Repeated Range Expansion and Glacial Endurance of Potentilla glabra (Rosaceae) in the Qinghai-Tibetan Plateau

To date, little is still known about how alpine species occurring in the Qinghai-Tibetan Plateau (QTP) responded to past climatic oscillations. Here, by using variations of the chloroplast trnJ-L, we examined the genetic distribution pattern of 101 individuals of Potentilla glabra, comprising both the interior QTP and the plateau edge. Phylogenetic and network analyses of 31 recovered haplotypes identified three tentative clades (A, B and C). Analysis of molecular variance (amova) revealed that most of the genetic variability was found within populations (0.693), while differentiations between populations were obviously distinct (Fst = 0.307). Two independent range expansions within clades A and B occurring at approximately 316 and 201 thousand years ago (kya) were recovered from the hierarchical mismatch analysis, and these two expansions were also confirmed by Fu's Fs values and 'g' tests. However, distant distributions of clade C and private haplotypes from clades A and B suggest that they had survived the Last Glacial Maximum (LGM) and previous glaciers in situ since their origins. Our findings based on available limited samples support that multiple refugia of a few cold-enduring species had been maintained in the QTP platform during LGM and/or previous glacial stages.     

多星韭分布格局对末次盛冰期以来气候的响应

该研究以分布区主要在横断山脉的多星韭为对象,基于最大熵模型(MaxEnt)和地理信息系统(ArcGIS)模拟了多星韭在末次盛冰期、全新世中期、当前以及未来的分布格局,以探讨多星韭对末次盛冰期以来气候变化的响应。结果显示:(1)多星韭当前的分布区主要受到最暖季度降水量、年均温变化范围和温度季节性变化标准差3个气候因子的影响;海拔对多星韭的当前分布也有着较大的影响。(2)最大熵模型的模拟精度较高(AUC=0.98)。(3)根据多星韭各个时期分布面积的变化得出多星韭与部分高山植物相似,相比当前的分布,多星韭末次盛冰期的分布区发生了较为明显的扩张。研究推测,未来多星韭的分布区将向西移动。     

Extensive population expansion of Pedicularis longiflora (Orobanchaceae) on the Qinghai‐Tibetan Plateau and its correlation with the Quaternary climate change

The Qinghai‐Tibetan Plateau (QTP) is thought to be more strongly affected by the Quaternary glaciations than most other regions of the same latitude. It would be of great interest to investigate the population genetic structure of organisms distributed on the platform and its correlation with the Quaternary climatic oscillations. Here we used the chloroplast (cp)DNA trnT‐trnF sequence to study genetic variation and phylogeography of Pedicularis longiflora, an alpine herb with extensive distribution on the QTP. Based on a range‐wide sampling comprising 41 populations and 910 individuals, we detected 30 cpDNA haplotypes that were divided into five clades by phylogenetic and network analyses and a strong phylogeographical structure. All haplotypes but one in the three basal clades occur exclusively in the southeast QTP, whereas haplotypes in the young clade V occupy almost the whole species range. In particular, the young haplotype H18 occurs in 420 individuals, even at a frequency of 100% in some QTP platform populations and the Altai population. The haplotype distribution pattern, together with molecular clock estimation and mismatch distribution analysis, suggests that the southeast QTP was either a refuge for P. longiflora during the Quaternary climatic change or is the place of origin of the species. The present wide distribution of the species on the QTP platform has resulted from recent population expansions which could be dated back to 120 000–17 000 years ago, a period mostly before the last glacial maximum. The possible relationships among geographic genetic structure, climatic change and species diversification in Pedicularis are also discussed.     

Host Dependence and Preference of the Root Hemiparasite, Pedicularis cephalantha Franch. (Orobanchaceae)

The interaction between parasitic plants and their hosts is an important topic in both agriculture and ecology. Little, however, is known about that of the hemiparasite Pedicularis. It is essential to understand the host dependence and preference of Pedicularis for successful cultivation of plants in this genus and for understanding the roles they play in natural communities. We tested the effects of two herbaceous host species (Trifolium repens and Polypogon monspeliensis) on the survival and growth performance of Pedicularis cephalantha. Five P. cephalantha seedlings and two host plants were planted in each pot. In the control, no host plants were planted (treatment 1). Host plants were planted in three combinations: only T. repens (treatment 2) or P. monspeliensis (treatment 3) or a mixture of both (treatment 4). The results showed that P. cephalantha performed better in the presence of host plants, and host plants are more essential to P. cephalantha for proper development than for survival. The grass host P. monspeliensis proved to be a better host plant for P. cephalantha than the legume host T. repens. The high dependence of P. cephalantha on host plants and its host preference were demonstrated in this study. This is the first report of the performance of Chinese Pedicularis species in cultivation throughout all life stages (from seeds to seeds).     

Brazilian populations of Drosophila maculifrons (Diptera: Drosophilidae): low diversity levels and signals of a population expansion after the Last Glacial Maximum

The Quaternary period was marked by considerable changes in climate. Such palaeoclimatic changes affected the population dynamics of many species, both in the Northern and in the Southern Hemisphere. However, the extent of these impacts on the demographic patterns of Neotropical species presenting different ecological requirements remains unclear. Drosophila maculifrons DUDA 1947 belongs to the guaramunu group of Drosophila and represents a potential indicator of the genetic consequences caused by the climatic fluctuations of the Quaternary, because it seems to be sensitive to temperature and humidity shifts. The aim of this study was to evaluate the evolutionary processes subjacent to the patterns of intraspecific diversity and structure of different populations of D. maculifrons. In total, 152 individuals were collected in the south and south‐east Brazil. Phylogenetic and phylogeographical analyses were performed based on sequences of COI and COII mitochondrial genes. In general, the results pointed to Brazilian populations of D. maculifrons being extremely impoverished in terms of mitochondrial diversity and population structure, which could be explained by a recent population expansion event dated to approximately 12 000 years ago. In fact, with the assistance of species palaeo‐distribution modelling strategies, it was possible to infer that most of the sampled region did not present the D. maculifrons environmental suitability requirements at least during the period of the Last Glacial Maximum. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 55–66.     

Long-Distance Dispersal by Sea-Drifted Seeds Has Maintained the Global Distribution of Ipomoea pes-caprae subsp. brasiliensis (Convolvulaceae)

Ipomoea pes-caprae (Convolvulaceae), a pantropical plant with sea-drifted seeds, is found globally in the littoral areas of tropical and subtropical regions. Unusual long-distance seed dispersal has been believed to be responsible for its extraordinarily wide distribution; however, the actual level of inter-population migration has never been studied. To clarify the level of migration among populations of I. pes-caprae across its range, we investigated nucleotide sequence variations by using seven low-copy nuclear markers and 272 samples collected from 34 populations that cover the range of the species. We applied coalescent-based approaches using Bayesian and maximum likelihood methods to assess migration rates, direction of migration, and genetic diversity among five regional populations. Our results showed a high number of migrants among the regional populations of I. pes-caprae subsp. brasiliensis, which suggests that migration among distant populations was maintained by long-distance seed dispersal across its global range. These results also provide strong evidence for recent trans-oceanic seed dispersal by ocean currents in all three oceanic regions. We also found migration crossing the American continents. Although this is an apparent land barrier for sea-dispersal, migration between populations of the East Pacific and West Atlantic regions was high, perhaps because of trans-isthmus migration via pollen dispersal. Therefore, the migration and gene flow among populations across the vast range of I. pes-caprae is maintained not only by seed dispersal by sea-drifted seeds, but also by pollen flow over the American continents. On the other hand, populations of subsp. pes-caprae that are restricted to only the northern part of the Indian Ocean region were highly differentiated from subsp. brasiliensis. Cryptic barriers that prevented migration by sea dispersal between the ranges of the two subspecies and/or historical differentiation that caused local adaptation to different environmental factors in each region could explain the genetic differentiation between the subspecies.     

Genetic and palaeo-climatic evidence for widespread persistence of the coastal tree species Eucalyptus gomphocephala (Myrtaceae) during the Last Glacial Maximum

Background and Aims

Few phylogeographic studies have been undertaken of species confined to narrow, linear coastal systems where past sea level and geomorphological changes may have had a profound effect on species population sizes and distributions. In this study, a phylogeographic analysis was conducted of Eucalyptus gomphocephala (tuart), a tree species restricted to a 400 × 10 km band of coastal sand-plain in south west Australia. Here, there is little known about the response of coastal vegetation to glacial/interglacial climate change, and a test was made as to whether this species was likely to have persisted widely through the Last Glacial Maximum (LGM), or conforms to a post-LGM dispersal model of recovery from few refugia.

Methods

The genetic structure over the entire range of tuart was assessed using seven nuclear (21 populations; n = 595) and four chloroplast (24 populations; n = 238) microsatellite markers designed for eucalypt species. Correlative palaeodistribution modelling was also conducted based on five climatic variables, within two LGM models.

Key Results

The chloroplast markers generated six haplotypes, which were strongly geographically structured (G_ST = 0·86 and R_ST = 0·75). Nuclear microsatellite diversity was high (overall mean H_E 0·75) and uniformly distributed (F_ST = 0·05), with a strong pattern of isolation by distance (r² = 0·362, P = 0·001). Distribution models of E. gomphocephala during the LGM showed a wide distribution that extended at least 30 km westward from the current distribution to the palaeo-coastline.

Conclusions

The chloroplast and nuclear data suggest wide persistence of E. gomphocephala during the LGM. Palaeodistribution modelling supports the conclusions drawn from genetic data and indicates a widespread westward shift of E. gomphocephala onto the exposed continental shelf during the LGM. This study highlights the importance of the inclusion of complementary, non-genetic data (information on geomorphology and palaeoclimate) to interpret phylogeographic patterns.     

History and evolution of alpine plants endemic to the Qinghai-Tibetan Plateau: Aconitum gymnandrum (Ranunculaceae)

How Quaternary climatic oscillations affected range distributions and intraspecific divergence of alpine plants on the Qinghai‐Tibetan Plateau (QTP) remains largely unknown. Here, we report a survey of chloroplast DNA (cpDNA) and nuclear ribosomal internal transcribed spacer (ITS) DNA variation aimed at exploring the phylogeographical history of the QTP alpine endemic Aconitum gymnandrum. We sequenced three cpDNA fragments (rpl20–rps12 intergenic spacer, the trnV intron and psbA‐trnH spacer) and also the nuclear (ITS) region in 245 individuals from 23 populations sampled throughout the species’ range. Two distinct lineages, with eastern and western geographical distributions respectively, were identified from a phylogenetic analysis of ITS sequence variation. Based on a fast substitution rate, these were estimated to have diverged from each other in the early Pleistocene approximately 1.45 Ma. The analysis of cpDNA variation identified nine chlorotypes that clustered into two major clades that were broadly congruent in geographical distribution with the two ITS lineages. The east–west split of cpDNA divergence was supported by an amova which partitioned approximately half of the total variance between these two groups of populations. Analysis of the spatial distribution of chlorotypes showed that each clade was subdivided into two groups of populations such that a total of four population groups existed in the species. It is suggested that these different groups derive from four independent glacial refugia that existed during the Last Glacial Maximum (LGM), and that three of these refugia were located at high altitude on the QTP platform itself at that time. Coalescent simulation of chlorotype genealogies supported both an early Pleistocene origin of the two main cpDNA clades and also the ‘four‐refugia’ hypothesis during the LGM. Two previous phylogeographical studies of QTP alpine plants indicated that such plants retreated to refugia at the eastern/south‐eastern plateau edge during the LGM and/or previous glacial maxima. However, the results for A. gymnandrum suggest that at least some of these cold‐tolerant species may have also survived centrally on the QTP platform throughout the Quaternary.     

Changes in Reproductive Allocation after Expansion from the Glacial Refugium and Implications for the Distribution Range in the Qinghai Tibet Plateau Native Herb,Gymnaconitum gymnandrum (Ranunculaceae)

A fundamental goal of ecology and evolution is to explain patterns of species distribution and abundance. However, the way in which stable distribution ranges are shaped by natural selection is still poorly understood, especially whether patterns of resource allocation have contributed to the range size and the formation of range boundary received little attention. For annual herb, the maximum reproductive allocation is predicted to be 50%, and thus we predicted that reproductive allocation might contribute to the formation of range boundary since plant will enhance allocations to reproduction in stressful environments. In this study, we presented our data on resource allocation between population from the glacial refegium and those from the marginal populations in Gymnaconitum gymnandrum, an alpine biennial native to the Qinghai Tibet Plateau, aiming to find the contribution of resource allocation to the formation of range boundary. Our results showed that resource allocations to vegetative organs, including roots, plant height and stem leaf biomass, were significantly higher in the refugium population that in the two marginal populations, and allocations to reproductive organs, including flower number and flower biomass, were significantly lower in one marginal population (Haibei population) than in the other marginal population (Xinghai population) and the refugium population (Tongren population). However, reproductive allocation was significantly higher in the marginal populations than in the refugium population. In addition, in each of the three populations, we found a positive relationship between the plant size and flower biomass but a negative relationship between the plant size and reproductive allocation. Our results indicated a size dependent reproductive allocation in Ggymnandrum, but we did not find a size threshold for reproduction in each of the three populations of this plant, which might be attributed to the life history of this biennial herb. We also suggested that reproductive allocation was increased during the process of range expansion and may rise to the optimal reproductive allocation in the marginal populations, which suggested the important role of sexual reproduction for plants in more stressful environments and the formation of range boundary. However, these conclusions need to be further proved in other plant species.     

青藏高原特有植物露蕊乌头 (毛茛科) 从冰期避难所扩张后繁殖资源分配的变化

物种分布范围的形成是进化生态学研究的基本问题之一,但植物的资源分配策略是否与物种边界形成有关一直没有相关研究。青藏高原特有植物露蕊乌头在末次最大冰期时有4个避难所,但冰期后只有一个避难所的种群发生了扩张并最终形成了现代分布格局。以露蕊乌头的避难所种群（同仁种群）和扩张后邻近分布区边缘的两个种群（兴海种群和海北种群）为研究对象,通过比较避难所种群和边缘种群的资源分配方式,探讨露蕊乌头的资源分配与该植物分布区及边界形成的关系。结果发现：1）兴海和海北种群的营养结构（包括根、植株高度和茎叶生物量）均显著低于同仁种群,海北种群的繁殖结构（花数量和花生物量）显著低于同仁和兴海种群,但海北和兴海的繁殖分配均显著高于同仁种群;2）3个种群的繁殖资源与个体大小呈现显著的正相关关系,投入到繁殖资源的比例（繁殖分配）与个体大小呈显著的负相关关系。对露蕊乌头的研究结果一方面进一步证明了个体大小依赖的繁殖分配,但不符合“植物开始繁殖必须达到一定的大小（阈值）”这一结论,这可能与露蕊乌头的生活史特征有关;而另一方面,露蕊乌头在扩张过程中逐渐增加了对繁殖资源投资的比例,说明胁迫生境中有性繁殖对该植物具有更为重要的意义,且露蕊乌头在扩张过程中可能逐渐实现繁殖产出最大化,并可能在边缘种群实现最优繁殖分配进而最终形成该物种分布区的边界,但这一结论仍需在更多的植物类群中验证。     

青藏高原及其毗邻山区蒙古绣线菊谱系地理学研究

以青藏高原及其毗邻山区的蒙古绣线菊23个居群324个个体为研究对象,选取叶绿体DNA非编码区trnL-trnF和rps15-ycf1片段对蒙古绣线菊进行谱系地理学研究。结果表明:(1)该研究区域中蒙古绣线菊亲缘关系相近的单倍型多发生于同一居群中,存在着明显的谱系地理学关系。(2)所检测得到的35个单倍型中,大约71.4%是居群内特有的单倍型,而出现频率最高的H1是最古老的单倍型,贝叶斯分析和单倍型简约网状图显示35个单倍型聚为地理分布范围各不相同的3个分支。(3)歧点分布分析得到分布图呈多峰曲线,说明蒙古绣线菊居群在较长的时间内发展稳定,没有经历突然的近期扩张。(4)BEAST分析结果显示,在45Mya左右开始出现蒙古绣线菊的谱系分支的分化。研究认为,蒙古绣线菊在青藏高原及其毗邻山区可能至少存在3个冰期避难所,其在青藏高原及其毗邻山区的分布格局主要是第四纪冰期-间冰期气候动荡、青藏高原隆升的共同作用的结果。     

青藏高原六种棘豆属植物的染色体数目及核型报道

对6种棘豆属植物（Oxytropis）的13个居群样进行细胞学研究,其中黄花棘豆（O．ochrocephala）、绢毛棘豆（O．tatarica）、甘肃棘豆（O．kansuensis）和铺地棘豆（0．humifusa）为首次报道染色体数目（2n=16）和核型;在胀果棘豆（O．stracheyana）中（2n=48）首次发现B染色体。现有的细胞学资料表明：棘豆属植物中多倍体占总报道数的58％,这说明多倍化在本属植物的进化过程中起着非常重要的作用,但青藏高原仅有一种植物发现多倍体,多倍化并不占主导地位,而主要表现为二倍体水平上的结构变异,即核型不对称性的变化。     

Into Tibet: An Early Pliocene Dispersal of Fossil Zokor (Rodentia: Spalacidae) from Mongolian Plateau to the Hinterland of Tibetan Plateau

This paper reports the fossil zokors (Myospalacinae) collected from the lower Pliocene (~4.4 Ma) of Zanda Basin, southwestern Tibet, which is the first record in the hinterland of Tibetan Plateau within the Himalayan Range. Materials include 29 isolated molars belonging to Prosiphneus eriksoni (Schlosser, 1924) by having characters including large size, highly fused roots, upper molars of orthomegodont type, m1 anterior cap small and centrally located, and first pair of m1 reentrants on opposing sides, high crowns, and high value of dentine tract parameters. Based on the cladistics analysis, all seven species of Prosiphneus and P. eriksoni of Zanda form a monophyletic clade. P. eriksoni from Zanda, on the other hand, is nearly the terminal taxon of this clade. The appearance of P. eriksoni in Zanda represents a significant dispersal in the early Pliocene from its center of origin in north China and Mongolian Plateau, possibly via the Hol Xil-Qiangtang hinterland in northern Tibet. The fast evolving zokors are highly adapted to open terrains at a time when regional climates had become increasingly drier in the desert zones north of Tibetan Plateau during the late Miocene to Pliocene. The occurrence of this zokor in Tibet thus suggests a rather open steppe environment. Based on fossils of large mammals, we have formulated an “out of Tibet” hypothesis that suggests earlier and more primitive large mammals from the Pliocene of Tibet giving rise to the Ice Age megafauna. However, fossil records for large mammals are still too poor to evaluate whether they have evolved from lineages endemic to the Tibetan Plateau or were immigrants from outside. The superior record of small mammals is in a better position to address this question. With relatively dense age intervals and numerous localities in much of northern Asia, fossil zokors provide the first example of an “into Tibet” scenario–earlier and more primitive taxa originated from outside of the Tibetan Plateau and the later the lineage became extinct in southwestern Tibet.     

Gene flow between alien and native races of the holoparasitic angiosperm Orobanche minor (Orobanchaceae)

The holoparasitic angiosperm Orobanche minor parasitizes a diverse range of flowering plants from at least 16 orders in both the monocots and eudicots. However, populations of O. minor show host specificity at a local level. Our previous work identified the potential for host specificity to act as a catalyst for genetic divergence among populations of O. minor. Here we have extended this investigation by sampling populations from multiple hosts, across a broad geographic range. Sequence characterised amplified region (SCAR) data identified an exotic host-generalist lineage and a native host-specialist lineage of O. minor, suggesting genetic structure in this species is defined by both host specificity and geography. In addition, host-range overlap, discordant tree topologies, and cryptic morphology indicate the presence of gene flow between alien races and endemic populations. Therefore, repeated introductions of alien races of O. minor from disparate sources leading to introgression with native populations, and cryptic race formation, seem to have contributed to the taxonomic confusion associated with this species. We speculate that radiations associated with broad host range and divergent host ecologies may have promoted the unusually wide geographic distribution and diversification of this species. Finally, evidence of multiple shifts to exotic hosts, coupled with the predicted northward shift in climatic suitability, identify the potential for range expansion in alien races of O. minor, which may threaten nationally scarce native taxa with genetic assimilation. Our phylogenetic analysis provides a framework for identifying host races in Orobanche with a view to setting conservation priorities.     

Phylogeography of Potentilla fruticosa (Rosaceae) in the Qinghai-Tibetan Plateau revisited: a reappraisal and new insights

Background: Most empirical studies to date have suggested that alpine plants in the central Qinghai-Tibetan Plateau (QTP) originated from the south-eastern QTP. However, previous phylogeographcial analysis of Potentilla fruticosa suggested that it diversified in the central QTP, which has also been assumed to have been a glacial refugium, and expanded to the north-eastern regions during the mid-Holocene period.

Aim: We reappraise this claim in the light of information acquired from sampling, haplotyping and analysing additional populations.

Methods: We sequenced the chloroplast trnT-L intergenic spacer of 346 individuals collected from 52 populations. We reconstructed phylogenetic relationships among haplotypes through Bayesian and Network analysis, and used several methods for demographic analysis.

Results: Some common and highly divergent haplotypes were distributed in the central, western and south-eastern QTP. Mismatch and other population genetic analyses applied to our data suggested that a distinct range expansion had occurred between approximately 30,000 and 325,000 years ago (kya).

Conclusions: Besides the possible postglacial expansion in the north-eastern QTP, our results further suggested that the range of the species radically expanded across the whole Plateau before the last glacial maximum (around 18 kya) and the south-eastern, western and central QTP regions had together provided important refugia during recent glacial stages. These findings, in contrast to the previous conclusions, highlight the importance of adequate sampling strategies in phylogeographical studies.