The fall and rise of active chloride transport: implications for regulation of intraocular pressure

Early study of transepithelial salt transfer focused on Cl(-) and not Na(+), partly because Cl(-) was readily measureable. The advent of flame photometry and tracer techniques brought Na(+) to the fore, especially since short-circuited frog skin (Rana temporaria) produces baseline net movement of Na(+) and not of Cl(-). Zadunaisky was among the first to describe what is currently termed secondary active Cl(-) transport, helping stimulate interest in Cl(-) handling by other tissues, notably the thick ascending limb of the loop of Henle important in renal counter-current multiplication. More recently, molecules responsible for electroneutral and electrogenic Cl(-) transfer have been cloned, and specific diseases resulting from their faulty expression have been identified. The clinical importance of transepithelial Cl(-) transfer is illustrated by studies of aqueous humor formation by the eye's bilayered ciliary epithelium. NaCl is taken up from the stroma by the pigmented ciliary epithelial (PE) layer, diffuses through gap junctions into the nonpigmented ciliary epithelial (NPE) layer, and is released into the aqueous humor largely through Na(+) pumps and Cl(-) channels. ATP released by NPE cells can be ecto-enzymatically metabolized to adenosine. Adenosine can mediate paracrine/autocrine stimulation of Cl(-) channels and aqueous humor secretion by occupying A(3) adenosine receptors (ARs). A(3)AR agonists indeed elevate, and A(3)AR antagonists lower, intraocular pressure (IOP) in wild-type mice. A(3)AR knockout mice have low IOP and their responses to A(3)AR agonists and antagonists are blunted; this suggests that reducing Cl(-)-channel activity with A(3)AR antagonists may provide a novel approach for treating glaucoma.     

Mechanisms of successional dynamics: Consumers and the rise and fall of species dominance

Insight into potential mechanisms of succession following disturbance to an ecological community can be gained by considering processes that contribute to the rise (colonization, interactions with established species) and demise (differential mortality) of specific stages within the successional sequence. Most successional theories focus on the rise to dominance, assuming demise is the result of competition, but other factors can cause differential mortality among species, including physical disturbance, senescence, and consumers. In rocky intertidal communities on the coast of Washington state, USA, gaps in mussel beds exhibit a succession from predator-susceptible to predator-resistant species following disturbance, suggesting that differential consumption by mobile species may play an important role in the demise of early succession species and the eventual dominance of the mussel Mytilus californianus. Experimental manipulation of a dominant species earlier in succession, the blue mussel Mytilus trossulus, demonstrated that this species inhibits the invasion of M. californianus in the absence of predators. Experimental manipulation of predatory snails (Nucella emarginata and Nucella canaliculata), which feed heavily on M. trossulus but not M. californianus, greatly increased the rate at which M. californianus invaded gaps. These results and those of other studies indicate that consumers frequently have important effects on the dynamics of succession in benthic marine systems, and might also play a role in other settings.     

The rise and fall of NMDA antagonists for ischemic stroke

It has long been accepted that high concentrations of glutamate can destroy neurons, and this is the basis of the theory of excitotoxicity during brain injury such as stroke. Glutamate N-methyl-D-aspartate (NMDA) receptor antagonists such as Selfotel, Aptiganel, Gavestinel and others failed to show neuroprotective efficacy in human clinical trials or produced intolerable central nervous system adverse effects. The failure of these agents has been attributed to poor studies in animal models and to poorly designed clinical trials. We also speculate that NMDA receptor antagonism may have hindered endogenous mechanisms for neuronal survival and neuroregeneration. It remains to be proven in human stroke whether NMDA receptor antagonism can be neuroprotective.     

The rise and fall of bacterial clones: Streptococcus pneumoniae

Globally spreading bacterial strains belong to clonal types that have the capacity to colonize, spread and cause disease in the community. Recent comparative genomic analyses of well-defined clinical isolates have led to the identification of bacterial properties that are required for the successful spread of bacterial clones. In this Review, we discuss the evolution of bacterial clones, the importance of recombination versus mutations for evolution of clones, common methods used to study clonal relationships among bacteria, factors that may contribute to the clonal spread of bacteria and the potential relevance of bacterial clones to clinical disease. We focus on the common pathogen Streptococcus pneumoniae, although other bacteria are also briefly discussed, such as Helicobacter pylori, Staphylococcus aureus and Mycobacterium tuberculosis.     

Avian foraging studies: an overlooked source of distribution data for macroecological and conservation studies

Macroecological and biogeographical studies and their applicability for biological conservation vitally depend on distribution data. These are usually taken from distribution atlases and databases or maps found in identification guides. A previous study pointed to another little explored source of data — local faunistic studies. Here, I would like to draw attention to another potential source. Papers that analysed the food composition of some taxa (e.g. insectivorous birds) are an overlooked source of rich information on taxa distributions. These studies frequently include an 'Appendix' with a list of food items determined to the species level. These studies also contain data on abundances, number of samples, sampling time, and geographical location as a rule. Foraging birds naturally provide data on invertebrate distributions with good spatio-temporal coverage and reasonably large samples. Importantly, birds frequently collect rare and by entomological methods hardly detectable species (i.e. those living high, in tree canopies, in very dense vegetation, or with secretive lifestyle). Data from bird dietary studies may help to ameliorate one of the most serious problems in distribution studies — zero inflation. I briefly discuss pros and cons of this so far neglected source of biogeographical data.     

The carbon–nutrient balance hypothesis: its rise and fall

The idea that the concentration of secondary metabolites in plant tissues is controlled by the availability of carbon and nitrogen in the environment has been termed the carbon–nutrient balance hypothesis (CNB). This hypothesis has been invoked both for prediction and for post hoc explanation of the results of hundreds of studies. Although it successfully predicts outcomes in some cases, it fails to such an extent that it cannot any longer be considered useful as a predictive tool. As information from studies has accumulated, many attempts have been made to save CNB, but these have been largely unsuccessful and have managed only to limit its utility. The failure of CNB is rooted in assumptions that are now known to be incorrect and it is time to abandon CNB because continued use of the hypothesis is now hindering understanding of plant–consumer interactions. In its place we propose development of theory with a firm evolutionary basis that is mechanistically sophisticated in terms of plant and herbivore physiology and genetics.     

The rise and fall of pineal N-acetyltransferase in vitro: The influence of age

Pineal glands of 4-day-old rats had a spontaneous rise and fall in N-acetyltransferase activity (NAT) in organ culture lasting 12–17 hr. Peak NAT increased until the pups were 10 days old, then gradually declined. Pineal glands of 28-day-old animals and of adult rats had no spontaneous rise and fall in 12–17 hr of culture. Thus, immature rat pineal glands have the capacity in vitro for the rise and fall of N-acetyltransferase in the absence of added norepinephrine.     

The fall and rise of US inequities in premature mortality: 1960-2002

Background

Debates exist as to whether, as overall population health improves, the absolute and relative magnitude of income- and race/ethnicity-related health disparities necessarily increase—or derease. We accordingly decided to test the hypothesis that health inequities widen—or shrink—in a context of declining mortality rates, by examining annual US mortality data over a 42 year period.

Methods and Findings

Using US county mortality data from 1960–2002 and county median family income data from the 1960–2000 decennial censuses, we analyzed the rates of premature mortality (deaths among persons under age 65) and infant death (deaths among persons under age 1) by quintiles of county median family income weighted by county population size. Between 1960 and 2002, as US premature mortality and infant death rates declined in all county income quintiles, socioeconomic and racial/ethnic inequities in premature mortality and infant death (both relative and absolute) shrank between 1966 and 1980, especially for US populations of color; thereafter, the relative health inequities widened and the absolute differences barely changed in magnitude. Had all persons experienced the same yearly age-specific premature mortality rates as the white population living in the highest income quintile, between 1960 and 2002, 14% of the white premature deaths and 30% of the premature deaths among populations of color would not have occurred.

Conclusions

The observed trends refute arguments that health inequities inevitably widen—or shrink—as population health improves. Instead, the magnitude of health inequalities can fall or rise; it is our job to understand why.     

Interpretation of steady-state current-voltage curves: Consequences and implications of current subtraction in transport studies

Summary A problem often confronted in analyses of chargecarrying transport processesin vivo lies in identifying porterspecific component currents and their dependence on membrane potential. Frequently, current-voltage (I–V)—or more precisely, difference-current-voltage (dI-V)—relations, both for primary and for secondary transport processes, have been extracted from the overall membrane current-voltage profiles by subtracting currents measured before and after experimental manipulations expected to alter the porter characteristics only. This paper examines the consequences of current subtraction within the context of a generalized kinetic carrier model for Class I transport mechanisms (U.-P. Hansen, D. Gradmann, D. Sanders and C.L. Slayman, 1981,J. Membrane Biol. 63:165–190). Attention is focused primarily ondI-V profiles associated with ion-driven secondary transport for which external solute concentrations usually serve as the experimental variable, but precisely analogous results and the same conclusions are indicated in relation to studies of primary electrogenesis. The model comprises a single transport loop linkingn (3 or more) discrete states of a carrier molecule. State transitions include one membrane chargetransport step and one solute-binding step. Fundamental properties ofdI-V relations are derived analytically for alln-state formulations by analogy to common experimental designs. Additional features are revealed through analysis of a reduced 2-state empirical form, and numerical examples, computed using this and a minimum 4-state formulation, illustratedI-V curves under principle limiting conditions. Class I models generate a wide range ofdI-V profiles which can accommodate essentially all of the data now extant for primary and secondary transport systems, including difference current relations showing regions of negative slope conductance. The particular features exhibited by the curves depend on the relative magnitudes and orderings of reaction rate constants within the transport loop. Two distinct classes ofdI-V curves result which reflect the relative rates of membrane charge transit and carrier recycling steps. Also evident in difference current relations are contributions from hidden carrier states not directly associated with charge translocation in circumstances which can give rise to observations of counterflow or exchange diffusion. Conductance-voltage relations provide a semi-quantitative means to obtaining pairs of empirical rate parameters. It is demonstrated thatdI-V relationscannot yield directly meaningful transport reversal potentials in most common experimental situations. Well-defined arramgements of reaction constants are shown to givedI-V curves which exhibit little or no voltage sensitivity and finite currents over many tens to hundreds of millivoltsincluding the true reversal potential. Furthermore, difference currents show apparent Michaelian kinetics with solute concentration atall membrane potentials. These findings bring into question several previous reports of reversal potentials, stoichiometries and apparent current-source behavior based primarily on difference current analysis. They also provide a coherent explanation for anomolous and shallow conductances and paradoxical situations in which charge stoichiometry varies with membrane potential.     

The fall and rise of Dr Pangloss: adaptationism and the Spandrels paper 20 years later

Twenty years have passed since Gould and Lewontin published their critique of 'the adaptationist program' - the tendency of some evolutionary biologists to assume, rather than demonstrate, the operation of natural selection. After the 'Spandrels paper', evolutionists were more careful about producing just-so stories based on selection, and paid more attention to a panoply of other processes. Then came reactions against the excesses of the anti-adaptationist movement, which ranged from a complete dismissal of Gould and Lewontin's contribution to a positive call to overcome the problems. We now have an excellent opportunity for finally affirming a more balanced and pluralistic approach to the study of evolutionary biology.     

Key traits in a threatened butterfly and its common sibling: implications for conservation

We ask here which traits predispose one species to extreme rarity and possible extinction while a sympatric sibling is geographically widespread. With background knowledge on the level of habitat specialization of the two species, the population structure and movement of the localized and threatened Orachrysops ariadne were compared to those of the common and highly sympatric O. subravus, using mark-release-recapture. Of a total of 290 marked O. ariadne individuals 42.8% were recaptured, while of 631 O. subravus individuals 49.3% were recaptured. The Jolly-Seber model was used to estimate daily population numbers (N _i ), survival rates (ϕ _i ), recruitment rates (B _i ), proportion of marked animals in the total population (∝_i), and the number of marked animals at risk (M _i ). O. ariadne is a remarkably rare animal, averaging only 10 individuals ha⁻¹ within its small, remaining colonies. Average residence times of male adults were generally similar in both species, being just over 5 days. O. ariadne is a strong and rapid back and forth flier, covering mean recapture distances of 157 m, almost twice that of O. subravus, principally in search of scarce nectar sources. In short, the rarity of O. ariadne is not so much to do with behaviour, survivorship or longevity, but rather with limited availability of the specialized habitat patches for both larvae and adults, and, in particular, the extreme scarcity of the host plant. Evidence suggests that there has been very high selection pressure on the key trait of strong flight as a compensation for going down the apparently highly risky path of extreme microhabitat specialization. Of concern for conservation of this rare species is that these rare habitat patches have become increasingly isolated through transformation of the surrounding landscape. Reduction of the barrier effects of agroforestry through creation of linkages between colonies is recommended, especially as O. ariadne is such a strong flier. Such corridors are indeed now being implemented.     

The rise and fall of the Lower Mississippi: effects of hydrologic connection on floodplain backwaters

In the last 150 years, the Lower Mississippi River (LMR) floodplain was extensively reduced in area with conversion of once regularly inundated floodplain wetlands to dry land. Yet, between the present levees, there remain substantial remnants of the historical floodplain, including various types of permanent backwater habitats. We hypothesized that degree and timing of hydrologic connection with the river main channel drives variation in physical and chemical properties, and phytoplankton community dynamics, in backwaters. Over 23 months, measurements were made in several sites varying in connection with the main channel. At high stages, the channel and backwaters converged in having elevated turbidity, suspended solids and dissolved nutrient concentrations, reduced algal biomass and production, a seston C:N ratio indicating predominantly allochthonous organic matter sources, and a diatom-dominated community. When connection was reduced, backwaters declined in suspended sediments and nutrients, surged in production and biomass, had a seston C:N ratio reflecting autochthonous production, and switched to a community dominated by cryptomonad algae. With prolonged isolation, biomass-specific production became nitrogen limited and declined. By a conceptual model, we illustrate the seasonally variable role of permanent floodplain backwaters as major sources of algal organic matter, and potentially for nutrient sequestration, within the Lower Mississippi system.     

The rise and fall of the mangrove forests in Maputo Bay, Mozambique

The change in area of mangrove forests since 1958 in Maputo Bay,Mozambique was studied. Around Maputo, a 44% reduction of the area was linkedtodifferences in accessibility, the areas closest to Maputo suffering most. Butsurprisingly, large expansions of mangrove forest were also observed. Thisincrease in area (+ 13%) was accompanied by an increase in tree cover from55 to 70%. The overall effect of mangrove forest reduction and growth resultedin a mean decrease of only 8%. The causes of the increase in mangrove area onInhaca island are discussed, and two possible factors are suggested: a changeinsedimentation and an increase in temperature. Sandbanks have increased atInhacaIsland, but no data are available for the other areas. An increase in sea andair temperature has also been noted by other authors and could explain thegrowth of the forests, which are situated at the southernmost limit of theirnormal distribution.     

Three-dimensional geometric morphometrics of Arvicanthis: implications for systematics and taxonomy

Arvicanthis is an African murid, found throughout sub-Saharan Africa, Sudan and Egypt. Although in the past 10 years several studies have been carried out to assess its systematics, there is still a need for a general revision of the genus. In this study the morphometric relationships between 71 populations throughout the range were investigated. A three-dimensional geometric morphometric approach was used to assess differences in the size and shape of the skull. These were related to the different biogeographical domains characterizing the range of the genus and to molecular and karyotypic phylogenies. Results agree only in part with phylogeny, and show a close relationship with the environmental backgrounds of each species. It is therefore suggested that the adaptation of Arvicanthis to local environment has played an important role in the phenotypic evolution of the skull. This leads to problems in taxonomic definitions based on morphometrics, which should not be used without comparison with other independently derived characters such as the DNA and the karyotype.     

甘肃省中国种子植物特有属物种多样性保护优先地区分析

以甘肃省境内11个主要天然林区作为基本的地理单元,选择天然分布在各林区的中国种子植物特有属的物种丰富度、相对特有性和等级性作为评价指标,对各林区中国种子植物特有属物种多样性进行综合评价,确定出甘肃省中国种子植物特有属物种多样性保护的关键林区,并且运用互补性原理设计出最低保护区域组合及其优先序。分析得出关键保护林区为白龙江下游（白水江）林区、白龙江中上游林区和小陇山林区;最低保护区域组合按其优先序依次为白龙江下游（白水江）林区、白龙江中上游林区、东祁连山林区、小陇山林区和太子山,大夏河林区。     

The relationship between geographic area and the latitudinal gradient in species richness in New World birds

One hypothesis for the latitudinal gradient in species richness observed in most animal taxa is that the richness of a region is determined by its geographic area. However, the relationship between geographic area and species richness across regions is generally weak. It has been suggested that this is because species from the tropics spill out of this region of high richness, artificially inflating the richness of other regions. This generates the interesting prediction that the area and richness of extra-tropical regions should be more strongly correlated if tropical species are excluded. We test this prediction using the avifauna of the New World. We find that there is indeed a relationship between the land area and species richness of a region once tropical species are excluded. This relationship is independent of the latitude and productivity of regions. Both latitude and productivity can explain variance in richness unexplained by land area. There is no relationship between land area and species richness if tropical species are not excluded from the analysis, suggesting that tropical species do indeed mask the relationship between richness and area. We conclude that our results generally support the geographic area hypothesis, although tests of its other predictions and on other land masses are required.     

The natural history of the ethical concept and its implications for the present natural equilibrium

The present article was originally published in the medical italian journal,Rassegna Medica, 1984. The author, on the basis of the recent development of the biotechnology, genetic engineering and environment exploitation by man, attempts to reconstruct the natural history of the ethical concept and its implications for the present natural equilibrium. On this basis he suggests a concept of bioethics which stresses Man-Environment interaction.     

The rise and fall of local populations of ortolan buntings Emberiza hortulana: importance of movements of adult males

Changes in population size of local populations of birds have usually been interpreted in relation to adult return rate and recruitment of young individuals after natal dispersal. Little is known about the importance of redistribution of adult individuals through breeding dispersal. The small Norwegian population of ortolan buntings Emberiza hortulana has a patchy distribution with about 30 long‐term local populations. During a period of general population decline (29% decrease over 7 years), the population trends of local populations (measured as number of males recorded) were highly variable, with some even increasing four‐fold. Comparisons of demographic parameters showed that adult immigration rate (i.e. dispersal of adult males) explained both yearly changes in male population size and population trends over the whole study period better than adult return rate or adult emigration rate, or a measure of recruitment of young males. Adult immigration rates and recruitment rates were correlated, suggesting that both young and adult males find the same places attractive. In the study area, adult sex ratio was strongly male‐biased, and immigration rate was higher when local sex ratio was less skewed. In addition, less skewed sex ratio was related to higher adult return rate and lower emigration rate. We found no relationships between measures of breeding success and population change. We suggest that conspecific attraction may explain the observed patterns. Some local populations may act as hot‐spots attracting adult males from other populations. Thus, local population changes need not reflect overall population growth rate, but may be a consequence of redistribution of adult birds.