about the chloroplast genome of Annonaceae.In this study,we collected the geographic distribution data of 618 species in Annonaceae,and calculated their climatic niche which based on six bioclimatic variables(Bio1,mean annual temperature;Bio5,max temperature of warmest month;Bio6,min temperature of coldest month;Bio12,mean annual precipitation;Bio16,precipitation of wettest quarter;Bio17,precipitation of driest quarter).Based on previous published phylogeny,we reconstructed ancestor state of climatic niche in Annonaceae and calculated evolutionary rates,analyzed the relationship between diversification rates and evolutionary rates.Our results showed:(1)Climatic niche of Annonaceae were narrow and mostly located in high temperature and high precipitation zone.Four subfamilies showed significant difference in climatic niche,two newly divergent subfamilies(Annonoideae and Malmeoideae)could live in relatively cooler and drier environment and have wider climatic niche breadth.(2)Ancestral climatic niche of Annonaceae was located in the warm and humid zone,while the family showed a general evolutionary trend towards relatively cooler and drier zone,which is consistent with the general climatic trend in the Cenozoic.Four subfamilies showed different evolutionary tendency,two older subfamilies(Ambavioideae and Anaxagoreoideae)showed trends towards relatively hotter and wetter habitats,while two newly divergent subfamilies(Annonoideae and Malmeoideae)toward drier and colder habitats.(3)The evolutionary rates of climatic niche were similar to global plants data,both lower than the rates of climate change.Recently diverged taxa had higher evolutionary rates of climatic niche,but there were no significant differences among the four subfamilies.Rates of lower boundary(cold and dry climate)of niche were significantly higher than upper boundary(heat and wet climate).(4)Significant correlation between net diversification rates and evolutionary rates of climatic niche was found,especially for rates of temperature niche.Combing with evolutionary tendency and characteristics of climatic niche,it is hypothesized that the diversification in Annonaceae was facilitated by a certain degree of low temperature and drought in the expansion of species to higher latitudes.(5)The whole chloroplast genome of Fenerivia ghesquierean,an endemic species in Madagascar,was sequenced.The sequence data can provide data support to better resolving the phylogenetic relationships within the family and explaining adaptative evolution of Annonaceae.In conclusion,the adaptation to changes in temperature and precipitation in geological time may be an important factor influencing the dispersal to higher latitude and species diversification of Annonaceae.Under future climate change,Annonaceae species would be at higher risk for their low evolutionary rates of climatic niche.There is a need to enhance the conservation for Annonaceae,especially those species with older species age,which may be more vulnerable to climate change.