沙蜥属一有效种贵德沙蜥及红原沙蜥的分类研究(蜥蜴亚目:鬣蜥科)

形态,染色体特征聚类分析表明过去归入青海沙蜥的天祝,贵德居群被聚为一支,而青海沙蜥的其它居群和红原沙蜥 聚为另一支,证明贵,在祝居群与青海沙蜥有显著区别,应当恢复贵德沙蜥Phrynocephalus putjatia为有效种。贵德沙蜥与青海沙蜥的主要鉴别特重是前者的尾长大于吻肛长,后者的尾短,小于吻肛长,前者背鳞100枚以上,后者背鳞不到100枚。红原沙蜥Phrynocephalus hongyuanensis与青海沙蜥的染色体和形态特征相似,应归隶青海沙蜥。     

基于线粒体基因组的沙蜥高海拔适应研究

高海拔地区的物种容易受到低温、低氧、强紫外辐射等极端环境因素的影响。研究这些物种对特殊环境的应对反应,能够为进一步理解适应进化的机制提供重要线索。线粒体是细胞的能量代谢中心,因此线粒体基因组很可能在动物高原适应中起着重要作用。鬣蜥科Agamidae沙蜥属Phrynocephalus物种广泛分布于海拔1000~5300 m范围内,是研究高原适应的良好材料。本研究对2种高海拔沙蜥和6种低海拔沙蜥的线粒体基因组进行了比较研究,检测了可能经历过正选择的蛋白编码基因,探讨了线粒体基因在沙蜥高海拔适应中的作用。结果发现,在不同物种间,高海拔西藏沙蜥Phrynocephalus theobaldi的线粒体基因组中蛋白编码基因的进化速率最快;在不同基因间,ATP8具有最快的进化速率。使用分支-位点模型进行正选择检测,发现ATP8基因在西藏沙蜥中存在明显的正选择信号(P<0.05,ω>1)。通过贝叶斯方法进一步计算每个位点的后验概率,发现在ATP8基因上存在2个正选择位点。这些结果说明ATP8基因可能在西藏沙蜥高海拔适应中起到了重要的作用。但在同为高海拔的青海沙蜥Phrynocephalus vlangalii中,却没有发现类似的正选择信号,这揭示不同物种高海拔适应的分子机制可能不同。     

贵南沙蜥染色体核型与聚类分析

贵南沙蜥Phrynocephalus guinanensis为近年沙蜥属新命名的物种,形态上区别于贵德沙蜥P.putjatia与青海沙蜥P.vlangalii,而最近沙蜥分子系统发育研究的结果不支持贵南沙蜥为一有效种,它在分子树拓扑结构上与贵德沙蜥一亚分支样本聚在一起。本文观察贵南沙蜥核型为2n=24I+24m,具有12对大染色体和12对小染色体,其中大染色体均为端部类型,且无性别相关的异型染色体。青海11个沙蜥种群染色体特征的聚类分析表明贵南沙蜥与贵德沙蜥聚于同一分支,该分支构成青海沙蜥分支的姐妹支,证实贵南沙蜥与贵德沙蜥具有较近的核型演化关系。研究结果不支持贵南沙蜥为有效物种。     

四种沙蜥的形态地理变异:Bergmann和Allen规律的检验

本文通过比较四种沙蜥近缘种:青海沙蜥(Phrynocephalus vlangalii)、荒漠沙蜥(P.przewalskii)、变色沙蜥(P.versicolor)和叶城沙蜥(P.axillaries)形态特征和分析青海沙蜥种群沿海拔梯度的变异来验证Bergmann和Allen规律在爬行动物沙蜥属的适用性。生存在邻近地区不同海拔梯度的四种沙蜥个体大小种间比较显示遵循Bergmann和Allen规律,分布于高海拔的青海沙蜥尾椎骨数显著少于其它三种低海拔沙蜥,这种沿海拔梯度种间形态变异可能主要由遗传因素决定。青海沙蜥随海拔梯度的上升个体变小,四肢变短,形态变异反Bergmann规律,相对尾长随海拔变异遵循Allen规律,但相对四肢长度反Allen规律。这种变异可能更受到不同海拔梯度环境特征,尤其是高海拔缺氧和食物短缺的影响。     

九种沙蜥的核型——兼论中国沙蜥属核型演化

报道了沙蜥属９种２１个不同居群的核型及银分带核型。荒漠沙蜥、草原沙蜥和斑点沙蜥２ｎ＝４６＝２２Ｉ＋２４ｍ,ＮＦ＝４６。叶城沙蜥２ｎ＝４６＝２ｓＩ＋２０Ｉ＋２４ｍ,ＮＦ＝４６。南疆沙蜥、泽当沙蜥、青海沙蜥和红原沙蜥２ｎ＝４８＝２４Ｉ＋２４ｍ,ＮＦ＝４８。青海沙蜥具有异型性染色体。大耳沙蜥２ｎ＝４８＝２Ｖ＋８ｓＶ＋１２ｓＩ＋２６ｍ,ＮＦ＝５８。９种中,ＮＯＲ均位于微小染色体对上。与本属已知核型比较,确认我国沙蜥属核型均来自共同的核型祖先,可分为３个核型类群：（１）２ｎ＝４６,１１对大染色体类群;（２）２ｎ＝４８,１２对大染色体类群;（３）大耳沙蜥。前两个类群核型与生态地理分布紧密相关。讨论了我国沙蜥属物种核型演化趋势,并结合地史资料探讨了本属核型演化与第三纪以来古地史变迁的关系。     

中国的沙蜥

简要概括地介绍了中国沙蜥的种类、生态地理分布、起源与进化以及沙蜥对栖息环境的适应。中国沙蜥据记载有18个种,分为荒漠和高寒两大种组,分别分布在中国广大荒漠地区和青藏高原。约从晚中新世开始,青藏高原迅速抬升促使了中国沙蜥祖先卵生和胎生的早期分化。高原隆升造成的环境演变促使中国沙蜥卵生和胎生物种分别进化出一系列的适应荒漠或高寒环境的个体特征。     

荒漠沙蜥食物的两性差异

对2008年4～6月在甘肃省甘塘、阿拉善左旗、民勤、山丹采集的荒漠沙蜥样本进行了食物两性差异的研究。主要采用剖胃法对219个荒漠沙蜥胃样的6021个食物做了识别和鉴定。结果表明,荒漠沙蜥的食性为动物性,食物多为昆虫,主要取食半翅目和膜翅目昆虫,尤其是长蝽科和蚁科(合计高于70%),取食猎物的体积大小集中在0.01～20mm3。4个种群的沙蜥对长蝽科昆虫均表现为正向选择,部分种群对蚁科昆虫表现负向选择。可能是因为沙蜥有食物选择性,对长蝽科昆虫取食较多,对拟步甲科摄食较少。较多地取食蚂蚁则是因为生境中喜好食物较少,而蚁科昆虫数量多,遇见率也较高。荒漠沙蜥雌雄个体食物生态位重叠度极高,但是卡方检验的结果却表明两性在食物组成和食物大小存在显著差异。由于雌雄个体对同种食物有相同的选择性,因此导致两性在食物组成和食物大小上存在显著差异的原因可能是雄性家域范围更大,对食物有更多选择。     

草原沙蜥秋季食性分析

利用剖胃法对采自内蒙古自治区鄂尔多斯库布齐沙漠的草原沙蜥(Phrynocephalus frontalis)进行食性分析研究。结果表明,该地区的草原沙蜥在8～9月间,以昆虫类动物为主要食物,占全部食物的95.8%。不同性别草原沙蜥取食的食物种类差异不显著,雌雄个体的食物百分率相似性指数及营养生态位重叠值均较大,雄性的食物多样性指数(IFD)及营养生态位宽度(BTN)均大于雌性。成体和亚成体之间以及亚成体和幼体之间食物种类存在差异但不显著,而成体和幼体间的食物种类差异极显著,不同年龄草原沙蜥的食物百分率相似性指数较小,IFD值与BTN值均是成体最大,幼体最小。总有益系数、不同性别的有益系数分别为V总=22.44%,V雌=12.76%,V雄=9.83%,草原沙蜥是对荒漠化草原有益的类群。     

基底颜色对两种沙蜥体色变异的影响

生存在不同基底颜色环境下的爬行动物种群通常表现出丰富的体色地理变异, 其体色变化的潜在机制具有多样性。变色沙蜥(Phrynocephalus versicolor)和草原沙蜥(P. frontalis)具有较近的遗传关系, 曾被认为与荒漠沙蜥(P. przewalskii)组成同一系统发育种组。本文应用光纤光谱仪(AvaSpec-2048), 通过记录沙蜥背部体表12个部位的皮肤光反射率, 定量比较在黑化环境下的深色变色沙蜥与非黑化环境下的浅色草原沙蜥自然体色变异, 研究其种群体色变异是否具有时间可逆性, 并探讨基底颜色对沙蜥体色的影响机制。研究结果表明, 黑化生境下的变色沙蜥体色显著深于非黑化枯黄色生境下的草原沙蜥。此外, 对黑化与非黑化样本开展的生境互换移植围栏实验, 即把枯黄色生境中非黑化的草原沙蜥移植于黑色的基底环境中饲养, 把黑化生境中黑化的变色沙蜥移植于枯黄色生境中饲养。结果表明, 饲养1周后黑化群体背部6个检测部位的光反射率显著变大, 其他部位均无显著变化; 而非黑化群体只有左后肢和背部右上方2个部位的皮肤光反射率发生显著变化, 其他部位反射率无显著变化。结果表明, 变色沙蜥体色变异能力比草原沙蜥强, 体色表型可能已经在两个近缘沙蜥物种中稳定遗传, 基底生境颜色的短期变化在统计学上能引起肉眼难以识别的轻微的体色变异, 个体发育相关的一些遗传因素可能对体色变异起控制 作用。     

旱地沙蜥的两性异形

旱地沙蜥Phrynocephalus helioscopus是一种在我国仅分布于新疆北部的蜥蜴。通过测量和比较采自新疆塔城地区旱地沙蜥的体长、口宽、头宽、头高、头长、眼间距、腹部长、尾长等8个形态特征研究旱地沙蜥的两性异形。本研究共采集到旱地沙蜥51只,其中,雌性23只,雄性28只。雌雄平均体长分别为48.03 mm和47.69 mm。结果表明旱地沙蜥两性体长的差异无统计学意义,其体长与口宽、头宽、头高、头长、眼间距、腹部长和尾长7个形态特征均显著正相关。在控制体长的基础上比较得出,雌雄个体在头高、头长、腹部长和尾长上的差异有统计学意义,口宽、头宽、眼间距的差异无统计学意义。其中,雄性的头高、头长和尾长均大于雌性,雌性的腹部长则明显大于雄性。旱地沙蜥的腹部长呈现明显的异形生长,雌性的生长速率明显大于雄性。旱地沙蜥的两性异形可能是性选择压力与生育力选择压力共同作用的结果,雄性头部更大、尾部更长,在性选择中具有优势;雌性腹部更长,能够繁育更多的后代。     

Cladogenesis and phylogeography of the lizard Phrynocephalus vlangalii (Agamidae) on the Tibetan plateau

Phrynocephalus vlangalii is restricted to dry sand or Gobi desert highlands between major mountain ranges in the Qinghai (Tibetan) Plateau. Mitochondrial DNA (mtDNA) sequence (partial ND2, tRNA(Trp) and partial tRNA(Ala)) was obtained from 293 Phrynocephalus sampled from 34 sites across the plateau. Partitioned Bayesian and maximum parsimony phylogenetic analyses revealed that P. vlangalii and two other proposed species (P. erythrus and P. putjatia) together form a monophyletic mtDNA clade which, in contrast with previous studies, does not include P. theobaldi and P. zetangensis. The main P. vlangalli clade comprises seven well-supported lineages that correspond to distinct geographical areas with little or no overlap, and share a most recent common ancestor at 5.06 +/- 0.68 million years ago (mya). This is much older than intraspecific lineages in other Tibetan animal groups. Analyses of molecular variance indicated that most of the observed genetic variation occurred among populations/regions implying long-term interruption of maternal gene flow. A combined approach based on tests of population expansion, estimation of node dates, and significance tests on clade areas indicated that phylogeographical structuring has been primarily shaped by three main periods of plateau uplift during the Pliocene and Pleistocene, specifically 3.4 mya, 2.5 mya and 1.7 mya. These periods corresponded to the appearance of several mountain ranges that formed physical barriers between lineages. Populations from the Qaidam Basin are shown to have undergone major demographic and range expansions in the early Pleistocene, consistent with colonization of areas previously covered by the huge Qaidam palaeolake, which desiccated at this time. The study represents one of the most detailed phylogeographical analyses of the Qinghai Plateau to date and shows how geological events have shaped current patterns of diversity.     

Microsatellite DNA markers for three toad-headed lizard species (Phrynocephalus vlangalii, P. przewalskii and P. guttatus)

To assess the impact of natural landscapes on the population structure of lizards, 10 polymorphic microsatellite DNA markers were developed for the Qinghai toad-headed lizard, Phrynocephalus vlangalii. The number of alleles at these informative loci ranged from four to 28. The novel markers and those previously developed for Phrynocephalus przewalskii were cross-tested among three toad-headed lizard species P. vlangalii, P. przewalskii and P. guttatus. A high cross-utility rate of more than 58% was observed among these three species. These markers are expected to be useful tools for taxonomic considerations as well as population genetic analysis and future conservation management.     

Inter-species hybridization among Neotropical cats of the genus Leopardus, and evidence for an introgressive hybrid zone between L. geoffroyi and L. tigrinus in southern Brazil

Natural hybrid zones between distinct species have been reported for many taxa, but so far, few examples involve carnivores or Neotropical mammals in general. In this study, we employed mitochondrial DNA (mtDNA) sequences and nine microsatellite loci to identify and characterize a hybrid zone between two Neotropical felids, Leopardus geoffroyi and L. tigrinus, both of which are well-established species having diverged from each other c. 1 million years ago. These two felids are mostly allopatric throughout their ranges in South America, with a narrow contact zone that includes southern Brazil. We present strong evidence for the occurrence of hybridization between these species and identify at least 14 individuals (most of them originating from the geographical contact zone) exhibiting signs of interspecific genomic introgression. The genetic structure of Brazilian L. tigrinus populations seems to be affected by this introgression process, showing a gradient of differentiation from L. geoffroyi correlated with distance from the contact zone. We also corroborate and extend previous findings of hybridization between L. tigrinus and a third related felid, L. colocolo, leading to an unusual situation for a mammal, in which the former species contains introgressed mtDNA lineages from two distinct taxa in addition to its own.     

Genetic and morphological characterization of a Lake Ohrid endemic, Salmo (Acantholingua) ohridanus with a comparison to sympatric Salmo trutta

Analysis of both uni‐(two mtDNA gene sequences) and bi‐parentally (seven microsatellite loci) inherited genetic markers, together with analysis of 40 morphological characters, described Salmo ohridanus as a highly divergent member of the genus Salmo . Based on comparative substitution rate differences at the cytochrome b gene, and a rough estimated age of the Salmo trutta complex ( i.e. at least 2 million years), the S . ohridanus and Salmo obtusirostris clade probably split from a common ancestor of brown trout Salmo trutta >4 million years ago, overlapping with minimum age estimates of the formation of Europe's oldest freshwater habitat, Lake Ohrid. Comparative analysis with Lake Ohrid brown trout (known regionally as Salmo letnica ), supported the notion that these fish have more recently colonized the lake and phylogenetically belong to the Adriatic lineage of brown trout. It is further suggested that species‐specific saturation in the mtDNA control region underestimated the divergence between S . ohridanus and S . trutta . Evidence of rare hybridization between S . ohridanus and Lake Ohrid brown trout was seen at both mtDNA and microsatellite markers, but there was no support for extensive introgression.     

Evidence for independent origin of two spring‐spawning ciscoes (Salmoniformes: Coregonidae) in Germany

Combined analyses of mitochondrial DNA (mtDNA) and microsatellite loci were performed to assess the genetic differentiation of two spring‐spawning ciscoes from each other and from sympatric Coregonus albula in two German lakes. Polymorphism was screened at six microsatellite loci and mtDNA for a total of 247 and 94 ciscoes, respectively. Microsatellite data showed a weak differentiation between spring‐spawning Coregonus fontanae and sympatric C. albula in Lake Stechlin ( F _ST = 0–0·008), whereas a significant differentiation was observed between spring‐spawning Coregonus lucinensis and sympatric C. albula in Lake Breiter Luzin ( F _ST = 0·013–0·039). A more pronounced genetic difference was observed between both spring‐spawning species ( F _ST = 0·05–0·128). Shared mtDNA haplotypes among sympatric species within both Lake Stechlin and Lake Breiter Luzin were observed, whereas no haplotype was shared between C. fontanae and C. lucinensis . These results suggest an independent origin for spring‐spawning ciscoes in each lake. Evidence is also provided for mtDNA introgression of Coregonus sardinella into C. lucinensis and C. albula in Lake Breiter Luzin. Postglacially, this species or at least a population which showed mtDNA introgression has colonized the Baltic Sea basin up to the glacial margin that was located between Lakes Stechlin and Breiter Luzin.     

Population structure in two sympatric species of the Lake Tanganyika cichlid tribe Eretmodini: evidence for introgression

Patterns of genetic differentiation were analysed and compared in two sympatric species of the endemic Lake Tanganyika cichlid tribe Eretmodini by means of mitochondrial DNA (mtDNA) sequences of the control region and six microsatellite DNA loci. The sample area covers a total of 138 km of mostly uninterrupted rocky shoreline in the Democratic Republic of Congo and includes the entire distribution range of Tanganicodus cf. irsacae that stretches over a distance of 35 km. Both markers detected significant genetic differentiation within and between the two species. T. cf. irsacae contained lower overall genetic variation than Eretmoduscyanostictus, possibly due to its more restricted range of distribution and its smaller effective population sizes. Complete fixation of Tanganicodus mtDNA haplotypes was observed in Eretmodus at two localities, while at two other localities some Tanganicodus individuals possessed Eretmodus mtDNA haplotypes. Taking into account the relatively large average sequence divergence of 6.2% between the two species, as well as the geographical distribution of mtDNA haplotypes in the lake, the observed pattern is more likely to be a consequence of asymmetric introgression than of shared ancestral polymorphism. As there is significant population differentiation between sympatric Tanganicodus and Eretmodus populations, the events of introgressions may have happened after secondary contact, but our data provide no evidence for ongoing gene flow and suggest that both species are reproductively isolated at present time.     

Partial island submergence and speciation in an adaptive radiation: a multilocus analysis of the Cuban green anoles

Sympatric speciation is often proposed to account for species-rich adaptive radiations within lakes or islands, where barriers to gene flow or dispersal may be lacking. However, allopatric speciation may also occur in such situations, especially when ranges are fragmented by fluctuating water levels. We test the hypothesis that Miocene fragmentation of Cuba into three palaeo-archipelagos accompanied species-level divergence in the adaptive radiation of West Indian Anolis lizards. Analysis of morphology, mitochondrial DNA (mt DNA) and nuclear DNA in the Cuban green anoles (carolinensis subgroup) strongly supports three pre dictions made by this hypothesis. First, three geographical sets of populations, whose ranges correspond with palaeo-archipelago boundaries, are distinct and warrant recognition as independent evolutionary lineages or species. Coalescence of nuclear sequence fragments sampled from these species and the large divergences observed between their mtDNA haplotypes suggest separation prior to the subsequent unification of Cuba ca. 5 Myr ago. Second, molecular phylogenetic relationships among these species reflect historical geographical relationships rather than morphological similarity. Third, all three species remain distinct despite extensive geographical contact subsequent to island unification, occasional hybridization and introgression of mtDNA haplotypes. Allopatric speciation initiated during partial island submergence may play an important role in speciation during the adaptive radiation of Anolis lizards.     

History cleans up messes: The impact of time in driving divergence and introgression in a tropical suture zone

Contact zones provide an excellent arena in which to address questions about how genomic divergence evolves during lineage divergence. They allow us to both infer patterns of genomic divergence in allopatric populations isolated from introgression and to characterize patterns of introgression after lineages meet. Thusly motivated, we analyze genome‐wide introgression data from four contact zones in three genera of lizards endemic to the Australian Wet Tropics. These contact zones all formed between morphologically cryptic lineage‐pairs within morphologically defined species, and the lineage‐pairs meeting in the contact zones diverged anywhere from 3.1 to 5.8 million years ago. By characterizing patterns of molecular divergence across an average of 11K genes and fitting geographic clines to an average of 7.5K variants, we characterize how patterns of genomic differentiation and introgression change through time. Across this range of divergences, we find that genome‐wide differentiation increases but becomes no less heterogeneous. In contrast, we find that introgression heterogeneity decreases dramatically, suggesting that time helps isolated genomes “congeal.” Thus, this work emphasizes the pivotal role that history plays in driving lineage divergence.     

Bidirectional introgressive hybridization between Lepus capensis and Lepus yarkandensis

Lepus capensis and Lepus yarkandensis are two well-established hare species with different habitat preferences and obvious morphological distinctions. L. capensis is common and widespread while L. yarkandensis is an endemic species with a restricted distribution in the Tarim Basin of western China. During field sampling, individuals with a distinct phenotype were found in the contact zone between the two species. To understand the origin of these unclassified individuals, we analyzed morphological and genetic data from 700 individuals including L. yarkandensis, L. capensis and the unclassified individuals. Morphological analyses of the unclassified individuals revealed that they lie between L. yarkandensis and L. capensis. Genetic analyses based on species-specific molecular markers (mitochondrial control region and SRY) showed that the unclassified populations have mtDNA and SRY genes from both L. capensis and L. yarkandensis, suggesting that the unclassified populations result from hybridization between the two species. Interestingly, many identical and/or very similar mtDNA haplotypes were shared between L. capensis populations and L. yarkandensis populations close to their contact zones, which further suggests the existence of extensive bidirectional mtDNA introgression. Similarly, we found evidence for SRY introgression, though it existed at a lower level compared to mtDNA introgression.