Genetic versus phenotypic models of selection: can genetics be neglected in a long-term perspective?

Game theoretical concepts in evolutionary biology have been criticized by populations geneticists, because they neglect such crucial aspects as the mating system or the mode of inheritance. In fact, the dynamics of natural selection does not necessarily lead to a fitness maximum or an ESS if genetic constraints are taken into account. Yet, it may be premature to conclude that game theoretical concepts do not have a dynamical justification. The new paradigm of long-term evolution postulates that genetic constraints, which may be dominant in a short-term perspective, will in the long run disappera in the face of the ongoing influx of mutations. Two basic results (see Hammerstein; this issue) seem to reconcile the dynamical approach of long-term population genetics with the static approach of evolutionary game theory: (1) only populations at local fitness optima (Nash strategies) can be long-term stable; and (2) in monomorphic populations, evolutionary stability is necessary and sufficient to ensure long-term dynamic stability. The present paper has a double purpose. On the one hand, it is demonstrated by fairly general arguments that the scope of the results mentioned above extends to non-linear frequency dependent selection, to multiple loci, and to quite general mating systems. On the other hand, some limitations of the theory of long-term evolution will also be stressed: (1) there is little hope for a game theoretical characterization of stability in polymorphic populations; (2) many interesting systems do not admit long-term stable equilibria; and (3) even if a long-term stable equilibrium exists, it is not at all clear whether and how it is attainable by a series of gene substition events.     

Vascular-derived artemin: a determinant of vascular sympathetic innervation?

Vascular sympathetic innervation is an important determinant of blood pressure and blood flow. The mechanisms that determine vascular sympathetic innervation are not well understood. The present study tests the hypothesis that vascular-derived artemin promotes the development of sympathetic innervation to blood vessels by promoting sympathetic axon growth. RT-PCR and Western analyses indicate that artemin is expressed by cultured vascular smooth muscle and arteries, and artemin coreceptors, glial cell-derived neurotrophic factor family receptor alpha3 and ret, are expressed by postganglionic sympathetic neurons. The effects of artemin on axon growth were assessed on explants of neonatal rat sympathetic ganglia. In the presence, but not in the absence, of nerve growth factor, exogenous artemin stimulated neurite growth. Femoral arteries (FA) from adult rats contain artemin, and these arteries stimulated sympathetic neurite growth. Growth in the presence of FA was 92.2 +/- 11.9 mm, and that in the absence of FA was 26.3 +/- 5.4 mm (P < 0.05). FA stimulation of axon growth was reduced by an antibody that neutralized the activity of artemin (P < 0.05). These data indicate that artemin is expressed in arteries, and its receptors are expressed and functional in the postganglionic sympathetic neurons that innervate them. This suggests that artemin may be a determinant of vascular sympathetic innervation.     

Foliar δ15N values characterize soil N cycling and reflect nitrate or ammonium preference of plants along a temperate grassland gradient

The natural abundance of stable (15)N isotopes in soils and plants is potentially a simple tool to assess ecosystem N dynamics. Several open questions remain, however, in particular regarding the mechanisms driving the variability of foliar delta(15)N values of non-N(2) fixing plants within and across ecosystems. The goal of the work presented here was therefore to: (1) characterize the relationship between soil net mineralization and variability of foliar Deltadelta(15)N (delta(15)Nleaf - delta(15)Nsoil) values from 20 different plant species within and across 18 grassland sites; (2) to determine in situ if a plant's preference for NO (3) (-) or NH (4) (+) uptake explains variability in foliar Deltadelta(15)N among different plant species within an ecosystem; and (3) test if variability in foliar Deltadelta(15)N among species or functional group is consistent across 18 grassland sites. Deltadelta(15)N values of the 20 different plant species were positively related to soil net mineralization rates across the 18 sites. We found that within a site, foliar Deltadelta(15)N values increased with the species' NO (3) (-) to NH (4) (+) uptake ratios. Interestingly, the slope of this relationship differed in direction from previously published studies. Finally, the variability in foliar Deltadelta(15)N values among species was not consistent across 18 grassland sites but was significantly influenced by N mineralization rates and the abundance of a particular species in a site. Our findings improve the mechanistic understanding of the commonly observed variability in foliar Deltadelta(15)N among different plant species. In particular we were able to show that within a site, foliar delta(15)N values nicely reflect a plant's N source but that the direction of the relationship between NO (3) (-) to NH (4) (+) uptake and foliar Deltadelta(15)N values is not universal. Using a large set of data, our study highlights that foliar Deltadelta(15)N values are valuable tools to assess plant N uptake patterns and to characterize the soil N cycle across different ecosystems.     

Fungi,a neglected component of acidophilic biofilms: do they have a potential for biotechnology?

Extremophiles - Fungi from extreme environments, including acidophilic ones, belong to biotechnologically most attractive organisms. They can serve as a source of enzymes and metabolites with...     

The evolution of preference strength under sensory bias: a role for indirect selection?

Evidence suggests that female preferences may sometimes arise through sensory bias, and that males may subsequently evolve traits that increase their conspicuousness to females. Here, we ask whether indirect selection, arising through genetic associations (linkage disequilibrium) during the sexual selection that sensory bias imposes, can itself influence the evolution of preference strength. Specifically, we use population genetic models to consider whether or not modifiers of preference strength can spread under different ecological conditions when female mate choice is driven by sensory bias. We focus on male traits that make a male more conspicuous in certain habitats-and thus both more visible to predators and more attractive to females-and examine modifiers of the strength of preference for conspicuous males. We first solve for the rate of spread of a modifier that strengthens preference within an environmentally uniform population; we illustrate that this spread will be extremely slow. Second, we used a series of simulations to consider the role of habitat structure and movement on the evolution of a modifier of preference strength, using male color polymorphisms as a case study. We find that in most cases, indirect selection does not allow the evolution of stronger or weaker preferences for sensory bias. Only in a "two-island" model, where there is restricted migration between different patches that favor different male phenotypes, did we find that preference strength could evolve. The role of indirect selection in the evolution of sensory bias is of particular interest because of ongoing speculation regarding the role of sensory bias in the evolution of reproductive isolation.     

Marine biodiversity and ecosystem functioning: what's known and what's next?

Marine ecosystems are experiencing rapid and pervasive changes in biodiversity and species composition. Understanding the ecosystem consequences of these changes is critical to effectively managing these systems. Over the last several years, numerous experimental manipulations of species richness have been performed, yet existing quantitative syntheses have focused on a just a subset of processes measured in experiments and, as such, have not summarized the full data available from marine systems. Here, we present the results of a meta‐analysis of 110 marine experiments from 42 studies that manipulated the species richness of organisms across a range of taxa and trophic levels and analysed the consequences for various ecosystem processes (categorised as production, consumption or biogeochemical fluxes). Our results show that, generally, mixtures of species tend to enhance levels of ecosystem function relative to the average component species in monoculture, but have no effect or a negative effect on functioning relative to the ‘highest‐ performing’ species. These results are largely consistent with those from other syntheses, and extend conclusions to ecological functions that are commonly measured in the marine realm (e.g. nutrient release from sediment bioturbation). For experiments that manipulated three or more levels of richness, we attempted to discern the functional form of the biodiversity–ecosystem functioning relationship. We found that, for response variables related to consumption, a power‐function best described the relationship, which is also consistent with previous findings. However, we identified a linear relationship between richness and production. Combined, our results suggest that changes in the number of species will, on average, tend to alter the functioning of marine ecosystems. We outline several research frontiers that will allow us to more fully understand how, why, and when diversity may drive the functioning of marine ecosystems. Synthesis The oceans host an incredible number and variety of species. However, human activities are driving rapid changes in the marine environment. It is imperative we understand ecosystem consequences of any associated loss of species. We summarized data from 110 experiments that manipulated species diversity and evaluated resulting changes to a range of ecosystem responses. We show that losing species, on average, decreases productivity, growth, and a myriad of other processes related to how marine organisms capture and utilize resources. Finally, we suggest that the loss of species may have stronger consequences for some processes than others.     

Attenuation of liver insoluble protein carbonyls: indicator of a longevity determinant?

Oxidative damage affects protein structure and function. Progressive accumulation of oxidized proteins is considered a putative mechanism of aging; however, empirical evidence supporting their role in aging is inconsistent. This inconsistency may reflect a failure to distinguish damage to particular cellular compartments. We found a significant reduction of protein carbonyls in the insoluble, but not in the soluble, fraction of liver tissues of long-lived compared with their short-lived counterpart. Of cellular components analyzed, only nuclear protein carbonyl level was uniformly reduced in long-lived compared with short-lived animals. This observation suggests that attenuated accumulation of protein carbonyls in the nucleus, where they can affect multiple aspects of gene expression and DNA repair, might contribute to the longevity in mammalian species.     

Direct and indirect effects of rats: does rat eradication restore ecosystem functioning of New Zealand seabird islands?

Introduced rats (Rattus spp.) can affect island vegetation structure and ecosystem functioning, both directly and indirectly (through the reduction of seabird populations). The extent to which structure and function of islands where rats have been eradicated will converge on uninvaded islands remains unclear. We compared three groups of islands in New Zealand: islands never invaded by rats, islands with rats, and islands on which rats have been controlled. Differences between island groups in soil and leaf chemistry and leaf production were largely explained by burrow densities. Community structure of woody seedlings differed by rat history and burrow density. Plots on islands with high seabird densities had the most non-native plant species. Since most impacts of rats were mediated through seabird density, the removal of rats without seabird recolonization is unlikely to result in a reversal of these processes. Even if seabirds return, a novel plant community may emerge.     

Glycerol: a neglected variable in metabolic processes?

Glycerol is a small and simple molecule produced in the breakdown of glucose, proteins, pyruvate, triacylglycerols and other glycerolipid, as well as release from dietary fats. An increasing number of observations show that glycerol is probably involved in a surprising variety of physiopathologic mechanisms. Glycerol has long been known to play fundamental roles in several vital physiological processes, in prokaryotes and eukaryotes, and is an important intermediate of energy metabolism. Despite some differences in the details of their operation, many of these mechanisms have been preserved throughout evolution, demonstrating their fundamental importance. In particular, glycerol can control osmotic activity and crystal formation and then act as a cryoprotective agent. Furthermore, its properties make it useful in numerous industrial, therapeutic and diagnostic applications. Few studies have focussed directly on glycerol, however, and while its metabolism is increasingly well documented, much of the details remain unknown. Considering the importance of glycerol in multiple vital physiological processes, its study could help unlock important physiopathological mechanisms.     

Influence of nitrate on uptake of ammonium by nitrogen-depleted soybean: is the effect located in roots or shoots?

In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom]plants that were subjected to 15 d of nitrogen deprivation inflowing hydroponic culture, concentrations of nitrogen declinedto 1.0 and 1.4mmol Ng^–1 dry weight in shoots and roots,respectively, and the concentration of soluble amino acids (determinedas primary amines) declined to 40µmol g^–1 dry weightin both shoots and roots. In one experiment, nitrogen was resuppliedfor 10 d to one set of nitrogen-depleted plants as 1.0 mol m^–3NH₄⁺ to the whole root system, to a second set as 0.5 mol m^–3NH₄⁺ plus 0.5 mol m^–3 NO₃^– to the whole root system,and to a third set as 1.0 mol m^–3 NH₄⁺ to one-half ofa split-root system and 1.0 mol m^–3 NO₃^– to theother half. In a second experiment, 1.0 mol m^–3 of nitrogenwas resupplied for 4 d to whole root systems in NH₄⁺ : NO₃^–ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintainedat pH 6.0. When NH₄⁺ was resupplied in combination with NO₃^– to thewhole root system in Experiment I, cumulative uptake of NH₄⁺for the 10 d of resupply was about twice as great as when NH₄⁺was resupplied alone. Also, about twice as much NH₄⁺ as NO₃^–was taken up when both ions were resupplied to the whole rootsystem. When NH₄⁺ and NO₃^– were resupplied to separatehalves of a split-root system, however, cumulative uptake ofNH₄⁺ was about half that of NO₃^–. The uptake of NH₄⁺,which is inhibited in nitrogen-depleted plants, thus is facilitatedby the presence of exogenous NO₃^–, and the stimulatingeffect of NO₃^– on uptake of NH₄⁺ appears to be confinedto processes within root tissues. In Experiment II, resupplyof nitrogen as both NH₄⁺ and NO₃^– in a ratio of either1:1 or 9:1 enhanced the uptake of NH₄⁺. The enhancement of NH₄⁺uptake was 1.8-fold greater when the NH₄⁺: NO₃^–-resupplyratio was 1:1 than when it was 9:1; however, only 1.3 timesas much NO₃^– was taken up by plants resupplied with the1 :1 exogenous ratio. The effect of NO₃^– on enhancementof uptake of NH₄⁺ apparently involves more than net uptake ofNO₃^– itself and perhaps entails an effect of NO₃^–uptake on maintenance of K⁺ availability within the plant. Theconcentration of K⁺ in plants declined slightly during nitrogendeprivation and continued to decline following resupply of nitrogen.The greatest decline in K⁺ concentration occurred when nitrogenwas resupplied as NH₄⁺ alone. It is proposed that decreasedavailability of K⁺ within the NH₄⁺-resup-plied plants inhibitedNH₄⁺ uptake through restricted transfer of amino acids fromthe root symplasm into the xylem. Key words: Ammonium, Glycine max, nitrate, nitrogen-nutrition, nitrogen stress, split-root cultures     

Governance options for science–policy interfaces on biodiversity and ecosystem services: comparing a network versus a platform approach

Science–policy-interfaces (SPIs) are expected to go beyond the linear model of scientific policy advice through creating spaces for exchange and dialogue between ‘policy’ and ‘knowledge’. Given that most environmental issues require inter- and transdisciplinary approaches, SPIs must take into account a variety of knowledge types, views and interests of scientists, policymakers and other decision makers. Moreover, acceptance and durability of SPIs depend largely on their perceived legitimacy and the credibility of their knowledge-gathering processes, providing additional challenges for their internal organisation. As the interplay between different knowledge types and decision making is far from neutral, a reflexive approach is required in the design of an SPI so that it is capable of learning from past experiences. The aim of this article is to discuss which governance arrangements could best support the development of an effective and legitimate SPI for European biodiversity politics. We analyse different options for facilitating the implementation of a ‘Network of Knowledge’ approach. This approach has been developed to improve the interface between diverse knowledge-holder communities and decision making processes for biodiversity and ecosystem services—a field where multi-scalar and multi-dimensional problems arise. In this article, we develop and discuss two stylized extreme governance models as our starting point: an `informal network model´, which almost entirely depends on the dedication of individuals, versus a more formalized `platform model´, predominantly based on the needs and interests of the organisations involved. We discuss the pros and cons of each of these models in reaching their objectives and in developing sound governing processes for a ‘Network of Knowledge’. From this discussion, we derive a recommended design for the reflexive governance of such a network in the context of the European Union and finish by discussing some more general lessons learnt.     

Plant–microbe interactions as drivers of ecosystem functions relevant for the biodegradation of organic contaminants

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