Evolution of extreme xeromorphic characters in wood: a study of nine evolutionary lines in Cactaceae

Vessels of xeric-adapted woods have been predicted to be narrower than those of mesic-adapted woods, to occur at higher densities, to occur in larger clusters, and to have a greater percentage of them in clusters. These predictions were tested by comparing wood structure of several evolutionary lines of xeric-adapted cacti to that of mesic-adapted Pereskia, which probably resembles the ancestral cacti. Although derived cacti occur in habitats with water stress ranging from mild (rain forests) to severe (open deserts with little vegetation other than cacti), as long as plants retain wood with an ordinary fibrous matrix, wood characters are remarkably uniform and not correlated with habitat aridity. However, in several evolutionary lines, novel wood types occur with characters that fulfill the predictions for xeric-adapted woods listed above. However, conductive area (fraction of wood transverse-sectional area occupied by conduits) and estimated specific conductance (conductance per square millimetre) are correlated with shoot height (the need for mechanical support from xylary fibers) rather than with habitat aridity: tall plants transport water through relatively few, wide vessels, permitting much of the wood volume to consist of fibers. Small plants with little wood use large numbers of narrow vessels rather than small numbers of wide ones, thereby achieving conductive safety.     

Pit membrane remnants in perforation plates and other vessel details of Cornales

Perforation plates and other vessel details as studied with scanning electron microscopy (SEM) have been reported for four species of Cornaceae (s.l.): similar features are shown by the four, suggesting that a more extensive sampling of the family might reveal similar phenomena. Perforation plates contain pit membrane remnants in the form of threads or, less commonly, laminar portions perforated by pores. When least well-represented, the pit membrane remnants are restricted to lateral ends of perforations and to the perforations transitional to lateral wall pitting. Perforations are all clearly bordered. Helical thickenings that do not form a continuous gyre are reported for the vessel walls ofAucuba. The presence of pit membrane remnants in vessel elements of Cornaceae correlates with the mesic habitats occupied by species in this family. The presence and type of pit membrane remnants reported by us in the three genera is very similar, although pit membrane remnants are doubtless a symplesiomorphy and thus not an indicator of relationships. The presence of pit membrane remnants in the three genera, however, does attest to the primitiveness of wood and other features of Cornaceae s.l.     

Ecological physiology of Pereskia guamacho, a cactus with leaves

The specialized physiology of leafless, stem-succulent cacti is relatively well understood. This is not true, however, for Pereskia (Cactaceae), the 17 species of leafy trees and shrubs that represent the earliest diverging lineages of the cacti. Here we report on the water relations and photosynthesis of Pereskia guamacho, a small tree of the semiarid scrubland of Venezuela's Caribbean coast. Sapwood-specific xylem conductivity (Ksp) is low when compared to other vessel-bearing trees of tropical dry systems, but leaf-specific xylem conductivity is relatively high due to the high Huber value afforded by P. guamacho's short shoot architecture. P. guamacho xylem is not particularly vulnerable to drought-induced cavitation, especially considering the high leaf water potentials maintained year round. This is confirmed by the lack of significant variation exhibited in Ksp between wet and dry seasons. In the rainy season, P. guamacho exhibited C3-like patterns of stomatal conductance, but during a prolonged drought we documented nocturnal stomatal opening with a concomitant accumulation of titratable acid in leaves. This suggests that P. guamacho can perform drought-induced crassulacean acid metabolism (CAM photosynthesis), although delta 13C values imply that most carbon is assimilated via the C3 pathway. P. guamacho leaves display very low stomatal densities, and maximum stomatal conductance is low whether stomata open during the day or night. We conclude that leaf performance is not limited by stem hydraulic capacity in this species, and that water use is conservative and tightly regulated at the leaf level.     

Influence of a salinity gradient on the vessel characters of the mangrove species Rhizophora mucronata

BACKGROUND AND AIMS: Although mangroves have been extensively studied, little is known about their ecological wood anatomy. This investigation examined the potential use of vessel density as a proxy for soil water salinity in the mangrove species Rhizophora mucronata (Rhizophoraceae) from Kenya. METHODS: In a time-standardized approach, 50 wood discs from trees growing in six salinity categories were investigated. Vessel densities, and tangential and radial diameters of rainy and dry season wood of one distinct year, at three positions on the stem discs, were measured. A repeated-measures ANOVA with the prevailing salinity was performed. KEY RESULTS: Vessel density showed a significant increase with salinity, supporting its use as a prospective measure of salinity. Interestingly, the negative salinity response of the radial diameter of vessels was less striking, and tangential diameter was constant under the varying environmental conditions. An effect of age or growth rate or the presence of vessel dimorphism could be excluded as the cause of the absence of any ecological trend. CONCLUSIONS: The clear trend in vessel density with salinity, together with the absence of a growth rate and age effect, validates the potential of vessel density as an environmental proxy. However, it can only be used as a relative measure of salinity given that other environmental variables such as inundation frequency have an additional influence on vessel density. With view to a reliable, absolute proxy, future research should focus on finding wood anatomical features correlated exclusively with soil water salinity or inundation frequency. The plasticity in vessel density with differing salinity suggests a role in the establishment of a safe water transport system. To confirm this hypothesis, the role of inter-vessel pits, their relationship to the rather constant vessel diameter and the underlying physiology and cell biology needs to be examined.     

Quercetin supplementation does not alter antioxidant status in humans

Abstract

This study measured the influence of ingesting quercetin on plasma measures for oxidative stress and antioxidant capacity. Male and female subjects (n = 1002) varying in age (18–85 years) and body mass index (BMI) (16.7–52.7 kg/m²) were studied. Subjects were randomized to one of three groups using double-blinded methods: placebo, 500 mg or 1000 mg quercetin/day with 125 mg or 250 mg vitamin C/day, respectively. Pre- and post-study fasting blood samples show that plasma quercetin increased in a dose-responsive manner. The pattern of change in plasma F₂-isoprostanes, oxidized low density lipoprotein, reduced glutathione, ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) did not differ between supplementation groups or after adjustment for gender, age, BMI and disease status. In summary, quercetin supplementation over 12 weeks in doses of 500 mg or 1000 mg/day significantly increased plasma quercetin levels, but had no influence on several measures of oxidative stress and antioxidant capacity.     

Diversity in specific gravity and water content of wood among Bornean tropical rainforest trees

Wood properties were measured for trees in lowland dipterocarp forests in West Kalimantan. In 1993 and 1994, 353 samples of 286 species were collected from trunk base of trees of approximately 5 cm in diameter, and the specific gravities (SG: oven dry weight/fresh volume) and water contents of wood including bark were measured. The SG of each species ranged from 0.21 to 0.84, and the mean ± SD was 0.53 ± 0.13. The wide range of SG suggests that the forest had a high diversity in wood properties. The most dominant and diversified genus in this area was Shorea, and the SG of 15 species varied from 0.21 to 0.71. The range covered SG of pioneer (six Macaranga, 0.29–0.43) and small trees in primary forests (nine Eugenia and 10 Xanthophyllum, 0.55–0.77). The SG average for tree species of secondary forests of 2–6 years old was 0.31. It was significantly smaller than that of primary forests (0.58). In a primary dipterocarp forest plot, light-wood species grew faster in diameter than heavy-wood species. Water content ranged from 0.26 to 0.76. Heavy wood had low water content. Among light-wood species, some (Shorea, Artocarpus) had low water contents and others (Ficus) had high water contents. Some riverine trees also had high water contents. These wood properties appear strongly related to the life history of trees and successional stage.     

Limited nonenzymatic glucosylation of low-density lipoprotein does not alter its catabolism in tissue culture

This study examines the effects of various degrees of chemical modification of low-density lipoprotein (LDL) on its catabolism by various cell types. Moderate glucosylation of LDL does not alter its interaction with the high-affinity receptor present on human fibroblasts at concentration of 5-2000 micrograms LDL-cholesterol/ml. Only heavily glucosylated LDL (more than 12 lysine residues glucosylated per apolipoprotein B) or LDL glucosylated in the presence of Na(CN)BH3, i.e., conditions not expected to occur in diabetes, inhibit receptor-mediated internalisation and degradation. Moderately glucosylated LDL is also readily recognized by cultured rat hepatocytes and porcine endothelial cells. Human monocyte-derived macrophages accumulate cholesteryl ester when incubated with acetylated LDL for 12 days but no enhanced cholesteryl ester formation was found when native or glucosylated LDL (3.3 lysines glucosylated per apolipoprotein B) were used.     

Single‐vessel flow measurements indicate scalariform perforation plates confer higher flow resistance than previously estimated

During vessel evolution in angiosperms, scalariform perforation plates with many slit‐like openings transformed into simple plates with a single circular opening. The transition is hypothesized to have resulted from selection for decreased hydraulic resistance. Previously, additional resistivity of scalariform plates was estimated to be small – generally 10% or less above lumen resistivity – based on numerical and physical models. Here, using the single‐vessel technique, we directly measured the hydraulic resistance of individual xylem vessels. The resistivity of simple‐plated lumens was not significantly different from the Hagen–Poiseuille (HP) prediction (+6 ± 3.3% mean deviation). In the 13 scalariform‐plated species measured, plate resistivity averaged 99 ± 13.7% higher than HP lumen resistivity. Scalariform species also showed higher resistivity than simple species at the whole vessel (+340%) and sapwood (+580%) levels. The strongest predictor of scalariform plate resistance was vessel diameter (r² = 0.84), followed by plate angle (r² = 0.60). An equation based on laminar flow through periodic slits predicted single‐vessel measurements reasonably well (r² = 0.79) and indicated that Baileyan trends in scalariform plate evolution maintain an approximate balance between lumen and plate resistances. In summary, we found scalariform plates of diverse morphology essentially double lumen flow resistance, impeding xylem flow much more than previously estimated.     

Chloraminated drinking water does not generate bacterial resistance to antibiotics in Pseudomonas aeruginosa biofilms

Aim: To determine if exposure of Pseudomonas aeruginosa biofilms to chloraminated drinking water can lead to individual bacteria with resistance to antibiotics. Methods and Results: Biofilms of P. aeruginosa PA14 were grown in drinking water in a Kadouri drip‐fed reactor; the biofilms were treated with either 0·5 mg l^‐1 or 1·0 mg l^‐1 of chloramine for 15 or 21 days; control biofilms were grown in water without chloramine. Fewer isolates with antibiotic resistance were obtained from the chloramine‐treated biofilms as compared to the control. Minimum inhibitory concentrations (MIC) for selected antibiotic‐resistant isolates were determined using ciprofloxacin, tobramycin, gentamicin, rifampicin and chloramphenicol. All of the isolates tested had increased resistance over the wildtype to ciprofloxacin, rifampicin and chloramphenicol, but were not resistant to tobramycin or gentamicin. Conclusions: Under these test conditions, there was no detectable increase in antibiotic resistance in P. aeruginosa exposed as biofilms to disinfectant residues in chloraminated drinking water. Significance and Impact of the study: Chloramine in drinking water, while unable to kill biofilm bacteria, does not increase the potential of P. aeruginosa to become resistant to antibiotics.     

Carbon isotope fractionation in tree ring early and late wood in relation to intra-growing season water balance

We determined the stable carbon isotope composition (δ^1.3C) of cellulose extracted from early and late wood in Douglas fir [Pseudotsuga menziexii (Mirb.) Franco] tree rings. Data were obtained for the period 1962 to 1981, at the start of which the trees were 20 years old. A water balance model was used to calculate daily stand transpiration and water deficit. The model incorporates site factors (soil water availability, slope and aspect) and environmental variables (solar radiation, air temperature and rainfall). There was far greater variability in late wood than in early wood δ^1.3C. In wet years, late wood δ^1.3C was significantly lighter (by as much as 2δ) than early wood δ^1.3C but in dry years this difference was reversed. Differences between spring and summer cumulative transpiration accounted for almost 60δ of the variability in differences between early and late wood δ^1.3C. We found excellent correspondence between summer cumulative transpiration and late wood δ^1.3C, with estimates of transpiration accounting for up to 93% of the variability in δ^1.3C. Correlations between early wood δ^1.3C and spring transpiration were generally poor (r2<0.4), but we were able to identify those exceptional years in which there had been a very dry spring. Our results indicate that, while tree ring δ^1.3C correlates reasonably well with basal area increment, it is a far better indicator of inter- and intra-annual variability in water availability than radial growth.     

Stem water storage capacity and efficiency of water transport: their functional significance in a Hawaiian dry forest

We investigated the contribution of internal water storage and efficiency of water transport to the maintenance of water balance in six evergreen tree species in a Hawaiian dry forest. Wood‐saturated water content, a surrogate for relative water storage capacity, ranged from 70 to 105%, and was inversely related to its morphological correlate, wood density, which ranged between 0·51 and 0·65 g cm^?3. Leaf‐specific conductivity (k_L) measured in stem segments from terminal branches ranged from 3 to 18 mmol m^?1 s^?1 MPa^?1, and whole‐plant hydraulic efficiency calculated as stomatal conductance (g) divided by the difference between predawn and midday leaf water potential (Ψ_L), ranged from 70 to 150 mmol m^?2 s^?1 MPa^?1. Hydraulic efficiency was positively correlated with k_L (r² = 0·86). Minimum annual Ψ_L ranged from ? 1·5 to ? 4·1 MPa among the six species. Seasonal and diurnal variation in Ψ_L were associated with differences among species in wood‐saturated water content, wood density and k_L. The species with higher wood‐saturated water content were more efficient in terms of long‐distance water transport, exhibited smaller diurnal variation in Ψ_L and higher maximum photosynthetic rates. Smaller diurnal variation in Ψ_L in species with higher wood‐saturated water content, k_L and hydraulic efficiency was not associated with stomatal restriction of transpiration when soil water deficit was moderate, but avoidance of low minimum seasonal Ψ_L in these species was associated with a substantial seasonal decline in g. Low seasonal minimum Ψ_L in species with low k_L, hydraulic efficiency, and wood‐saturated water content was associated with higher leaf solute content and corresponding lower leaf turgor loss point. Despite the species‐specific differences in leaf water relations characteristics, all six evergreen tree species shared a common functional relationship defined primarily by k_L and stem water storage capacity.     

Living cells in wood. 1. Absence,scarcity and histology of axial parenchyma as keys to function

The diversity of expression in axial parenchyma (or lack of it) in woods is reviewed and synthesized with recent work in wood physiology, and questions and hypotheses relative to axial parenchyma anatomy are offered. Cell shape, location, abundance, size, wall characteristics and contents are all characteristics for the assessment of the physiological functions of axial parenchyma, a tissue that has been neglected in the consideration of how wood histology has evolved. Axial parenchyma occurrence should be considered with respect to mechanisms for the prevention and reversal of embolisms in tracheary elements. This mechanism complements cohesion–tension‐based water movement and root pressure as a way of maintaining flow in xylem. Septate fibres can substitute for axial parenchyma (‘axial parenchyma absent’) and account for water movement in xylem and for the supply of carbohydrate abundance underlying massive and sudden events of foliation, flowering and fruiting, as can fibre dimorphism and the co‐occurrence of septate fibres and axial parenchyma. Rayless woods may or may not contain axial parenchyma and are informative when analysing parenchyma function. Interconnections between ray and axial parenchyma are common, and so axial and radial parenchyma must be considered as complementary parts of a network, with distinctive but interactive functions. Upright ray cells and more numerous rays per millimetre enhance interconnection and are more often found in woods that contain tracheids. Vesselless woods in both gymnosperms and angiosperms have axial parenchyma, the distribution of which suggests a function in osmotic water shifting. Water and photosynthate storage in axial parenchyma may be associated with seasonal changes and with succulent or subsucculent modes of construction. Apotracheal axial parenchyma distribution often demonstrates storage functions that can be read independently of osmotic water shifting capabilities. Axial parenchyma may serve to both enhance mechanical strength or, when parenchyma is thin‐walled, as a tissue that adapts to volume change with a change in water content. Other functions of axial parenchyma (contributing resistance to pathogens; a site for the recovery of physical damage) are considered. The diagnostic features of axial parenchyma and septate fibres are reviewed in order to clarify distinctions and to aid in cell type identification. Systematic listings are given for particular axial parenchyma conditions (e.g. axial parenchyma ‘absent’ with septate fibres substituting). A knowledge of the axial parenchyma information presented here is desirable for a full understanding of xylem function. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 291–321.     

Changes in water content of two agricultural soils does not alter labile P and C pools

Aims

An incubation study was conducted to investigate how changes in soil water content affect labile phosphorus and carbon pools, mineralisation patterns and microbial community composition.

Methods

Two soils from different climatic histories were subjected to four long-term (15 weeks) soil water regimes (constant field capacity (m); 3 dry-rewet (DRW) cycles evenly spaced (intermittent, int); 3 DRW cycles with a shorter interval after a long dry period (false break, fb); constantly air-dry (d)) (incubation period 1). In the subsequent incubation period 2, a set of cores from each treatment were subjected to one DRW cycle (air-dry for 7 day; field capacity for 14 day) or maintained at field capacity.

Results

Long-term soil water regime altered soil respiration with the largest CO₂ pulse occurring in soil with the longest dry period. However, changing the distribution of the 3 DRW events within incubation period 1 (int/fb) did not alter cumulative CO₂. In addition, DRW during incubation period 2 did not affect cumulative CO₂ in either treatment (m, int, fb, d) (except for Hamilton int). Our results show that carbon and phosphorus availability and the size and community composition of the microbial biomass were largely unaffected by fluctuating soil water content.

Conclusions

Changes in soil water content altered respiration, phosphatase activity and microbial C:P ratio and indicate physiological and/or functional changes in the microbial community. However, it appeared that these would have little impact on plant P availability.     

中国伐木制品碳储量时空差异

森林生态系统碳储量是全球变化研究的热点问题之一,在国内外已经进行了深入的研究。然而,森林采伐后生产的伐木制品碳储量研究相对较少,因此基于IPCC提出的大气流动法,综合考虑伐木制品废弃情形,以2000年为基准年,估算了我国2000—2009新生产伐木制品的碳储量。结果表明,我国伐木制品是一个巨大碳库,且碳储量呈不断增加趋势。2000—2009年我国新生产的伐木制品,在2009年净碳储量为306.52 TgC,非纸木制品、纸类和竹材制品碳储量分别为114.71 TgC、4.33 TgC和199.07 TgC,而薪材燃烧累计碳释放量为11.60TgC,其他伐木制品累计碳释放量共为37.76 TgC。在2009年,终端伐木制品碳储量为318.12TgC,木材制品和竹制品碳储量分别占37.42%和62.58%;在木材制品中,非纸木制品和纸类碳储量为114.71TgC和4.33 TgC,各占96.36%和3.64%。与方精云估算的我国1999—2003年森林年碳汇量168.1 TgC/a相比,这一时期生产的伐木制品年净碳储量为25.21 Tg/a,占森林年碳汇量的15%,这说明伐木制品在维持碳平衡具有重要的作用。本文估算的竹制品碳储量约为木材制品碳储量的1.67倍,这说明竹材制品碳储量在伐木制品碳储量中占相当大的比重,是一个重要的碳库。此外,按照终端伐木制品净碳储量情况,可将我国分成高储量区、中储量区和低储量区。高储量区包括福建、浙江、湖南、云南、广西、江西6个省,这些地区终端伐木制品净碳储量占全国的67%;中储量区包括安徽、广东、湖北、四川、黑龙江、吉林和内蒙古等地区,其他地区为低储量区。我国7个地区按终端伐木制品净碳储量顺序排列为:华东、华中、华南、西南、东北、华北、西北。此外,研究还表明我国南方和北方伐木制品碳储量分别以竹材制品和木材制品储存为主。     

A shared coevolutionary history does not alter the outcome of coalescence in experimental populations of Pseudomonas fluorescens

Community coalescence, the mixing of multiple communities, is ubiquitous in natural microbial communities. During coalescence, theory suggests the success of a population will be enhanced by the presence of species it has coevolved with (relative to foreign species), because coevolution will result in greater resource specialization to minimize competition. Thus, more coevolved communities should dominate over less coevolved communities during coalescence events. We test these hypotheses using the bacterium Pseudomonas fluorescens which diversifies into coexisting niche‐specialist morphotypes. We first evolved replicate populations for ~40 generations and then isolated evolved genotypes. In a series of competition trials, we determined if using coevolved versus random genotypes affected the relative performance of “communities” of single and multiple genotypes. We found no effect of coevolutionary history on either genotype fitness or community performance, which suggests parallel (co)evolution between communities. However, fitness was enhanced by the presence of other genotypes of the same strain type (wild‐type or an isogenic strain with a LacZ marker; the inclusion of the latter necessary to distinguish genotypes during competition), indicative of local adaptation with respect to genetic background. Our results are the first to investigate the effect of (co)evolution on the outcome of coalescence and suggest that when input populations are functionally similar and added at equal mixing ratios, the outcome community may not be asymmetrically dominated by either input population.     

Relationships between water,nutrients and productivity in Australian forests: Application to wood production and quality

The application of knowledge of water and nutrient relationships to improve forest management is discussed from an Australian perspective. The objectives of tree planting and forest management have become diverse, and there are outstanding examples of successful application of research results to forestry.Experiments seeking to explain the way water and nutrients influence growth tend to use treatments designed to ensure large differences in growth to increase the opportunities for identifying the mechanisms involved. The application of results from such research to many forestry situations, however, is harder than from research in which there is a closer match between treatments and management practices. The expectations of process-based models as management tools for economic decision-making is yet to be fulfilled. More progress is required in our ability to predict accurately the effects of soil and stand management practices on the production of marketable wood.The extent to which results of research on silvicultural practices are applied in practice is ultimately dependent upon economic return from investment. Water and nutrient relations have a significant influence on production, harvest index and log and wood quality. Recognition and understanding of this influence and the availability of management-oriented growth models incorporating process-based information, will permit better assessment of potential returns from management options.     

Shoot apex removal does not alter autoregulation of Modulation in soybean

The suppression of new nodule development in soybean (Glycine max (L.) Merr.) has been previously demonstrated to involve the shoot through reciprocal grafts between the wild-type cultivar Bragg and its supernodulating mutant nts382. Using the same grafting technique, but modified through the excision of the shoot apex region and emerging lateral shoots, we show here that autoregulation of nodule number still existed despite apex removal. This radical treatment lowered total nodule number per plant as well as root, shoot and nodule dry weight. Bragg shoots grafted onto nts382 roots gave wild-type nodulation (26 nodules, 15mg total nodule mass) as compared to nts382 shoots grafted onto Bragg roots (340 nodules, 277 mg total nodule mass). Specific nodule mass differed between supernodulating (about 0·5-1·0mg per nodule) and wild-type nodulating (2·3 mg per nodule) plants. In contrast to other growth characteristics, apex removal did not affect specific nodule size, except in plants with wild-type shoots and nts382 (supernodulation) roots. Apex removal only slightly affected the percentage of nodule weight per total root weight in nts382, but had a severe effect in wild type. Growth reductions varied between the normal and supernodulating plants. The fact that autoregulation of nodulation still functions in plants devoid of functional shoot apices suggests that the autoregulation signal may not be derived from the apex regions and that the leaf may be a likely source.     

Postponed sowing does not alter the fibre/wood ratio or fibre extractability of fibre hemp (Cannabis sativa)

Because hemp is a short-day plant, postponing the sowing date might be a suitable strategy to obtain shorter and smaller plants around flowering, when primary fibres are 'ripe' enough to be harvested. Smaller plants can be processed on existing flax scutching and hackling lines and might have fibre characteristics that are desirable for producing high-quality 'long fibres' for yarn spinning.
It was investigated whether sowing beyond the normal sowing period in the Netherlands affects the ratio in which fibres and wood are produced, and what proportion of these fibres are long fibres, suitable for long fibre spinning. About 400 stem samples were fractioned into retting losses, wood, tow, and long fibre, and the ratios between fractions were analysed using multiple linear regression analyses.
A normal sowing date at the end of April was compared with a postponed sowing date at the end of May. The total fibre/wood ratio was not affected. More than 95% of the variance in total fibre was accounted for by the wood weight per stem (55.5%), the variety (+33.3%) and the stem part (+6.5%). The amount of long fibre per stem mainly depended on the amount of the total fibre per stem (95.4% variance was accounted for) and the stem part (+2.0%).
For economic reasons, it could be interesting to grow two successive high-quality hemp crops in one growing season. Therefore, in an additional experiment with one variety, the effect of sowing fibre hemp up to 12 weeks later than normal on the quantity and quality of the fibres was studied. Postponing the sowing date up to 12 weeks had no important effects on retting losses, the total fibre/wood ratio, and the long fibre/total fibre ratio. It is therefore technically possible to grow two successive hemp crops. Whether this fits well in farming systems and a hemp production chain remains to be studied.     

Irreversible habitat specialization does not constrain diversification in hypersaline water beetles

Specialization to extreme environments is often considered an evolutionary dead‐end, leading to irreversible adaptations and reduced evolvability. There is, however, mixed evidence for this macroevolutionary pattern, and limited data from speciose lineages. Here, we tested the effect of habitat specialization to hypersaline waters in the diversification rates of aquatic beetles of the genus Ochthebius (Coleoptera, Hydraenidae), using a molecular phylogeny with more than 50% of the 546 recognized species, including representatives of all but one of the nine recognized subgenera and 17 species groups. Phylogenies were built combining mitochondrial and nuclear genes, with the addition of 42 mitochondrial genomes. Using Bayesian methods of character reconstruction, we show that hypersaline tolerance is an irreversible ecological specialization that arose multiple times. Two lineages of Ochthebius experienced a significant increase in diversification rates, one of them inhabiting hypersaline waters, but there was no overall correlation with habitat or any significant decrease in diversification rates despite the irreversibility of hypersaline tolerance. Our study tested for the first time the impact of hypersaline habitat specialization on diversification rates, finding no support for it to be an evolutionary dead‐end. On the contrary, multiple and ancient lineages fully adapted to these extreme osmotic conditions have persisted and diversified over a long evolutionary timescale.     

Pit membrane remnants in perforation plates of Hydrangeales with comments on pit membrane remnant occurrence, physiological significance and phylogenetic distribution in dicotyledons

Perforation plates from ten species of seven genera of Hydrangeales sensu Thorne were studied using scanning electron microscopy (SEM). The presence of pit membranes in perforations ranges from abundant, as in Carpenteria and Hydrangea, to minimal, as in Deutzia, Escallonia and Philadelphus. Abnormally great pit membrane presence may result from the presence of secondary compounds that inhibit lysis, as in Quintinia serrata; such interference with the natural lysis process may or may not be evident from coarseness and irregularity of pit membrane surface and of threads composing the pit membrane remnants. The presence of pit membrane remnants in perforation plates is hypothesized to be a symplesiomorphy, found in a fraction of dicotyledons with scalariform perforation plates (but still in an appreciable number of species). Pit membrane remnant presence may represent incomplete lysis of primary wall material (cellulose microfibrils) in species that occupy highly mesic habitats, where such impedance in the conductive stream does not have an appreciable negative selective value. This physiological interpretation of pit membrane remnants in perforations is enhanced by the phylogenetic distribution as well as the strongly mesic ecological preferences of species that exemplify this phenomenon in dicotyledons at large. Families with pit membrane presence in perforations are scattered throughout phylogenetic trees, but they occur most often in basal branches of major clades (superorders) or as basal branches of orders within the major clades. Further study will doubtless reveal other families and genera in which this phenomenon occurs, although it is readily detected only with SEM. Phylogenetic stages in the disappearance of pit membrane remnants from perforation plates are described, ranging from intact pit membranes except for presence of pores of various sizes, to presence of membrane remnants only at lateral ends of perforations and in one or two perforations (arguably pits) at the transition between a perforation plate and subadjacent lateral wall pitting. Developmental study of the mechanism and timing of lysis of pit membranes in perforations, and assessment of the role of the conductive stream in their removal, are needed to enhance present understanding of vessel evolution. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 146 , 41–51.