Is cell-mediated immunity related to the evolution of life-history strategies in birds?

According to life-history theory, the development of immune function should be balanced through evolutionary optimization of the allocation of resources to reproduction and through mechanisms that promote survival. We investigated interspecific variability in cell-mediated immune response (CMI), as measured by the phytohaemagglutinin (PHA) assay, in relation to clutch size, longevity and other life-history traits in 50 species of birds. CMI exhibited significant repeatability within species, and PHA responses in chicks were consistently stronger than in adults. Univariate tests showed a variety of significant relationships between the CMI of both chicks and adults with respect to size, development period and lifespan, but not clutch size or prevalence of blood parasites in adults. Multivariate analyses confirmed these patterns but independent variables were too highly correlated to isolate unique influences on CMI. The positive relationship of chick CMI to nestling period is further complicated by a parallel relationship of chick CMI to the age at testing. However, multivariate analysis showed that chick CMI varies uniquely with length of the nestling period. Adult CMI was associated with a strong life-history axis of body size, development rate and longevity. Therefore, adult CMI may be associated with prevention and repair mechanisms related to long lifespan, but it also may be allometrically related to body size through other pathways. Neither chick CMI nor adult CMI was related to clutch size, contradicting previous results linking parasite-related mortality to CMI and the evolution of clutch size (reproductive investment) in birds.     

Do migratory pathways affect the regional abundance of wintering birds? A test in northern Spain

Aim The abundance distribution of organisms at regional scales is commonly interpreted as the result of spatial variation in habitat suitability. However, the possibility that geography itself may affect patterns of distribution has received less attention. For example, the abundance of wintering bird populations might be influenced by the cost of reaching areas located far away from the main migratory pathways. We studied the abundance distribution of three common migratory passerines (meadow pipits, Anthus pratensis; common chaffinches, Fringilla coelebs; and European robins, Erithacus rubecula) wintering in farmlands located in the 600‐km long Cantabrian coastal sector of northern Spain, roughly perpendicular to the west Pyrenean migratory pathway that drives European migrant birds into the Iberian Peninsula. Location The study area occupies a belt located between the Atlantic coast and the Cantabrian Mountains in northern Spain. Methods We counted wintering and breeding birds and measured the structure of vegetation and environmental variables (altitude, rainfall, temperature) in 68 farmlands distributed at different distances from the west Pyrenean migratory flyway. We also studied the distribution of birds ringed in central and northern Europe and recovered in the study area between October and February. Analyses were based on single univariate statistics (chi‐square tests), ordination by principal components analysis and multiple regression. Results Controlling for the effects of climate, vegetation structure and local abundance of breeding conspecifics, the winter abundance of all three species decreased with the distance from their main migratory route in the western Pyrenees. Such patterns fitted well to the observed distribution of ringing recoveries. Main conclusions Our results support a link between the movements of birds along the Pyrenean migratory pathway and their winter abundance in northern Spain. According to this view, the sectors located near the migratory pathway seem to be more easily occupied by migrants, supporting the idea that proximity to passage areas may explain the fine‐grain regional patterning of species abundance in wintering grounds.     

Is it time to test biguanide metformin in the treatment of melanoma?

Metformin is the most widely used antidiabetic drug that belongs to the biguanide class. It is very well tolerated and has the major clinical advantage of not inducing hypoglycemia. Metformin decreases hepatic glucose production via a mechanism requiring liver kinase B1, which controls the metabolic checkpoint, AMP‐activated protein kinase‐mammalian target of rapamycin and neoglucogenic genes. The effects of metformin on this pathway results in reduced protein synthesis and cell proliferation. These observations have given the impetus for many investigations on the role of metformin in the regulation of tumor cell proliferation, cell‐cycle regulation, apoptosis, and autophagy. Encouraging results from these studies have shown that metformin could potentially be used as an efficient anticancer drug in various neoplasms such as prostate, breast, lung, pancreas cancers, and melanoma. These findings are strengthened by retrospective epidemiological studies that have found a decrease in cancer risk in diabetic patients treated with metformin. In this review, we have focused our discussion on recent molecular mechanisms of metformin that have been described in various solid tumors in general and in melanoma in particular.     

Are levels of digestive enzyme activity related to the natural diet in passerine birds?

Digestive capabilities, such as the rates nutrient hydrolysis and absorption, may affect energy intake and ultimately feeding behavior. In birds, a high diversity in gut biochemical capabilities seems to support the existence of a correlation between the morphology and physiology of the intestinal tract and chemical features of the natural diet. However, studies correlating the activity of digestive enzymes and the feeding habits at an evolutionary scale are scarce. We investigated the effect of dietary habits on the digestive physiological characteristics of eight species of passerine birds from Central Chile. The Order Passeriformes is a speciose group with a broad dietary spectrum that includes omnivorous, granivorous and insectivorous species. We measured the activity of three enzymes: maltase, sucrase and aminopeptidase-N. Using an autocorrelation analysis to remove the phylogenetic effect, we found that dietary habits had no effect on enzymatic activity. However, we found that granivorous and omnivorous species had higher levels of disaccharidase activities and insectivores had the lowest. The major difference in enzymatic activity found at the inter-specific level, compared to the reported lower magnitude of enzyme modulation owing to dietary acclimation, suggests that these differences to some extent have a genetic basis. However, the lack of a clear association between diet categories and gut physiology suggested us that dietary categorizations do not always reflect the chemical composition of the ingested food.     

Conundrums of competitive ability in plants: what to measure?

A survey of recent literature indicates that competitive ability in plants has been measured, in most studies, only in terms of the relative intensity of size suppression experienced by competitors within one growing season. Far fewer studies have recorded relative success in terms of survival and even fewer studies have recorded fecundity under competition. Differences in size suppression are usually assumed to reflect differences in relative abilities to deny resources to competitors. However, most previous studies have failed to control or account for other sources of variation in the size suppression that plants experience under competition, i.e. variation between mixtures in the resource supply/demand ratio (approach to carrying capacity), or variation in the degree of niche overlap between competitors, or variation in the intensity of concurrent facilitative interactions between competitors. For future studies, much greater caution is required in recognizing these inherent limitations of traditional measures of competitive ability and, hence, guarding against unfounded conclusions or predictions about potential for competitive success that are based on these measures. There is also a significant challenge for future studies to adopt empirical approaches for minimizing these limitations. Some initial recommendations are considered here based on an emerging view of competitive ability measured in terms of traits associated with all three conventional components of Darwinian fitness, i.e. not just growth (plant size) but also survival and fecundity allocation (offspring production per unit plant size per unit time). According to this model, differences in competitive ability imply differences in the ability, despite intense competition (i.e. low resource supply/demand ratio), to recruit offspring into the next generation and thereby limit offspring recruitment by other plants. The important traits of competitive ability, therefore, are not only those that allow a plant to deny resources to competitors, suppress their sizes and hence, maximize the plant's own size, but also those traits that allow the plant to withstand suppression from competition enough to persist, both as an individual (through survival) and across generations (through descendants).     

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.     

Can changes in the distributions of resident birds in China over the past 50?years be attributed to climate change?

The distributions of bird species have changed over the past 50 years in China. To evaluate whether the changes can be attributed to the changing climate, we analyzed the distributions of 20 subspecies of resident birds in relation to climate change. Long‐term records of bird distributions, gray relational analysis, fuzzy‐set classification techniques, and attribution methods were used. Among the 20 subspecies of resident birds, the northern limits of over half of the subspecies have shifted northward since the 1960s, and most changes have been related to the thermal index. Driven by climate change over the past 50 years, the suitable range and latitude or longitude of the distribution centers of certain birds have exhibited increased fluctuations. The northern boundaries of over half of the subspecies have shifted northward compared with those in the 1960s. The consistency between the observed and predicted changes in the range limits was quite high for some subspecies. The changes in the northern boundaries or the latitudes of the centers of distribution of nearly half of the subspecies can be attributed to climate change. The results suggest that climate change has affected the distributions of particular birds. The method used to attribute changes in bird distributions to climate change may also be effective for other animals.     

Which factors influence the ability of a computational model to predict the in vivo deformation behaviour of skeletal muscle?

Deep tissue injury (DTI) is a severe form of pressure ulcer where tissue damage starts in deep tissues underneath intact skin. Tissue deformation may play an important role in the aetiology, which can be investigated using an experimental–numerical approach. Recently, an animal-specific finite element model has been developed to simulate experiments in which muscle tissue was compressed with an indenter. In this study, the material behaviour and boundary conditions were adapted to improve the agreement between model and experiment and to investigate the influence of these adaptations on the predicted strain distribution. The use of a highly nonlinear material law and including friction between the indenter and the muscle both improved the quality of the model and considerably influenced the estimated strain distribution. With the improved model, the required sample size to detect significant differences between loading conditions can be diminished, which is clearly relevant in experiments involving animals.     

Does the location of a mutation determine the ability to form amyloid fibrils?

We have previously reported studies of fibril formation by a set of protein G B1 domain (beta1) variants, with mutations located around the central parallel beta-strands. In this study, we designed multiple mutations in the edge strands of beta1 to create proteins with a stability range comparable to that of the set of central mutants. All the edge variants are able to form amyloid fibrils when they are incubated at their melting temperatures. This result suggests that overall protein stability is the key determinant for amyloid formation and not the specific location of destabilizing mutations. The edge strand and variants cross-seed with each other and with members of the central variant family. Interesting fibrillar morphology was observed in some cross-seeding cases and its implications for a better understanding of nucleation and elongation events are discussed.     

What determines the impact of alien birds and mammals in Europe?

An often-cited reason for studying the process of invasion by alien species is that the understanding sought can be used to mitigate the impacts of the invaders. Here, we present an analysis of the correlates of local impacts of established alien bird and mammal species in Europe, using a recently described metric to quantify impact. Large-bodied, habitat generalist bird and mammal species that are widespread in their native range, have the greatest impacts in their alien European ranges, supporting our hypothesis that surrogates for the breadth and the amount of resources a species uses are good indicators of its impact. However, not all surrogates are equally suitable. Impacts are generally greater for mammal species giving birth to larger litters, but in contrast are greater for bird species laying smaller clutches. There is no effect of diet breadth on impacts in birds or mammals. On average, mammals have higher impacts than birds. However, the relationships between impact and several traits show common slopes for birds and mammals, and relationships between impact and body mass and latitude do not differ between birds and mammals. These results may help to anticipate which species would have large impacts if introduced, and so direct efforts to prevent such introductions.     

What affects the magnitude of change in first arrival dates of migrant birds?

We analysed which among four factors (mean first arrival date, migration distance, changes in population size, detectability of species) influenced the magnitude of change (regression coefficient) in the first arrival dates of 30 migrant bird species in western Poland during 1983–2003. An examination suggested that several of these factors could be important: the regression coefficient was positively related to mean first arrival date (early species advancing their arrival date more) and negatively with change in population size (species in decline changing less). Moreover, significant differences in regression coefficient were detected between short and long distance migrants and between low detectable and highly detectable species. Undertaking a principal components analysis on the four factors produced an axis explaining 59% of the variance and whose positive values were associated with late arriving, long distance and low detectable species which were more likely to be in decline. However, the multi-collinearity of these factors is a problem that cannot be resolved here and we recommend that further work from different areas is needed to tease apart these effects.     

Manipulative signals in family conflict? On the function of maternal yolk hormones in birds

Maternal hormones in the yolk of birds' eggs have been a focus of attention in behavioral and evolutionary ecology stimulated by the pioneering work of Hubert Schwabl. Since then, knowledge of both the factors that influence maternal deposition patterns and their consequences for offspring development has accumulated rapidly. To date, the field has been dominated by the idea that mothers use yolk hormones to adaptively adjust offspring development, a view that assigns control over hormone deposition and its effects on the offspring to the mother. This neglects the possibility that the evolutionary interests of the mother and offspring differ. When there is such parent-offspring conflict, the offspring are selected to respond to the hormones in a way that is adaptive for themselves rather than for the mother. Moreover, sexual conflict between the parents over parental investment may shape the evolution of yolk hormone deposition: females may manipulate the male's contribution to parental care through the effect of yolk hormones on offspring begging, competitiveness, and developmental rate. We therefore suggest that for a full understanding of the evolution of hormone-mediated maternal effects, it is essential to study both fitness consequences and physiological mechanisms and constraints from the perspective of all family members.     

What factors potentially influence the ability of phylogenetic distance to predict trait dispersion in a temperate forest?

Although phylogenetic‐based approaches have been frequently used to infer ecological processes, they have been increasingly criticized in recent years. To date, the factors that affect phylogenetic signals and further the ability of phylogenetic distance to predict trait dispersion have been assumed but not empirically tested. Therefore, we investigate which factors potentially influence the ability of phylogenetic distance to predict trait dispersion. We quantified the phylogenetic and trait dispersions across size classes and spatial scales in a 9‐ha old‐growth temperate forest dynamics plot in northeastern China. Phylogenetic signals at the community level were generally lower than those at the species pool level, and phylogenetically clustered communities showed lower phylogenetic signals than did overdispersed communities. This pattern might explain the other three findings of our study. First, phylogenetically overdispersed communities performed better at predicting trait dispersion than did clustered communities. Second, the mean pairwise distance (MPD)‐based metric exhibited a stronger correlation with trait dispersion than did the mean nearest taxon distance (MNTD)‐based metric. Finally, the MNTD‐based metric showed that the prediction accuracy for trait dispersion decreased with increasing spatial scales, whereas its effects were weak on the MPD‐based metric. In addition, phylogeny could not determine the dispersions of all functional axes but was able to predict certain traits depending on whether they were evolutionarily conserved. These results were conserved when we removed the effects of space and environment. Our findings highlighted that using phylogenetic distance as a proxy of trait similarity might work in a temperate forest depending on the species in local communities sampled from total pool as well as the traits measured. Utilizing these rules, we should rethink the conclusions of previous studies that were based on phylogenetic‐based approaches.     

Are the low protein requirements of nectarivorous birds the consequence of their sugary and watery diet? A test with an omnivore

Nectar-feeding birds have remarkably low nitrogen requirements. These may be due either to adaptation to a low-protein diet or simply to feeding on a fluid diet that minimizes metabolic fecal nitrogen losses. We measured minimal nitrogen requirements (MNR) and total endogenous nitrogen loss (TENL) in the omnivorous European starling Sturnus vulgaris, fed on an artificial nectar-like fluid diet of varying concentrations of sugar and protein. The MNR and TENL of the birds were similar and even slightly higher than allometrically expected values for birds of the starlings' mass (140% and 103%, respectively). This suggests that the low measured nitrogen requirements of nectar-feeding birds are not simply the result of their sugary and watery diets but a physiological adaptation to the low nitrogen input. We also measured the effect of water and protein intake on the nitrogenous waste form in the excreta and ureteral urine in European starlings. Neither high water intake nor low protein intake increased the fraction of nitrogen excreted as ammonia. Ammonia was excreted at consistently low levels by the starlings, and its concentration was significantly higher in ureteral urine than in excreta. We hypothesize that ureteral ammonia was reabsorbed in the lower intestine, indicating a postrenal modification of the urine.