Effects of global environmental change on carbon partitioning in vegetative plants of Triticum aestivum and closely related Aegilops species

The use of fossil fuel is predicted to cause an increase of the atmospheric CO₂ concentration, which will affect the global pattern of temperature and precipitation. It is therefore essential to incorporate effects of temperature and water supply on carbon partitioning of plants to predict effects of elevated [CO₂] on growth and yield of Triticum aestivum. Although earlier papers have emphasized that elevated [CO₂] favours investment of biomass in roots relative to that in leaves, it has now become clear that these are indirect effects, due to the more rapid depletion of nutrients in the root environment as a consequence of enhanced growth. Broadly generalized, the effect of temperature on biomass allocation in the vegetative stage is that the relative investment of biomass in roots is lowest at a certain optimum temperature and increases at both higher and lower temperatures. This is found not only when the temperature of the entire plant is varied, but also when only root temperature is changed whilst shoot temperature is kept constant. Effects of temperature on the allocation pattern can be explained largely by the effect of root temperature on the roots' capacity to transport water. Effects of a shortage in water supply on carbon partitioning are unambiguous: roots receive relatively more carbon. The pattern of biomass allocation in the vegetative stage and variation in water-use efficiency are prime factors determining a plant's potential for early growth and yield in different environments. In a comparison of a range of T. aestivum cultivars, a high water-use efficiency at the plant level correlates positively with a large investment in both leaf and root biomass, a low stomatal conductance and a large investment in photosynthetic capacity. We also present evidence that a lower investment of biomass in roots is not only associated with lower respiratory costs for root growth, but also with lower specific costs for ion uptake. We suggest the combination of a number of traits in future wheat cultivars, i.e. a high investment of biomass in leaves, which have a low stomatal conductance and a high photosynthetic capacity, and a low investment of biomass in roots, which have low respiratory costs. Such cultivars are considered highly appropriate in a future world, especially in the dryer regions. Although variation for the desired traits already exists among wheat cultivars, it is much larger among wild Aegilops species, which can readily be crossed with T. aestivum. Such wild relatives may be exploited to develop new wheat cultivars well-adapted to changed climatic conditions.     

Taphonomy as a guide to hnctional morphology of Holocrinus, the first post-Paleozoic crinoid

Baumiller, T. K. & Hagdorn, H. 1995 1130: Taphonomy as a guide to functional morphology of Holoainus , the first post-Paleozoic crinoid.
A taphonomic approach, in which patterns of fragmentation are used to infer the organization of soft tissue and function in crinoid stalks, was applied to pluricolumnals of the first post-Paleozoic crinoid, Holocrinus . The observed patterns are analogous to those for isocrinid crinoids, suggesting that Holoctinus and isocrinid stalks are functionally similar in having specialized sites for autotomy. Stalk autotomy in Holocrinus could not have been predicted based on morphological criteria alone: the stalk of Holocrinus lacks synostosial articulations, which among the isocrinids are the sites of autotomy. This implies that taphonomic data can supplement and sometimes supersede morphological data as a basis for functional reconstructions. Stalk autotomy in Holocrinus indicates that this trait was not derived independently by the isocrinids and comatulids, but rather that it was primitively shared by them. If pentacrinitids could not autotomize their stalks, as is likely, this would represent a loss of this ability through paedomorphosis. □ Holocrinus, articulates, arinoids, taphonomy, autotomy, heterochrony .     

GENETIC AND MORPHOLOGICAL VARIATION OF POPULATIONS BELONGING TO THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA; PLANORBIDAE) IN SOUTH WESTERN ZIMBABWE

Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.29–0.80among populations from Plumtree and expected heterozygosity(H_e) from 0.02–0.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998)     

Environment versus dispersal in the assembly of western Amazonian palm communities

Aim It is a central issue in ecology and biogeography to understand what governs community assembly and the maintenance of biodiversity in tropical rain forest ecosystems. A key question is the relative importance of environmental species sorting (niche assembly) and dispersal limitation (dispersal assembly), which we investigate using a large dataset from diverse palm communities. Location Lowland rain forest, western Amazon River Basin, Peru. Methods We inventoried palm communities, registering all palm individuals and recording environmental conditions in 149 transects of 5 m × 500 m. We used ordination, Mantel tests and indicator species analysis (ISA) to assess compositional patterns, species responses to geographical location and environmental factors. Mantel tests were used to assess the relative importance of geographical distance (as a proxy for dispersal limitation) and environmental differences as possible drivers of dissimilarity in palm species composition. We repeated the Mantel tests for subsets of species that differ in traits of likely importance for habitat specialization and dispersal (height and range size). Results We found a strong relationship between compositional dissimilarity and environmental distance and a weaker but also significant relationship between compositional dissimilarity and geographical distance. Consistent with expectations, relationships with environmental and geographical distance were stronger for understorey species than for canopy species. Geographical distance had a higher correlation with compositional dissimilarity for small‐ranged species compared with large‐ranged species, whereas the opposite was true for environmental distance. The main environmental correlates were inundation and soil nutrient levels. Main conclusions The assembly of palm communities in the western Amazon appears to be driven primarily by species sorting according to hydrology and soil, but with dispersal limitation also playing an important role. The importance of environmental characteristics and geographical distance varies depending on plant height and geographical range size in agreement with functional predictions, increasing our confidence in the inferred assembly mechanisms.     

Proportioning a Hydra

SYNOPSIS. Pieces of hydra tissue of various sizes and shapeswere cut from the body columns of adult hydra and allowed toregenerate. The proportions of the resulting animals were determinedfirst by counting cells in the head and body, and secondly bymeasuring the structures directly using an ocular micrometer. Head-body proportions were found to be constant over a tenfoldsize range. Very small regenerates had a larger head fractionand large budding regenerates had a smaller head fraction. Extrastructures developed in certain shape pieces, but total head-bodytissue remained proportional. More detailed measurement of thehead showed that the hypostome regulated only slightly withtotal size change, while the tentacle tissue varied considerablyto maintain the head-body ratio. This suggested that the patterningof the hypostome and the tentacles might involve separate processes,with the latter being responsible for proportion regulation.While the body mass appeared to be determined by the proportioningmechanism, its circumference was related to the circumferenceof the hypostome, suggesting a causal relationship between thetwo organizers and the column shaping. The basal disc remainedproportional to the body except in the smallest pieces. A Gierer-Meinhardtpattern formation scheme could account for the results found.     

Cyanide-Resistant Root Respiration and Tap Root Formation in Two Subspecies of Hypochaeris radicata

Root respiration of the tap root forming species Hypochaeris radicata L. was measured during tap root formation. A comparison was made of two subspecies: H. radicata L. ssp. radicata L., a subspecies from relatively rich soils, and H. radicata L. ssp. ericetorum Van Soest, a subspecies from poor acidic soils. Root respiration was high and to a large extent inhibited by hydroxamic acid (SHAM) before the start of the tap root formation, indicating a high activity of an alternative non-phosphorylative electron transport chain. The rate of root respiration was much lower and less sensitive to SHAM when a considerable tap root was present. However, root respiration was also cyanide-resistant when a tap root was present, indicating that the alternative pathway was still present. A decreased rate of root respiration coincided with an increase of the content of storage carbohydrates, mainly in the tap root. The level of reducing sugars was constant throughout the experimental period, and it was concluded that the activity of the alternative oxidative pathway was significant in oxidation of sugars that could not be utilized for purposes like energy production, the formation of intermediates for growth or for storage. Root respiration decreased after the formation of a tap root. This decrease could neither be attributed to a gradual disappearance of the alternative chain, nor to a decreased level of reducing sugars. No differences in respiratory metabolism between the two subspecies have been observed, suggesting that a high activity of the alternative oxidative pathway is not significant in adaptation of the present two subspecies to relatively nutrient-rich or poor soils.     

The Minimum Intercellular-space CO2-Concentration (T) of Maize Leaves and its Influence on Stomatal Movements

Unlike other leaves investigated, maize leaves were found tobe able to exhaust atmospheric CO₂-content to zero concentration.This occurred at 20? C. with a light intensity of 100 f.c. andat 30? C. with a light intensity of 500 f.c. The influences of temperature, light intensity, and waterstrainon this property of maize leaves were investigated systematicallyand a permanent aftereffect of waterstrain on the leaves wasfound. Stomatal conductance measurements showed that maize stomataare sensitive to CO₂-concentrations between zero and 100 p.p.m.,a circumstance not yet reported for other leaves.     

A sublethal effect on native Anthocoris nemoralis through competitive interactions with invasive Harmonia axyridis

1. The invasive ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae) is implicated in declines of native ladybirds with intraguild predation identified as an underlying mechanism, however, less studied are the effects on non‐coccinellid predators. Intraguild predation between Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) and H. axyridis and the relative effects of inter‐ and intraspecific competition on predators on potted Tilia cordata Mill. was investigated, at two aphid densities. 2. Intraguild predation was unidirectional in favour of H. axyridis in Petri dishes although a low level of ladybird egg predation by A. nemoralis occurred. However, on trees intraguild predation was rare. 3. A positive effect of aphid density on H. axyridis weight gain, and increased survival when reared with A. nemoralis on potted trees indicated stronger effects of intraspecific competition on H. axyridis. Consistent suppression of aphids by ladybirds revealed their superior competition for aphids. 4. Anthocoris nemoralis weight gain was reduced when reared with H. axyridis on potted trees, indicating a potential for a sublethal effect through interspecific competition. Survivorship of A. nemoralis did not differ between con‐ and heterospecific treatments, but high aphid density enhanced A. nemoralis survival. Overall, high mortality among nymphs across treatments suggested effects related to both inter‐ and intraspecific competition for resources. 5. Results provide evidence of a sublethal effect by invasive H. axyridis through resource competition, suggesting that where these predators co‐occur, competitive interactions for shared prey are more likely to affect A. nemoralis populations than intraguild predation by H. axyridis.     

Effects of diet and host access on fecundity and lifespan in two fruit fly species with different life‐history patterns

The reproductive ability of female tephritids can be limited and prevented by denying access to host plants and restricting the dietary precursors of vitellogenesis. The mechanisms underlying the delayed egg production in each case are initiated by different physiological processes that are anticipated to have dissimilar effects on lifespan and reproductive ability later in life. The egg‐laying abilities of laboratory‐reared females of the Mediterranean fruit fly (Ceratitis capitata Wiedmann) and melon fly (Bactrocera cucurbitae Coquillett) from Hawaii are delayed or suppressed by limiting access to host fruits and dietary protein. In each case, this is expected to prevent the loss of lifespan associated with reproduction until protein or hosts are introduced. Two trends are observed in each species: first, access to protein at eclosion leads to a greater probability of survival and a higher reproductive ability than if it is delayed and, second, delayed host access reduces lifetime reproductive ability without improving life expectancy. When host access and protein availability are delayed, the rate of reproductive senescence is reduced in the medfly, whereas the rate of reproductive senescence is generally increased in the melon fly. Overall, delaying reproduction lowers the fitness of females by constraining their fecundity for the remainder of the lifespan without extending the lifespan. © 2013 The Royal Entomological Society     

Zur Feinstruktur der spermatogenetischen Stadien von Myxine glutinosa L. (Cyclostomata)

The fine structure of the spermatogonia, spermatocytes, spermatids, the Sertoli cell and the epithelial cells of the mesorchial sheath is described. In an early spermatid stage a transient close relationship between the Chromatoid body and the acrosome is demonstrated.