Joint evolution of sex ratio and reproductive group size under local mate competition with inbreeding depression

Local mate competition (LMC) may involve some amount of inbreeding between siblings. Because sib-mating is generally accompanied by inbreeding depression, natural selection may favor a reduced rate of sib-mating, possibly affecting the evolution of sex ratio and reproductive group size. The present study theoretically investigated the evolution of these traits under LMC in the presence of inbreeding depression. When the reproductive group size evolves, the determination mechanism of sex ratio is important because the timescale of the sex ratio response to reproductive group size can affect the evolutionary process. We consider a spectrum of sex ratio determination mechanisms from purely unconditional to purely conditional, including intermediate modes with various relative strengths of unconditional and conditional effects. This analysis revealed that both the evolutionarily stable reproductive group size and ratio of males increase with higher inbreeding depression and with a larger relative strength of an unconditional effect in sex ratio determination. Unexpectedly, when the sex ratio is controlled purely conditionally, the reproductive group size cannot exceed three even under the severest level of inbreeding depression (i.e., lethal effect). The present study reveals the conditions for LMC to evolve through the analysis of the joint evolution of reproductive group size and sex ratio.     

The evolution of fidelity in sensory systems

We investigate the effect that noise has on the evolution of measurement strategies and competition in populations of organisms with sensory systems of differing fidelities. We address two questions motivated by experimental and theoretical work on sensory systems in noisy environments: (1) How complex must a sensory system be in order to face the need to develop adaptive measurement strategies that change depending on the noise level? (2) Does the principle of competitive exclusion for sensory systems force one population to win out over all others? We find that the answer to the first question is that even very simple sensory systems will need to change measurement strategies depending on the amount of noise in the environment. Interestingly, the answer to the second question is that, in general, at most two populations with different fidelity sensory systems may co-exist within a single environment.     

Contract theory for the evolution of cooperation: The right incentives attract the right partners

Partner choice is a critical stage of many biological interactions, from mating to cooperation. When the quality of the potential partners is unknown, one way to choose is to rely on signaling: costly signals can reveal the quality of the sender and allow the receiver to choose. In some cases, however, signaling (or an active choice based on signals) is not possible, for example in the initiation of the symbiosis between the squid Euprymna scolopes and the bioluminescent bacterium Vibrio fischeri. How is partner choice possible in this and other similar cases? I show that in a game with asymmetric information without signaling, imposing a deliberate cost for establishing the interaction allows the non-informed individual to attract the right partner if the cost induces only high quality individuals to accept the interaction. Furthermore, imposing different costs and rewards may induce the informed individuals to screen themselves according to their types, and therefore allow the non-informed individual to establish an association with the correct partners in the absence of signaling.     

The evolution of cultural evolution

Humans are unique in their range of environments and in the nature and diversity of their behavioral adaptations. While a variety of local genetic adaptations exist within our species, it seems certain that the same basic genetic endowment produces arctic foraging, tropical horticulture, and desert pastoralism, a constellation that represents a greater range of subsistence behavior than the rest of the Primate Order combined. The behavioral adaptations that explain the immense success of our species are cultural in the sense that they are transmitted among individuals by social learning and have accumulated over generations. Understanding how and when such culturally evolved adaptations arise requires understanding of both the evolution of the psychological mechanisms that underlie human social learning and the evolutionary (population) dynamics of cultural systems.     

Play and the evolution of fairness: a game theory model

Bekoff [J. Consci. Stud. 8 (2001) 81] argued that mammalian social play is a useful behavioral phenotype on which to concentrate in order to learn more about the evolution of fairness. Here, we build a game theoretical model designed to formalize some of the ideas laid out by Bekoff, and to examine whether ‘fair’ strategies can in fact be evolutionarily stable. The models we present examine fairness at two different developmental stages during an individual's ontogeny, and hence we create four strategies—fair at time 1/fair at time 2, not fair at time 1/not fair at time 2, fair at time 1/not fair at time 2, not fair at time 1/fair at time 2. Our results suggest that when considering species where fairness can be expressed during two different developmental stages, acting fairly should be more common than never acting fairly. In addition, when no one strategy was evolutionarily stable, we found that all four strategies we model can coexist at evolutionary equilibrium. Even in the absence of an overwhelming database from which to test our model, the general predictions we make have significant implications for the evolution of fairness.     

The limits of adaptation: humans and the predator-prey arms race

In the history of life, species have adapted to their consumers by evolving a wide variety of defenses. By contrast, animal species harvested in the wild by humans have not adapted structurally. Nonhuman predators have high failure rates at one or more stages of an attack, indicating that victim species have spatial refuges or phenotypic defenses that permit further functional improvement. A new compilation confirms that species in the wild cannot achieve immunity from human predation with structural defenses. The only remaining options are to become undesirable or to live in or escape to places where harvesting by people is curtailed. Escalation between prey defenses and predators' weapons may be restricted under human dominance to interactions involving those low-level predators that have benefited from human overexploitation of top consumers.     

Feedback selection and the evolution of modifiers

The problem of modifier evolution was examined with regard to the idea that modifier evolution can be considered as a result of selection for adaptation speed in populations far from equilibrium. This kind of selection was called feedback selection in order to emphasize the difference to theories which consider modifier evolution near the equilibrium. The basic principles of this kind of selection are derived for asexual populations and the problem of dominance is discussed in the light of this concept. In general the results support the view, that the genetic properties of a character are selected along with the character itself.This work was supported by the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung (Proj. Nr. 3502).     

Neighbor intervention: a game-theoretic model

It has long been argued that a resident may benefit from helping its neighbor defend a territory against a challenger to avoid renegotiating its boundaries with a new and potentially stronger individual. We quantify this theory by exploring games involving challengers, residents and potential allies. In a simplified discrete game with zero variation of fighting strength, helping neighbors is part of an evolutionarily stable strategy (ESS) only if fighting costs are low relative to those of renegotiation. However, if relative fighting costs are high then an interventional ESS remains possible with finite variation of strength. Under these conditions, neighbors may help residents fight off intruders, but only when the resident does not stand a reliable chance of winning alone. We show that neighbor intervention is more likely with low home advantage to occupying a territory, strengths combining synergistically or low probability that an ally will be usurped, amongst other factors. Our parameterized model readily explains occasional intervention in the Australian fiddler crab, including why the ally tended to be larger than both the assisted neighbor and the intruder. Reciprocity is not necessary for this type of cooperation to persist, but also it is by no means inevitable in territorial species.     

Frustrative reward omission increases aggressive behaviour of inferior fighters

Animals use aggressive behaviour to gain access to resources, and individuals adjust their behaviour relative to resource value and own resource holding potential (RHP). Normally, smaller individuals have inferior fighting abilities compared with larger conspecifics. Affective and cognitive processes can alter contest dynamics, but the interaction between such effects and that of differing RHPs has not been adjudged. We investigated effects of omission of expected reward (OER) on competing individuals with contrasting RHPs. Small and large rainbow trout (Oncorhynchus mykiss) were conditioned to associate a light with reward. Thereafter, the reward was omitted for half of the fish prior to a contest between individuals possessing a 36–40% difference in RHP. Small control individuals displayed submissive behaviour and virtually no aggression. By contrast, small OER individuals were more aggressive, and two out of 11 became socially dominant. Increased aggression in small OER individuals was accompanied by increased serotonin levels in the dorsomedial pallium (proposed amygdala homologue), but no changes in limbic dopamine neurochemistry were observed in OER-exposed individuals. The behavioural and physiological response to OER in fish indicates that frustration is an evolutionarily conserved affective state. Moreover, our results indicate that aggressive motivation to reward unpredictability affects low RHP individuals strongest.     

菌心进化论:一种对于动物进化的新理解

达尔文进化论强调了"物竞天择,适者生存"的理念与逻辑,对动物起源与进化提供了重要解释;然而,为什么会有动物、以及为什么会进化出人类等问题,却仍无答案。在我们实验室近年来从事肥胖及相关慢病研究中发现"饥饿源于菌群"并发展出可通过控制肠道菌群向人体传递的饥饿感的生物技术之后,提出科学假说认为,和人类同样具有消化道结构的动物,很有可能也是受到肠道菌群摄食的胁迫压力而进化的,即动物和人体的消化道以"中空"的拓扑学结构为基础,形成可容纳与相应动物种类相适应的肠道菌群微生态系统。这些肠道菌群终生共生于肠道,通过向动物传递饥饿感而迫使动物摄食而生存,同时肠道菌群也通过动物摄食的营养物质繁殖自己的后代,从而提出了以肠道菌群为中心、动物受肠道菌群胁迫而协同进化的"菌心进化论",是对"宿主进化论"的重要补充和完善,有利于我们从新的角度来理解和诠释动物的起源、进化和发展过程,乃至促进我们逐渐理解自然界从动物进化到人类之后,有可能是在实现从菌群主导的以食物为代表的"物质需求"向人类智慧主导的"精神需求"的新跃迁。     

分子生物学与进化的新理论

论述了由于分子生物学取得的成就,而形成的生物进化的新理论,并阐述了若干新理论指导生产实践取得的巨大应用成果。     

A mathematical model of biological evolution

In order to understand generally how the biological evolution rate depends on relevant parameters such as mutation rate, intensity of selection pressure and its persistence time, the following mathematical model is proposed: dN _n (t)/dt=(m _n (t-)N _n (t)+N _n-1(t) (n=0,1,2,3...), where N _n (t) and m _n (t) are respectively the number and Malthusian parameter of replicons with step number n in a population at time t and is the mutation rate, assumed to be a positive constant. The step number of each replicon is defined as either equal to or larger by one than that of its parent, the latter case occurring when and only when mutation has taken place. The average evolution rate defined by is rigorously obtained for the case (i) m _n (t)=m _n is independent of t (constant fitness model), where m _n is essentially periodic with respect to n, and for the case (ii) (periodic fitness model), together with the long time average m of the average Malthusian parameter . The biological meaning of the results is discussed, comparing them with the features of actual molecular evolution and with some results of computer simulation of the model for finite populations.An early version of this study was read at the International Symposium on Mathematical Topics in Biological held in kyoto, Japan, on September 11–12, 1978, and was published in its Procedings.     

The story of a largely unknown evolution – Germ theory hoax

The Piltdown Man debacle provides us with the most infamous forgery in science. However, another equally intriguing story exists concerning a document by a Bostonian called George Sleeper, which purported to be a pre-Darwin–Wallace anticipation of evolution and an equally convincing account of the germ theory published before Louis Pasteur’s famous studies on this subject. The story involves two giants in the world of evolutionary theory, Alfred Russel Wallace and E.B. Poulton. While Wallace was convinced that the Sleeper document was genuine, Poulton’s detailed investigations showed that it was a fake and a hoax. Despite this conclusion, doubts still exist about the authenticity of the Sleeper document.     

Classes of communication and the conditions for their evolution

Evolution of communication is conceptualized as a coevolutionary process in which evolution of signaler and that of receiver occur in an interdependent manner. Three classes of communication, mutualistic, altruistic, and exploiting, are distinguished depending on who gains a benefit or suffers a cost from successful communication. Communication is also dichotomized according to whether individuals are innately able to send and receive relevant signals or they have to acquire those signals culturally. We develop two-locus haploid models that represent the coevolutionary nature of the evolution of communication, and derive the conditions under which communicators can invade a population of non-communicators and those under which a population of communicators is evolutionarily stable against the invasion by non-communicators for each of the three classes of communication. Analysis of the models reveals that interaction among siblings enables the invasion of communication and that the optimal probability of interaction with siblings depends on the class of communication and the mode of signal transmission. In addition, cultural exploiting communication is more likely to invade a population of non-communicators than is genetic exploiting communication under certain circumstances.     

The theory of everything and molecular evolution

The theory of everything is discussed in relationship to early bacterial molecular evolution. The emphasis is on time, space (or location at the molecular level), the universal construction kit (elements contained in periodic table) and change per units of time that were necessary for early bacterial molecular evolution to occur.     

Fairness evolution in the ultimatum game is a function of reward size

I formulate a simple model of the ultimatum game, in which a proposer and a responder can receive a reward if they agree on how to divide this reward between them. The model is easy to analyse and shows that strong tendencies to fair division are expected when evolution of strategy frequencies follow the traditional gradient dynamics assumed in evolutionary models. The mean stable offer is typically around 20-40% although this depends on the maximum payoff and if rejection thresholds can evolve independently from proposals. The stable proportion offered at evolutionary equilibrium increases with the maximum payoff, if proposal and acceptance thresholds are dictated by the same strategy and cannot evolve independently. If proposal and acceptance evolve independently, the stable proportion instead decreases with the maximum payoff. The stable outcome may also show substantial variation.     

The evolution of respect for property

Although possession is ‘nine‐tenths of the law’, respect for ownership is widespread in the animal kingdom even without third‐party enforcement. Thus, the first individuals to find objects are frequently left unchallenged by potential competitors and tend to win contests when disputes arise. Game theory has shown that respect for ownership (‘Bourgeois’ behaviour) can arise as an arbitrary convention to avoid costly disputes. However, the same theory predicts that a paradoxical respect for lack of ownership (‘anti‐Bourgeois’ behaviour) can evolve under the same conditions and in some cases is the only stable outcome. Despite these predictions, anti‐Bourgeois behaviour is rare in nature, whereas respect for ownership is frequently not absolute. Here, we review extensions of the classic models involving repeated interactions, confusion over roles, strategic coordination of behaviour (‘secret handshakes’), owner–intruder asymmetries and continuous control of fighting investment. Confusion over roles and owner–intruder asymmetries in fighting ability may explain why respect for ownership is often partial. Moreover, although most model extensions facilitate the evolution of Bourgeois‐like behaviour, secret handshakes and continuous control of fighting investment render the alternative anti‐Bourgeois convention unstable. We develop these insights to highlight several key areas for future investigation.     

The probability of parallel evolution

Abstract How often will natural selection drive parallel evolution at the DNA sequence level? More precisely, what is the probability that selection will cause two populations that live in identical environments to substitute the same beneficial mutation? Here I show that, under fairly general conditions, the answer is simple: if a wild‐type sequence can mutate to n different beneficial mutations, replicate populations will on average fix the same mutation with probability P= 2/(n + 1). This probability, which is derived using extreme value theory, is independent of most biological details, including the length of the gene in question and the precise distribution of fitness effects among alleles. I conclude that the probability of parallel evolution under natural selection is nearly twice as large as that under neutrality.     

Effects of metabolic rate on protein evolution

Since the modern evolutionary synthesis was first proposed early in the twentieth century, attention has focused on assessing the relative contribution of mutation versus natural selection on protein evolution. Here we test a model that yields general quantitative predictions on rates of protein evolution by combining principles of individual energetics with Kimura's neutral theory. The model successfully predicts much of the heterogeneity in rates of protein evolution for diverse eukaryotes (i.e. fishes, amphibians, reptiles, birds, mammals) from different thermal environments. Data also show that the ratio of non-synonymous to synonymous nucleotide substitution is independent of body size, and thus presumably of effective population size. These findings indicate that rates of protein evolution are largely controlled by mutation rates, which in turn are strongly influenced by individual metabolic rate.