Do changes in rainfall patterns affect semiarid annual plant communities?

Question: Climate change models forecast a reduction in annual precipitation and more extreme events (less rainy days and longer drought periods between rainfall events), which may have profound effects on terrestrial ecosystems. Plant growth, population and community dynamics in dry environments are likely to be affected by these changes since productivity is already limited by water availability. We tested the effects of reduced precipitation and fewer rain events on three semiarid plant communities dominated by annual species. Location: Three semiarid plant communities from Almería province (SE Spain). Methods: Rain‐out shelters were set up in each community and watering quantity and frequency were manipulated from autumn to early summer. Plant productivity, cover and diversity were measured at the end of the experimental period. Results: We found that a 50% reduction in watering reduced productivity, plant cover and diversity in all three communities. However, neither the 25% reduction in watering nor changes in the frequency of watering events affected these parameters. Conclusions: The lack of response to small reductions in water could be due to the identity and resistance of the plant communities involved, which are adapted to rainfall variability characteristic of arid environments. Therefore, a rainfall reduction of 25% or less may not affect these plant communities in the short term, although higher reductions or long‐term changes in water availability would probably reduce productivity and diversity in these communities.     

Do ectomycorrhizal fungi exhibit adaptive tolerance to potentially toxic metals in the environment ?

The effects of potentially toxic metals on ectomycorrhizal (ECM) fungi and their higher plant hosts are examined in this review. Investigations at a species and community level have revealed wide inter- and intraspecific variation in sensitivity to metals. Adaptive and constitutive mechanisms of ECM tolerance are proposed and discussed in relation to proven tolerance mechanisms in bacteria, yeasts and plants. Problems with methodology and research priorities are highlighted. These include the need for a detailed understanding of the genetic basis of tolerance in the ECM symbiosis, and for studies of ECM community dynamics in polluted sites.     

Do different portions of the boar ejaculate vary in their ability to sustain cryopreservation?

Previous studies have shown sperm quality post-cryopreservation differs depending on the fraction of the seminal plasma boar spermatozoa are fortuitously contained in. As such, spermatozoa contained in the first 10 mL of the sperm-rich fraction (portion I) have better sustained handling procedures (extension, handling and freezing/thawing) than those contained in the ulterior part of a fractionated ejaculate (second portion of the sperm-rich fraction and the post-spermatic fraction, portion II). However, those studies were performed using pooled samples. In the present study, individual ejaculates were used. Split ejaculates (portions I and II) from five boars were frozen and thawed using a conventional freezing protocol, followed by computer-assisted motility and morphology analysis (CASA and ASMA, respectively), as well as an Annexin-V assay for spermatozoa from each boar and ejaculate portion. Significant differences between portions were observed in all ASMA-derived variables, except in one boar. Also significant differences were observed between boars and ejaculate portions in sperm quality post-thaw. We identified, however, boars showing best results of motility and sperm membrane integrity post-thaw in portion I, while in other boar the best results was observed in portion II. It is concluded that the identification of the ejaculate portion more suitable to sustain cryopreservation in each individual boar may be a readily applicable and easy technique to diminish variation in sperm freezability among boars.     

Do haddock select habitats to maximize condition?

Haddock Melanogrammus aeglefinus in the North sea increased their distributional range when more abundant, but this density dependent habitat selection (DDHS) explained only a small part of the year‐on‐year variation in distribution patterns. The condition of haddock was examined at 24 sites in the North Sea in August and September 2004 and related to their abundance, to examine if the ideal free distribution theory (IFD), which assumes that organisms select habitats that maximize their rate of food intake, can be used to explain this variation in large scale distribution patterns. At a given temperature, condition (hepato‐somatic index, I _H) was better at stations where haddock were most abundant. Therefore, haddock were not distributed perfectly according to the IFD in 2004. The positive correlation between abundance and I _H, however, indicated there was some habitat selection by haddock, as in the total absence of habitat selection no correlation between I _H and abundance, and no spatial variation in abundance was expected. DDHS may only explain a small part of the yearly variation in the distribution because haddock did not equalize and maximize their fitness at the scale of the North Sea. In addition, stable isotope analysis of muscle samples showed that haddock did not avoid competition for food when at high abundance by feeding at a lower or wider range of trophic levels.     

Does the management of surrounding terrestrial habitats increase the tendency of odonates to leave aquatic habitats?

Generally, dragonflies and damselflies (odonates) are considered aquatic invertebrates. However, the ecological requirements of their adults are not different from those of fully, terrestrial insects. Surprisingly, there is a very little information on whether the management and structure of surrounding habitats has any influence on the diversity and seasonal dynamics of odonates. This is important to know because recently, a large proportion of freshwater habitats in Central Europe have becomes surrounded by intensively managed habitats. The aim of this study was to investigate the effects of different types of terrestrial habitats on their long-term utilization by dragonflies and damselflies. I assumed that this pattern varied over time; therefore, I used generalized additive mixed models to analyze the effects of management on seasonal changes in the abundance of individuals in terrestrial environments. From my results, it was evident that the management practices of surrounding terrestrial habitats had a significant impact on the population dynamics of dragonflies. The abundance of dragonfly adults in surrounding terrestrial habitats increased toward the end of the season. However, this was only, when the natal aquatic habitat was not affected by fish farming and was able to supply surrounding terrestrial habitats with offspring. This was evidenced by the fact that, compared to areas with extensive water management, in sites with fish farming, seasonal increases in abundance was negligible. There is no doubt that the structure of surrounding terrestrial habitats has a significant influence on the diversity of terrestrial invertebrates. However, we must not forget that terrestrial habitats, regardless of their management, are not able to replace the poor quality of the aquatic (natal) habitat. Interestingly, the abundance of damselflies decreased toward the end of the season, regardless of the management practices of the surrounding areas. This indicates that their dynamics is more controlled by time stress or other similar mechanisms than that of dragonflies.     

Do Great Tit Parus major parents gear their brood defence to the quality of their young?

Parental investment theory suggests that animals should increase their reproductive success by investing more heavily in higher-quality offspring than in lower-quality offspring. Great Tit Parus major nestlings of higher body weight have been shown to enjoy a higher survival rate after fledging. We examine for the first time whether Great Tit parents invest more heavily in heavier nestlings as measured by defence (six variables) against a Pygmy Owl Glaucidium perlatum, similar to G. passerinum, which is a predator of both adult and nestling birds including hole-nesters like the Great Tit. Thirty-two parent Great Tit pairs in a wood- and parkland study area in Essen-Stadtwald did not vary their antipredator behaviour in relation to nestling weight; between-brood variation of weight was similar to that found in different populations and in different years. However, parental defence behaviour varied, as expected, with parent's sex and nestling number, though overall responsivity of parents to many other independent variables appeared lower than found previously.     

Do female Drosophila melanogaster adaptively bias offspring sex ratios in relation to the age of their mate?

Modification of offspring sex ratios in response to parental quality is predicted when the long-term fitness returns of sons and daughters differ. One factor that may influence a mother's sex allocation decision is the quality (or attractiveness) of her mate. We investigated whether the sex ratios of offspring produced by female Drosophila melanogaster are biased with respect to the age of the males to which they are mated, and whether there is an adaptive basis for this phenomenon. We found that females mated to old males (13 d post-eclosion) initially produced a greater proportion of daughters than did females mated to young males (1 d post-eclosion). This pattern does not appear to be due to a systematic difference in the numbers or mortality of the X- and Y-bearing sperm originating from old and young fathers, as the overall sex ratios of all offspring produced from a single copulation did not differ between broods fathered by the two types of males. The sons of older males fared worse in competitive mating assays than did the sons of younger males, while daughters of old and young males were of comparable fitness. These results suggest that there is an adaptive basis for the observed sex ratio modification.     

Do spider diversity and assemblages change in different contiguous habitats? A case study in the protected habitats of the humid chaco ecoregion, northeast Argentina

Spiders are a megadiverse group that can be useful indicators of the overall species richness and health of biotic communities. The spider diversity in subtropical forests of the Neotropical region are not yet well known, especially in Argentinean subtropical forests where systematic fieldwork has not been done until recently. The Great Chaco is very important as the unique dry subtropical forest of the earth, but it is suffering increasing degradation by the advance of agriculture. Spider communities have been shown to be more directly influenced by vegetation architecture than vegetation species composition. In this study, we aim to assess whether spider diversity and assemblages change in adjacent habitats with different types of vegetation. We compare the diversity and spider assemblages in two different contiguous protected habitats (hygrophilous woodland and savannah parkland) of the Mburucuyá National Park, (Humid Chaco ecoregion). Seasonal samples were obtained using three types of sampling methods: pitfall trapping, beating, and manual litter extraction. The spider assemblages were different in the studied areas, and the abundance, diversity, evenness, and species richness were higher in the hygrophilous woodland than the savannah parkland. These differences in spider diversity and assemblages indicate that both types of habitats are important if the biodiversity is to be conserved in the Chaco ecoregion, where different types of habitat are shown as a patchy distribution.     

Do species of invaded communities differ in their vulnerability to being eliminated by the dominant alien plants?

Invasions are associated with loss of diversity and changes in species composition. This study aims to provide evidence if this loss happens at random or if the loss is related to functional traits of native species. Traits of species in communities dominated by 13 plants alien to Central Europe were compared to those found in the adjacent uninvaded vegetation. There is a weak but significant non-random pattern in the distribution of traits between the invaded and adjacent uninvaded vegetation. For example, species possessing a taproot, annuals but also juveniles of trees tend to be proportionally more abundant in the invaded vegetation, suggesting they are impacted less than species with high clonal index, perennial polycarpic species and species without a taproot, which are proportionally more represented in the uninvaded vegetation. Fast laterally spreading species, trees’ juveniles and woody species in general are proportionally more frequent in the invaded vegetation, while biennials, slow laterally spreading species but also shrubs are proportionally more frequent in the uninvaded vegetation. Juveniles of trees may compete successfully with the aliens due to being adapted to thrive in low light conditions. Annuals may thrive in the invaded communities by possessing a life strategy different from most of the selected aliens. Possessing a taproot appears to be another trait important for the successful coexistence with the dominant invasive aliens, possibly pointing to the importance of underground competition. Clonal perennial polycarpic herbs are species functionally most similar to most of the selected aliens, and these species were found to be most underrepresented in the invaded vegetation.     

Do enzymes bind their substrates in the ground state because of a physico-chemical requirement?

Transition state theory has provided no convincing explanation for the nearly universal observation of complexes of enzymes with substrates. Bimolecular catalytic reactions are assumed here to take place through reactive encounter complexes defined as the subset of reactant state species able to proceed directly to low lying energy levels at the transition state. By assessing the probability of these complexes from the maximum efficiency of intramolecular reactions, an upper limit for the rate constants promoted by hypothetical catalysts unable to bind substrates is deduced. This limit, which is below the ordinary range of bimolecular rate constants (k(cat)/K(M)) for enzyme reactions, results from a kinetic limitation in the formation of reactive encounter complexes. Exceeding this limit requires a stabilization of these complexes. Using the terminology of transition state theory, the need for enzymes to form complexes with substrates is then expressed as a necessity to restore Boltzmann distribution at the transition state.     

Do Evolutionary Changes in Astrocytes Contribute to the Computational Power of the Hominid Brain?

It is now well accepted that astrocytes are essential in all major nervous system functions of the rodent brain, including neurotransmission, energy metabolism, modulation of blood flow, ion and water homeostasis, and, indeed, higher cognitive functions, although the contribution of astrocytes in cognition is still in early stages of study. Here we review the most current research findings on human astrocytes, including their structure, molecular characterization, and functional properties. We also highlight novel tools that have been established for translational approaches to the comparative study of astrocytes from humans and experimental animals. Understanding the differences in astrocytes is essential to elucidate the contribution of astrocytes to normal physiology, cognitive processing and diverse pathologies of the central nervous system.     

Do distantly related parasites rely on the same proximate factors to alter the behaviour of their hosts?

Phylogenetically unrelated parasites often increase the chances of their transmission by inducing similar phenotypic changes in their hosts. However, it is not known whether these convergent strategies rely on the same biochemical precursors. In this paper, we explored such aspects by studying two gammarid species (Gammarus insensibilis and Gammarus pulex; Crustacea: Amphipoda: Gammaridae) serving as intermediate hosts in the life cycle of two distantly related parasites: the trematode, Microphallus papillorobustus and the acanthocephalan, Polymorphus minutus. Both these parasite species are known to manipulate the behaviour of their amphipod hosts, bringing them towards the water surface, where they are preferentially eaten by aquatic birds (definitive hosts). By studying and comparing the brains of infected G. insensibilis and G. pulex with proteomics tools, we have elucidated some of the proximate causes involved in the parasite-induced alterations of host behaviour for each system. Protein identifications suggest that altered physiological compartments in hosts can be similar (e.g. immunoneural connexions) or different (e.g. vision process), and hence specific to the host-parasite association considered. Moreover, proteins required to alter the same physiological compartment can be specific or conversely common in both systems, illustrating in the latter case a molecular convergence in the proximate mechanisms of manipulation.     

Do evolutionary changes in cytochrome c structure reflect functional adaptations?

Following the demonstration that the rate of evolutionary change in the amino acid sequences of cytochromes c of eukaryotic species was not constant either for a single line of phylogenetic descent during different evolutionary intervals or for separate lines of descent, the concept that neutral mutations account for the vast majority of the evolutionary variations could no longer be accepted. Previous studies had shown that all eukaryotic cytochromes c tested appeared to be functionally indistinguishable in their reaction with mitochondrial respiratory chain components. However, an examination of the kinetics at low ionic strength led to the discovery of a high affinity reaction of cytochrome c with cytochrome c oxidase that revealed large differences in activity between the cytochromes of the horse, baker's yeast and the protist Euglena. Observed Km values for this reaction of 10(-7) to 10(-8) M appear to represent actual dissociation constants, as demonstrated by direct binding studies of cytochrome c with purified cytochrome c oxidase. The high affinity reaction is sensitive to ionic strength and inhibited by ADP and ATP in the range of physiological concentrations, ATP being three times as effective as ADP. The possibility is discussed that this effect of ATP on cytochrome c binding to its oxidase could provide the basis of a mechanism for mitochondrial respiratory control. The demonstration of differences between cytochrome c of various species in this kinetic system opens the way to a systematic study of the possible evolutionary adaptations of cytochromes c to their oxidases.     

Do differences in understory light contribute to species distributions along a tropical rainfall gradient?

In tropical forests, regional differences in annual rainfall correlate with differences in plant species composition. Although water availability is clearly one factor determining species distribution, other environmental variables that covary with rainfall may contribute to distributions. One such variable is light availability in the understory, which decreases towards wetter forests due to differences in canopy density and phenology. We established common garden experiments in three sites along a rainfall gradient across the Isthmus of Panama in order to measure the differences in understory light availability, and to evaluate their influence on the performance of 24 shade-tolerant species with contrasting distributions. Within sites, the effect of understory light availability on species performance depended strongly on water availability. When water was not limiting, either naturally in the wetter site or through water supplementation in drier sites, seedling performance improved at higher light. In contrast, when water was limiting at the drier sites, seedling performance was reduced at higher light, presumably due to an increase in water stress that affected mostly wet-distribution species. Although wetter forest understories were on average darker, wet-distribution species were not more shade-tolerant than dry-distribution species. Instead, wet-distribution species had higher absolute growth rates and, when water was not limiting, were better able to take advantage of small increases in light than dry-distribution species. Our results suggest that in wet forests the ability to grow fast during temporary increases in light may be a key trait for successful recruitment. The slower growth rates of the dry-distribution species, possibly due to trade-offs associated with greater drought tolerance, may exclude these species from wetter forests.     

Do plants adjust their sex allocation and secondary sexual morphology in response to their neighbours?

Background and aims

Changes in the sex allocation (i.e. in pollen versus seed production) of hermaphroditic plants often occur in response to the environment. In some homosporous ferns, gametophytes choose their gender in response to chemical cues sent by neighbours, such that spores develop as male gametophytes if they perceive a female or hermaphrodite nearby. Here it is considered whether a similar process might occur in the androdioecious angiosperm species Mercurialis annua, in which males co-occur with hermaphrodites; previous work on a Spanish population of M. annua found that individuals were more likely to develop as males at high density.

Methods

Using a novel approach to treat plants with leachate from pots containing males or hermaphrodites of M. annua, the hypothesis that individuals assess their mating opportunities, and adjust their sex expression accordingly, was tested through an exchange of chemical cues through the soil.

Key Results

For the population under study, from Morocco, no evidence was found for soil-signal-dependent sex expression: neither sex ratios nor sex allocation differed among experimental treatments.

Conclusions

The results imply either that the Moroccan population under study behaves differently from that previously studied in Spain (pointing to potential geographical variation in plasticity for sex expression), or that our method failed to capture the signals used by M. annua for adjustment of sex expression.