From The New World To The Old World,the Origin And Dispersal Of The Strictly Amauboriine Spiders

There are complex and diverse distribution patterns of organisms on earth,among which disjuncted distribution patten of biological groups in the northern hemisphere is a typical representative,and this distribution pattern has been the research object of researchers.There is an important biological discontinuity area in the northern hemisphere:the Eurasia(the Old World)-North American(the New World)discontinuity area.Regarding the reasons for the formation of the Eurasia-North America distribution area,there are many statements in the scientific community,such as long-distance or land bridge spreading across the ocean,continental plate drift,or geographical isolation due to climate change.In addition,there is also discontinuous distribution area within Eurasia,namely the disjunct area of the ancient Mediterranean.During the Paleogene period,animals and plants could spread long distances between East Asia and the Mediterranean.As the climate became more arid in the Miocene period,the warm and humid flora that once connected the two regions disappeared,and the species in the Mediterranean and east Asia finally separated.In order to investigate the reasons for the intermittent distribution of biological groups,biologists combined molecular biology with bioinformatics to reconstruct the phylogenetic tree and ancestral distribution area,and deeply explore the origin and dispersal process of biological groups.The strictly amauboriine spiders refer to the family Amaurobiidae of the Araneae,which include the type genus Amaurobius and three closely related genera: Pimus,Callobius and Taira.Because the monophysical problem of the Amaurobiidae and the Amaurobiinae has not been resolved,this article uses the informal name of the strictly amauboriines.The distribution range of the strictly amauboriines belong to the Eurasian continent and North America,and the fragments are distributed in North America,southern Europe,northeastern China,and the warm and humid mountain areas south of the Qinling Huaihe River.Although the predecessors have thoroughly studied the distribution range,environmental preferences,the morphological characteristics and evolutionary history of the strictly amauboriines and the Taira have not been clearly studied so far.In order to understand the origin and dispersal of the strictly amauboriines and the Taira,this study explored from the three levels of family,genera and species,using mitochondrial gene fragments(12S,16 S,COI)and nuclear genes fragments(18S,28 S,H3)constructed a phylogenetic tree,and performed divergence time estimation and historical biogeographic analysis.The main conclusions are as follows:1.Phylogenetic trees constructed based on the maximum likelihood method(ML method)and the Bayesian inference(BI method)obtained similar results,and both have good support rates.The results showed that the strictly amauboriines is a monophyletic group.The genus Pimus is located at the base of the tree.And the Callobius and the Amaurobius + Taira are sister groups to each other.Within the spider genus,Callobius sp.1 in northeast China and Callobius Claustrarius in Europe form a large branch with the spiders distributed in North America.The Amaurobius is clearly divided into two branches: the southern branch of China(Clade South China)and the southern branch of Europe(Clade South Europe).Compared with the Amaurobius,the genus Taira is larger and consists of three major branches(A,B,and C branches).Branch A(Clade A)is located at the base of the tree.Branches B and C(Clade B and Clade C in Fig 3-1)are sister groups to each other.Eight small sub-branches were formed in the A,B,and C branches,of which the B and C branches had three sub-branches,respectively.2.The results of the divergence time estimation show that the common ancestor of the strictly amauboriines is formed at the middle Cretaceous(ca.108.2Ma),and the first differentiation occurred in the late Cretaceous period(ca.97.01Ma),forming the genus Pimus and its sisters.The second divergence time appeared in the Paleozoic period,causing the Callobius to be separated.Until 65.5Ma,the Amaurobius and the Taira appeared in southern China.In the genus Amaurobius,I branch line began to differentiate before 46.21 Ma,and gradually formed new species.The differentiation time of the II branch was relatively late,which occurred in the late Eocene(about 39.7Ma).The genus Taira formed two branches(branch A,B + C)for the first time in the late Paleozoic(ca.54.25Ma),and until the early Eocene(ca.50.15Ma),B and C branches were formed.The latest large-scale differentiation event occurred during the Pliocene-Pleistocene.The three sub-branches of the B-branched and the C-branches form a plurality of small branches.In addition,Callobius sp.1 distributed in the northeast of China,formed in the early Miocene(ca.8.04Ma).3.Historical biogeographic analysis shows that the strictly amauboriine spiders originated in North America,and spread to the Eurasia twice through the Bering Land Bridge in the late Cretaceous(97.01?73Ma)and Miocene periods(8.04Ma).The first dispersal event involved the formation of Amaurobius and Taira.At the end of the Cretaceous,the Bering Land Bridge was in an open state,and the environment on both sides of the strait was warm and humid,which was conducive to the dispersal of Amaurobius.The second dispersal event occurred during the global temperature plateau period.The spiders spread to the northeast of China through the Bering Land Bridge.In addition,we found that the ancestral area of the genus Taira is the Yunnan-Guizhou Plateau.Based on the BBM method,the results show that the three ancestral ancestors(A,B,C)in the genus also formed in the Yunnan-Guizhou Plateau,forming a trend of northward dispersal.Branches B and C spread to the Sichuan Basin and the southern Qinling Mountains.The difference is that Taira sp.2 and Taira sp.3of the B-clade line appear in the Hengduan Mountains,and Taira zhui in the C-clade are widely distributed in the central-south-southeast region.4.The LTT diagram shows that the evolution rate of the lineages number of the Taira was slow in the paleogene period.After pliocene(ca.5Ma),many small lineages(populations)were formed in the species of Taira zhui,Taira qiuae,Taira sichuanensis and Taira liboensis.5.Based on the analysis of the genetic structure of the Taira zhui and Taira qiuae,it is concluded that the gene flow between the various groups is very small and highly differentiated.Severe uplift of the Qinghai-Tibet Plateau during the Pliocene played an important role in the differentiation of the Taira populations.By studying the phylogeny and biogeography of the strictly amauboriine spiders,it is found that the dispersal mechanism plays an important role in the evolution of the amauboriines from the end of cretaceous period to the tertiary period.