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Honesty and cheating in cleaning symbioses: evolutionarily stable strategies defined by variable pay-offs.

ABSTRACT: Game-theory models have indicated that the evolution of mixed strategies of cheating and honesty in many mutualisms is unlikely. Moreover, the mutualistic nature of interspecific interactions has often been difficult to demonstrate empirically. We present a game-theory analysis that addresses these issues using cleaning symbioses among fishes as a model system. We show that the assumption of constant pay-offs in existing models prevents the evolution of evolutionarily stable mixed strategies of cheating and honesty. However, when interaction pay-offs are assumed to be density dependent, mixed strategies of cheating and honesty become possible. In nature, cheating by clients often takes the form of retaliation by clients against cheating cleaners, and we show that mixed strategies of cheating and honesty evolve within the cleaner population when clients retaliate. The dynamics of strategies include both negative and positive effects of interactions, as well as density-dependent interactions. Consequently, the effects of perturbations to the model are nonlinear. In particular, we show that under certain conditions the removal of cleaners may have little impact on client populations. This indicates that the underlying mutualistic nature of some interspecific interactions may be difficult to demonstrate using simple manipulation experiments.

SUBMITTER: Freckleton RP

PROVIDER: S-EPMC1691242 | biostudies-literature | 2003 Feb

REPOSITORIES: biostudies-literature

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Honesty and cheating in cleaning symbioses: evolutionarily stable strategies defined by variable pay-offs.

Freckleton Robert P RP Côté Isabelle M IM

Proceedings. Biological sciences 20030201 1512

Game-theory models have indicated that the evolution of mixed strategies of cheating and honesty in many mutualisms is unlikely. Moreover, the mutualistic nature of interspecific interactions has often been difficult to demonstrate empirically. We present a game-theory analysis that addresses these issues using cleaning symbioses among fishes as a model system. We show that the assumption of constant pay-offs in existing models prevents the evolution of evolutionarily stable mixed strategies of ...[more]

PMID: 12614580

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Project description:BackgroundThe reliability of signals is a key issue in the study of animal communication. Both empirical work and theoretical models show that communication need not be entirely honest, and thus signals can be deceitful. Aggressive communication appears to be a prime candidate for such deceitful communication, because bluffing has been described in several species. Bluffing in these situations are supposed to be maintained by frequency dependent selection where the fitness of a given type depends on the frequencies of the other types in the population. Previous efforts to model such a scenario through individual based simulations have yielded conflicting results. Studies have either found a rich set of polymorphic strategies including the traditional cheating scenario or found none. Thus, the modelling assumptions responsible for these diverging conclusions remain unclear.ResultsIn this study, I investigate the effects of four modelling assumptions: the role of an extended strategy set, the initial population composition (seeding), the differences in pay-offs and finally different parameter spaces. I investigate the effects of these factors on the evolvability of both honest and mixed cheating strategies. I show that both honest and cheating equilibria readily evolve and that the investigated parameter range and the seeding of the starting populations have the greatest influence on the outcome.ConclusionsBoth honest signalling and polymorphic cheating equilibria are more likely to evolve from a narrow strategy set than from a random mixture of strategies. A large potential strategy set is not a setback for the evolution of communication -honest or cheating- as long as the initial population is seeded with only a few strategies. In addition, different sections of the parameter space show consistently different behaviour. Thus, frequency dependent selection has the potential to explain various empirical observations that show consistent differences in aggressive behaviour.

Project description:Host preference of symbionts evolves from fitness trade-offs. However, it is often unclear how interspecific variations in host response traits influence this evolutionary process. Using the association between the polyclad flatworm Paraprostatum echinolittorinae and its intertidal snail hosts on the Pacific Coast of Panama, we assessed how a symbiont's host preference is associated with varying host defenses and post-infestation performances. We first characterized the prevalence and intensity of worm infestation in five snail hosts (Tegula pellisserpentis, Nerita scabricosta, N. funiculata, Planaxis planicostatus, and Cerithium stercusmuscarum). We then used manipulative experiments to test flatworm's host choice, hosts' behavioral rejection of flatworms, and hosts' growth and survival following the infestation. In the field, flatworms were orders of magnitude more prevalent and dense in T. pellisserpentis, N. scabricosta, N. funiculata than P. planicostatus and C. stercusmuscarum, although the three former hosts were not necessarily more abundant. The results from our laboratory host selection trials mirrored these patterns; flatworms were 3 to 14 times more likely to choose T. pellisserpentis, N. scabricosta, N. funiculata over P. planicostatus and C. stercusmuscarum. The less preferred hosts frequently rejected flatworms via mantle contractions and foot withdrawals, which reduced the infestation rate by 39%-67%. These behaviors were less frequent or absent in the preferred hosts. Flatworm infestation variably influenced host performances in the field, negligibly affecting the growth and survival of T. pellisserpentis and N. funiculata but reducing the growth of P. planicostatus. Flatworms thus preferred less defended hosts that can also support higher worm densities without being harmed. Stable isotope analysis further revealed that flatworms are unlikely to feed on snail tissues and may live as a commensal in their preferred hosts. Our study demonstrates that host response traits can modulate a symbiont's host choice and calls for more explicit considerations of host response variability in host preference research.

Project description:IntroductionLife-history theory predicts that organisms trade off survival against reproduction. However, the time scales on which various consequences become evident and the physiology mediating the cost of reproduction remain poorly understood. Yet, explaining not only which mechanisms mediate this trade-off, but also how fast or slow the mechanisms act, is crucial for an improved understanding of life-history evolution. We investigated three time scales on which an experimental increase in body mass could affect this trade-off: within broods, within season and between years. We handicapped adult skylarks (Alauda arvensis) by attaching extra weight during first broods to both adults of a pair. We measured body mass, immune function and return rates in these birds. We also measured nest success, feeding rates, diet composition, nestling size, nestling immune function and recruitment rates.ResultsWhen nestlings of first broods fledged, parent body condition had not changed, but experimental birds experienced higher nest failure. Depending on the year, immune parameters of nestlings from experimental parents were either higher or lower than of control nestlings. Later, when parents were feeding their second brood, the balance between self-maintenance and nest success had shifted. Control and experimental adults differed in immune function, while mass and immune function of their nestlings did not differ. Although weights were removed after breeding, immune measurements during the second brood had the capacity to predict return rates to the next breeding season. Among birds that returned the next year, body condition and reproductive performance a year after the experiment did not differ between treatment groups.ConclusionsWe conclude that the balance between current reproduction and survival shifts from affecting nestlings to affecting parents as the reproductive season progresses. Furthermore, immune function is apparently one physiological mechanism involved in this trade-off. By unravelling a physiological mechanism underlying the trade-offs between current and future reproduction and by demonstrating the different time scales on which it acts, our study represents an important step in understanding a central theory of life-history evolution.

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Honesty and cheating in cleaning symbioses: evolutionarily stable strategies defined by variable pay-offs.

Publications

Honesty and cheating in cleaning symbioses: evolutionarily stable strategies defined by variable pay-offs.

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