Social Control and Physiological Cost of Cheating in Status Signalling Male House Sparrows (Passer domesticus)

Flock-forming passerines often use plumage characteristics to signal their social dominance. While the benefits to signal dominance seem obvious, costs associated with status signalling are ambiguous. The social control hypothesis predicts that individuals of high social status – with large badges – are involved in more social interactions with individuals of similar badge size. Cheaters are therefore exposed to increased risk of fighting with high quality individuals and the costs associated with enhanced fights with dominant males are supposed to outweigh the benefits of cheating. We tested the social control hypothesis in male house sparrows ( Passer domesticus ), by observing social interactions in captive flocks and determining dominance relationships. Two low status individuals within each flock had the size of their badge experimentally increased and the interactions involving experimental and control birds were recorded. We also assessed the potential physiological cost of cheating in terms of enhanced levels of the stress hormone, corticosterone. Dominance was significantly positively correlated with badge size, but not with other morphological traits. We found little support for the social control hypothesis. Birds did not have significantly more interactions with individuals of similar badge size, before the manipulation. Similarly, after the experimental increase in badge size, experimental birds did not tend to have more encounters with large-badged males. Experimental birds with enlarged badges won more fights compared with prior to the manipulation, suggesting that badge size is used as a signal of social dominance even in small and stable flocks. Finally, corticosterone levels in the blood did not increase significantly after the manipulation of badge size, suggesting that there is no measurable cost, resulting from stress, in cheaters.     

Female Choice for Male Morphological Traits in House Sparrows,Passer domesticus

Female mate choice for male morphological traits was examined in captive house sparrows in New Mexico, USA. A study of house sparrows in Denmark indicated that male bib size is important in female choice (Moller 1988, 1989). To examine this issue further, and to compare the selective pressures on male morphological traits between the two populations, bibs of males were manipulated to one of four standard sizes and females were allowed to choose from four males, one of each bib size. The amount of time the female spent with each male was recorded for 40 trials. Males were then ranked in each trial, with a rank of 4 given to the male the female spent the most time with. The ranks a male obtained were then averaged to provide an indication of a male's attractiveness to females. Data from 23 different males indicated that bib size was not correlated with a male's average rank, even when the effects of other traits were controlled statistically. In addition, the size of the original (unaltered) bib was not correlated with male average rank. Bill depth was the only trait significantly correlated with a male's average rank. Differences in the populations studied or the methodologies used may have led to differences between the results obtained in this study and that of Moller (1988).     

Single Aggressive Interactions Increase Urinary Glucocorticoid Levels in Wild Male Chimpanzees

A basic premise in behavioural ecology is the cost-benefit arithmetic, which determines both behavioural decisions and evolutionary processes. Aggressive interactions can be costly on an energetic level, demanding increased energy or causing injuries, and on a psychological level, in the form of increased anxiety and damaged relationships between opponents. Here we used urinary glucocorticoid (uGC) levels to assess the costs of aggression in wild chimpanzees of Budongo Forest, Uganda. We collected 169 urine samples from nine adult male chimpanzees following 14 aggressive interactions (test condition) and 10 resting events (control condition). Subjects showed significantly higher uGC levels after single aggressive interactions compared to control conditions, likely for aggressors as well as victims. Higher ranking males had greater increases of uGC levels after aggression than lower ranking males. In contrast, uGC levels showed no significant change in relation to aggression length or intensity, indicating that psychological factors might have played a larger role than mere energetic expenditure. We concluded that aggressive behaviour is costly for both aggressors and victims and that costs seem poorly explained by energetic demands of the interaction. Our findings are relevant for studies of post-conflict interactions, since we provide evidence that both aggressors and victims experience a stress response to conflict.     

The Role of Redox Mechanisms in Cell Signalling

Functioning and efficient cell signalling is vital for the survival of cells. Over the years various components have been identified and recognised as crucial for the transduction of signals in cells. Many of the mechanisms allow for a relatively rapid switching of signals, on or off, with common examples being the G proteins and protein phosphorylation. However, recently it has become apparent that other modifications of amino acids are also important, and this includes reactions with nitric oxide, for example S-nitrosylation, and of particular relevance here, oxidation of cysteine residues. Such oxidation will be dependent on the redox status of the intracellular environment in which that protein resides, and this will in turn be dictated by the presence of pro-oxidants and antioxidants. Here, the chemistry of redox modification of amino acids is introduced, and a general overview of the role of redox in mediating signal transduction is given.     

Low frequency of extra-pair fertilisations in House Sparrows breeding at high density

The importance that the density of breeders has on the opportunity for extra-pair fertilisations (EPFs) is controversial. Some evidence supports the idea that population density and frequency of extra-pair paternity are positively associated, whereas other work does not. In the present paper we estimate EPF frequency in a dense House Sparrow Passer domesticus colony. We detected extra-pair nestlings in 9.3% of 54 broods studied, and 7% of 171 nestlings were sired by extra-pair fathers. The number of clutches laid per female, the change of male or female between two consecutive breeding attempts and the age of the partners showed no association with the presence or absence of extra-pair fertilisations. Morphometric variables of paired males and females did not discriminate broods with EPFs from those without. We detected a single case of a female laying a parasitic egg in the nest of a male that in a previous breeding attempt was the extra-pair genetic father of her entire brood. The frequency of extra-pair fertilisation recorded in this study was low compared with that in other House Sparrow populations breeding at lower densities, or other species that breed in colonies. This result does not support the claim that EPF frequency is associated with population density. We propose, as an explanation for this result, that under high intra-sexual competition for nest sites (1) males may have limited opportunities to search for females for extra-pair copulations and (2) the high quality of male nest-owners may reduce female propensity to search for additional sexual partners.     

Photoperiodic control of testicular regression and moult in male House Sparrows Passer domesticus

Testis size, bill colour and moult were monitored in male House Sparrows Passer domesticus kept under a natural daylength regime between February and November. On three occasions (at the summer solstice, 25 days later and 39 days later), groups of birds were transferred to a daylength of 18 h of light and 6 h of darkness per day (18L: 6D), the natural daylength at the solstice. In birds under natural daylengths, the testes had regressed significantly by 2 5 days after the solstice. In those transferred to 18L:6D at the solstice, the onset of regression was delayed by about 4 weeks. Transfer to 18L: 6D after the solstice did not cause recrudescence; the testes continued to regress. In birds transferred to 18L: 6D at the solstice, moult was delayed by 4 weeks and progressed more slowly. These results suggest that photoperiodically induced gonadal regression in this species contains elements characteristic of both absolute and relative photorefractoriness.     

Evidence for Co-evolution of West Nile Virus and House Sparrows in North America

West Nile virus (WNV) has been maintained in North America in enzootic cycles between mosquitoes and birds since it was first described in North America in 1999. House sparrows (HOSPs; Passer domesticus) are a highly competent host for WNV that have contributed to the rapid spread of WNV across the U.S.; however, their competence has been evaluated primarily using an early WNV strain (NY99) that is no longer circulating. Herein, we report that the competence of wild HOSPs for the NY99 strain has decreased significantly over time, suggesting that HOSPs may have developed resistance to this early WNV strain. Moreover, recently isolated WNV strains generate higher peak viremias and mortality in contemporary HOSPs compared to NY99. These data indicate that opposing selective pressures in both the virus and avian host have resulted in a net increase in the level of host competence of North American HOSPs for currently circulating WNV strains.     

Dynamics of West Nile Virus Persistence in House Sparrows (Passer domesticus)

West Nile Virus (WNV) is now endemic throughout North America, with annual recurrence dependent upon successful overwintering when cold temperatures drive mosquito vectors into inactivity and halt transmission. To investigate whether avian hosts may serve as an overwintering mechanism, groups of eight to ten House Sparrows were experimentally infected with a WN02 genotype of WNV and then held until necropsy at 3, 5, 7, 9, 12, 15, or 18 weeks post-infection (pi) when they were assessed for the presence of persistent infection. Blood was collected from all remaining birds every two weeks pi, and sera tested for WNV RNA and WNV neutralizing antibodies. West Nile virus RNA was present in the sera of some birds up to 7 weeks pi and all birds retained neutralizing antibodies throughout the experiment. The detection of persistently infected birds decreased with time, from 100% (n = 13) positive at 3 weeks post-infection (pi) to 12.5% (n = 8) at 18 weeks pi. Infectious virus was isolated from the spleens of birds necropsied at 3, 5, 7 and 12 weeks pi. The current study confirmed previous reports of infectious WNV persistence in avian hosts, and further characterized the temporal nature of these infections. Although these persistent infections supported the hypothesis that infected birds may serve as an overwintering mechanism, mosquito-infectious recrudescent viremias have yet to be demonstrated thereby providing proof of principle.     

Status Signalling by Parus major: An Experiment in Deception

The ‘social control’ and ‘incongruence’ hypotheses, first put forward by ROHWER (1977) to explain how attempted ‘deceit’ status signalling is kept in check among winter-flocking birds, were tested under semi-natural conditions for Parus major. This species signals its social status by the width of its breast stripe. The lowest-ranked male in experimental flocks, each made up of four individuals, was manipulated in one of three ways: 1) the status signal was altered by painting the breast stripe to make it broader; 2) agonistic behaviour was altered by injecting testosterone; 3) both status signal and behaviour were manipulated. A study of the outcome of subsequent agonistic encounters by these birds revealed that the status of the manipulated individuals only rose when both their behaviour and status signal were altered. This indicates that the ‘social control’ hypothesis must be rejected, but not the ‘incongruence’ hypothesis.     

Effects of Eavesdropping on Subsequent Signalling Behaviours in Male Canaries

Signalling interactions could provide information for an observing third party. This behaviour has been labelled as eavesdropping. Studies on eavesdropping in birds have concerned only few species and have mainly been conducted in the wild. Our experiment was designed to evaluate the effects of eavesdropping on subsequent interactions in male canaries in a controlled laboratory context. The experiment had two stages: a presentation stage and a test stage. During the presentation stage, subjects heard three different interaction types: an alternating interaction, an overlapping interaction or two song sequences presented separately one after the other, i.e. without interaction. Then during the test stage, subjects were allowed to listen to the songs previously heard separately. We noted calls emitted by subjects during the two stages. During the presentation stage, responses of male canaries did not differ according to the type of interaction they could hear. During the test stage, we found a clear effect of the song status on the calls emitted by subjects. They emitted less calls during the songs of the winner than during all other songs. Surprisingly, subjects also produced intermediate responses by emitting fewer calls during the second song previously heard during the presentation phase, and during the song of the looser when compared to the three other songs. Our results show that male canaries obtain information on the relative threat from an overlapping interaction whereas an alternating interaction does not seem to provide any kind of relative information on singers' status. In following encounters, the higher the potential threat of a singer was, the less the subjects emitted calls, probably to avoid the more serious rival. This inhibiting effect is discussed.     

The Role of Solvent Interactions in Protein Conformatio

Abstract

For many years, the ease with which the pH of enzyme reactions could be varied has led to innumerable reports of the pH-dependence of the kinetic parameters of such reactions. These studies have been provided with a veneer of respectability by suggestions that they allow deductions to be made about the nature of the ionizing groups upon which the catalytic activity of the enzyme depends. It is the purpose of this article to summarize some of the reasons why a large proportion of pH-dependence studies yields little information about the real pK_a-values of ionizing groups in enzymes, and still less about the identity of these groups.     

The Role of FilGAP-Filamin A Interactions in Mechanoprotection

Cells in mechanically active environments are subjected to high-amplitude exogenous forces that can lead to cell death. Filamin A (FLNa) may protect cells from mechanically induced death by mechanisms that are not yet defined. We found that mechanical forces applied through integrins enhanced Rac-mediated lamellae formation in FLNa-null but not FLNa-expressing cells. Suppression of force-induced lamella formation was mediated by repeat 23 of FLNa, which also binds FilGAP, a recently discovered Rac GTPase-activating protein (GAP). We found that FilGAP is targeted to sites of force transfer by FLNa. This force-induced redistribution of FilGAP was essential for the suppression of Rac activity and lamellae formation in cells treated with tensile forces. Depletion of FilGAP by small interfering RNA, inhibition of FilGAP activity by dominant-negative mutation or deletion of its FLNa-binding domain, all resulted in a dramatic force-induced increase of the percentage of annexin-V–positive cells. FilGAP therefore plays a role in protecting cells against force-induced apoptosis, and this function is mediated by FLNa.     

Photoperiodic control of the termination of breeding and the induction ofmoult in House Sparrows Passer domesticus

Two photoperiodic mechanisms controlling gonadal regression in birds have been identified: absolute photorefractoriness, typical of species with short breeding seasons, where gonadal regression occurs spontaneously during long days, and relative photorefractoriness, where a decrease in daylength is required to induce regression. An experiment was designed to test whether these simply represent extremes of one underlying mechanism. Three groups of male House Sparrows Passer domesticus were transferred from a short photoperiod, 8 h of light: 16 h of darkness per day (8L:16D) to long photoperiods of either 18L:6D, 16L:8D or 13L:11D. Gonadal maturation rates were similar in all three groups; gonadal regression and moult began latest in the 13L:11D group. Four additional groups of sparrows were transferred from 8L:16D to 18L:6D and then transferred to either 13L: 11D or 16L:8D prior to, or shortly after, the onset of gonadal regression. The decrease in daylength prior to regression had no effect on the timing of regression but did advance the onset of moult. Decrease in daylength after the onset of regression increased the rate of regression and the rate of moult. Because a decrease in daylength did not affect the timing of regression, the data do not support the hypothesis that absolute and relative photorefractoriness represent extremes of a single underlying photoperiodic control mechanism. The adaptive significance of the effects of decreasing daylength on the rate of regression and moult is discussed.     

Individual Variation in Cone Photoreceptor Density in House Sparrows: Implications for Between-Individual Differences in Visual Resolution and Chromatic Contrast

Between-individual variation has been documented in a wide variety of taxa, especially for behavioral characteristics; however, intra-population variation in sensory systems has not received similar attention in wild animals. We measured a key trait of the visual system, the density of retinal cone photoreceptors, in a wild population of house sparrows (Passer domesticus). We tested whether individuals differed from each other in cone densities given within-individual variation across the retina and across eyes. We further tested whether the existing variation could lead to individual differences in two aspects of perception: visual resolution and chromatic contrast. We found consistent between-individual variation in the densities of all five types of avian cones, involved in chromatic and achromatic vision. Using perceptual modeling, we found that this degree of variation translated into significant between-individual differences in visual resolution and the chromatic contrast of a plumage signal that has been associated with mate choice and agonistic interactions. However, there was no evidence for a relationship between individual visual resolution and chromatic contrast. The implication is that some birds may have the sensory potential to perform “better” in certain visual tasks, but not necessarily in both resolution and contrast simultaneously. Overall, our findings (a) highlight the need to consider multiple individuals when characterizing sensory traits of a species, and (b) provide some mechanistic basis for between-individual variation in different behaviors (i.e., animal personalities) and for testing the predictions of several widely accepted hypotheses (e.g., honest signaling).     

Housing Shortages in Urban Regions: Aggressive Interactions at Tree Hollows in Forest Remnants

Urbanisation typically results in a reduction of hollow-bearing trees and an increase in the density of particularly species, potentially resulting in an increased level of competition as cavity-nesting species compete for a limited resource. To improve understanding of hollow usage between urban cavity-nesting species in Australia, particularly parrots, we investigated how the hollow-using assemblage, visitation rate, diversity and number of interactions varied between hollows within urban remnant forest and continuous forest. Motion-activated video cameras were installed, via roped access to the canopy, and hollow usage was monitored at 61 hollows over a two-year period. Tree hollows within urban remnants had a significantly different assemblage of visitors to those in continuous forest as well as a higher rate of visitation than hollows within continuous forest, with the rainbow lorikeet making significantly more visitations than any other taxa. Hollows within urban remnants were characterised by significantly higher usage rates and significantly more aggressive interactions than hollows within continuous forest, with parrots responsible for almost all interactions. Within urban remnants, high rates of hollow visitation and both interspecific and intraspecific interactions observed at tree hollows suggest the number of available optimal hollows may be limiting. Understanding the usage of urban remnant hollows by wildlife, as well as the role of parrots as a potential flagship for the conservation of tree-hollows, is vital to prevent a decrease in the diversity of urban fauna, particularly as other less competitive species risk being outcompeted by abundant native species.     

The Mechanisms of Water Exchange: The Regulatory Roles of Multiple Interactions in Social Wasps

Evolutionary benefits of task fidelity and improving information acquisition via multiple transfers of materials between individuals in a task partitioned system have been shown before, but in this paper we provide a mechanistic explanation of these phenomena. Using a simple mathematical model describing the individual interactions of the wasps, we explain the functioning of the common stomach, an information center, which governs construction behavior and task change. Our central hypothesis is a symmetry between foragers who deposit water and foragers who withdraw water into and out of the common stomach. We combine this with a trade-off between acceptance and resistance to water transfer. We ultimately derive a mathematical function that relates the number of interactions that foragers complete with common stomach wasps during a foraging cycle. We use field data and additional model assumptions to calculate values of our model parameters, and we use these to explain why the fullness of the common stomach stabilizes just below 50 percent, why the average number of successful interactions between foragers and the wasps forming the common stomach is between 5 and 7, and why there is a variation in this number of interactions over time. Our explanation is that our proposed water exchange mechanism places natural bounds on the number of successful interactions possible, water exchange is set to optimize mediation of water through the common stomach, and the chance that foragers abort their task prematurely is very low.     

Signal Interception and the Use of Soft Song in Aggressive Interactions

Song sparrows, like many species of songbirds, produce songs of especially low amplitude during aggressive contests. Such ‘soft songs’ have been shown to be reliable signals of intention to attack in song sparrows. Low intensity is a paradoxical feature in a highly aggressive signal, in that it seems likely to make the signal less intimidating to an opponent. A hypothesis that resolves this paradox is that use of soft songs benefits a signaler by limiting the interception of his signals by third party receivers. Here, we test this hypothesis with respect to song sparrows and two classes of third party receivers, predators and conspecific males. We tested whether selection to avoid predation is responsible for use of soft song by examining whether male song sparrows increase production of soft song in an aggressive context when they also receive signals (alarm calls) that indicate a predator is present. We found that the proportion of soft song produced by male song sparrows was actually significantly lower in the predator context than in a control context, directly contradicting the prediction. We tested whether avoiding eavesdropping by conspecific males is a benefit of soft song by removing territory owners and simulating interactions on their territories using playback from two loudspeakers. We found that intrusions by third party males were more likely in trials in which the simulated owner countered an intruder's songs using soft songs than in trials in which the simulated owner countered with loud song, again directly contradicting the hypothesis. We conclude that limiting interception by predators and conspecific males does not provide an explanation for use of soft song by song sparrows.