Variety in evolutionary strategies favours biodiversity in habitats of moderate productivity

The mechanism whereby biodiversity varies between habitats differing in productivity is a missing link between ecological and evolutionary theory with vital implications for biodiversity conservation, management and the assessment of ecosystem services. A unimodal, humped-back relationship, with biodiversity greatest at intermediate productivities, is evident when plant, animal and microbial communities are compared across productivities in nature. However, the mechanistic, evolutionary basis of this observation remains enigmatic. We show, for natural and semi-natural plant communities across a range of bioclimatic zones, that biodiversity is greatest where communities include species with widely divergent values for phenotypic traits involved in resource economics and reproductive timing, coinciding with intermediate biomass production, whilst each productivity extreme is associated with small numbers of specialised species with similar trait values. Our data demonstrate that evolution can generate a greater range of phenotypes where large, fast-growing species are prevented from attaining dominance and extreme adaptation to a harsh abiotic environment is not a prerequisite for survival

The Jeweled Armor of Tillandsia—Multifaceted or Elongated Trichomes Provide Photoprotection

Foliar trichomes of gray-leaved Tillandsioideae (Bromeliaceae) are highly reflective, suggesting a role in protecting the leaf against direct sunlight in exposed niches. The performance of photosystem II, as denoted by the chlorophyll fluorescence characteristic Fv /Fm , was determined for seven Tillandsia species and Vriesea barclayana that were exposed to excessive light, with trichomes either present or removed. Additionally, trichome structure and interaction with light was recorded using extended depth-of-field photomicrography, and reflectance quantified using a novel photographic technique. Trichomes of mesomorphic Type IV life forms (T. cryptantha, T. cyanea) and of the intermediate life form V. barclayana conferred reflectance of between 1 and 11%, which did not significantly influence Fv /Fm when exposed to a high light intensity of 1500 µmol m-2 s-1 (photosynthetically active radiation) for one hour. However, the ornate trichomes of atmospheric species increased the reflectivity of the leaf blade by as much as 18– 40%, with a positive correlation apparent between reflectance and photoprotection. Type V Tillandsia andrieuxii, T. caput-medusae, and T. mitlaensis have attenuated trichome wings extending perpendicular to the leaf surface and catching the light (with leaf surfaces appearing gray and fuzzy). This open configuration was observed to facilitate leaf ventilation and the condensation of water vapor on the cooler underlying cuticle, with liquid water subsequently enveloping the trichomes, suggesting a trade-off between water acquisition and light reflectance for air plants from xeric habitats. However, Type IV-V T. albida and T. concolor impound water in leaf bases and the flattened, circular, and overlapping trichome wings did not facilitate dew formation on the cuticle. For these plants with white, smooth leaf surfaces, trichomes are multifaceted and provide more effective photoprotection by scattering light in the manner of cut gemstones

What life is: the conversion of thermodynamic disequilibria into directional motion

Life is traditionally defined by a long list of properties, but classifying structures as living or non-living would require a single recognizable difference. Recent evidence shows that a range of biological molecules, including ribozymes and enzymes with rotating or ratcheting subunits, undergo repetitive conformation state changes driven by thermal agitation and energy exchanges, in turn governing catalysis of reactions fundamental to metabolism and cellular replication. These molecules exhibit disparate structures, but share the principle of repetitive unidirectional conformation changes, driven by thermodynamic gradients, that produce directional motion. Here, life is defined as a process whereby matter undergoes cyclic, unidirectional conformation state changes that convert thermal agitation and excitation into directed motion, performing work that locally reduces entropy. The principle of conversion of thermal agitation into directed motion is independent of any specific chemical environment or any particular molecular structure; this definition should apply universally across biospheres characterized by differing biochemistries.Comment: 4 page

Resource allocation in the Pseudoviviparous alpine meadow grass (Poa alpine L.)

Many biotypes of the northern-hemisphere Arctic-Alpine grass Poa alpina L. reproduce asexually via prolification of the spikelet axis to produce dehiscing shoots. Although such pseudoviviparous plantlets are capable of photosynthesis, the source-sink characteristics of these synflorescence systems are unknown, including the degree to which plantlets are capable of providing for their own carbon requirements, or contributing to parental sinks. An initial anatomical investigation of the culm revealed that transpiration flow, as delimited by Lucifer Yellow tracer dye, was maintained despite advanced senescence (as evidenced by loss of chlorophyll and chloroplasts), with plantlet leaves driving transpiration flow. Transpiration flow was not hindered by cavitation or tylosis in older culms, the low frequencies of these processes beingbypassed via nodal plexi. Despite this, water content of plantlets declined over time and visual indications of water stress became apparent, suggesting that water supply via the determinate culm was not sufficient for the increasing transpirational demand of indeterminate plantlets. Photosynthetic rates within the paracladial zone, as determined by infrared gas analysis (IRGA), exceeded respiratory rates by 3-4 fold, indicating that plantlets were sources of carbon. 14C tracer studies determined that the paracladial zone was not only as efficient at fixing carbon as the youngest fully expanded leaf, but that both organs exported carbon basipetally (c.f acropetal export from this leaf in seminiferous grasses). Distal plantlets fixed approx. 20% more 14C than proximal plantlets, by virtue of greater dry weight. Manipulative growth analysis of the paracladial zone suggests the operation of a system of apicaldominance, with distal plantlets becoming dominant over proximal plantlets. At dehiscence, distal plantlets were more likely to become established, and possessed relative growth rates more than ten times those of proximal plantlets. Paracladial heterogeneity was also apparent as an increased proportion of aborted spikelets on proximal paracladia. Data indicate that this abortion was, at least in part, a result of constraint imposed by the pseudostem on the developing synflorescence. When grown in conditions of differing resource availability (altered nutrient supply and atmospheric C02 concentration), low nutrient availability in concert with elevated C02 concentration induced particularly low photosynthetic nitrogen and phosphorus use efficiencies inboth parent and plantlet tissues. This occurred in concert with acclimatory loss of photosynthetic capacity leading to a decreased reproductive response of the plant; a product of the number of tillers in flower and the subsequent growth of attached plantlets. lt is predicted that in future climatic conditions Poa alpina will decline in habitats that include species which exhibit less acclimatory loss, no change, or an increase in photosynthetic capacity. These experiments alsorule out resource availability as a cause of heterogeneity within the paracladial zone. A direct study of the phytohormonal characteristics of the pseudoviviparous system is therefore proposed in order to elucidate the mechanism of control within the paracladial zone

Resource allocation in the pseudoviviparous alpine meadow grass (Poa alpina l.)

Many biotypes of the northem-hemisphere Arctic-Alpine grass Poa alpina L. reproduce asexually via prolification of the spikelet axis to produce dehiscing shoots. Although such pseudoviviparous plantlets are capable of photosynthesis, the source-sink characteristics of these synflorescence systems are unknown, including the degree to which plantlets are capable of providing for their own carbon requirements, or contributing to parental sinks. An initial anatomical investigation of the culm revealed that transpiration flow, as delimited by Lucifer Yellow tracer dye, was maintained despite advanced senescence (as evidenced by loss of chlorophyll and chloroplasts), with plantlet leaves driving transpiration flow. Transpiration flow was not hindered by cavitation or tylosis in older culms, the low frequencies of these processes being bypassed via nodal plexi. Despite this, water content of plantlets declined over time and visual indications of water stress became apparent, suggesting that water supply via the determinate culm was not sufficient for the increasing transpirational demand of indeterminate plantlets. Photosynthetic rates within the paracladial zone, as determined by infrared gas analysis (IRGA), exceeded respiratory rates by 3-4 fold, indicating that plantlets were sources of carbon. 14C tracer studies determined that the paracladial zone was not only as efficient at fixing carbon as the youngest fully expanded leaf, but that both organs exported carbon basipetally (c.f acropetal export from this leaf in seminiferous grasses). Distal plantlets fixed approx. 20% more 14C than proximal plantlets, by virtue of greater dry weight. Manipulative growth analysis of the paracladial zone suggests the operation of a system of apical dominance, with distal plantlets becoming dominant over proximal plantlets. At dehiscence, distal plantlets were more likely to become established, and possessed relative growth rates more than ten times those of proximal plantlets. Paracladial heterogeneity was also apparent as an increased proportion of aborted spikelets on proximal paracladia. Data indicate that this abortion was, at least in part, a result of constraint imposed by the pseudostem on the developing synflorescence. When grown in conditions of differing resource availability (altered nutrient supply and atmospheric C02 concentration), low nutrient availability in concert with elevated C02 concentration induced particularly low photosynthetic nitrogen and phosphorus use efficiencies in both parent and plantlet tissues. This occurred in concert with acclimatory loss of photosynthetic capacity leading to a decreased reproductive response of the plant; a product of the number of tillers in flower and the subsequent growth of attached plantlets. lt is predicted that in future climatic conditions Poa alpina will decline in habitats that include species which exhibit less acclimatory loss, no change, or an increase in photosynthetic capacity. These experiments also rule out resource availability as a cause of heterogeneity within the paracladial zone. A direct study of the phytohormonal characteristics of the pseudoviviparous system is therefore proposed in order to elucidate the mechanism of control within the paracladial zone

Endemism in recently diverged angiosperms is associated with polyploidy

Endemic (range restricted or precinctive) plant species are frequently observed to exhibit polyploidy (chromosome set duplication), which can drive shifts in ecology for angiosperms, but whether endemism is generally associated with polyploidy throughout the flowering plants has not been determined. We tested the hypothesis that polyploidy is more frequent and more pronounced (higher evident ploidy levels) for recently evolved endemic angiosperms. Chromosome count data, molecular dating and distribution for 4210 species (representing all major clades of angiosperms and including the largest families) were mined from literature-based databases. Upper boundary regression was used to investigate the relationship between the maximum number of chromosomes and time since taxon divergence, across clades and separately for families, comparing endemic with non-endemic species. A significant negative exponential relationship between maximum number of chromosomes and taxon age was evident across angiosperms (R2adj = 0.48 for all species, R2adj = 0.49 for endemics; R2adj = 0.44 for non-endemics; p always < 0.0001), recent endemics demonstrating greater maximum chromosome numbers (y intercept = 164 cf. 111) declining more rapidly with taxon age (decay constant = 0.12, cf. 0.04) with respect to non-endemics. The majority of families exhibited this relationship, with a steeper regression slope for endemic Campanulaceae, Asteraceae, Fabaceae, Poaceae, Caryophyllaceae and Rosaceae, cf. non-endemics. Chromosome set duplication is more frequent and extensive in recent angiosperms, particularly young endemics, supporting the hypothesis of recent polyploidy as a key explanation of range restriction. However, as young endemics may also be diploid, polyploidy is not an exclusive driver of endemism

Diaphragm Force and Mitochondrial Function Ex Vivo Following GSNOR Inhibition In Vivo Preceding Mechanical Ventilation

During mechanical ventilation (MV), force developed by the diaphragm is decreased over time much faster than locomotor muscles. This is known as ventilator-induced diaphragm dysfunction (VIDD), and VIDD may be accelerated by intramyofiber oxidative stress. An important free radical used for the treatment of acute respiratory distress syndrome (ARDS) is nitric oxide (NO) which can diffuse to diaphragm myofibers during treatment. However, little is known whether NO or NO by-products such as S-nitrosothiols (RSNO), can accelerate or prevent VIDD. PURPOSE: To investigate whether inhibiting S-nitrosoglutathione reductase (GSNORi) during MV could affect ex vivo diaphragm force and mitochondrial respiration. METHODS: Male (C57BL6J) mice (n=27) were anesthetized and subjected to MV for 2, 4, or 6h, and non-MV mice (0 h) were used as controls. Alternatively, mice were treated with PBS/10% DMSO (n=6) or 25 µg SPL-334 (GSNORi, n=6) or 25 µg SPL-334 + 1.7 mg isosorbide dinitrate (ISDN; n=6), and then subjected to MV for 2 h. After MV, mice were euthanized, and diaphragm strips were used for force or for mitochondrial oxidative phosphorylation and reactive oxygen species generation measurements. RESULTS: Peak tetanic force was decreased by MV starting at 4 h (30 ± 2 N/cm2 vs 26 ± 1 N/cm2 vs 23 ± 2 N/cm2 vs 18 ± 4 N/cm2, for 0 vs 2 vs 4 vs 6h MV, P=0.0097 one-way ANOVA). Peak force was not different between DMSO vs GSNORi (P=0.3834). Leak respiration (Mann-Whitney p=0.26; CI95 7, 45 vs 10, 68 pmol/s/mg), coupled-phosphorylating mitochondrial respiration (Mann-Whitney p=0.91; CI95 121, 180 vs 107, 215 pmol/s/mg), and H2O2 flux in any of the respiratory states (e.g. coupled-phosphorylating Mann-Whitney p=0.26; CI95 30, 245 vs 4, 543 fmol/s/mg), were not different between DMSO vs GSNORi. CONCLUSION: VIDD was developed at 4 hours MV, but GSNORi treatment for 2 h did not produce any changes to VIDD and to mitochondrial function. These data suggest that if exogenous NO is not provided, inhibiting GSNOR in vivo alone does not affect diaphragm function ex vivo. Support: SDSU 2023 SEED Grant (to L.N.