Global patterns of species richness of the holarctic alpine herb Saxifraga: The role of temperature and habitat heterogeneity

Postponed access: the file will be available after 2022-08-03The effects of contemporary climate, habitat heterogeneity and long-term climate change on species richness are well studied for woody plants in forest ecosystems, but poorly understood for herbaceous plants, especially in alpine–arctic ecosystems. Here, we aim to test if the previously proposed hypothesis based on the richness–environment relationship could explain the variation in richness patterns of the typical alpine–arctic herbaceous genus Saxifraga. Using a newly compiled distribution database of 437 Saxifraga species, we estimated the species richness patterns for all species, narrow- and wide-ranged species. We used generalized linear models and simultaneous autoregressive models to evaluate the effects of contemporary climate, habitat heterogeneity and historical climate on species richness patterns. Partial regressions were used to determine the independent and shared effects of different variables. Four widely used models were tested to identify their predictive power in explaining patterns of species richness. We found that temperature was negatively correlated with the richness patterns of all and wide-ranged species, and that was the most important environmental factor, indicating a strong conservatism of its ancestral temperate niche. Habitat heterogeneity and long-term climate change were the best predictors of the spatial variation of narrow-ranged species richness. Overall, the combined model containing five predictors can explain ca. 40%–50% of the variation in species richness. We further argued that additional evolutionary and biogeographical processes might have also played an essential role in shaping the Saxifraga diversity patterns and should be considered in future studies.acceptedVersio

Global distribution and evolutionary transitions of angiosperm sexual systems

Angiosperm sexual systems are fundamental to the evolution and distribution of plant diversity, yet spatiotemporal patterns in angiosperm sexual systems and their drivers remain poorly known. Using data on sexual systems and distributions of 68453 angiosperm species, we present the first global maps of sexual system frequencies and evaluate sexual system evolution during the Cenozoic. Frequencies of dioecy and monoecy increase with latitude, while hermaphrodites are more frequent in warm and arid regions. Transitions to dioecy from other states were higher than to hermaphroditism, but transitions away from dioecy increased since the Cenozoic, suggesting that dioecy is not an evolutionary end point. Transitions between hermaphroditism and dioecy increased, while transitions to monoecy decreased with paleo-temperature when paleo-temperature >0℃. Our study demonstrates the biogeography of angiosperm sexual systems from a macroecological perspective, and enhances our understanding of plant diversity patterns and their response to climate change.acceptedVersio

Diversification of flowering plants in space and time

The rapid diversification and high species richness of flowering plants is regarded as ‘Darwin’s second abominable mystery’. Today the global spatiotemporal pattern of plant diversification remains elusive. Using a newly generated genus-level phylogeny and global distribution data for 14,244 flowering plant genera, we describe the diversification dynamics of angiosperms through space and time. Our analyses show that diversification rates increased throughout the early Cretaceous and then slightly decreased or remained mostly stable until the end of the Cretaceous–Paleogene mass extinction event 66 million years ago. After that, diversification rates increased again towards the present. Younger genera with high diversification rates dominate temperate and dryland regions, whereas old genera with low diversification dominate the tropics. This leads to a negative correlation between spatial patterns of diversification and genus diversity. Our findings suggest that global changes since the Cenozoic shaped the patterns of flowering plant diversity and support an emerging consensus that diversification rates are higher outside the tropics

Spatio-temporal patterns in the woodiness of flowering plants

Under embargo until: 2023-12-31Aim Woody and herbaceous habits represent one of the most distinct contrasts among angiosperms, and the proportion of woody species in floras (i.e., “woodiness” hereafter) represents a fundamental structural element of plant diversity. Despite its core influence on ecosystem processes, spatio-temporal patterns in woodiness remain poorly understood. Here, we aim to demonstrate the global spatio-temporal patterns in angiosperm woodiness and their relationship with environmental factors. Location Global. Time period Cenozoic, 66 Ma to present. Major taxa studied Angiosperms. Methods Using newly compiled data on the growth forms and distributions of c. 300,000 angiosperm species and an angiosperm phylogeny, we mapped the current global geographical patterns in angiosperm woodiness, reconstructed ancestral states of growth forms through the angiosperm phylogeny and demonstrated the Cenozoic evolutionary dynamics of woodiness. We evaluated the relationships between woodiness and current climate and palaeoclimate. Results We found that c. 42.7% of angiosperms are woody. Woodiness decreased spatially from the equator towards high latitudes, temporally since the early Cenozoic. Temperature was the best predictor of the spatio-temporal decline in woodiness and was positively correlated with woodiness. Despite the temporal decline in woodiness, macroevolutionary herbaceous-to-woody transitions increased through time and contributed to the evolution of woody floras in temperate drylands, whereas the opposite transitions decreased through time and contributed to herbaceous floras in tropical and subtropical drylands. Main conclusions Our study improves understanding of the spatio-temporal dynamics of angiosperm woodiness. Our findings suggest that temperature is likely to be a determinant of spatio-temporal variations in woodiness, highlighting the role of temperature in maintaining the growth form composition of ecosystems. Our study also calls for attention to growth form transitions (e.g., secondary woodiness) in temperate drylands that have been neglected before.acceptedVersio

Leaf size of woody dicots predicts ecosystem primary productivity

A key challenge in ecology is to understand the relationships between organismal traits and ecosystem processes. Here, with a novel dataset of leaf length and width for 10 480 woody dicots in China and 2374 in North America, we show that the variation in community mean leaf size is highly correlated with the variation in climate and ecosystem primary productivity, independent of plant life form. These relationships likely reflect how natural selection modifies leaf size across varying climates in conjunction with how climate influences canopy total leaf area. We find that the leaf size–primary productivity functions based on the Chinese dataset can predict productivity in North America and vice-versa. In addition to advancing understanding of the relationship between a climate-driven trait and ecosystem functioning, our findings suggest that leaf size can also be a promising tool in palaeoecology for scaling from fossil leaves to palaeo-primary productivity of woody ecosystems

Geographical patterns in phylogenetic diversity of Chinese woody plants and its application for conservation planning

Aim Biodiversity hotspots are widely used as conservation priorities to preserve the tree of life. However, many conservation practices identify biodiversity hotspots without considering phylogenetic diversity (PD), which reflects total evolutionary history and feature diversity of a region. Moreover, conservation planning rarely distinguishes between neo- and palaeo-biodiversity hotspots despite their differences. Here, we (a) estimated large-scale patterns in PD of woody plants, (b) identified neo- and palaeo-biodiversity hotspots and (c) demonstrated their implication in conservation planning, with special focus on Hengduan Mountains and southern China. Location China. Methods Distributions of 11,405 woody species from the Atlas of Woody Plants in China were updated and were transformed into a grid of 50 x 50 km(2). By integrating distribution maps with a genus-level phylogeny of angiosperms, we estimated Faith's PD of each grid cell and evaluated the contribution of species relatedness to PD at given levels of species diversity (i.e. standardized PD, sPD) using regressions and three null models. Then, we identified areas with significantly lower or higher sPD than expected as neo- and palaeo-hotspots and estimated the coverage of protected areas in these regions. Results Species diversity and PD decreased towards the north. Southern China had high species diversity, PD and sPD, while Hengduan Mountains had high species diversity and PD but low sPD. The coverage of protected areas in southern China was less than half of that in Hengduan Mountains and entire China. Main conclusions Our results identified Hengduan Mountains as a neo-hotspot and southern China as a palaeo-hotspot, highlighting their importance for biodiversity conservation. Compared to Hengduan Mountains, southern China has low coverage of protected areas, which calls for more conservation attention. Our study demonstrates a way of incorporating the phylogenetic component in the identification of neo- and palaeo-hotspots, and hence of achieving a more complete perception of biodiversity patterns for conserving the tree of life.ISSN:1366-9516ISSN:1472-464

Phylogenetic conservatism and biogeographic affinity influence woody plant species richness–climate relationships in eastern Eurasia

Mechanisms underlying species richness patterns remain a central yet controversial issue in biology. Climate has been regarded as a major determinant of species richness. However, the relative influences of different evolutionary processes, (i.e. niche conservatism, diversification rate and time for speciation) on species richness–climate relationships remain to be tested. Here, using newly compiled distribution maps for 11 422 woody plant species in eastern Eurasia, we estimated species richness patterns for all species and for families with tropical and temperate affinities separately, and explored the phylogenetic signals in species richness patterns of different families and their relationships with contemporary climate and climate change since the Last Glacial Maximum (LGM). We further compared the effects of niche conservatism (represented by contemporary‐ancestral climatic niches differences), diversification rate and time for speciation (represented by family age) on variation in the slopes of species richness–climate relationships. We found that winter coldness was the best predictor for species richness patterns of most tropical families while Quaternary climate change was the best predictor for those of most temperate families. Species richness patterns of closely‐related families were more similar than those of distantly‐related families within eudicots, and significant phylogenetic signals characterized the slopes of species richness–climate relationships across all angiosperm families. Contemporary‐ancestral climatic niche differences dominated variation in the relationships between family‐level species richness and most climate variables. Our results indicate significant phylogenetic conservatism in family‐level species richness patterns and their relationships with contemporary climate within eudicots. These findings shed light on the mechanisms underlying large‐scale species richness patterns and suggest that ancestral climatic niche may influence the evolution of species richness–climate relationships in plants through niche conservatism

Tetrahydroxystilbene Glycoside Improves Microvascular Endothelial Dysfunction and Ameliorates Obesity-Associated Hypertension in Obese ZDF Rats Via Inhibition of Endothelial Autophagy

Aims: Obesity is a major risk for hypertension. Endothelial dysfunction contributes to increased peripheral vascular resistance and subsequent hypertension. Autophagy regulates endothelial function, however, whether autophagy is related to hypertension in obesity remains largely unclear. We wished to ascertain: (i) the role of autophagy in obesity-induced hypertension and the underlying mechanisms; (ii) if tetrahydroxystilbene glycoside (TSG) influences endothelial dysfunction and obesity-associated hypertension. Methods: (TSG-treated) male Zucker diabetic fatty (ZDF) rats and cultured human umbilical vein endothelial cells (HUVECs) were used. Blood pressure was measured non-invasively with a tail-cuff system. Westernblotting was performed to determine the expression of autophagy-associated proteins. Autophagy flux was assessed by transfection HUVECs with the Ad-mGFP–RFP–LC3. Results: Compared with their lean counterparts, obese ZDF rats exhibited hypertension and endothelial dysfunction, along with impaired Akt/mTOR signaling and upregulated expression of autophagy-associated proteins beclin1, microtubule-associated protein 1 light chain 3 II/I, autophagy protein (ATG)5 and ATG7. Two-week TSG administration restored blood pressure and endothelial function, reactivated Akt/mTOR pathway and decreased endothelial autophagy in ZDF rats. Rapamycin pretreatment blocked the hypotensive effect of TSG in ZDF rats. Suppression of Akt/mTOR expression with siRNA significantly blunted the anti-autophagic effect of TSG in HUVECs as evidenced by abnormal autophagic flux and increased expression of autophagy-associated proteins. Conclusion: Endothelial dysfunction in ZDF rats is partially attributable to excessive autophagy. TSG improves endothelial function and exerts hypotensive effects via regulation of endothelial autophagy

Magnolol administration in normotensive young spontaneously hypertensive rats postpones the development of hypertension: role of increased PPAR gamma, reduced TRB3 and resultant alleviative vascular insulin resistance.

Patients with prehypertension are more likely to progress to manifest hypertension than those with optimal or normal blood pressure. However, the mechanisms underlying the development from prehypertension to hypertension still remain largely elusive and the drugs for antihypertensive treatment in prehypertension are absent. Here we determined the effects of magnolol (MAG) on blood pressure and aortic vasodilatation to insulin, and investigated the underlying mechanisms. Four-week-old male spontaneous hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) control rats were used. Our results shown that treatment of young SHRs with MAG (100 mg/kg/day, o.g.) for 3 weeks decreased blood pressure, improved insulin-induced aorta vasodilation, restored Akt and eNOS activation stimulated by insulin, and increased PPARγ and decreased TRB3 expressions. In cultured human umbilical vein endothelial cells (HUVECs), MAG incubation increased PPARγ, decreased TRB3 expressions, and restored insulin-induced phosphorylated Akt and eNOS levels and NO production, which was blocked by both PPARγ antagonist and siRNA targeting PPARγ. Improved insulin signaling in HUVECs by MAG was abolished by upregulating TRB3 expression. In conclusion, treatment of young SHRs with MAG beginning at the prehypertensive stage decreases blood pressure via improving vascular insulin resistance that is at least partly attributable to upregulated PPARγ, downregulated TRB3 and consequently increased Akt and eNOS activations in blood vessels in SHRs