Complete taxon sampling of the avian genus Pica (magpies) reveals ancient relictual populations and synchronous Late‐Pleistocene demographic expansion across the Northern Hemisphere

Previous studies have suggested that bird populations in east Asia were less affected by Pleistocene climatic fluctuations than those in Europe and North America. However, this is mainly based on comparisons among species. It would be more relevant to analyse geographical populations of widespread species or species complexes. We analyzed two mitochondrial genes and two nuclear introns for all taxa of Pica to investigate 1) which Earth history factors have shaped the lineage divergence, and 2) whether different geographical populations were differently affected by the Pleistocene climatic changes. Our mitochondrial tree recovered three widespread lineages, 1) in east Asia, 2) across north Eurasia, and 3) in North America, respectively, with three isolated lineages in northwest Africa, Arabia and the Qinghai‐Tibet Plateau, respectively. Divergences among lineages took place 1.4–3.1 million yr ago. The northwest African population was sister to the others, which formed two main clades. In one of these, Arabia was sister to Qinghai‐Tibet, and these formed the sister clade to the east Asia clade. The other main clade comprised the North American and north Eurasian clades. There was no or very slight structure within these six geographical clades, including a lack of differentiation between the two North American species black‐billed magpie P. hudsonia and yellow‐billed magpie P. nutalli. Demographic expansion was recorded in the three most widespread lineages after 0.06 Ma. Asymmetric gene flow was recorded in the north Eurasian clade from southwestern Europe eastward, whereas the east Asian clade was rooted in south central China. Our results indicate that the fragmentation of the six clades of Pica was related to climatic cooling and aridification during periods of the Pliocene–Pleistocene. Populations on both sides of the Eurasian continent were similarly influenced by the Pleistocene climate changes and expanded concomitantly with the expansion of steppes. Based on results we also propose a revised taxonomy recognising seven species of Pica.     

Phylogeography of a widespread small carnivore,the western spotted skunk (Spilogale gracilis) reveals temporally variable signatures of isolation across western North America

We analyzed phylogeographic patterns in the western spotted skunk, Spilogale gracilis Merriam, 1890 (Carnivora: Mephitidae) in relation to historical events associated with Pre‐Pleistocene Divergence (PPD) and Quaternary climate change (QCC) using mitochondrial DNA from 97 individuals distributed across Western North America. Divergence times were generated using BEAST to estimate when isolation in putative refugia occurred. Patterns and timing of demographic expansion was performed using Bayesian skyline plot. Putative climatic refugia resulting from Quaternary climate change were identified using paleoecological niche modeling and divergence dates compared to major vicariant events associated with Pre‐Pleistocene conditions. We recovered three major mitochondrial clades corresponding to western North America (California, Baja, and across the Great Basin), east‐central North America (Texas, central Mexico, New Mexico), and southwestern Arizona/northwestern Mexico. Time to most recent common ancestor for S. gracilis occurred ~1.36 Ma. Divergence times for each major clade occurred between 0.25 and 0.12 Ma, with signature of population expansion occurring 0.15 and 0.10 Ma. Ecological niche models identified three potential climatic refugia during the Last Interglacial, (1) west coast of California and Oregon, (2) northwestern Mexico, and (3) southern Texas/northeastern Mexico as well as two refugia during the Last Glacial Maximum, (1) western USA and (2) southern Texas/northeastern Mexico. This study supports PPD in shaping species‐level diversity compared to QCC‐driven changes at the intraspecific level for Spilogale, similar to the patterns reported for other small mammals (e.g., rodents and bats). Phylogeographic patterns also appear to have been shaped by both habitat and river vicariance, especially across the desert southwest. Further, continuing climate change during the Holocene coupled with anthropogenic modifications during the Anthropocene appears to be removing both of these barriers to current dispersal of western spotted skunks.     

Reticulate evolution in North American black-fruited hawthorns (Crataegus section Douglasia; Rosaceae): evidence from nuclear ITS2 and plastid sequences

Background and Aims

The taxonomic complexity of Crataegus (hawthorn; Rosaceae, Maleae), especially in North America, has been attributed by some to hybridization in combination with gametophytic apomixis and polyploidization, whereas others have considered the roles of hybridization and apomixis to be minimal. Study of the chemical composition and therapeutic value of hawthorn extracts requires reproducible differentiation of entities that may be difficult to distinguish by morphology alone. This study sought to address this by using the nuclear ribosomal spacer region ITS2 as a supplementary DNA barcode; however, a lack of success prompted an investigation to discover why this locus gave unsatisfactory results.

Methods

ITS2 was extensively cloned so as to document inter- and intraindividual variation in this locus, using hawthorns of western North America where the genus Crataegus is represented by only two widely divergent groups, the red-fruited section Coccineae and the black-fruited section Douglasia. Additional sequence data from selected loci on the plastid genome were obtained to enhance further the interpretation of the ITS2 results.

Key Results

In the ITS2 gene tree, ribotypes from western North American hawthorns are found in two clades. Ribotypes from diploid members of section Douglasia occur in one clade (with representatives of the east-Asian section Sanguineae). The other clade comprises those from diploid and polyploid members of section Coccineae. Both clades contribute ribotypes to polyploid Douglasia. Data from four plastid-derived intergenic spacers demonstrate the maternal parentage of these allopolyploids.

Conclusions

Repeated hybridization between species of section Douglasia and western North American members of section Coccineae involving the fertilization of unreduced female gametes explains the observed distribution of ribotypes and accounts for the phenetic intermediacy of many members of section Douglasia.     

Molecular phylogeny and biogeography of Astilbe (Saxifragaceae) in Asia and eastern North America

Phylogenetic analyses were conducted for Astilbe (Saxifragaceae), an Asian/eastern North American disjunct genus, using sequences of nuclear ribosomal internal transcribed spacer (ITS) and plastid matK, trnL‐trnF and psbA‐trnH regions. The monophyly of Astilbe is well supported by both ITS and plastid sequences. Topological incongruence was detected between the plastid and the ITS trees, particularly concerning the placement of the single North American species, A. biternata, which may be most probably explained by its origin involving hybridization and/or allopolyploidy with plastid capture. In Astilbe, all species with hermaphroditic flowers constitute a well‐supported clade; dioecious species form a basal grade to the hermaphroditic clade. Astilbe was estimated to have split with Saxifragopsis from western North America at 20.69 Ma (95% HPD: 12.14–30.22 Ma) in the early Miocene. This intercontinental disjunction between Astilbe and Saxifragopsis most likely occurred via the Bering land bridge. The major clade of Astilbe (all species of the genus excluding A. platyphylla) was inferred to have a continental Asian origin. At least three subsequent migrations or dispersals were hypothesized to explain the expansion of Astilbe into North America, Japan and tropical Asian islands. The intercontinental disjunct lineage in Astilbe invokes a hybridization event either in eastern Asia or in North America. This disjunction in Astilbe may be explained by a Beringian migration around 3.54 Ma (95% high posterior density: 1.29–6.18 Ma) in the late Tertiary, although long‐distance dispersal from eastern Asia to North America is also likely. The biogeographical connection between continental Asia, Taiwan, the Philippines and other tropical Asian islands in Astilbe provides evidence for the close floristic affinity between temperate or alpine south‐western China and tropical Asia. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Construction of the phylogenetic model for the genera of the tribe Arctiini (Lepidoptera,Arctiidae) with the SYNAP method

A new scheme of the phylogeny of the tribe Arctiini is proposed. The Western Mediterranean genus Atlantarctia is considered the most primitive one in the tribe; the rest of genera form two large clades Arctia-Pericallia and Gonerda-Platyprepia. The first clade is supposed to have been subjected to radiation in western Eurasia, and the second clade, in Asia and North America in the Palaeogene when the eastern part of Asia was isolated from western Eurasia. Subsequently, most probably in the Neogene-Pleistocene, representatives of both clades spread over the whole Eurasia and North America. The Arctiini fauna of the tundra zone, which includes the genera Acerbia and Pararctia, was formed in Asia and North America, whereas the subboreal fauna (both steppe and nemoral) originated in western Eurasia. The boreal genus Borearctia has most likely also originated in Asia.     

Phylogeography of Lagochilus ilicifolius (Lamiaceae) in relation to Quaternary climatic oscillation and aridification in northern China

Using two chloroplast DNA intergenic spacers, a phylogeographical study of Lagochilus ilicifolius with 168 individuals from 14 populations was performed to assess geographical patterns and genetic variation in relation to past climate change. Population structure and history were inferred by nested clade analysis, neutrality tests, divergence time estimates, and mismatch distribution analysis. Twelve haplotypes were identified. Genetic differentiation among populations within groups was also elevated (F_SC = 0.772), suggesting restricted gene flow among populations within groups. Divergence time was at approximately 0.71 Ma, consistent with aridification and desert expansion during the middle Pleistocene. The Helan Mountains contained a large proportion of the haplotypes, which implies that the region may be the center of diversification for the species, whereas the Loess Plateau as a dispersal corridor for postglacial re-colonization northward. Climatic oscillation, aridification, and desert expansion within these regions have molded current distribution and biodiversity of L. ilicifolius.     

基于SPEI指数的华北冬麦区干旱时空分布特征分析

气候变化的背景下,华北地区干旱化趋势不断加剧。利用华北冬麦区45个气象站1961—2010逐月温度与降水数据,选取标准化降水蒸散指数SPEI(Standardized Precipitation Evapotranspiration Index)作为区域干旱指数进行华北冬麦区近50年干旱时空特征分析。研究表明:(1)近50年来华北地区平均温度明显上升,研究区整体呈现干旱化加剧趋势。华北地区平均SPEI指数对于典型干旱年份的表征准确,与历史资料相符合。(2)华北不同区域之间增温率不同,导致干旱化趋势存在差异。通过对典型站点的分析,发现增温率越大的区域干旱化趋势越严重。(3)不同等级干旱发生的站次比能够较好地反映不同年型干旱的发生特点。对SPEI指数矩阵的EOF分析结果显示出华北地区典型的干旱时空分布特征,第一模态呈现全区旱涝变化一致型的分布形式,高值区包括山东西部、河南北部、河北南部地区,表明这些地区对干旱的反应最为敏感。时间系数序列未显示出明显的变化趋势;第二模态呈现南北相反的分布型,河北及山东的大部分地区空间系数均为正值,而河南大部分地区为负值。时间系数序列整体呈下降趋势,表明研究区北部干旱化趋势加剧,南部干旱化有所缓解;第三模态呈现东西相反的分布形式,这种分布特征的变化趋势不明显。     

Large Shift in Symbiont Assemblage in the Invasive Red Turpentine Beetle

Changes in symbiont assemblages can affect the success and impact of invasive species, and may provide knowledge regarding the invasion histories of their vectors. Bark beetle symbioses are ideal systems to study changes in symbiont assemblages resulting from invasions. The red turpentine beetle (Dendroctonus valens) is a bark beetle species that recently invaded China from its native range in North America. It is associated with ophiostomatalean fungi in both locations, although the fungi have previously been well-surveyed only in China. We surveyed the ophiostomatalean fungi associated with D. valens in eastern and western North America, and identified the fungal species using multi-gene phylogenies. From the 307 collected isolates (147 in eastern North America and 160 in western North America), we identified 20 species: 11 in eastern North America and 13 in western North America. Four species were shared between eastern North America and western North America, one species (Ophiostoma floccosum) was shared between western North America and China, and three species (Grosmannia koreana, Leptographium procerum, and Ophiostoma abietinum) were shared between eastern North America and China. Ophiostoma floccosum and O. abietinum have worldwide distributions, and were rarely isolated from D. valens. However, G. koreana and L. procerum are primarily limited to Asia and North America respectively. Leptographium procerum, which is thought to be native to North America, represented >45% of the symbionts of D. valens in eastern North America and China, suggesting D. valens may have been introduced to China from eastern North America. These results are surprising, as previous population genetics studies on D. valens based on the cytochrome oxidase I gene have suggested that the insect was introduced into China from western North America.     

Multiple Pleistocene refugia and Holocene range expansion of an abundant southwestern American desert plant species (Melampodium leucanthum,Asteraceae)

Pleistocene climatic fluctuations had major impacts on desert biota in southwestern North America. During cooler and wetter periods, drought‐adapted species were isolated into refugia, in contrast to expansion of their ranges during the massive aridification in the Holocene. Here, we use Melampodium leucanthum (Asteraceae), a species of the North American desert and semi‐desert regions, to investigate the impact of major aridification in southwestern North America on phylogeography and evolution in a widespread and abundant drought‐adapted plant species. The evidence for three separate Pleistocene refugia at different time levels suggests that this species responded to the Quaternary climatic oscillations in a cyclic manner. In the Holocene, once differentiated lineages came into secondary contact and intermixed, but these range expansions did not follow the eastwardly progressing aridification, but instead occurred independently out of separate Pleistocene refugia. As found in other desert biota, the Continental Divide has acted as a major migration barrier for M. leucanthum since the Pleistocene. Despite being geographically restricted to the eastern part of the species’ distribution, autotetraploids in M. leucanthum originated multiple times and do not form a genetically cohesive group.     

Molecular Phylogeny and Biogeographic Diversification of Linnaeoideae (Caprifoliaceae s. l.) Disjunctly Distributed in Eurasia,North America and Mexico

Linnaeoideae is a small subfamily of erect or creeping shrubs to small trees in Caprifoliaceae that exhibits a wide disjunct distribution in Eurasia, North America and Mexico. Most taxa of the subfamily occur in eastern Asia and Mexico but the monospecific genus Linnaea has a circumboreal to north temperate distribution. In this study, we conducted phylogenetic and biogeographic analyses for Linnaeoideae and its close relatives based on sequences of the nuclear ribosomal ITS and nine plastid (rbcL, trnS-G, matK, trnL-F, ndhA, trnD-psbM, petB-D, trnL-rpl32 and trnH-psbA) markers. Our results support that Linnaeoideae is monophyletic, consisting of four eastern Asian lineages (Abelia, Diabelia, Dipelta and Kolkwitzia), the Mexican Vesalea, and Linnaea. The Mexican Vesalea was formerly placed in Abelia, but it did not form a clade with the eastern Asian Abelia; instead Vesalea and Linnaea are sisters. The divergence time between the eastern Asian lineages and the Mexican Vesalea plus the Linnaea clade was dated to be 50.86 Ma, with a 95% highest posterior density of 42.8 Ma (middle Eocene) to 60.19 Ma (early Paleocene) using the Bayesian relaxed clock estimation. Reconstructed ancestral areas indicated that the common ancestor of Linnaea plus Vesalea may have been widespread in eastern Asia and Mexico or originated in eastern Asia during the Eocene and likely migrated across continents in the Northern Hemisphere via the North Atlantic Land Bridges or the Bering Land Bridge. The Qinling Mountains of eastern Asia are the modern-day center of diversity of Kolkwitzia-Dipelta-Diabelia clade. The Diabeliaclade became highly diversified in Japan and eastern China. Populations of Diabelia serrata in Japan and eastern China were found to be genetically identical in this study, suggesting a recent disjunction across the East China Sea, following the last glacial event.     

Mitochondrial genomes reveal the extinct Hippidion as an outgroup to all living equids

Hippidions were equids with very distinctive anatomical features. They lived in South America 2.5 million years ago (Ma) until their extinction approximately 10 000 years ago. The evolutionary origin of the three known Hippidion morphospecies is still disputed. Based on palaeontological data, Hippidion could have diverged from the lineage leading to modern equids before 10 Ma. In contrast, a much later divergence date, with Hippidion nesting within modern equids, was indicated by partial ancient mitochondrial DNA sequences. Here, we characterized eight Hippidion complete mitochondrial genomes at 3.4–386.3-fold coverage using target-enrichment capture and next-generation sequencing. Our dataset reveals that the two morphospecies sequenced (H. saldiasi and H. principale) formed a monophyletic clade, basal to extant and extinct Equus lineages. This contrasts with previous genetic analyses and supports Hippidion as a distinct genus, in agreement with palaeontological models. We date the Hippidion split from Equus at 5.6–6.5 Ma, suggesting an early divergence in North America prior to the colonization of South America, after the formation of the Panamanian Isthmus 3.5 Ma and the Great American Biotic Interchange.     

Dispersal of Pleistocene Equus (Family Equidae) into South America and Calibration of GABI 3 Based on Evidence from Tarija,Bolivia

The dispersal of Equus into South America during the Great American Biotic Interchange (GABI) represented a major event for Pleistocene land-mammal age chronology on that continent. It has been argued that this dispersal occurred during the late Pleistocene, ∼0.125 Ma, and it defines the base of the Lujanian South American Land Mammal Age (SALMA). In this scenario, Equus dispersed during the fourth and latest recognized phase of the interchange, i.e., GABI 4. Although Equus was widely distributed in South America during the Pleistocene, only a few localities are calibrated by independent chronostratigraphic data. In this paper, new biostratigraphic evidence documents that Equus occurs from 15 superposed faunal horizons or zones throughout the Tolomosa Formation at Tarija, Bolivia. This biostratigraphic sequence is independently calibrated to occur between ∼0.99 to <0.76 Ma during the middle Pleistocene Ensenadan SALMA and coincident with GABI 3, not GABI 4. Tarija remains the only well calibrated Ensenadan locality at which Equus is found. The new biostratigraphic data presented here are unambiguous and document the earlier (pre-Lujanian) occurrence of this genus in South America. The hypothesized dispersal of the genus Equus into South America at ∼0.125 Ma is no longer supportable in light of the new biostratigraphic evidence presented here. The new data from Tarija thus have continent-wide implications for the origins and biogeography of Equus in South America as well as the calibration of GABI 3.     

Phylogeny and biogeography of the carnivorous plant family Sarraceniaceae

The carnivorous plant family Sarraceniaceae comprises three genera of wetland-inhabiting pitcher plants: Darlingtonia in the northwestern United States, Sarracenia in eastern North America, and Heliamphora in northern South America. Hypotheses concerning the biogeographic history leading to this unusual disjunct distribution are controversial, in part because genus- and species-level phylogenies have not been clearly resolved. Here, we present a robust, species-rich phylogeny of Sarraceniaceae based on seven mitochondrial, nuclear, and plastid loci, which we use to illuminate this family's phylogenetic and biogeographic history. The family and genera are monophyletic: Darlingtonia is sister to a clade consisting of Heliamphora+Sarracenia. Within Sarracenia, two clades were strongly supported: one consisting of S. purpurea, its subspecies, and S. rosea; the other consisting of nine species endemic to the southeastern United States. Divergence time estimates revealed that stem group Sarraceniaceae likely originated in South America 44-53 million years ago (Mya) (highest posterior density [HPD] estimate = 47 Mya). By 25-44 (HPD = 35) Mya, crown-group Sarraceniaceae appears to have been widespread across North and South America, and Darlingtonia (western North America) had diverged from Heliamphora+Sarracenia (eastern North America+South America). This disjunction and apparent range contraction is consistent with late Eocene cooling and aridification, which may have severed the continuity of Sarraceniaceae across much of North America. Sarracenia and Heliamphora subsequently diverged in the late Oligocene, 14-32 (HPD = 23) Mya, perhaps when direct overland continuity between North and South America became reduced. Initial diversification of South American Heliamphora began at least 8 Mya, but diversification of Sarracenia was more recent (2-7, HPD = 4 Mya); the bulk of southeastern United States Sarracenia originated co-incident with Pleistocene glaciation, <3 Mya. Overall, these results suggest climatic change at different temporal and spatial scales in part shaped the distribution and diversity of this carnivorous plant clade.     

Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America

The extremes of dinosaur body size have long fascinated scientists. The smallest (<1 m length) known dinosaurs are carnivorous saurischian theropods, and similarly diminutive herbivorous or omnivorous ornithischians (the other major group of dinosaurs) are unknown. We report a new ornithischian dinosaur, Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.     

Climate change and evolution of the New World pitviper genus Agkistrodon (Viperidae)

Aim We derived phylogenies, phylogeographies, and population demographies for two North American pitvipers, Agkistrodon contortrix (Linnaeus, 1766) and A. piscivorus (Lacépède, 1789) (Viperidae: Crotalinae), as a mechanism to evaluate the impact of rapid climatic change on these taxa. Location Midwestern and eastern North America. Methods We reconstructed maximum parsimony (MP) and maximum likelihood (ML) relationships based on 846 base pairs of mitochondrial DNA (mtDNA) ATPase 8 and ATPase 6 genes sequenced over 178 individuals. We quantified range expansions, demographic histories, divergence dates and potential size differences among clades since their last period of rapid expansion. We used the Shimodaira–Hasegawa (SH) test to compare our ML tree against three biogeographical hypotheses. Results A significant SH test supported diversification of A. contortrix from northeastern Mexico into midwestern–eastern North America, where its trajectory was sundered by two vicariant events. The first (c. 5.1 Ma) segregated clades at 3.1% sequence divergence (SD) along a continental east–west moisture gradient. The second (c. 1.4 Ma) segregated clades at 2.4% SD along the Mississippi River, coincident with the formation of the modern Ohio River as a major meltwater tributary. A single glacial refugium was detected within the Apalachicola region of southeastern North America. Significant support was also found for a hypothesis of trans‐Gulf rafting by the common ancestor of A. piscivorus from eastern Mexico (possibly the Yucatan Peninsula) to northern Florida. There, a Mid–Late Pliocene marine transgression separated it at 4.8% SD from mainland North America. Significant range expansions followed compressive glacial effects in three (of four) A. contortrix clades and in two (of three) A. piscivorus clades, with the Florida A. piscivorus clade exhibiting significant distributional stasis. Main conclusions Pliocene glaciations, rapidly developing western aridity, and Pleistocene glacial meltwaters seemingly led to the diversification of A. contortrix and A. piscivorus in North America. Both species were pushed southwards by Pleistocene climate change, with subsequent northward expansions uninhibited topographically. The subspecific taxonomy used for A. contortrix and A. piscivorus today, however, appear non‐representative. The monophyletic Florida subspecies of A. piscivorus may be a distinct species (at 4.8% SD), whereas two western subspecies of A. contortrix also appear to constitute a single distinct species, pending additional analyses. We conclude that both species of Agkistrodon can be used as suitable ectothermic models to gauge impacts of future climate change.     

From Africa via Europe to South America: migrational route of a species‐rich genus of Neotropical lowland rain forest trees (Guatteria,Annonaceae)

Aim Several recent studies have suggested that a substantial portion of today’s plant diversity in the Neotropics has resulted from the dispersal of taxa into that region rather than by vicariance. In general, three routes have been documented for the dispersal of taxa onto the South American continent: (1) via the North Atlantic Land Bridge, (2) via the Bering Land Bridge, or (3) from Africa directly onto the continent. Here a species‐rich genus of Neotropical lowland rain forest trees (Guatteria, Annonaceae) is used as a model to investigate these three hypotheses. Location The Neotropics. Methods The phylogenetic relationships within the long‐branch clade of Annonaceae were reconstructed (using maximum parsimony, maximum likelihood and Bayesian inference) in order to gain insight in the phylogenetic position of Guatteria. Furthermore, Bayesian molecular dating and Bayesian dispersal–vicariance (Bayes‐DIVA) analyses were undertaken. Results Most of the relationships within the long‐branch clade of Annonaceae were reconstructed and had high support. However, the relationship between the Duguetia clade, the Xylopia–Artabotrys clade and Guatteria remained unclear. The stem node age estimate of Guatteria ranged between 49.2 and 51.3 Ma, whereas the crown node age estimate ranged between 11.4 and 17.8 Ma. For the ancestral area of Guatteria and its sister group, the area North America–Africa was reconstructed in 99% of 10,000 DIVA analyses, while South America–North America was found just 1% of the time. Main conclusions The estimated stem to crown node ages of Guatteria in combination with the Bayes‐DIVA analyses imply a scenario congruent with an African origin followed by dispersal across the North Atlantic Land Bridge in the early to middle Eocene and further dispersal into North and Central America (and ultimately South America) in the Miocene. The phylogenetically and morphologically isolated position of the genus is probably due to extinction of the North American and European stem lineages in the Tertiary.     

Evolutionary history of Gymnocarpos (Caryophyllaceae) in the arid regions from North Africa to Central Asia

Gymnocarpos has only about ten species distributed in the arid regions of Asia and Africa, but it exhibits a geographical disjunction between eastern Central Asia and western North Africa and Minor Asia. We sampled eight species of the genus and sequenced two chloroplast regions (rps16 and psbB–psbH), and the nuclear rDNA (ITS) to study the phylogeny and biogeography. The results of the phylogenetic analyses corroborated that Gymnocarpos is monophyletic, in the phylogenetic tree two well supported clades are recognized: clade 1 includes Gymnocarpos sclerocephalus and G. decandrus, mainly the North African group, whereas clade 2 comprises the remaining species, mainly in the Southern Arabian Peninsula. Molecular dating analysis revealed that the divergence age of Gymnocarpos was c. 31.33 Mya near the Eocene and Oligocene transition boundary, the initial diversification within Gymnocarpos dated to c. 6.69 Mya in the late Miocene, and the intraspecific diversification mostly occurred during the Quaternary climate oscillations. Ancestral area reconstruction suggested that the Southern Arabian Peninsula was the ancestral area for Gymnocarpos. Our conclusions revealed that the aridification since mid‐late Miocene significantly affected the diversification of the genus in these areas.     

Site-contingent responses to drought of core and relict Tetraclinis articulata populations from Morocco and Spain

The growth responses to climate variability are still unknown in locally threatened conifers from dry regions, but this information is necessary for improving the conservation of relict populations under increasing aridification. We characterized the radial growth patterns and responses to climate of Tetraclinis articulata, a Cupressaceae tree endemic to the western Mediterranean Basin, in a relict population located in southwestern Spain (Doñana) and two populations from the northern Morocco where the species core habitat is found (Tétouan, Ifarten). We assessed climate-growth relationships by using tree-ring width, climate data, drought and North Atlantic Oscillation (NAO) indices. Climate-growth analyses were refined using the climwin R package to select the most informative statistical models. The main climatic constraints of growth were inferred by using the process-based Vaganov-Shashkin (VS) model explicitly considering non-linear climate-growth relationships. Tetraclinis articulata growth was favored by wet conditions from the prior autumn to the spring of the growth year. In Doñana, warmer May conditions led to growth decline but this negative effect could be reversed by wet-warm conditions in the prior late autumn. Growth in the two Moroccan sites was constrained by 6- to 18-month long droughts peaking in summer, which account for cumulative water deficit since the previous autumn. Winter and early spring precipitation were the main climate drivers of growth in the Moroccan T. articulata populations, and their year-to-year variability was linked to the NAO. The VS model simulations showed that T. articulata growth is enhanced by wet soil conditions in late winter and early spring, probably recharging shallow soil water pools. The VS model also confirmed that warmer spring-summer conditions could amplify drought stress and threaten the long-term persistence of the relict Doñana population.     

Molecular evidence for the age, origin, and evolutionary history of the American desert plant genus Tiquilia (Boraginaceae)

Although the deserts of North America are of very recent origin, their characteristic arid-adapted endemic plant lineages have been suggested to be much older. Earlier researchers have hypothesized that the ancestors of many of these modern desert lineages first adapted to aridity in highly localized arid or semi-arid sites as early as the late Cretaceous or early Tertiary, and that these lineages subsequently spread and diversified as global climate became increasingly arid during the Cenozoic. No study has explicitly examined these hypotheses for any North American arid-adapted plant group. The current paper tests these hypotheses using the genus Tiquilia (Boraginaceae), a diverse North American desert plant group. A strongly supported phylogeny of the genus is estimated using combined sequence data from three chloroplast markers (matK, ndhF, and rps16) and two nuclear markers (ITS and waxy). Ages of divergence events within the genus are estimated using penalized likelihood and a molecular clock approach on the ndhF tree for Tiquilia and representative outgroups, including most of the major lineages of Boraginales. The dating analysis suggests that the stem lineage of Tiquilia split from its nearest extant relative in the Paleocene or Eocene ( approximately 59-48 Ma). This was followed by a relatively long period before the first divergence in the crown group near the Eocene/Oligocene boundary ( approximately 33-29 Ma), shortly after the greatest Cenozoic episode of rapid aridification. Divergence of seven major lineages of Tiquilia is dated to the early-to-mid Miocene ( approximately 23-13 Ma). Several major lineages show a marked increase in diversification concomitant with the onset of more widespread semi-arid and then arid conditions beginning in the late Miocene ( approximately 7 Ma). This sequence of divergence events in Tiquilia agrees well with earlier researchers' ideas concerning North American desert flora assembly.