Evolutionary Studies On Phrynocephalus (Agamidae) Along Elevational Gradients

Phrynocephalus lizards are widely distributed at deserts and semi-deserts habitats of the Qinghai-Tibetan Plateau(QTP)and outside of QTP.The Phrynocephalus lizards distributed at low altitude are oviparous,while they are viviparous at high altitudes.Vertebrates endemic to high altitude must have formed their adaptive mechanisms to deal with the extreme environmental factors(hypoxia,low temperature and intensive ultraviolet)via morphological,physiological and behavioral changes.Though plenty of studies have conducted on high altitude adaptation of mammals and avian,few attentions are payed on poikilotherms.We used all the Chinese Phrynocephalus lizards to study their color adaptation in high altitudes,and preliminarily discuss the potential genes and mechanism response to body color variation,mitochondrial respiratory metabolism and other phenotypic adaptation.The main contents and results are as follows: 1.Impacts of phenotypic characteristics on thermoregulation in P.guinanensisThe heating/cooling rates of tails and limbs,under the environment with/without solar radiation,were relatively faster than the torsos,as heating/cooling time was extended,rates gradually slowed before stabilizing.In addition,the heating rates with solar radiation were quicker than the cooling rates without solar radiation.Under the environment with solar radiation,our results also showed that the heating rates of the abdominal black-speckled skin area were faster than the nearby non-black-speckled skin area.These obtained results increase our insights into the functional thermo-regulating significance of above morphological characteristics and help to explain their covariation with the thermal environment among these cold-climate agamid lizards.2.Evolutionary analysis of all mitochondrial-encoded proteins in Phrynocephalus along the elevational gradientUsing 19 complete mitogenomic sequences of all Chinese Phrynocephalus species,a total of ten positively selected sites,estimated from Random-sites and Branch-sites analysis in PAML,were discovered in six mitochondrial-encoded genes,i.e.,ND2,ND3,COXIII,ND4,ND5,ND6,among them,four long-term selected sites were discovered by application of PAML analyses by using Random-sites and Branch-sites models.Our results showed that several lineages had undergone significantly strong positive selection in the process of historical evolution.TreeSAAP analysis indicated that three sites in three protein-coding genes(ND1,ND3,ND6)have experienced significant changes on basic physicochemical properties,and its positively selected sites on ND3 and ND6 were consistent with the results in PAML analysis.Nine of ten sites,were related to the mitochondrial complex I protein,and a total of four amino acid residues in ND2,ND4,ND5 and ND6 proteins had significantly co-evolving relationship with other residues of proton transport channel.All these results supported that mitochondrial complex I experienced significant selection during the evolutionary process along elevational gradients,comparing with other complexes.3.Genetic evolution of MC1 R gene in P.theobaldi populations along the elevational gradientSignificant body color variation exists between high(>4200m)and low(<4200m)altitude populations in P.theobaldi.We initially cloned and sequenced the complete 942 bp coding sequence of MC1 R gene in two altitudinal groups,and a significantly statistical association was confirmed between a total of five MC1 R mutations(T20P,V22 M,R28Q,V52 M,V165I)and body color variation between both groups,among them,two sites situated at transmembrane area may affect the MC1R's function.Three sites in N-terminal extramembranous domain,suggested by Random-sites analysis,had undergone long-term positive selection,while no episodic selected sites were screened through Branch-sites analysis,which indicated that N-terminal extramembranous domain are more susceptible to experience selection during the genetic evolution of MC1 R gene,and the body color variation in P.theobaldi along elevational gradient may be influenced by the MC1 R mutations.4.An intraspecific transcriptomic analysis in P.vlangalii along the elevational gradientThe intraspecific comparative transcriptomic analysis between long-term diverged subclade populations of P.vlangalii pylzowi with 1400 m in elevational interval indentified 140 genes experienced strong positive selection(Ka/Ks>1),and 352 genes had undergone potential positive selection(1?Ka/Ks>0.5).Among them,11 positively selected genes(PSGs)and 14 potential PSGs were most possibly related to high altitude adaptation of P.vlangalii.Besides,the overall gene expression was similar between two populations,but the expression for each population was different between all the unigenes and candidate genes with Ka/Ks > 0.5.Our results provided some candidate genes for genetic studies of Phrynocephalus on high altitude adaptation,and may shed light on our understanding of ectothermic evolution in high altitude.