Unequal contributions of species’ persistence and migration on plant communities’ response to climate warming throughout forests

Community reshuffling is lagging behind climate warming for many taxa, thereby generating a climatic debt. However, only few studies have attempted to assess the underlying factors that explain this debt. Here I examine how effects of species’ migration and persistence on the current climatic debt vary spatially in forest herbaceous communities throughout the French territory. I show that Mediterranean communities are responding to climate warming through both high species’ migration and persistence effects, while alpine forest is the only ecosystem where species’ migration overtakes species’ persistence mechanisms. Such an approach seems promising in assessing the underlying mechanisms of the biodiversity response to climate change locally, and it can be applied for conservation issues to assess biodiversity sensitivity and optimize its management.     

Lineage-specific late pleistocene expansion of an endemic subtropical gossamer-wing damselfly, Euphaea formosa, in Taiwan

Background  

Pleistocene glacial oscillations have significantly affected the historical population dynamics of temperate taxa. However, the general effects of recent climatic changes on the evolutionary history and genetic structure of extant subtropical species remain poorly understood. In the present study, phylogeographic and historical demographic analyses based on mitochondrial and nuclear DNA sequences were used. The aim was to investigate whether Pleistocene climatic cycles, paleo-drainages or mountain vicariance of Taiwan shaped the evolutionary diversification of a subtropical gossamer-wing damselfly, Euphaea formosa.     

Molecular phylogeography of four endemic Sagittaria species (Alismataceae) in the Sino‐Japanese Floristic Region of East Asia

To reveal the role of climate oscillations of the Quaternary in forming the contemporary plant diversity in the temperate Sino‐Japanese Floristic Region of mainland China, we assess the phylogeographical patterns of four Sagittaria species in the region using sequence data from plastid DNA non‐coding regions (psbA‐trnH, the rpl16 intron and trnC‐ycf6) and the internal transcribed spacers of nuclear ribosomal DNA (nrITS). Based on both datasets, the divergence time among the four studied species was estimated to fall in the Late Tertiary (plastid DNA: 7.1–13.7 Mya; ITS: 11.1–16.1 Mya). The ancestral distribution analyses revealed that regions with a great diversity in topography, climate and ecological conditions, e.g. the Hengduan Mountains, Central China and East China, were the areas where the endemics originated. Mismatch distribution analyses revealed that each species had experienced a range expansion in response to Quaternary climatic oscillations. Our findings contradict the hypothesis of Quaternary origins of the endemic Sagittaria spp.; we support the view that modern species in the Northern Hemisphere originated mostly during the Tertiary. Range expansion may have profoundly modified the current distribution ranges of Sagittaria species in the Sino‐Japanese Floristic Region. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 6–20.     

Spatial patterns of genetic diversity among Australian alpine flora communities revealed by comparative phylogenomics

Aim

The alpine region of mainland Australia is one of the world's 187 biodiversity hotspots. Genetic analyses of Australian alpine fauna indicate high levels of endemism on fine spatial scales, unlike Northern Hemisphere alpine systems where shallow genetic differentiation is typically observed among populations. These discrepancies have been attributed to differences in elevation and influence from glacial activity, and point to a unique phylogeographic history affecting Australian alpine biodiversity. To test generality of these findings across Australian alpine biota, we assessed patterns of genetic structure across plant species.

Location

The Australian Alps, Victoria, eastern Australia.

Methods

We used an economical pooled genotyping‐by‐sequencing (GBS) approach to examine patterns of genetic diversity among seven widespread species including shrubs and forbs from 16 mountain summits in the Australian Alpine National Park. Patterns of genetic structure among summit populations for each species were inferred from an average of 2,778 independent SNP loci using Bayesian phylogenomic inference and clustering approaches.

Results

SNP results were consistent across species in identifying deep evolutionary splits among summit communities from the Northern and Central Victorian Alpine regions. These patterns of genetic structure are also consistent with those previously reported for invertebrate and mammal taxa. However, local genetic structure was less pronounced in the plants, supporting the notion that population connectivity tends to be higher in plant species.

Main conclusion

There is deep lineage diversification between the North and Central Victorian Alpine regions, reflecting a high level of endemism. These findings differ from those reported for alpine biodiversity from New South Wales and much of the Northern Hemisphere, and support the notion that genetic diversity is typically greatest in areas least affected by historical ice sheet formation. We discuss the implications of our findings in the context of conservation planning, and highlight the benefits of this rapid and cost‐effective genome scan approach for characterizing evolutionary processes at multispecies and landscape scales.     

Enough space in a warmer world? Microhabitat diversity and small‐scale distribution of alpine plants on mountain summits

Aim

Global warming is predicted to shift distributions of mountain species upwards, driven by a release from climatic restrictions at their upper distribution limit and increased biotic pressure at their lower distribution limit. In alpine ecosystems, which are characterized by large microclimatic diversity and sparse vegetation cover, the relative importance of abiotic and biotic drivers for species distribution is poorly understood. To disentangle abiotic and biotic mechanisms affecting distributions of alpine species, we investigated how alpine plant species with differing elevational ranges and frequency trends over the past century differ in their microhabitat distribution, and how they respond to neighbouring vegetation.

Location

A total of 11 summits (2635—3410 m a.s.l.) in SE‐Switzerland.

Methods

We quantified the microscale abundance of 12 species in relation to biogeographic (frequency trend, i.e., change in occurrences over the past century, and elevational range on summits) and local microhabitat characteristics (temperature, substrate type). We assessed species size traits in relation to neighbouring vegetation characteristics to investigate possible neighbour interactions.

Results

Species with increasing frequency on summits over the past century were most abundant on scree and warmer slopes. Species with negative or stable frequency trends on summits were more abundant on organic soil and colder slopes. The preferred microhabitats of the latter were rarest overall, decreased with increasing elevation, and had the most competitive neighbours. Size of one high‐alpine specialist, Ranunculus glacialis was negatively related to cover of neighbouring vegetation, whereas other species showed no response to neighbours.

Main conclusions

Long‐term frequency trends of species correlate with their microhabitat association. Species with most negative frequency trends show preferences for the rarest microhabitat conditions, where they likely experience higher competitive pressure in a warming climate. This finding emphasizes the importance of characterizing microhabitat associations and microclimatic diversity to assess present and future distributions of alpine plant species.

     

Culturable root endophyte communities are shaped by both warming and plant host identity in the Rocky Mountains,USA

Understanding the biogeographic patterns of root-associated fungi and their sensitivity to temperature may improve predictions of future changes in terrestrial biodiversity and associated ecosystem processes, but data are currently limited. Anticipating change will require combining observational data, which predict how climatic factors limit current species distributions, with direct manipulations of climate, which can isolate responses to specific climate variables. Root endophytes are common symbionts of plants, particularly in arctic and alpine environments, yet their responses to climate warming are not resolved. Here, we directly cultured endophytic fungi from roots collected along altitudinal gradients in replicated mountain watersheds and from a 27 y field warming experiment in the Rocky Mountains, USA, to improve understanding of climate impacts on fungal root endophytes. Fungal taxa that were common at high elevations declined most under climate warming, whereas low elevation dominants responded neutrally or increased with experimental warming. Altitudinal gradients in fungal communities were strongly specific to the plant host species. Specifically, Poa species had 25–60% greater fungal isolate abundance and 25–38% greater fungal diversity at high elevations than at low elevation sites. In contrast, Festuca thurberi had 64% lower fungal diversity on roots at high elevation than at low elevation. Our results help to improve understanding of the potential for climate change to alter plant-fungal interactions in mountain ecosystems.     

Staying in situ or shifting range under ongoing climate change: A case of an endemic herb in the Himalaya-Hengduan Mountains across elevational gradients

Aim

How species respond to ongoing climate change has been a hot research topic, especially with the controversy in shifting range (movement) or persisting in local habitat (in situ) as the primary response. Assessing the relative roles of range shifts, phenotypic plasticity and genetic adaptation helps us predict the evolutionary fate of species. We aim to explore the evolutionary strategies of plants under climate change from a keystone herb in alpine ecosystems, Mirabilis himalaica, along its elevational gradient.

Location

Himalaya-Hengduan Mountains, China.

Methods

We combined evidence from population genomics and ecological data in both space and time to investigate the state of “staying” or “moving”. We identified migration events by assessing historical and contemporary gene flow and changes in species distribution. Morphological variation was compared by measuring five traits using specimen data. Moreover, we explored climate-driven genetic variation and local selection regimes acting on populations in the alpine landscape along an elevational gradient.

Results

Our results argue that staying in situ by morphological variation and local genetic evolution rather than range shifting plays an important role in M. himalaica response to climate change. We first found trace evidence of upward or climatic-driven shifting along an elevational gradient, although asymmetric gene flow was restricted within microenvironments of mid-elevational populations. Furthermore, morphological variation comparisons revealed clinal variation, as resource allocation showed a declining pattern in vegetative growth but increased reproductive growth with increasing elevation. Outlier tests and environment association analyses indicated adaptative loci primarily related to thermal-driven selection and continuous adaptations to high elevation in the Himalaya-Hengduan Mountains.

Main Conclusions

Our findings show M. himalaica may persist in local habitats rather than shifting range under climate change, exhibiting a low risk of genomic vulnerability in current habitats. This study has important implications in improving our understanding of the evolutionary response in alpine plants to climate change.     

Evolutionary diversification of cryophilic <Emphasis Type="Italic">Grylloblatta</Emphasis>species (Grylloblattodea: Grylloblattidae) in alpine habitats of California

Background  

Climate in alpine habitats has undergone extreme variation during Pliocene and Pleistocene epochs, resulting in repeated expansion and contraction of alpine glaciers. Many cold-adapted alpine species have responded to these climatic changes with long-distance range shifts. These species typically exhibit shallow genetic differentiation over a large geographical area. In contrast, poorly dispersing organisms often form species complexes within mountain ranges, such as the California endemic ice-crawlers (Grylloblattodea: Grylloblattidae: Grylloblatta). The diversification pattern of poorly dispersing species might provide more information on the localized effects of historical climate change, the importance of particular climatic events, as well as the history of dispersal. Here we use multi-locus genetic data to examine the phylogenetic relationships and geographic pattern of diversification in California Grylloblatta.     

Human land use is comparable to climate as a driver of global plant occurrence and abundance across life forms

Aim

Historically, climate has been a dominant driver of global vegetation patterns. Recently, ecological understanding has been updated to acknowledge the influence of human land use (the dominant driver of biodiversity change) in shaping global vegetation patterns. We test whether Raunkiær's life form, a plant classification system designed to reflect climatic drivers, affects how plants respond to both land use and climate.

Location

Forty-one countries across six continents.

Time period

1990 to 2013.

Major taxa studied

Terrestrial plants.

Methods

Combining data from the biodiversity and land use database PREDICTS, and plant trait databases TRY and BIEN, we use generalized linear mixed models with weighted effects coding to test whether Raunkiær's life form affects plant response to land use and climate in over 4800 species at over 300 sites globally.

Results

We provide evidence that human land use is comparable to climate in influencing life form occurrence and that land use produces divergent outcomes across life forms.

Main conclusions

Combined with climatic suitability, land use acts as a filter contracting the realized niche of trees and expanding the realized niche of disturbance-tolerant species. Our results highlight the fundamental role of human activity in shaping species' distribution.     

Past and future demographic dynamics of alpine species: limited genetic consequences despite dramatic range contraction in a plant from the Spanish Sierra Nevada

Anthropogenic global climate change is expected to cause severe range contractions among alpine plants. Alpine areas in the Mediterranean region are of special concern because of the high abundance of endemic species with narrow ranges. This study combined species distribution models, population structure analyses and Bayesian skyline plots to trace the past and future distribution and diversity of Linaria glacialis, an endangered narrow endemic species that inhabits summits of Sierra Nevada (Spain). The results showed that: (i) the habitat of this alpine‐Mediterranean species in Sierra Nevada suffered little changes during glacial and interglacial stages of late Quaternary; (ii) climatic oscillations in the last millennium (Medieval Warm Period and Little Ice Age) moderately affected the demographic trends of L. glacialis; (iii) future warming conditions will cause severe range contractions; and (iv) genetic diversity will not diminish at the same pace as the distribution range. As a consequence of the low population structure of this species, genetic impoverishment in the alpine zones of Sierra Nevada should be limited during range contraction. We conclude that maintenance of large effective population sizes via high mutation rates and high levels of gene flow may promote the resilience of alpine plant species when confronted with global warming.     

Smaller,more diverse and on the way to the top: Rapid community shifts of montane wild bees within an extraordinary hot decade

Aim

Global warming is assumed to restructure mountain insect communities in space and time. Theory and observations along climate gradients predict that insect abundance and richness, especially of small-bodied species, will increase with increasing temperature. However, the specific responses of single species to rising temperatures, such as spatial range shifts, also alter communities, calling for intensive monitoring of real-world communities over time.

Location

German Alps and pre-alpine forests in south-east Germany.

Methods

We empirically examined the temporal and spatial change in wild bee communities and its drivers along two largely well-protected elevational gradients (alpine grassland vs. pre-alpine forest), each sampled twice within the last decade.

Results

We detected clear abundance-based upward shifts in bee communities, particularly in cold-adapted bumble bee species, demonstrating the speed with which mobile organisms can respond to climatic changes. Mean annual temperature was identified as the main driver of species richness in both regions. Accordingly, and in large overlap with expectations under climate warming, we detected an increase in bee richness and abundance, and an increase in small-bodied species in low- and mid-elevations along the grassland gradient. Community responses in the pre-alpine forest gradient were only partly consistent with community responses in alpine grasslands.

Main Conclusion

In well-protected temperate mountain regions, small-bodied bees may initially profit from warming temperatures, by getting more abundant and diverse. Less severe warming, and differences in habitat openness along the forested gradient, however, might moderate species responses. Our study further highlights the utility of standardized abundance data for revealing rapid changes in bee communities over only one decade.     

Testing the environmental warming responses of Brachyscome daisy species using a common garden approach

As temperatures increase in a warming world, there will be different responses among related plant species, with some species able to increase growth rate under warmer conditions and others less likely. Here, we identify survival and growth parameters in a group of 19 related Australian daisies from the genera Brachyscome and Pembertonia when exposed to higher soil temperature, focusing particularly on species from the alpine environment. We used a common garden approach to measure growth and survival under warming. We tested for the effects of evolutionary history by investigating phylogeny and testing for a phylogenetic signal, and for the effects of ecological history by considering climatic variables associated with species distributions in their native range. Evolutionary history did not have a detectable effect on warming responses. While there was a moderate signal for plant growth in the absence of warming, there was no signal for growth changes in response to warming, despite variability among species to warming that ranged from positive to negative growth responses. There was no strong effect of climate context, as species that showed a positive response to warming did not necessarily originate from hotter environments. In fact, several species from hot environments grew relatively poorly when exposed to higher soil temperature. However, species endemic to alpine areas were less likely to benefit from warming than widespread species. We found a strong phylogenetic signal for climate history, in that closely related species tend to occur in areas with similar annual variability in precipitation. Species differences in response to soil warming were variable and difficult to link to climate conditions except for the poor response of alpine endemics. There was no significant association between survival and warming responses of species. However, as some species showed weak growth responses, this may reduce their fitness into the future.     

Phylogeography suggest the Yili Valley being the glacial refuge of the genus Ixiolirion (Amaryllidaceae) in China

The Pleistocene climatic oscillations had profound effects on the demographic history and genetic diversification of plants in arid north-west China where some glacial refugia have been recognized. The genus Ixiolirion comprises three species, of which two, I. tataricum and I. songaricum (endemic), occur in China. In some locations they are sympatric. We investigated their population structure and population history in response to past climatic change using a sample of 619 individuals in 34 populations with nITS and ptDNA sequences. A significant genetic divergence between the two species was supported by a high level of pairwise genetic differentiation, very low gene flow, and phylogenetic analysis showing that I. songaricum haplotypes were monophyletic, whereas those of I. tataricum were polyphyletic. We found significant differentiation and phylogeographic structure in both species. The split of the two species was dated to the late Miocene (～7?Ma), but deep divergence occurred in the mid-late Quaternary. A similar haplotype distribution pattern was found in both species: one to two dominant haplotypes across most populations, with unique haplotypes in a few populations or a geographic group. The genetic diversity, haplotype number, and haplotype diversity decreased from the Yili Valley to the central Tianshan and Barluk Mountains. Additionally, ptDNA analysis showed that I. tataricum diversified in the eastern Tianshan and Barluk Mountains, which might be due to physical barriers to long distance seed dispersal such as desert. In conclusion, our results indicated that the Yili Valley was likely a glacial refuge for Ixiolirion in China, with postglacial dispersal from the Yili Valley eastward to the eastern Tianshan Mountains, and northward to the Barluk Mountains. The climatic changes in the Miocene and Pleistocene and geographic barriers are important factors driving species divergence and differentiation of Ixiolirion and other taxa.     

Species interactions weakly modify climate‐induced tree co‐occurrence patterns

Aims

Species distributions are hypothesized to be underlain by a complex association of processes that span multiple spatial scales including biotic interactions, dispersal limitation, fine‐scale resource gradients and climate. Species disequilibrium with climate may reflect the effects of non‐climatic processes on species distributions, yet distribution models have rarely directly considered non‐climatic processes. Here, we use a Joint Species Distribution Model (JSDM) to investigate the influence of non‐climatic factors on species co‐occurrence patterns and to directly quantify the relative influences of climate and alternative processes that may generate correlated responses in species distributions, such as species interactions, on tree co‐occurrence patterns.

Location

US Rocky Mountains.

Methods

We apply a Bayesian JSDM to simultaneously model the co‐occurrence patterns of ten dominant tree species across the Rocky Mountains, and evaluate climatic and residual correlations from the fitted model to determine the relative contribution of each component to observed co‐occurrence patterns. We also evaluate predictions generated from the fitted model relative to a single‐species modelling approach.

Results

For most species, correlation due to climate covariates exceeded residual correlation, indicating an overriding influence of broad‐scale climate on co‐occurrence patterns. Accounting for covariance among species did not significantly improve predictions relative to a single‐species approach, providing limited evidence for a strong independent influence of species interactions on distribution patterns.

Conclusions

Overall, our findings indicate that climate is an important driver of regional biodiversity patterns and that interactions between dominant tree species contribute little to explain species co‐occurrence patterns among Rocky Mountain trees.     

AFLP markers reveal high clonal diversity and extreme longevity in four key arctic-alpine species

We investigated clonal diversity, genet size structure and genet longevity in populations of four arctic‐alpine plants (Carex curvula, Dryas octopetala, Salix herbacea and Vaccinium uliginosum) to evaluate their persistence under past climatic oscillations and their potential resistance to future climate change. The size and number of genets were determined by an analysis of amplified fragment length polymorphisms and a standardized sampling design in several European arctic‐alpine populations, where these species are dominant in the vegetation. Genet age was estimated by dividing the size by the annual horizontal size increment from in situ growth measurements. Clonal diversity was generally high but differed among species, and the frequency distribution of genet size was strongly left‐skewed. The largest C. curvula genet had an estimated minimum age of c. 4100 years and a maximum age of c. 5000 years, although 84.8% of the genets in this species were <200 years old. The oldest genets of D. octopetala, S. herbacea and V. uliginosum were found to be at least 500, 450 and 1400 years old, respectively. These results indicate that individuals in the studied populations have survived pronounced climatic oscillations, including the Little Ice Age and the postindustrial warming. The presence of genets in all size classes and the dominance of presumably young individuals suggest repeated recruitment over time, a precondition for adaptation to changing environmental conditions. Together, persistence and continuous genet turnover may ensure maximum ecosystem resilience. Thus, our results indicate that long‐lived clonal plants in arctic‐alpine ecosystems can persist, despite considerable climatic change.     

短期增温对西藏念青唐古拉山典型植物群落结构和稳定性的影响

青藏高原气候变暖幅度显著高于全球其他区域,深刻影响着该地区植物群落的结构和稳定性。选择西藏念青唐古拉山的三种典型植物群落(高寒草原、高寒草甸和流石滩)作为研究对象,采用开顶式增温箱(OTC)模拟增温,研究了短期增温对植物群落结构和稳定性的影响。结果表明:(1)增温改变了群落的优势物种,影响其结构组成,而对物种多样性无显著影响;(2)增温显著降低了高寒草甸的地上生物量(P < 0.05),增加地下生物量(P < 0.01),从而导致了群落地下地上生物量分配策略的改变;(3)增温降低群落中部分物种的生态位宽度,进而影响群落稳定性,其中高寒草甸变化最大,达到-66.8%。研究结果可为青藏高原高寒草地生态系统应对和适应未来气候变化提供一定科学依据。     

Linking thaw depth with soil moisture and plant community composition: effects of permafrost degradation on alpine ecosystems on the Qinghai-Tibet Plateau

Background and aims

The warming of the planet in recent decades has caused rapid, widespread permafrost degradation on the Qinghai–Tibet Plateau. These changes may significantly affect soil moisture content and nutrient supply, thereby affecting ecosystem structure and function. This study aimed to describe the dynamic changes in thaw depth, assess the relationship between thaw depth and soil moisture content, and analyze the changes in species composition and water-use efficiency in response to permafrost degradation.

Methods

We surveyed species composition, thaw depth, ground temperature, soil moisture, nutrient content, and foliar stable carbon isotope compositions to gain insights into the response of alpine grassland ecosystems to permafrost degradation on the Qinghai-Tibet Plateau.

Results

Moisture content of the surface layer decreased with increasing thaw depth. The correlation between thaw depth and surface soil moisture content was strongest in June and decreased in July and August. The strongest correlation occurred at a depth of 20 cm to 30 cm. The dominant species shifted from Cyperaceae in alpine meadow to mesoxerophytes in alpine steppe before finally shifting to xerophytes in alpine desert steppe. Thaw depth correlation was significantly negative with organic C content (r?=??0.49, P?<?0.05) and with total N content (r?=??0.62, P?<?0.01). The leaf δ¹³C of Carex moorcroftii increased with increasing thaw depth and followed a linear relationship (R ²?=?0.85, P?=?0.008).

Conclusions

Permafrost degradation decreases surface soil moisture and soil nutrient supply capacity. Increasing permafrost degradation decreases the number of plant families and species, with hygrophytes and mesophytes gradually replaced by mesoxerophytes and xerophytes. The water-use efficiency of plants improved in response to increasing water stress as surface layers dried during permafrost degradation. Permafrost on the Qinghai–Tibetan Plateau is expected to further degrade as global warming worsens. Therefore, more attention should be dedicated to the response of alpine ecosystems during permafrost degradation.     

Limited genetic divergence among Australian alpine Poa tussock grasses coupled with regional structuring points to ongoing gene flow and taxonomic challenges

Background and Aims

While molecular approaches can often accurately reconstruct species relationships, taxa that are incompletely differentiated pose a challenge even with extensive data. Such taxa are functionally differentiated, but may be genetically differentiated only at small and/or patchy regions of the genome. This issue is considered here in Poa tussock grass species that dominate grassland and herbfields in the Australian alpine zone.

Methods

Previously reported tetraploidy was confirmed in all species by sequencing seven nuclear regions and five microsatellite markers. A Bayesian approach was used to co-estimate nuclear and chloroplast gene trees with an overall dated species tree. The resulting species tree was used to examine species structure and recent hybridization, and intertaxon fertility was tested by experimental crosses.

Key Results

Species tree estimation revealed Poa gunnii, a Tasmanian endemic species, as sister to the rest of the Australian alpine Poa. The taxa have radiated in the last 0·5–1·2 million years and the non-gunnii taxa are not supported as genetically distinct. Recent hybridization following past species divergence was also not supported. Ongoing gene flow is suggested, with some broad-scale geographic structure within the group.

Conclusions

The Australian alpine Poa species are not genetically distinct despite being distinguishable phenotypically, suggesting recent adaptive divergence with ongoing intertaxon gene flow. This highlights challenges in using conventional molecular taxonomy to infer species relationships in recent, rapid radiations.     

Phylogeographic study of Apodemus ilex (Rodentia: Muridae) in Southwest China

Background

The Mountains of southwest China have complex river systems and a profoundly complex topography and are among the most important biodiversity hotspots in the world. However, only a few studies have shed light on how the mountains and river valleys promote genetic diversity. Apodemus ilex is a fine model for investigating this subject.

Methodology/Principal Findings

To assess the genetic diversity and biogeographic patterns of Apodemus ilex, the complete cytochrome b gene sequences (1,140 bp) were determined from 203 samples of A. draco/ilex that were collected from southwest China. The results obtained suggested that A. ilex and A. draco are sistergroups and diverged from each other approximately 2.25 million years ago. A. ilex could be divided into Eastern and Western phylogroups, each containing two sub-groups and being widespread in different geographical regions of the southern Hengduan Mountains and the western Yunnan - Guizhou Plateau. The population expansions of A. ilex were roughly from 0.089 Mya to 0.023 Mya.

Conclusions

Our result suggested that A. ilex is a valid species rather than synonym of A. draco. As a middle-high elevation inhabitant, the phylogenetic pattern of A. ilex was strongly related to the complex geographical structures in southwest China, particularly the existence of deep river valley systems, such as the Mekong and Salween rivers. Also, it appears that the evolutionary history of A. ilex, such as lineage divergences and population expansions were strongly affected by climate fluctuation in the Late Pleistocene.     

The impact of early Quaternary climate change on the diversification and population dynamics of a South American cactus species

Aim

Climatic oscillations have been suggested to promote speciation and changes in species distributions, mostly in connection with the Last Glacial Maximum (LGM). However, the LGM is just the most recent of the 20+ glacial‐interglacial periods that characterise the Quaternary. Here, we investigate the role of climatic changes and geomorphological features in shaping the evolution, distribution and population dynamics of the South American cactus Cereus hildmannianus.

Location

South‐eastern South America.

Methods

We built a large fossil‐calibrated phylogeny for cacti (family Cactaceae), comprising 128 species distributed in all subfamilies, using a Bayesian relaxed clock. We used the results to derive a secondary calibration for a population‐level phylogeny in C. hildmannianus. We amplified two plastid (trnQ‐5′rps16 and psbJ‐petA) and one nuclear marker (PhyC) for 24 populations. We estimated population dynamics, ancestral areas, and species distribution models to infer the clade's evolutionary history in time and space.

Results

Our results show a major population divergence of C. hildmannianus at c. 2.60 Ma, which is strikingly coincident with the transition of the Pliocene–Pleistocene and onset of Quaternary glaciations. This was followed by a complex phylogeographic scenario involving population expansions across ecologically diverse regions.

Main conclusions

Contrary to the dominant research focus on the LGM, our study indicates a major impact of the first Quaternary glaciation on the distribution and population divergence of a South American plant species. Further intraspecific events seem related to successive climatic changes and geomorphology, including the development of the coastal plain and its peculiar diversity. We propose that the first Quaternary glaciation acted as a major evolutionary bottleneck, whereby many warm‐adapted lineages succumbed, while those that survived could diversify and better cope with subsequent climatic oscillations.