Self-serving punishment and the evolution of cooperation.
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Altruism↗
Biomedical subjects
R A Johnstone
Publications and source records attributed to R A Johnstone.
Begging and sibling competition: how should offspring respond to their rivals?
Godfray's influential model of competitive begging predicted that offspring should respond to each other's behavior, displaying more intensely when competing with needier rivals. Empirical tests of this prediction have, however, yielded equivocal results. Here, I develop a series of evolutionarily stable strategy models of begging as a signal of need, which show that this prediction holds only for competitive aspects of display that influence the division of food among the brood. No such response is expected for cooperative begging (which influences the total level of provisioning by the parent), and the models even predict the opposite trend under some circumstances (where the indirect costs of extracting additional resources from the parent are high). These contrasting sets of predictions may help to explain the varying empirical results obtained by studies of sibling interaction. Cooperative (as opposed to competitive) begging is likely to be of greater significance in cases where dominant young can gain direct control of allocation (or enjoy some competitive advantage). Dominants are then predicted to parasitize the efforts of their weaker rivals and reduce their own investment in cooperative signaling while continuing to claim a disproportionately large share of the resources provided by the parent.
Animal Communication↗
Eavesdropping and animal conflict.
Fights between pairs of animals frequently take place within a wider social context. The displays exchanged during conflict, and the outcome of an encounter, are often detectable by individuals who are not immediately involved. In at least some species, such bystanders are known to eavesdrop on contests between others, and to modify their behavior toward the contestants in response to the observed interaction. Here, I extend Maynard Smith's well known model of animal aggression, the Hawk-Dove game, to incorporate the possibility of eavesdroppers. I show that some eavesdropping is favored whenever the cost of losing an escalated fight exceeds the value of the contested resource, and that its equilibrium frequency is greatest when costs are relatively high. Eavesdropping reduces the risk of escalated conflict relative to that expected by chance, given the level of aggression in the population. However, it also promotes increased aggression, because it enhances the value of victory. The net result is that escalated conflicts are predicted to occur more frequently when eavesdropping is possible.
Aggression↗
Cooperation in the dark: signalling and collective action in quorum-sensing bacteria.
The study of quorum-sensing bacteria has revealed a widespread mechanism of coordinating bacterial gene expression with cell density. By monitoring a constitutively produced signal molecule, individual bacteria can limit their expression of group-beneficial phenotypes to cell densities that guarantee an effective group outcome. In this paper, we attempt to move away from a commonly expressed view that these impressive feats of coordination are examples of multicellularity in prokaryotic populations. Here, we look more closely at the individual conflict underlying this cooperation, illustrating that, even under significant levels of genetic conflict, signalling and resultant cooperative behaviour can stably exist. A predictive two-trait model of signal strength and of the extent of cooperation is developed as a function of relatedness (reflecting multiplicity of infection) and basic population demographic parameters. The model predicts that the strength of quorum signalling will increase as conflict (multiplicity of infecting strains) increases, as individuals attempt to coax more cooperative contributions from their competitors, leading to a devaluation of the signal as an indicator of density. Conversely, as genetic conflict increases, the model predicts that the threshold density for cooperation will increase and the subsequent strength of group cooperation will be depressed.
Bacterial Physiological Phenomena↗
The evolution of cooperative breeding through group augmentation.
Some individuals (helpers) in cooperatively breeding species provide alloparental care and often suppress their own reproduction. Kin selection is clearly an important explanation for such behaviour, but a possible alternative is group augmentation where individuals survive or reproduce better in large groups and where it therefore pays to recruit new members to the group. The evolutionary stability of group augmentation is currently disputed. We model evolutionarily stable helping strategies by following the dynamics of social groups with varying degrees of subordinate help. We also distinguish between passive augmentation, where a group member benefits from the mere presence of others, and active augmentation, where their presence as such is neutral or harmful, but where helping to recruit new group members may still be beneficial if they in turn actively provide help for the current reproductives ('delayed reciprocity'). The results show that group augmentation (either passive or active) can be evolutionarily stable and explain costly helping by non-reproductive subordinates, either alone or leading to elevated help levels when acting in concert with kin selection. Group augmentation can thus potentially explain the weak relationships between relatedness and helping behaviour that are observed in some cooperatively breeding species. In some cases, the superior mutualistic performance of cooperatively behaving groups can generate an incentive to stay and help which is strong enough to make ecological constraints unnecessary for explaining the stability of cooperatively breeding groups.
Animals↗
Begging and bleating: the evolution of parent-offspring signalling.
The evolution of biological signalling in the face of evolutionary conflicts of interest is an active area of evolutionary ecology, and one to which Maynard Smith has made important contributions. We explore the major theoretical challenges in the field, concentrating largely on how offspring signal to their parents when there is the potential for parent-offspring conflict. Costly offspring solicitation (begging etc.) has been interpreted in terms of a Zahavi Grafen honest handicap signal, but this has been challenged on the grounds of' the costs of signalling. We review this controversy and also explore the issue of pooling versus separating signalling equilibrium. An alternative explanation for costly begging is that it is due to sibling competition, and we discuss the relationship between these ideas and signalling models in families with more than one offspring. Finally we consider signal uncertainty, how signalling models can be made dynamic, and briefly how they may be tested experimentally.
Animal Communication↗
Coalition formation in animals and the nature of winner and loser effects.
Coalition formation has been documented in a diverse array of taxa, yet there has been little formal analysis of polyadic interactions such as coalitions. Here, we develop an optimality model which examines the role of winner and loser effects in shaping coalition formation. We demonstrate that the predicted patterns of alliances are strongly dependent on the way in which winner and loser effects change with contestant strength. When winner and loser effects decrease with the resource-holding power (RHP) of the combatants, coalitions will be favoured between the strongest members of a group, but not between the weakest. If, in contrast, winner and loser effects increase with RHP, exactly the opposite predictions emerge. All other things being equal, intervention is more likely to prove worthwhile when the beneficiary of the aid is weaker (and its opponent is stronger), because the beneficiary is then less likely to win without help. Consequently, intervention is more probable when the impact of victory on the subsequent performance of a combatant increases with that individual's strength because this selects for intervention in favour of weaker combatants. The published literature on hierarchy formation does not reveal how winner and loser effects actually change with contestant strength and we therefore hope that our model will spur others to collect such data; in this light we suggest an experiment which will help to elucidate the nature of winner and loser effects and their impact on coalition formation in animals.
Aggression↗
Signaling of need, sibling competition, and the cost of honesty.
Young birds and mammals frequently solicit food by means of extravagant and apparently costly begging displays. Much attention has been devoted to the idea that these displays are honest signals of need, and that their apparent cost serves to maintain their honesty. Recent analyses, however, have shown that the cost needed to maintain a fully informative, honest signal may often be so great that both offspring (signaler) and parent (receiver) would do better to refrain from communication. This apparently calls into question the relevance of the costly signaling hypothesis. Here, I show that this argument overlooks the impact of sibling competition. When multiple signalers must compete for the attention of a receiver (as is commonly the case in parent-offspring interactions), I show that (all other things being equal) individual equilibrium signal costs will typically be lower. The greater the number of competitors, the smaller the mean cost, though the maximum level of signal intensity employed by very needy signalers may actually increase with the number of competitors. At the same time, costs become increasingly sensitive to relatedness among signalers as opposed to relatedness between signalers and receivers. As a result of these trends, signaling proves profitable for signalers under a much wider range of conditions when there is competition (though it is still likely to be unprofitable for receivers).
Journal Article↗
The evolution of exploitation and honesty in animal communication: a model using artificial neural networks.
Conflicts of interest arise between signaller and receiver in most kinds of biological communication. Some authors have argued that this conflict is likely to give rise to deceit and exploitation, as receivers lag behind in the coevolutionary 'arms race' with signallers. Others have argued that such manipulation is likely to be short-lived and that receivers can avoid being deceived by paying attention to signals that are costly and hence 'unfakeable.' These two views have been hard to reconcile. Here, we present results from simulations of signal evolution using artificial neural networks, which demonstrate that honesty can coexist with a degree of exploitation. Signal cost ensures that receivers are able to obtain some honest information, but is unable to prevent exploitative signalling strategies from gaining short-term benefits. Although any one receiver bias that is open to exploitation will subsist for only a short period of time once signallers begin to take advantage of it, new preferences of this kind are constantly regenerated through selection and random drift. Hidden preferences and sensory exploitation are thus likely to have an enduring influence on the evolution of honest, costly signals. At the same time, honesty and cost are prerequisites for the evolution of exploitation. When signalling is cost-free, selection cannot act to maintain honesty, and receivers rapidly evolve to ignore signals. This leads to a reduction in the extent of hidden preference, and a consequent loss of potential for exploitation.
Animal Communication↗
Sexual selection, honest advertisement and the handicap principle: reviewing the evidence.
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Amphibians↗
Female preference for symmetrical males as a by-product of selection for mate recognition.
Fluctuating asymmetry (FA) refers to the random, stress-induced deviations from perfect symmetry that develop during the growth of bilaterally symmetrical traits. Individual differences in the level of FA may influence mate choice: in a number of species, females prefer to mate with males that have more symmetrical sexual ornaments. As the degree of FA has been shown to reflect the ability of individuals to cope with a wide variety of environmental stresses, it has been suggested that mating preferences for symmetry evolve for adaptive reasons, because the degree of FA provides honest information about male quality. Here I use simple, artificial neural networks to show that such preferences are likely to arise in the absence of any link between symmetry and quality, as a by-product of selection for mate recognition.
Animals↗
Why we need ESS signalling theory.
Evolutionarily stable strategy (ESS) models of biological signalling are important because the intimate coevolution of signalling and receiving strategies is complicated. Tentative results from a numerical study of error-prone signalling show the value of formal modelling. Error in perception can create discreteness in the distribution of signals produced, and so observed discreteness in nature may call for no more complicated explanation. Further developments in the theory of signalling may include a link with theories of aggression such as the sequential assessment game. The technical device of a 'scratch space' may allow a natural development of 'two-way' information games in which each contestant plays the roles of signaller and receiver simultaneously. This device may also incidentally derive mental states from purely strategic considerations.
Animal Communication↗
Variation across species in the size of the nuclear genome supports the junk-DNA explanation for the C-value paradox.
The amount of DNA in the nuclear genome (the DNA C-value) of eukaryotes varies at least 80,000-fold across species, and yet bears little or no relation to organismic complexity or to the number of protein-coding genes. This phenomenon is known as the C-value paradox. One explanation for the C-value paradox attributes the size of the nuclear genome to 'junk' (typically non-coding) genetic elements that accumulate until the costs to the organism of replicating excess DNA select against it. Across species, organisms that develop at a slower rate should tolerate more junk DNA. Alternatively, junk DNA may function as a nucleo-skeleton to maintain the volume of the nucleus at a size proportional to the volume of the cytoplasm in the cell. Across species, the DNA C-value is predicted to vary with the nuclear and cytoplasmic volumes of cells. Previous studies have not been able to distinguish between the skeletal-DNA and junk-DNA explanations for the C-value paradox. We report a study of DNA content in 24 salamander species which does. The size of the nuclear genome is correlated with developmental rate even after the effects of nuclear and cytoplasmic volume have been removed. However, genome size is not correlated with cytoplasmic volume after controlling for developmental rate. These results support the view that junk DNA accumulates in the nuclear genome until the costs of replicating it become too great, rather than that it functions as a nucleo-skeleton.
Animals↗
Error-prone signalling.
The handicap principle of Zahavi is potentially of great importance to the study of biological communication. Existing models of the handicap principle, however, make the unrealistic assumption that communication is error free. It seems possible, therefore, that Zahavi's arguments do not apply to real signalling systems, in which some degree of error is inevitable. Here, we present a general evolutionarily stable strategy (ESS) model of the handicap principle which incorporates perceptual error. We show that, for a wide range of error functions, error-prone signalling systems must be honest at equilibrium. Perceptual error is thus unlikely to threaten the validity of the handicap principle. Our model represents a step towards greater realism, and also opens up new possibilities for biological signalling theory. Concurrent displays, direct perception of quality, and the evolution of 'amplifiers' and 'attenuators' are all probable features of real signalling systems, yet handicap models based on the assumption of error-free communication cannot accommodate these possibilities.
Animal Communication↗
The continuous Sir Philip Sidney game: a simple model of biological signalling.
An analysis of Maynard Smith's two-player, ESS model of biological signalling, the "Sir Philip Sidney game", is presented. The stable strategies of the players in this game are shown to satisfy the conditions of Zahavi's handicap principle. At equilibrium, signals are honest, costly, and costly in a way that is related to the true quality revealed. Further analysis reveals that the level of cost required to maintain stability is inversely related to the degree of relatedness between the players. It therefore seems likely that stable biological signalling systems will feature lower signalling costs when communication occurs between relatives. A three-player, extended version of the model is investigated, in which signals are passed via an intermediate, or "messenger". It is shown that this destabilizes the signalling system, and leads to increased signalling costs. This result suggests that "kin conflict" theories of the evolution of the endosperm in flowering plants require further refinement. The introduction of a novel resource acquisition tissue, which mediates parent-offspring interaction during development, cannot be assumed to limit parent-offspring conflict simply because it carries an extra copy of the maternally inherited genes. The ability to add such complications to the Sir Philip Sidney game and still obtain solutions makes it a very useful modelling tool.
Animals↗
A review of fatal road accidents in Oxfordshire over a 2-year period.
The records of 131 road accident fatalities which occurred in Oxfordshire over a 2-year period were reviewed. Aspects of the accident circumstances, the injuries incurred and the cause of death were examined. The majority of fatal accidents occurred during daylight hours and in dry weather. Deaths were mainly due to cerebral injury (34.4 per cent) or uncontrollable (mainly thoracic) haemorrhage (25.2 per cent), or a combination of both (8.4 per cent). A number of deaths occurred in hospital from complications rather than from the injury itself. In addition to this, there were four deaths from natural causes. Where death occurred at the scene of the accident, blood alcohol levels were determined. Almost 50 per cent of the drivers for whom a level was obtained had measurable alcohol in their bloodstream, and 28 per cent of such drivers were over the legal limit. Three cases who reached hospital alive were, on review, assessed to have potentially survivable injuries, and a further two patients died in the post-accident period of potentially survivable complications.
Accidents, Traffic↗
Biomechanical aspects of pelvic and hip injuries in road traffic accidents.
The mechanism of pelvic fractures has been well documented from radiographs but little is known of the forces required to produce these injuries. We examined 40 cases of pelvic injury sustained in road traffic accidents where the direction of impact and the velocity differential was known. In frontal impacts, indirect shear injuries of the pelvis were prominent, while in side impacts, lateral compressive injuries occurred. With increasing velocity differentials and vehicle deformation and intrusion, more severe pelvic injury occurred, often in association with significant head, chest, and lower limb injuries. Side impacts were noted to produce more severe injuries at lower velocity differentials when compared with frontal crashes.
Accidents, Traffic↗
Incidence and consequences of ejection in motor vehicle accidents.
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Accidents, Traffic↗