Sex-biased survival and philopatry in birds: Do they interact?

A review of studies of sex-biased dispersal and philopatry and sex-biased survival in birds is presented. The comparison between sex-related mortality and natal and breeding dispersal at the species-level shows that dispersing birds (mainly females) suffer higher mortality, while philopatric birds (mainly males) have higher survival. The interaction between sex-biased survival and spatial behavior is a crucial component of avian vital strategy, which determine population dynamics and genetic structure.     

Do nutrients and invertebrate herbivory interact in an artificial plant community?

The addition of nutrients has been shown to decrease the species richness of plant communities. Herbivores feed on dominant plant species and should release subdominant species from competitive exclusion at high levels of nutrient availability with a severe competitive regime. Therefore, the effects of nutrients and invertebrate herbivory on the structure and diversity of plant communities should interact. To test this hypothesis, we used artificial plant communities in microcosms with different levels of productivity (applying fertilizer) and herbivory (adding different numbers of the snail, Cepaea hortensis, and the grasshopper, Chorthippus parallelus). For analyses, we assigned species to three functional groups: grasses, legumes and (non-leguminous) herbs. With the addition of nutrients aboveground biomass increased and species richness of plants decreased. Along the nutrient gradient, species composition shifted from a legume-dominated community to a community dominated by fast-growing annuals. But only legumes showed a consistent negative response to nutrients, while species of grasses and herbs showed idiosyncratic patterns. Herbivory had only minor effects, and bottom–up control was more important than top–down control. With increasing herbivory the biomass of the dominant plant species decreased and evenness increased. We found no interaction between nutrient availability and invertebrate herbivory. Again, species within functional groups showed no consistent responses to herbivory. Overall, the use of the functional groups grasses, legumes and non-leguminous herbs was of limited value to interpret the effects of nutrients and herbivory during our experiments.     

Do yeasts and Drosophila interact just by chance?

The fruit fly Drosophila melanogaster and the baker's yeast Saccharomyces cerevisiae are classic research model organisms that are also associated in nature, at least around vineyards. Sharing the same ephemeral fruit niche, winged Drosophila feed on immotile yeasts. That a yeast diet is essential for larval development, and that saprophagous fruit flies are attracted to a suite of yeast volatiles, has been well established over the last century. Recently, research has focussed on the potential mutual benefit of this interaction hypothesising yeasts also benefit via dispersal from ephemeral fruits. It now appears that the concept of a co-evolved mutualism between yeasts and Drosophila has permeated the literature. However, until robust evidence regarding the evolution and maintenance of this yeast-fly association has been provided, we suggest there is no compelling evidence to reject the more simplistic null hypothesis that these interactions are due to exaptation, and not a mutualism driven by natural selection.     

Are rodents a source of biotic resistance to tree invasion in Pampean grasslands? Tree seed consumption under different conditions

Biotic resistance has been invoked as a major barrier to woody species invasion, although the role of resident generalist consumers and their interaction with seed availability in a local community has received little attention. We assessed tree seed consumption by rodents under two different scenarios: (i) We documented in field spatio‐temporal patterns of seed predation by native rodents on two exotic tree species, Gleditsia triacanthos or ‘honey locust’ and Robinia pseudoacacia or ‘white locust’ (family Leguminosae), in five grassland habitats of the Inland Pampa, Argentina. (ii) We conducted laboratory feeding trials to evaluate tree seed consumption in the presence (cafeteria‐style feeding trials) and in the absence (non‐choice feeding trials) of alternative food supplies. Seed predation was generally higher for Robinia than for Gleditsia seeds, both in field and laboratory conditions. For both tree species, seed predation varied between habitats and seasons and was higher in the native tussock grassland than in the remaining studied communities, whereas the crop field showed the lowest levels of consumption along with the absence of captured rodents. Seed consumption of Gleditsia and Robinia among the four grassland communities (which did not differ in rodent abundance) was negatively associated with the availability of alternative food. Laboratory feeding trials showed a higher consumption of Gleditsia seeds in the non‐choice than in the cafeteria‐style feeding trials, while the consumption of Robinia seeds did not differ in the absence or presence of alternative seeds. These patterns indicate that the contribution of resident granivores to invasion resistance might depend on colonizer species identity, recipient community type and season of the year. We suggest that rodent preferences for different invader seeds will interact with the availability of alternative food in the local habitat in influencing the amount of predator‐mediated biotic resistance to invasion.     

Do coinage metal anions interact with substituted benzene derivatives?

The nature of the anion–π interaction has been investigated by carrying out ab initio calculations of the complexes of coinage metal anions (Au^?, Ag^?, and Cu^?) with different kinds of π-systems. The binding energies indicate that gold anion has the highest and copper anion has the lowest affinity for interactions with π-systems. Different aspects of the anion–π interaction in these systems have been investigated, including charge-transfer effects (using the Merz–Kollman method), “atoms-in-molecules” (AIM) topological parameters, and interaction energies (using energy decomposition analysis, EDA). Our results indicated that, for most M^?···π interactions, the electrostatic term provides the dominant contribution, whereas polarization, charge transfer, and dispersion effects contribute less than 25 % of the interaction. We believe that the present results should lead to a greater understanding of the basis for anion–π interactions of coinage metal anions.     

Do symplasmic networks in cambial zones correspond with secondary growth patterns?

The plasmodesmal (PD) network in the cambial zone of Arabidopsis thaliana hypocotyls was analysed using electron microscopy and dye-coupling studies and compared to those of internodes of Populus nigra and Solanum lycopersicum. In all species, PD densities and frequencies undergo alterations in topologically successive cambial walls reflecting species-specific patterns of PD degradation and PD insertion during cell development. Longitudinal PD fission is responsible for an abrupt increment of PD numbers in specific walls of the youngest derivatives at the xylem and/or phloem side. Here, PDs seem to mediate positional signalling to control tissue fate and early cell determination. PD numbers at all cambial interfaces of A. thaliana correspond to those of the herbaceous tomato, but are higher with the woody poplar. This suggests a positive correlation between PD frequencies and the rapidity of cell division activity. Photoactivated green fluorescent protein (26 kDa) did not diffuse through cambial PDs of A. thaliana. This is in keeping with the common size exclusion limit (SEL) of 8–10 kDa observed for PDs at the youngest interfaces of tomato and poplar which may mediate diffusive exchange of developmental signals of equal molecular size. The regular growth patterns in internodal cambial zones of poplar and tomato result from synchronized cell division activity of neighbouring initials. A. thaliana hypocotyls have an irregular mode of secondary growth. Here, signalling through PDs in misaligned radial walls between non-homologous derivatives may control tissue development. The observed organizational differences between the cambia cast doubts on the suitability of A. thaliana as a model plant for cambial research.     

Divergent small-scale spatial patterns in New?Zealand?s short tussock grasslands

>Spatial studies of ecology rarely look at small-scale spatial community organisation within multiple plots on multiple sites therefore it is difficult to draw conclusions that can be generalised. We hypothesised that small-scale spatial patterns of Festuca tussock grasslands should be consistent within a site and between various sites because their functional ecology is likely to be similar. Tussocks were mapped in 15 plots ranging in size from 56 to 400 m² spread over four sites. Ripley's K, inhomogeneous Ripley?s K and inhomogeneous pair correlation functions were implemented to detect patterns of aggregation, regularity and not significantly different from random at scales up to 300 cm. While Ripley?s K indicated a general trend of regularity up to small scales (c.?20?cm) and aggregation up to larger scales (>40?cm), these patterns were not upheld by the inhomogeneous Ripley?s K and inhomogeneous pair correlation function analyses, which did not yield consistent patterns. Our results suggest that within- and between-site variation of spatial patterns cannot be assumed to be consistent.     

Does disturbance affect bud bank size and belowground structures diversity in Brazilian subtropical grasslands?

Brazilian Campos grasslands are ecosystems under high frequency of disturbance by grazing and fires. Absence of such disturbances may lead to shrub encroachment and loss of plant diversity. Vegetation regeneration after disturbance in these grasslands occurs mostly by resprouting from belowground structures. We analyzed the importance of bud bank and belowground bud bearing organs in Campos grasslands. We hypothesize that the longer the intervals between disturbances are, the smaller the size of the bud bank is. Additionally, diversity and frequency of belowground organs should also decrease in areas without disturbance for many years. We sampled 20 soil cores from areas under different types of disturbance: grazed, exclusion from disturbance for two, six, 15 and 30 years. Belowground biomass was sorted for different growth forms and types of bud bearing organs. We found a decrease in bud bank size with longer disturbance intervals. Forbs showed the most drastic decrease in bud bank size in the absence of disturbance, which indicates that they are very sensitive to changes in disturbance regimes. Xylopodia (woody gemmiferous belowground organs with hypocotyl-root origin) were typical for areas under influence of recurrent fires. The diversity of belowground bud bearing structures decreased in the absence of disturbance. Longer intervals between disturbance events, resulting in decrease of bud bank size and heterogeneity of belowground organs may lead to the decline and even disappearance of species that relay on resprouting from the bud bank upon disturbance.     

Do local processes scale to global patterns? The role of drought and the species pool in determining treehole insect diversity

Global patterns in community species richness may represent limitations operating at the local scale, such as competitive exclusion and habitat suitability, or, in the case of unsaturated communities, limitations to the species pool of biogeographic regions. Separating the effects of local and regional processes on community richness requires combining small-scale experiments with broad surveys. I examine limitations to the number of aquatic insect species per treehole at the scale of a single woodland, and between eight biogeographic regions. Variation in species richness at the woodland scale can largely be explained by small-scale differences between treeholes in drought disturbance, as shown for British treehole insects for 2 years. At the global scale, drought disturbance is a relatively poor predictor of patterns in the local richness of treehole mosquitoes. Instead, regional differences in the species pool explain most of the variation in local mosquito richness. Treeholes in at least the most species-poor regions appear to be unsaturated with mosquito species. In this system, therefore, local processes do not necessarily scale to global patterns.     

Do changes in DNA methylation mediate or interact with SNP variation? A pharmacoepigenetic analysis

Background

In studies with multi-omics data available, there is an opportunity to investigate interdependent mechanisms of biological causality. The GAW20 data set includes both DNA genotype and methylation measures before and after fenofibrate treatment. Using change in triglyceride (TG) levels pre- to posttreatment as outcome, we present a mediation analysis that incorporates methylation. This approach allows us to simultaneously consider a mediation hypothesis that genotype affects change in TG level by means of its effect on methylation, and an interaction hypothesis that the effect of change in methylation on change in TG levels differs by genotype. We select 322 single-nucleotide polymorphism–cytosine-phosphate-guanine (SNP-CpG) site pairs for mediation analysis on the basis of proximity and marginal genome-wide association study (GWAS) and epigenome-wide association study (EWAS) significance, and present results from the real-data sample of 407 individuals with complete genotype, methylation, TG levels, and covariate data.

Results

We identified 3 SNP-CpG site pairs with significant interaction effects at a Bonferroni-corrected significance threshold of 1.55E-4. None of the analyzed sites showed significant evidence of mediation. Power analysis by simulation showed that a sample size of at least 19,500 is needed to detect nominally significant indirect effects with true effect sizes equal to the point estimates at the locus with strongest evidence of mediation.

Conclusions

These results suggest that there is stronger evidence for interaction between genotype and methylation on change in triglycerides than for methylation mediating the effect of genotype.

     

Do electromagnetic fields interact with electrons in the Na,K‐ATPase?

The effects of low frequency electric and magnetic fields on several biochemical systems, including the Na,K-ATPase, indicate that electromagnetic (EM) fields interact with electrons. The frequency optima for two enzymes in response to EM fields are very close to their turnover numbers, suggesting that these interactions directly affect reaction rates. Nevertheless, generally accepted ideas about Na,K-ATPase function and ion transport mechanisms do not consider interactions with electrons. To resolve the clash of paradigms, we hypothesize interaction with transient electrons and protons that arise from flickering of H-bonds in the hydrated protein. These transient charges in the enzyme could provide a trigger for the sequence of conformation changes that are part of the ion transport mechanism. If the distributions of transient electrons and protons in the membrane are affected by their concentration and the membrane potential, as expected from electric double layer theory, this can account for the different effects of low frequency electric and magnetic fields, as well as for the observation that membrane hyperpolarization reverses the ATPase reaction to generate ATP.     

Why some species cannot colonise restored habitats? The effects of seed and microsite availability

Restoration of calcareous grasslands was promoted as a conservation strategy to reduce the risks imposed by habitat loss and fragmentation. Restoration already provided promising results for several taxa, however some specialist species still fail at colonising restored habitats. We aimed at explaining this lack of colonisation success for three calcareous grasslands specialist species in southern Belgium: Pulsatilla vulgaris; Trifolium montanum; and, Veronica prostrata. We studied: (i) germination in control and outdoor conditions (cold, heat, smoke and litter effects); (ii) in situ seedling emergence patterns (effects of seed addition and germination microsites availability). The three species were able to germinate in Petri dishes in the absence of treatment. Cold enhanced the germination of V. prostrata. Fire-related treatments (heat shock and smoke exposure) did not enhance germination and were deleterious to V. prostrata. Litter cover improved P. vulgaris emergence in outdoor containers, but had a negative effect on V. prostrata. In the field, V. prostrata did not emerge. T. montanum seedlings were observed in the reference grasslands when seeds were added, but not in the restored grasslands. P. vulgaris emerged in the reference grasslands, and to a lower degree in the restored grasslands. The combination of seed addition and microsites availability for seed germination resulted in enhanced seedling emergence for P. vulgaris. Our results suggest that seed and microsite availability can be limiting factors for site colonisation, but the combination of both is likely much more limiting. Lower seedling emergence in restored than in reference grasslands suggests a lower habitat quality in restored grasslands.     

Gene expression patterns in seed plant shoot meristems and leaves: homoplasy or homology?

The fossil record reveals that seed plant leaves evolved from ancestral lateral branch systems. Over time, the lateral branch systems evolved to become determinate, planar and eventually laminar. Considering their evolutionary histories, it is instructive to compare the developmental genetics of shoot apical meristems (SAMs) and leaves in extant seed plants. Genetic experiments in model angiosperm species have assigned functions of meristem maintenance, specification of stem cell identity, boundary formation, polarity establishment and primordium initiation to specific genes. Investigation of roles of the same or homologous genes during leaf development has revealed strikingly similar functions in leaves compared to SAMs. Specifically, the marginal blastozone that characterizes many angiosperm leaves appears to function in a manner mechanistically similar to the SAM. We argue here that the similarities may be homologous due to descent from ancestral roles in an ancestral shoot system. Molecular aspects of SAM and leaf development in gymnosperms is largely neglected and could provide insight into seed plant leaf evolution.     

Biotic resistance to plant invasion in grassland: Does seed predation increase with resident plant diversity?

Seed predation impacts heavily on plant populations and community composition in grasslands. In particular, generalist seed predators may contribute to biotic resistance, i.e. the ability of resident species in a community to reduce the success of non-indigenous plant invaders. However, little is known of predators’ preferences for seeds of indigenous or non-indigenous plant species or how seed predation varies across communities. We hypothesize that seed predation does not differ between indigenous and non-indigenous plant species and that seed predation is positively related to plant species diversity in the resident community. The seed removal of 36 indigenous and non-indigenous grassland species in seven extensively or intensively managed hay meadows across Switzerland covering a species-richness gradient of 18–50 plant species per unit area (c. 2 m²) was studied. In mid-summer 2011, c. 24,000 seeds were exposed to predators in Petri dishes filled with sterilized soil, and the proportions of seeds removed were determined after three days’ exposure. These proportions varied among species (9.2–62.5%) and hay meadows (17.8–48.6%). Seed removal was not related to seed size. Moreover, it did not differ between indigenous and non-indigenous species, suggesting that mainly generalist seed predators were active. However, seed predation was positively related to plant species richness across a gradient in the range of 18–38 species per unit area, representing common hay meadows in Switzerland. Our results suggest that generalist post-dispersal seed predation contributes to biotic resistance and may act as a filter to plant invasion by reducing the propagule pressure of non-local plant species.     

Pollen availability,seed production and seed predator clutch size in a tephritid—thistle system

Summary We develop a simple model explaining clutch size behaviour ofOrellia ruficauda on its principle host in North America,Cirsium arvense. Offspring of flies feed solely on thistle seeds and seed production is pollen-limited. Thus, female flies risk reduced offspring fitness when committing large clutches to hosts (female flower heads) occurring in localities where male plants are locally absent. We therefore predict that attacked hosts will contain fewer eggs in such localities, a prediction that is consistent with data obtained in the field: large clutches are never laid in flower heads in low-pollination localities. However, larvae reared from such low-quality hosts are significantly smaller on average and will therefore carry smaller egg loads as adults. Small clutches in poor-quality hosts may thus be an expression of lower per-adult fecundity. Nevertheless, sufficient numbers of large, fecund flies are produced in low-pollination localities to make this last explanation less convincing.     

Is fire a selective force of seed size in pine species?

Fire is selectively shaping most of the traits of plants growing in fire-prone environments. However, seed size and other features related to seed production have not been studied in the light of the evolutionary role of fire. Our research tests the hypothesis that larger seeds have a higher chance of surviving wildfires and produce more vigorous seedlings with a lower death rate. To test this hypothesis the germination and early seedling growth of five Spanish pine species were studied. Weight, length and width of all seeds were measured. The biomass (fresh and dry weight) and length (root and total) of subsequent seedlings were also measured after 30 d from emergence. Seeds were submitted to elevated temperatures for periods in which the chance of survival was 50 % (calculated by means of a logistic model for each pine species). The differences observed among species suggests that fire may be adaptively shaping seed size in pines with larger seeds (Pinus canariensis and P. pinaster), because larger seeds are more likely to survive after heat shocks. Furthermore, in P. canariensis, seedlings after heat treatment are even larger than those submitted to control. In P. halepensis, despite being well adapted to fire, our results indicated no relationships between fire and seed characteristics. Finally, although heat treatment has a general adverse effect on seedling growth in the case of the two subalpine pines, we have detected a positive relationship between seed size and seedling growth but only in the largest seeds. This might also suggest the relevance of fire as a selective force for these pines which is outperformed by the relevance of dispersal and emergence time as adaptive traits in the post-fire scenario.