On the evolutionary stability of zero-cost pooled-equilibrium signals

A key question in the development of understanding of animal communication has been what maintains the honesty of signals, stopping dishonesty (cheating) from spreading. The dominant theory used to address this question is a refinement of Zahavi's handicap principle. The vital thing about handicap signals is that their honesty requires that those signals are costly to the sender over and above the minimum costs associated with transmission; these costs are generally called strategic costs. An alternative "pooled equilibria" has been proposed. If signalling is constrained to two levels, then it can be demonstrated that even if there is no cost associated with giving a signal, there can be a signalling evolutionarily stable strategy (ESS) where signallers are arranged into pools according to their state: those below a threshold give one signal, those above this threshold always give the other. Further, this can be generalized to any finite number of discrete signals. Here we explore the consequence of generalizing to a continuously varying signal form. We show that unless there is some physical impediment to the diversity of signals possible, then pooled-equilibrium signalling strategies are not stable. Such a strategy would be invaded by a more complex signal, where some individuals within a "pool" benefit from signalling their difference from other individuals within the pool. We suggest that such impediments to variation in signal form will be uncommon in nature, and thus so will pooled equilibria

The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins

BACKGROUND: Many quadrupedal species stand bipedally on their hindlimbs to fight. This posture may provide a performance advantage by allowing the forelimbs to strike an opponent with the range of motion that is intrinsic to high-speed running, jumping, rapid braking and turning; the range of motion over which peak force and power can be produced. METHODOLOGY/PRINCIPAL FINDINGS: To test the hypothesis that bipedal (i.e., orthograde) posture provides a performance advantage when striking with the forelimbs, I measured the force and energy produced when human subjects struck from "quadrupedal" (i.e., pronograde) and bipedal postures. Downward and upward directed striking energy was measured with a custom designed pendulum transducer. Side and forward strikes were measured with a punching bag instrumented with an accelerometer. When subjects struck downward from a bipedal posture the work was 43.70±12.59% (mean ± S.E.) greater than when they struck from a quadrupedal posture. Similarly, 47.49±17.95% more work was produced when subjects struck upward from a bipedal stance compared to a quadrupedal stance. Importantly, subjects did 229.69±44.19% more work in downward than upward directed strikes. During side and forward strikes the force impulses were 30.12±3.68 and 43.04±9.00% greater from a bipedal posture than a quadrupedal posture, respectively. CONCLUSIONS/SIGNIFICANCE: These results indicate that bipedal posture does provide a performance advantage for striking with the forelimbs. The mating systems of great apes are characterized by intense male-male competition in which conflict is resolved through force or the threat of force. Great apes often fight from bipedal posture, striking with both the fore- and hindlimbs. These observations, plus the findings of this study, suggest that sexual selection contributed to the evolution of habitual bipedalism in hominins

Divergent receiver responses to components of multimodal signals in two foot-flagging frog species.

Multimodal communication of acoustic and visual signals serves a vital role in the mating system of anuran amphibians. To understand signal evolution and function in multimodal signal design it is critical to test receiver responses to unimodal signal components versus multimodal composite signals. We investigated two anuran species displaying a conspicuous foot-flagging behavior in addition to or in combination with advertisement calls while announcing their signaling sites to conspecifics. To investigate the conspicuousness of the foot-flagging signals, we measured and compared spectral reflectance of foot webbings of Micrixalus saxicola and Staurois parvus using a spectrophotometer. We performed behavioral field experiments using a model frog including an extendable leg combined with acoustic playbacks to test receiver responses to acoustic, visual and combined audio-visual stimuli. Our results indicated that the foot webbings of S. parvus achieved a 13 times higher contrast against their visual background than feet of M. saxicola. The main response to all experimental stimuli in S. parvus was foot flagging, whereas M. saxicola responded primarily with calls but never foot flagged. Together these across-species differences suggest that in S. parvus foot-flagging behavior is applied as a salient and frequently used communicative signal during agonistic behavior, whereas we propose it constitutes an evolutionary nascent state in ritualization of the current fighting behavior in M. saxicola

Four Puzzles of Reputation-Based Cooperation Content, Process, Honesty, and Structure

Research in various disciplines has highlighted that humans are uniquely able to solve the problem of cooperation through the informal mechanisms of reputation and gossip. Reputation coordinates the evaluative judgments of individuals about one another. Direct observation of actions and communication are the essential routes that are used to establish and update reputations. In large groups, where opportunities for direct observation are limited, gossip becomes an important channel to share individual perceptions and evaluations of others that can be used to condition cooperative action. Although reputation and gossip might consequently support large-scale human cooperation, four puzzles need to be resolved to understand the operation of reputation-based mechanisms. First, we need empirical evidence of the processes and content that form reputations and how this may vary cross-culturally. Second, we lack an understanding of how reputation is determined from the muddle of imperfect, biased inputs people receive. Third, coordination between individuals is only possible if reputation sharing and signaling is to a large extent reliable and valid. Communication, however, is not necessarily honest and reliable, so theoretical and empirical work is needed to understand how gossip and reputation can effectively promote cooperation despite the circulation of dishonest gossip. Fourth, reputation is not constructed in a social vacuum; hence we need a better understanding of the way in which the structure of interactions affects the efficiency of gossip for establishing reputations and fostering cooperation.Funding Agencies|Linkoping University; National Research, Development and Innovation Office - NKFIH (OTKA) grantOrszagos Tudomanyos Kutatasi Alapprogramok (OTKA) [K 132250]; European Research Council (ERC) under the European Unions research and innovation programmeEuropean Research Council (ERC) [648693]</p

Is honesty the best policy? Testing signal reliability in fiddler crabs when receiver-dependent costs are high

Contests between conspecific males are an important method of establishing mating rights or territories, yet the potential costs of injuries are high. To reduce potential risks, males can use signals to convey information about their underlying strength to competitors, and although individuals could signal deceptively to gain an advantage, most signals seem to be reliable. Theory suggests that signal reliability is maintained because individuals that signal unreliably may be punished (i.e. receiver-imposed costs). Manipulative studies support this idea, showing that low-quality individuals that are given high-quality signals bear substantial costs. Here, we explore the importance of receiver-imposed costs in natural, un-manipulated populations. Specifically, we show how the likelihood of being exposed (i.e. potential receiver density) and the potential severity of punishment (i.e. average receiver size) affect the predominance of unreliable signalling among populations. Male fiddler crabs, Uca vomeris, use their enlarged claws as signals and weapons in combat, and the relationship between claw size (signal) and strength (quality) determines whether or not a male is a reliable signaller. We predicted that the prevalence of unreliable signalling among individual males would increase in populations where the receiver-imposed costs of deception were low. That is, males should produce unreliable (large but weak) claws. We show that individual crabs produce more reliable signals of strength in populations with a high biomass, where there are both higher densities and larger average body sizes of potential receivers. Our study provides evidence that receiver-imposed costs can maintain signal reliability in natural un-manipulated populations and supports contemporary models of aggressive signalling. © 2012 The Authors. Functional Ecolog

Restrictions on biological adaptation in language evolution

Language acquisition and processing are governed by genetic constraints. A crucial unresolved question is how far these genetic constraints have coevolved with language, perhaps resulting in a highly specialized and species-specific language "module," and how much language acquisition and processing redeploy preexisting cognitive machinery. In the present work, we explored the circumstances under which genes encoding language-specific properties could have coevolved with language itself. We present a theoretical model, implemented in computer simulations, of key aspects of the interaction of genes and language. Our results show that genes for language could have coevolved only with highly stable aspects of the linguistic environment; a rapidly changing linguistic environment does not provide a stable target for natural selection. Thus, a biological endowment could not coevolve with properties of language that began as learned cultural conventions, because cultural conventions change much more rapidly than genes. We argue that this rules out the possibility that arbitrary properties of language, including abstract syntactic principles governing phrase structure, case marking, and agreement, have been built into a "language module" by natural selection. The genetic basis of human language acquisition and processing did not coevolve with language, but primarily predates the emergence of language. As suggested by Darwin, the fit between language and its underlying mechanisms arose because language has evolved to fit the human brain, rather than the reverse

Resolving current disagreements and ambiguities in the terminology of animal communication

Communication is central to most interactions between organisms. There is currently considerable controversy about the evolution, function and even about the most basic definition of communication. The controversy is linked to definitional ambiguities and disagreements. Here we discuss how some recent disagreements can be resolved and offer a clear set of definitions. Central to our approach is a definition of communication as being a trade between one organism (the informer) and another (the perceiver). The informer exerts influence on the perceiver through the communication process, and the perceiver experiences a change in its informational state (that is, gains information) as a consequence of detecting the communication. We define both influence and information explicitly and delineate between signalling, deceptive communication, and situations where perceivers respond to cues rather than signals. We demonstrate how our definitions allow resolution of conflicts arising in recent publications on the definitions on communication and related term