Do Nest Light Conditions Affect Rejection of Parasitic Eggs? A Test of the Light Environment Hypothesis

Discrimination of foreign eggs is one of the most studied aspects of host defences against avian brood parasites. Although many factors affecting host egg‐recognition processes have already been evaluated, only a few attempts have been made to test the importance of light conditions in microhabitats of host nests. Here, we examined whether the objectively measured nest light environment affects great reed warbler (Acrocephalus arundinaceus) responses towards real common cuckoo (Cuculus canorus) eggs. More specifically, we predicted that parasitic eggs will be rejected with a lower frequency from nests placed in darker conditions than those in lighter conditions. However, we found no effect of the ambient light on egg‐rejection behaviour alone, but the photosynthetically active radiation exhibited a positive interactive effect with chromatic contrast between cuckoo and host eggs. Most rejection events were accomplished when cuckoo eggs of poor mimicry were laid in well‐lit nests. Our study suggests that this phenomenon may have important implications for the evolution of egg mimicry and host egg discrimination. We encourage further testing of the light environment hypothesis in other host species breeding in variable nest microhabitats and light conditions.     

Why Does Rhinopithecus bieti Prefer the Highest Elevation Range in Winter? A Test of the Sunshine Hypothesis

Environmental factors that affect spatiotemporal distribution patterns of animals usually include resource availability, temperature, and the risk of predation. However, they do not explain the counterintuitive preference of high elevation range in winter by the black-and-white snub-nosed monkey (Rhinopithecus bieti). We asked whether variation of sunshine along with elevations is the key driving force. To test this hypothesis, we conducted field surveys to demonstrate that there was a statistically significant pattern of high elevation use during winter. We then asked whether this pattern can be explained by certain environmental factors, namely temperature, sunshine duration and solar radiation. Finally, we concluded with a possible ecological mechanism for this pattern. In this study, we employed GIS technology to quantify solar radiation and sunshine duration across the monkey's range. Our results showed that: 1) R. bieti used the high altitude range between 4100-4400 m in winter although the yearly home range spanned from 3500-4500 m; 2) both solar radiation and sunshine duration increased with elevation while temperature decreased with elevation; 3) within the winter range, the use of range was significantly correlated with solar radiation and sunshine duration; 4) monkeys moved to the areas with high solar radiation and duration following a snowfall, where the snow melts faster and food is exposed earlier. We concluded that sunshine was the main factor that influences selection of high elevation habitat for R. bieti in winter. Since some other endotherms in the area exhibit similar winter distributional patterns, we developed a sunshine hypothesis to explain this phenomenon. In addition, our work also represented a new method of integrating GIS models into traditional field ecology research to study spatiotemporal distribution pattern of wildlife. We suggest that further theoretical and empirical studies are necessary for better understanding of sunshine influence on wildlife range use.     

Does Temporal Variation in Predation Risk Influence the Intensity of Antipredator Responses? A Test of the Risk Allocation Hypothesis

Temporal variation in predation risk may fundamentally influence antipredator responses of prey animals. To maximize lifetime fitness, prey must be able to optimize energy gain and minimize predation risk, and responses to current levels of risk may be influenced by background levels of risk. A ‘risk allocation’ model has recently been proposed to predict the intensity of antipredator responses that should occur as predation risk varies over time. Prey animals from high‐risk environments should respond to predators with relatively low intensities of antipredator behaviour because long periods of antipredator behaviour may result in unacceptable decreases in levels of foraging activity. Moreover, animals that are under frequent risk should devote more energy to foraging during brief pulses of safety compared with animals under infrequent attack. In this study, we experimentally tested the risk allocation hypothesis. We exposed juvenile rainbow trout, Oncorhynchus mykiss, to three levels of risk (high, moderate and low) crossed with two levels of temporal variation (exposed to risk three times a day and once a day). In accordance with the model, we found that trout exposed to risky situations more frequently responded with significantly less intense antipredator behaviour than trout exposed to risk infrequently. The intensity of response of trout exposed to moderate risk three times a day decreased to levels similar to situations of no risk. However, in contrast to the second prediction of the model, animals under frequent risk were not more active during periods of safety compared with animals under infrequent risk. Although behaviour in the face of predation risk was dependent on the broader temporal context in which risk varied, the specific predictions of the risk allocation model were only partly supported.     

A simple model of host-parasite evolutionary relationships. Parasitism: compromise or conflict?

The evolutionary biology of host-parasite relationships are considered here using a simple game-theory model in which hosts play against parasite and vice versa. In this model, the players can choose between two strategies (aggressive or not aggressive) and the utility of the game is envisaged in terms of fitness and selective costs. The game solutions suggest that the two types of confrontation are encountered in symbiotic relationships and thus constitute two Evolutionary Stable Strategies (ESS). These observations lead us to discuss: (i) the status of different kinds of symbiotic relationships (i.e. parasitoidism; parasitism, commensalism and mutualism) related to selective costs and (ii) the position of coevolution in this game theory context.     

Resource Defence or Exploded Lek? – A Question of Perspective

It becomes increasingly obvious that animal mating systems cannot be classified into distinct categories, but transitions between mating system classes are continuous. Positioning a certain mating system at this continuum is often not straightforward, however. Depending on which characteristic is considered, a mating system may end up at very different positions on this gradient. Here, we explore the potential conflict between mating system classifications that may arise when they are based on different criteria by investigating the mating system of the cichlid fish Simochromis pleurospilus in which males defend small patches of homogeneously distributed food resources (turf algae) vigorously against food competitors, but they allow specific females to use them. We hypothesized that male defence may generate high‐quality feeding patches serving to attract females, and hence male territoriality constitutes a form of courtship. Our field data show that males selectively allow approximately one‐third of the visiting females to feed on their territory and that females preferentially feed in male territories and usually sample several territories successively. As males protect food patches against other algae grazers and guard females from harassment by food competitors, females gain nutritional benefits from visiting male territories. Hence, males appear to generate essential resources for females, which is the key feature of resource‐defence mating systems, although the distributions of resources and of males and females are characteristics of an exploded lek.     

Male-Driven Evolution Among Eoaves? A Test of the Replicative Division Hypothesis in a Heterogametic Female (ZW) System

Because avian females are heterogametic, the reverse of mammals, avian sex chromosomes undergo significantly different patterns and numbers of DNA replications than do those in mammals. This makes the W (female-specific) and the Z chromosomes an excellent model system for the study of the replicative division hypothesis, which purports that DNA substitution rate is determined by the number of germline replications. The sex-specific chromosome in birds (the W) is predicted to change at the slowest rate of all avian chromosomes because it undergoes the fewest rounds of replication per unit of evolutionary time. Using published data on gametogenesis from a variety of sources, we estimated the ratio of male-to-female germline replications (c) in galliforms and anseriforms to be approximately 4.4. The value of c should predict the value of the ratio of male-to-female mutation rates (α_m) if the replicative division hypothesis is true. Homologous DNA sequences including an intron and parts of two exons of the CHD gene were obtained from the W and the Z chromosomes in ostrich, sage grouse, canvasback duck, tundra swan, and snow goose. The exons show significantly different nucleotide composition from the introns, and the W-linked exons show evidence of relaxed constraint. The Z-linked intron is diverging ≈ 3.1 times faster than the W-linked intron. From this, α_m was calculated to be approximately 4.1, with a confidence interval of 3.1 to 5.1. The data support the idea that the number of replicative divisions is a major determinant of substitution rate in the Eoavian genome. Received: 19 January 1999 / Accepted: 8 June 1999     

Does Social Mating System Influence Nest Defence Behaviour in Great Reed Warbler (Acrocephalus arundinaceus) Males?

In birds with biparental care, males and females often conflict over how much care to provide to their offspring and it may be substantially influenced by increased level of polygamy. In accordance with sexual conflict theory, males of socially polygynous bird species provide much less care to their nestlings than do males of most socially monogamous species. Most of previous studies, however, have used feeding behaviour as an index for variations in male parental care only. However, this may be skewed if polygynous males compensate for lower feeding assistance through the provision of other parental care such as protection of nests from predators. In this paper, we examine nest defence behaviour in the facultatively polygynous great reed warbler with respect to sex and type of social mating system. We recorded latency to the first arrival, distance from the predator and defensive reaction of each parent towards a human intruder. Socially polygynous males with two simultaneously active nests defended primary females’ nests less vigorously than socially monogamous males, whereas no differences were found between monogamous and primary females. Generally, however, they took a bigger role in nest defence than males in all cases. Our results support an idea that sexual conflict is driven by polygamy and that type of social mating system can influence nest defence behaviour of facultatively polygynous birds. This finding should be taken into consideration when studying nest defence parental care in polygynous mating systems.     

Does the Refuge Availability Influence the Spawning Behavior of Mature Male Parr in Salmonids? A Test in the Miyabe Charr

In many salmon and charr, both 'migratory males' and 'precocious males' are maintained as alternative life-histories within a population. During breeding, precocious males gather around the mating pair of migratory fish and attempt to sneak in the spawning between larger male and female charr. Refuges such as debris and shallow areas may provide shelter from aggressive attacks and allow precocious males to hold positions closer to the pair (nest) and/or sneak more easily during the mating. Here we examine whether the availability of refuges influences the breeding behavior of precocious male parr of the Miyabe charr under experimental and natural conditions. Aggressive attacks directed toward precocious parr by the mating pair or other parr was not influenced by the refuge availability either under experimental conditions or in the wild. We did not find the effect of high refuge availability on the proximity of parr to the nest beyond the experimental conditions where the density of refuges was probably higher than in the natural stream. There were no effects of high refuge availability either on parr's attempts at sneak mating or on their success in spawning. Thus, our results provide little evidence that the refuge availability influences parr sneaking behavior. Other possible effects of high refuge availability, for example, the increase of fertilization success and the decrease of energy expenditure and risk taking, remain to be considered.     

Does the type of matrix matter? A quantitative review of the evidence

It has been increasingly recognized that the type of matrix surrounding habitat patches can affect biodiversity in landscapes, but there were only qualitative reviews of the subject focused on particular taxonomic groups. We present a quantitative review of studies from 1985 to 2008 that compared effects of different matrix types on individuals, populations and communities. We compiled 104 studies, most on animals, covering a broad range of landscape types and spatial scales. Most studies were empirical, focused on individuals and communities, and evaluated abundance/richness in the patch as the dependent variable. The type of matrix surrounding habitat patches influenced the studied parameters in 95% of the studies, but such effects were overall smaller compared to patch size or isolation effects. Matrix type effects were strongly species-specific, with different species responding differently to matrix type in 96% of studies comparing species or group of species. In 88% of studies, matrix types more similar in structure to the patch had higher quality for the studied organisms from the point of view of functional connectivity. Overall, the type of matrix is important, but patch size and isolation are the main determinants of ecological parameters in landscapes. Matrix quality generally increases with increasing structural similarity with habitat patches, a pattern that could be used as a general guideline for management of the matrix in fragmented landscapes.     

Do Scientific Advancements Lean on the Shoulders of Giants? A Bibliometric Investigation of the Ortega Hypothesis

Background

In contrast to Newton''s well-known aphorism that he had been able “to see further only by standing on the shoulders of giants,” one attributes to the Spanish philosopher Ortega y Gasset the hypothesis saying that top-level research cannot be successful without a mass of medium researchers on which the top rests comparable to an iceberg.

Methodology/Principal Findings

The Ortega hypothesis predicts that highly-cited papers and medium-cited (or lowly-cited) papers would equally refer to papers with a medium impact. The Newton hypothesis would be supported if the top-level research more frequently cites previously highly-cited work than that medium-level research cites highly-cited work. Our analysis is based on (i) all articles and proceedings papers which were published in 2003 in the life sciences, health sciences, physical sciences, and social sciences, and (ii) all articles and proceeding papers which were cited within these publications. The results show that highly-cited work in all scientific fields more frequently cites previously highly-cited papers than that medium-cited work cites highly-cited work.

Conclusions/Significance

We demonstrate that papers contributing to the scientific progress in a field lean to a larger extent on previously important contributions than papers contributing little. These findings support the Newton hypothesis and call into question the Ortega hypothesis (given our usage of citation counts as a proxy for impact).     

Hypothesis: hemimelia and the maintenance of pentadactyly?

The limbs of extant terrestrial vertebrates possess five or fewer digits, yet, polydactyly is accepted as being the ancestral state. Therefore, I propose a hypothesis to account for the maintenance of digital number at five or fewer digits, based on a selective disadvantage associated with polydactylous states in terrestrial vertebrates. This disadvantage is not associated with the polydactyly per se, but rather with the hemimelia which is a common feature of polydactylies in mammals. Hemimelia causes a twisting, or luxation, of the distal segment of the limb, which is due to a malformation of the radius/tibia of the limb. This defect results in the limb being held in an abnormal gait, which causes problems in the locomotion of the animal which would compromise their ability to flourish. Therefore, the abnormal gait and torsion of the limb caused by the hemimelia is acting as a stabilizing force to maintain the dactyly of the tetrapod limb with five or fewer digits.     

Does competition or facilitation regulate migrant ungulate populations in the Serengeti? A test of hypotheses

Summary Interspecific competition and facilitation have both been proposed as processes promoting species separation and co-existence in African ungulates. In one group of grazers on the Serengeti plains, comprising wildebeest (Connochaetes taurinus), zebra (Equus burchelli), and Thomson's gazelle (Gazella thomsoni), these processes have also been suggested to regulate the populations. Censuses of these populations over 20 years have shown changes that allow a test of which, if either, process regulates population numbers. Wildebeest numbers have levelled off as a result of intraspecific competition for food following a five-fold increase due to release from disease and an increase in food supply. Zebra numbers have remained stationary throughout the same period. Gazelle numbers have declined in the last 10 years. These results are contrary to the facilitation hypothesis, which predicts that wildebeest numbers should not have increased if those of zebra did not, and that gazelle numbers should have increased since the wildebeest population increased. The gazelle results are consistent with the interspecific competition hypothesis, but the zebra results are contrary to it. We propose an alternative hypothesis that predation regulates the zebra population, and we suggest ways of testing this.     

Does domain swapping improve the stability of RNase A?

Self-assembling complexes have potential as novel supramolecular biomaterials but domain swapped complexes have yet to investigated in this capacity. Bovine ribonuclease A (RNase A) is a useful model protein as it is able to form a range of three dimensional domain swapped structures, including dimers, trimers and tetramers that have similar catalytic ability. However, little work has been carried out investigating the physical characteristics of these complexes. In an effort to characterise the strength of these oligomeric interactions, analytical ultracentrifugation was carried out to measure the dissociation of higher order complexes, using fluorescent tags to test for dissociation at very low concentrations. Results of this work suggest that the oligomers form a very tight complex, with no evidence of dissociation down to 250 pM. RNase A oligomers also had similar thermal stability to that of monomeric enzyme, suggesting that the main limiting factor in RNase A stability is the tertiary, rather than quaternary structure. Following thermal unfolding of RNase A, the protein refolded upon cooling, but returned to the monomeric state. This latter result may limit the potential of domain swapping as a means of material assembly.