Are invasive species the drivers of ecological change?

Invasive species are widely accepted as one of the leading direct causes of biodiversity loss. However, much of the evidence for this contention is based on simple correlations between exotic dominance and native species decline in degraded systems. Although appealing, direct causality is not the only possible interpretation. A plausible alternative hypothesis is that exotic dominance could be the indirect consequence of habitat modification driving native species loss. In a new paper, MacDougall and Turkington now provide the first direct test of whether invasive species are the drivers of community change, or merely 'passengers' along for the environmental ride.     

Genome change in wheat observed through the structure and expression of α/β-gliadin genes

To better understand genome structure and the expression of α/β-gliadin multigenes in hexaploid wheat, bacterial artificial chromosome (BAC) clones containing α/β-gliadin genes from the three loci, Gli-A2, Gli-B2, and Gli-D2, were screened. Based on their restriction fragment patterns, we selected five BAC clones, namely, two clones for Gli-A2, two clones for Gli-B2, and one clone for Gli-D2, to fully sequence. Approximately 200 kb was sequenced for each locus. In total, twelve α/β-gliadin intact genes and four pseudogenes were found, and retrotransposons or other transposons existed in each BAC clone. Dot-plot analysis revealed the pattern of genome segmental duplication within each BAC. We calculated time since duplication of each set of α/β-gliadin genes and insertion of retrotransposons. Duplication of all adjacent genes within the same BAC clone took place before or after allotetrapolyploidization, but duplication of certain genes occurred before diploid differentiation of wheat species. Retrotransposons were also inserted before and after the segmental duplication events. Furthermore, translocation of α/β-gliadin genes from chromosomes 1 to 6 apparently occurred before the diversification of various wheat genomes. Duplication of genome segments containing α/β-gliadin genes and retrotransposons were brought about through unequal crossing-over or saltatory replication and α/β-gliadin genes per se were duplicated without any recombination events. Out of twelve intact α/β-gliadin genes detected from their sequences, nine were expressed, although their patterns of expression were distinct. Since they have similar cis-elements and promoter structures, the mechanisms underlying their distinct gene expression and possible applications are discussed.     

Why change a good thing? Revisiting the fleur-de-lis reconstruction of the breast

Although the latissimus flap is known for its simplicity and reliability, use of the fleur-de-lis pattern was plagued by undesirable T-shaped donor sites and small breast volumes in thin patients. We report a modified technique for optimal shaping of the standard latissimus with the successful application of a modified fleur-de-lis pattern. Because a "wet" tumescent infiltration was utilized and large amounts of subcutaneous fat were harvested, these changes permitted application to a wide variety of patients, with generous breast volumes reducing the size of the implant placed and resulting in excellent donor-site scars.This is a retrospective cohort study of 53 delayed or immediate reconstructions performed consecutively by the principal author (M.E.A.) on 48 patients at a university-based, urban hospital. Each case was analyzed between April of 1995 and February of 1999, with a follow-up from 2.5 to 44 months. All patients underwent injection of tumescent solution into the subcutaneous plane and harvest of large amounts of subcutaneous fat with the neurologically intact latissimus muscle. The last 25 reconstructions utilized the modified fleur-de-lis skin pattern, an inferiorly based vertical limb and replacement of skin deficiency in both axes.Of 11 perioperatively irradiated patients, none required skin grafting, whereas 6 percent of all native mastectomy flaps were grafted. There was one instance of minor distal tip flap necrosis in a nonirradiated patient. No implants became infected or were extruded. Donor sites were without wound complications and unveiled a 16 percent overall seroma rate.Through selective addition of harvested tissue, this modified technique, particularly the fleur-de-lis pattern, permits improved volume and projection in the inferior pole. The T-shaped donor-site closure is not only acceptable, but is also desirable, with reduced wound tension and minimization of dog-ear formation. With a relative paucity of complications, this conceptually ideal modification is technically simple and aesthetically comparable to our transverse rectus abdominis muscle flap results.     

Climate change: is the dark Soay sheep endangered?

It was recently reported that the proportion of dark-coloured Soay sheep (Ovis aries) in the Hebrides has decreased, despite the fact that dark sheep tend to be larger than lighter sheep, and there exists a selective advantage to large body size. It was concluded that an apparent genetic linkage between loci for the coat colour polymorphism and loci with antagonistic effects on body size explained the decrease. Those results explain why the proportion of dark animals is not increasing, but not why it is decreasing. Between 1985 and 2005 there was a significant increase in mean ambient temperature near the islands. We suggest that, while in the past a dark coat has offset the metabolic costs of thermoregulation by absorbing solar radiation, the selective advantage of a dark coat may be waning as the climate warms in the North Atlantic. In parallel, Bergman''s rule may be operating, reducing the selective advantage of large body size in the cold. Either or both of these mechanisms can explain the decrease in the proportion of dark-coloured larger sheep in this population in which smaller (and light-coloured) sheep should be favoured by their lower gross energy demand. If environmental effects are the cause of the decline, then we can expect the proportion of dark-coloured Soay sheep to decrease further.     

Metabolic pathways: does the actual Gibbs free-energy change affect the flux rate?

Energy dissipation fulfils an important function in metabolism driving the flux of matter through metabolic pathways. The flux rate is a multivariable function. One of such variables affecting the flux is the actual free energy change. A particular case of metabolic pathway is analysed to illustrate this fact, using only general enzymic and thermodynamic concepts.     

How does reorganization energy change upon protein unfolding? Monitoring the structural perturbations in the heme cavity of cytochrome c

In several classes of proteins the redox center provides an additional intrinsic biophysical probe that could be used to study the protein structure and function. In present report reorganization energy (lambda, as a parameter describing electron transfer properties) was used to study the protein structural changes around the heme prosthetic group in cytochrome c (cyt c). We attempted to monitor the value of this parameter upon the unfolding process of cyt c by urea, during which it was increased sigmoidally from about 0.52 to 0.82 eV for native and unfold protein, respectively. Results indicate that by structural changes in the heme site, lambda provides a complementary tool for following the unfolding process. Assuming a reversible two-state model for cyt c unfolding, Delta G(H2O), Cm and m values were determined to be 8.32+/-0.7 kcal mol(-1), 1.53+/-0.19 kcalmol(-1)M(-1) and 5.03 M, respectively.     

Mediterranean island biodiversity and climate change: the last 10,000 years and the future

Mediterranean islands (MI) are hotspots of global biodiversity and lie in one of the most susceptible to climate change (CC) areas of the world; a big challenge for any conservation strategy. In fact, there is already increasing evidence for CC in the region and associated biological responses in MI ecosystems. These include phenological changes and upward elevation shifts of species and plant communities; although evidence is frequently contrasting for different taxa. Threats are also evident, mainly for endemic species from most taxonomic groups, while communities in mountain and coastal regions are likely to be affected most. For MI conservation under CC additional factors need to be considered: (i) their position at the crossroads of three continents; with which they share common environmental characteristics, (ii) their great variability in sizes and topography and (iii) their climatic differences; with a clear west-east basin divide. CC synergies with changing tourist aspiration and agricultural practices will, in the medium term, modify island landscapes and provide further challenges for biodiversity conservation. Such a combined impact from CC, land-use change, fragmentation of habitats and tourism is difficult to predict. Furthermore, the limited space on islands (especially habitat availability and climatic range limitations) imposes a barrier to species range expansion. Thus, conservation of MI biodiversity under CC requires: (i) future research to focus on improved climate predictions linked to improved understanding of ecological (climate-biotic) responses, incorporating lessons learnt from (island) biogeography, (ii) specific adaptation measures for spatial planning and improvement in regional institutional capacities.     

Does the reduction of c heme trigger the conformational change of crystalline nitrite reductase?

The structures of nitrite reductase from Paracoccus denitrificans GB17 (NiR-Pd) and Pseudomonas aeruginosa (NiR-Pa) have been described for the oxidized and reduced state (Fül?p, V., Moir, J. W. B., Ferguson, S. J., and Hajdu, J. (1995) Cell 81, 369-377; Nurizzo, D., Silvestrini, M. C., Mathieu, M., Cutruzzolà, F., Bourgeois, D., Fül?p, V., Hajdu, J., Brunori, M., Tegoni, M., and Cambillau, C. (1997) Structure 5, 1157-1171; Nurizzo, D., Cutruzzolà, F., Arese, M., Bourgeois, D., Brunori, M., Cambillau, C. , and Tegoni, M. (1998) Biochemistry 37, 13987-13996). Major conformational rearrangements are observed in the extreme states although they are more substantial in NiR-Pd. The four structures differ significantly in the c heme domains. Upon reduction, a His17/Met106 heme-ligand switch is observed in NiR-Pd together with concerted movements of the Tyr in the distal site of the d1 heme (Tyr10 in NiR-Pa, Tyr25 in NiR-Pd) and of a loop of the c heme domain (56-62 in NiR-Pa, 99-116 in NiR-Pd). Whether the reduction of the c heme, which undergoes the major rearrangements, is the trigger of these movements is the question addressed by our study. This conformational reorganization is not observed in the partially reduced species, in which the c heme is partially or largely (15-90%) reduced but the d1 heme is still oxidized. These results suggest that the d1 heme reduction is likely to be responsible of the movements. We speculate about the mechanistic explanation as to why the opening of the d1 heme distal pocket only occurs upon electron transfer to the d1 heme itself, to allow binding of the physiological substrate NO2- exclusively to the reduced metal center.     

The enthalpy change for the reduction of nicotinamide–adenine dinucleotide

The heat of the reaction NAD(+)+propan-2-ol=NADH+acetone+H(+) was determined to be 42.5+/-0.6kJ/mol (10.17+/-0.15kcal/mol) from equilibrium measurements at 9-42 degrees C catalysed by yeast alcohol dehydrogenase. With the aid of thermochemical data for acetone and propan-2-ol the values of DeltaH=-29.2kJ/mol (-6.99kcal/mol) and DeltaG(0)=22.1kJ/mol (5.28kcal/mol) are derived for the reduction of NAD (NAD(+)+H(2)=NADH+H(+)). These values are consistent with analogous but less accurate data for the ethanol-acetaldehyde reaction. Thermodynamic data for the reduction of NAD and NADP are summarized.     

How does global change affect the strength of trophic interactions?

Recent research has generally shown that a small change in the number of species in a food web can have consequences both for community structure and ecosystem processes. However ‘change’ is not limited to just the number of species in a community, but might include an alteration to such properties as precipitation, nutrient cycling and temperature, all of which are correlated with productivity. Here we argue that predicted scenarios of global change will result in increased plant productivity. We model three scenarios of change using simple Lotka–Volterra dynamics, which explore how a global change in productivity might affect the strength of local species interactions and detail the consequences for community and ecosystem level stability. Our results indicate that (i) at local scales the average population size of consumers may decline because of poor quality food resources, (ii) that the strength of species interactions at equilibrium may become weaker because of reduced population size, and (iii) that species populations may become more variable and may take longer to recover from environmental or anthropogenic disturbances. At local scales interaction strengths encompass such properties as feeding rates and assimilation efficiencies, and encapsulate functionally important information with regard to ecosystem processes. Interaction strengths represent the pathways and transfer of energy through an ecosystem. We examine how such local patterns might be affected given various scenarios of ‘global change’ and discuss the consequences for community stability and ecosystem functioning.

Zusammenfassung

Die neuere Forschung hat im Allgemeinen gezeigt, dass eine kleine Veränderung in der Zahl der Arten in einem Nahrungsnetz sowohl Konsequenzen für die Gemeinschaftsstruktur als auch für die Ökosystemprozesse haben kann. „Wandel“ist jedoch nicht nur auf die Anzahl der Arten in einer Gemeinschaft beschränkt, sondern kann auch Veränderungen von Eigenschaften wie Niederschlag, Nährstoffkreisläufe und Temperatur beinhalten, die alle mit der Produktivität korreliert sind. Hier argumentieren wir, dass vorhergesagte Szenarios des globalen Wandels in einer erhöhten Pflanzenproduktivität resultieren werden. Wir modellieren drei Szenarien des Wandels unter der Verwendung einfacher Lotka–Volterra–Dynamiken, die erkunden, wie ein globaler Wandel in der Produktivität die Stärke von lokalen Arteninteraktionen beeinflusst, und wir beschreiben detailliert die Konsequenzen für die Gemeinschaft und die Stabilität des Ökosystemlevels. Unsere Ergebnisse deuten darauf hin, (i) dass auf einer lokalen Skala die durchschnittliche Populationsgröße der Konsumenten aufgrund der geringen Qualität der Nahrungsressourcen abnehmen könnte, (ii) dass die Stärke der Arteninteraktionen im Gleichgewicht aufgrund der reduzierten Populationsgröße schwächer werden könnte und (iii) dass die Populationen der Arten variabler werden und länger brauchen könnten, um sich von umweltbedingten oder anthropogenen Störungen zu erholen. Auf lokalen Skalen umfassen Interaktionsstärken Eigenschaften wie Fraßraten und Assimilationseffizienzen und enthalten wichtige funktionelle Information in Bezug auf Ökosystemprozesse. Interaktionsstärken repräsentieren die Energiewege und den Energietransfer in einem Ökosystem. Wir untersuchen, wie solche lokalen Muster unter der Voraussetzung verschiedener gegebener Szenarios des „globalen Wandels“beeinflusst werden könnten und diskutieren die Konsequenzen für die Gemeinschaftsstabilität und Ökosystemfunktion.     

The role of Quaternary environmental change in plant macroevolution: the exception or the rule?

The Quaternary has been described as an important time for genetic diversification and speciation. This is based on the premise that Quaternary climatic conditions fostered the isolation of populations and, in some instances, allopatric speciation. However, the 'Quaternary Ice-Age speciation model' rests on two key assumptions: (i) that biotic responses to climate change during the Quaternary were significantly different from those of other periods in Earth's history; and (ii) that the mechanisms of isolation during the Quaternary were sufficient in time and space for genetic diversification to foster speciation. These assumptions are addressed by examining the plant fossil record for the Quaternary (in detail) and for the past 410 Myr, which encompasses previous intervals of icehouse Earth. Our examination of the Quaternary record indicates that floristic responses to climate changes during the past 1.8 Myr were complex and that a distinction has to be made between those plants that were able to withstand the extremes of glacial conditions and those that could not. Generation times are also important as are different growth forms (e.g. herbaceous annuals and arborescent perennials), resulting in different responses in terms of genetic divergence rates during isolation. Because of these variations in the duration of isolation of populations and genomic diversification rates, no canonical statement about the predominant floristic response to climatic changes during the Quaternary (i.e. elevated rates of speciation or extinction, or stasis) is currently possible. This is especially true because of a sampling bias in terms of the fossil record of tree species over that of species with non-arborescent growth forms. Nevertheless, based on the available information, it appears that the dominant response of arborescent species during the Quaternary was extinction rather than speciation or stasis. By contrast, our examination of the fossil record of vascular plants for the past 410 Myr indicates that speciation rates often increased during long intervals of icehouse Earth (spanning up to 50 Myr). Therefore, longer periods of icehouse Earth than those occurring during the Quaternary may have isolated plant populations for sufficiently long periods of time to foster genomic diversification and allopatric speciation. Our results highlight the need for more detailed study of the fossil record in terms of finer temporal and spatial resolution than is currently available to examine the significance of intervals of icehouse Earth. It is equally clear that additional and detailed molecular studies of extant populations of Quaternary species are required in order to determine the extent to which these 'relic' species have genomically diversified across their current populations.     

Does scope for growth change as a result of salinity stress in the amphipod Gammarus oceanicus?

Physiological performance (feeding, metabolism, growth and excretion) across a broad range of salinity (5-30 psu) were determined for the benthic amphipod Gammarus oceanicus, a species of marine origin inhabiting brackish waters of the southern Baltic Sea. Feeding rates decreased with increasing salinity, whereas the nutritive absorption efficiency increased. Faeces production and ammonia excretion rates decreased strongly from the lowest to the highest salinity by 60% and 58%, respectively. Increasing salinity was accompanied by a reduction in the metabolic rate from 438 J g^− 1 dry wt d^− 1 (5.1 mW g^− 1) at 5 psu to 245 J g^− 1 (2.8 mW g^− 1) at 30 psu. Individuals were able to maintain a positive energy balance at all experimental salinities. The greatest values for scope for growth were recorded at the environmental salinity (7 psu) with a mean of 769 J g^− 1 dry wt d^− 1 (8.7 mW g^− 1).     

How fast could HIV change gene frequencies in the human population?

Infectious diseases have the potential to act as strong forces for genetic selection on the populations they affect. Human immunodeficiency virus (HIV) is a prime candidate to impose such genetic selection owing to the vast number of people it infects and the varying susceptibility of different human leucocyte antigen (HLA) types to HIV disease progression. We have constructed a model of HIV infection that differentiates between these HLA types, and have used reported estimates of the number of people infected with HIV and the different rates of progression to acquired immunodeficiency syndrome (AIDS) to provide a lower bound estimate on the length of time it would take for HIV to impose major genetic change in humans. We find that an HIV infection similar to that currently affecting sub-Saharan Africa could not yet have caused more than a 3 per cent decrease in the proportion of individuals who progress quickly to disease. Such an infection is unlikely to cause major genetic change (defined as a decrease in the proportion of quickly progressing individuals to under 50 per cent of their starting proportion) until 400 years have passed since HIV emergence. However, in very severely affected populations, there is a chance of observing such major genetic changes after another 50 years.     

Is the additional effort of renesting linked to a hormonal change in the common tern?

The production of and care for a replacement clutch can bear costs in terms of future reproduction or survival. However, renesting is quite common among seabirds and can contribute considerably to individual fitness. Prolactin and corticosterone are two hormones involved in the mediation of breeding behavior and, as they are linked to body condition or effort, it is of interest if these hormone values change during a second demanding breeding phase within a year. We compared baseline prolactin and corticosterone between the first and the renesting attempt in common terns (Sterna hirundo) on individual level. Therefore, in addition to control birds, 37 breeders were sampled during incubation of their first and their replacement clutch in 2008 and 2009. Blood samples were taken non-invasively by blood-sucking bugs. Prolactin level was lower during the renesting period, especially in birds which abandoned their clutch afterwards, whereas corticosterone did not change. Excluding the deserting birds, the reduced prolactin level was not linked to minor success, but could be related to seasonal processes. The control group of late laying common terns showed comparably low prolactin values, but increased corticosterone concentrations. Renesting individuals exhibited higher prolactin during incubation of their first clutch than non-renesting birds, probably indicating their higher quality. The fact that terns still have relatively high prolactin and low corticosterone values during renesting might confirm their higher quality and suggests that they are able to meet the costs of a second demanding breeding period without being considerably stressed.