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PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗
PubMed2003

The hitchhiker's guide to altruism: gene-culture coevolution, and the internalization of norms.

An internal norm is a pattern of behavior enforced in part by internal sanctions, such as shame, guilt and loss of self-esteem, as opposed to purely external sanctions, such as material rewards and punishment. The ability to internalize norms is widespread among humans, although in some so-called "sociopaths", this capacity is diminished or lacking. Suppose there is one genetic locus that controls the capacity to internalize norms. This model shows that if an internal norm is fitness enhancing, then for plausible patterns of socialization, the allele for internalization of norms is evolutionarily stable. This framework can be used to model Herbert Simon's (1990) explanation of altruism, showing that altruistic norms can "hitchhike" on the general tendency of internal norms to be personally fitness-enhancing. A multi-level selection, gene-culture coevolution argument then explains why individually fitness-reducing internal norms are likely to be prosocial as opposed to socially harmful.

Altruism↗
PubMed2005

Spatial effects in social dilemmas.

Social dilemmas and the evolutionary conundrum of cooperation are traditionally studied through various kinds of game theoretical models such as the prisoner's dilemma, public goods games, snowdrift games or by-product mutualism. All of them exemplify situations which are characterized by different degrees of conflicting interests between the individuals and the community. In groups of interacting individuals, cooperators produce a common good benefitting the entire group at some cost to themselves, whereas defectors attempt to exploit the resource by avoiding the costly contributions. Based on synergistic or discounted accumulation of cooperative benefits a unifying theoretical framework was recently introduced that encompasses all games that have traditionally been studied separately (Hauert, Michor, Nowak, Doebeli, 2005. Synergy and discounting of cooperation in social dilemmas. J. Theor. Biol., in press.). Within this framework we investigate the effects of spatial structure with limited local interactions on the evolutionary fate of cooperators and defectors. The quantitative effects of space turn out to be quite sensitive to the underlying microscopic update mechanisms but, more general, we demonstrate that in prisoner's dilemma type interactions spatial structure benefits cooperation-although the parameter range is quite limited-whereas in snowdrift type interactions spatial structure may be beneficial too, but often turns out to be detrimental to cooperation.

Biological Evolution↗
PubMed2005

Punishing and abstaining for public goods.

The evolution of cooperation within sizable groups of nonrelated humans offers many challenges for our understanding. Current research has highlighted two factors boosting cooperation in public goods interactions, namely, costly punishment of defectors and the option to abstain from the joint enterprise. A recent modeling approach has suggested that the autarkic option acts as a catalyzer for the ultimate fixation of altruistic punishment. We present an alternative, more microeconomically based model that yields a bistable outcome instead. Evolutionary dynamics can lead either to a Nash equilibrium of punishing and nonpunishing cooperators or to an oscillating state without punishers.

Altruism↗
PubMed2000

Evolution of serpin specificity: cooperative interactions in the reactive-site loop sequence of antithrombin specifically restrict the inhibition of activated protein C.

Protease cascades and their inhibitors are a common feature of many biological regulatory systems, and the various components of such cascades have been subjected to a long and concerted evolution. We present here evidence that in the coagulation cascade, the sequence of the protease-binding reactive-site loop of antithrombin has evolved such that the majority of its residues has been acquired not for the efficient inhibition of its target proteases, thrombin and factor Xa, but to avoid the inhibition of activated protein C (APC). We substituted residues of the reactive-site loop of antithrombin into alpha(1)-antitrypsin and tested the chimeras against thrombin, factor Xa, and APC. With respect to factor Xa and thrombin, the difference in association rate between the fastest and the slowest inhibitors was 5.5- and 88-fold, respectively. However, with respect to APC the difference was 12,500-fold. While most of the variation in the inhibition rates of thrombin could be accounted for by P2 Gly-to-Pro substitutions, for APC almost every residue had an effect on inhibition. In 22 of 25 direct comparisons of antitrypsin residues with antithrombin residues, either singly or in blocs, the antithrombin residues caused a decrease in the rate of inhibition of APC. The antithrombin residue Asn393, at position P'3, emerged as particularly important for avoiding the inhibition of APC, however, its 190-fold effect was seen only when in conjunction with antithrombin P7 to P'2 residues. Cooperative effects among residues of the reactive-site loop thus emerged as critical for restricting the activity of this sequence against APC.

Amino Acid Substitution↗
PubMed2003

Cooperation and conflict in the evolution of individuality. IV. Conflict mediation and evolvability in Volvox carteri.

The continued well being of evolutionary individuals (units of selection and evolution) depends upon their evolvability, that is their capacity to generate and evolve adaptations at their level of organization, as well as their longer term capacity for diversifying into more complex evolutionary forms. During a transition from a lower- to higher-level individual, such as the transition between unicellular and multicellular organisms, the evolvability of the lower-level (cells) must be restricted, while the evolvability of the new higher-level unit (multicellular organism) must be enhanced. For these reasons, understanding the factors leading to an evolutionary transition should help us to understand the factors underlying the emergence of evolvability of a new evolutionary unit. Cooperation among lower-level units is fundamental to the origin of new functions in the higher-level unit. Cooperation can produce a new more complex evolutionary unit, with the requisite properties of heritable fitness variations, because cooperation trades fitness from a lower-level (the costs of cooperation) to the higher-level (the benefits for the group). For this reason, the evolution of cooperative interactions helps us to understand the origin of new and higher-levels of fitness and organization. As cooperation creates a new level of fitness, it also creates the opportunity for conflict between levels of selection, as deleterious mutants with differing effects at the two levels arise and spread. This conflict can interfere with the evolvability of the higher-level unit, since the lower and higher-levels of selection will often "disagree" on what adaptations are most beneficial to their respective interests. Mediation of this conflict is essential to the emergence of the new evolutionary unit and to its continued evolvability. As an example, we consider the transition from unicellular to multicellular organisms and study the evolution of an early-sequestered germ-line in terms of its role in mediating conflict between the two levels of selection, the cell and the cell group. We apply our theoretical framework to the evolution of germ/soma differentiation in the green algal group Volvocales. In the most complex member of the group, Volvox carteri, the potential conflicts among lower-level cells as to the "right" to reproduce the higher-level individual (i.e. the colony) have been mediated by restricting immortality and totipotency to the germ-line. However, this mediation, and the evolution of an early segregated germ-line, was achieved by suppressing mitotic and differentiation capabilities in all post-embryonic cells. By handicapping the soma in this way, individuality is ensured, but the solution has affected the long-term evolvability of this lineage. We think that although conflict mediation is pivotal to the emergence of individuality at the higher-level, the way in which the mediation is achieved can greatly affect the longer-term evolvability of the lineage.

Adaptation, Physiological↗
PubMed2006

Evolutionary dynamics of social dilemmas in structured heterogeneous populations.

Real populations have been shown to be heterogeneous, in which some individuals have many more contacts than others. This fact contrasts with the traditional homogeneous setting used in studies of evolutionary game dynamics. We incorporate heterogeneity in the population by studying games on graphs, in which the variability in connectivity ranges from single-scale graphs, for which heterogeneity is small and associated degree distributions exhibit a Gaussian tale, to scale-free graphs, for which heterogeneity is large with degree distributions exhibiting a power-law behavior. We study the evolution of cooperation, modeled in terms of the most popular dilemmas of cooperation. We show that, for all dilemmas, increasing heterogeneity favors the emergence of cooperation, such that long-term cooperative behavior easily resists short-term noncooperative behavior. Moreover, we show how cooperation depends on the intricate ties between individuals in scale-free populations.

Biological Evolution↗
PubMed2004

Learning from directed evolution: theoretical investigations into cooperative mutations in lipase enantioselectivity.

Molecular modeling with classical force-fields has been used to study the reactant complex and the tetrahedral intermediate in lipase-catalyzed ester hydrolysis in 20 enzyme/substrate combinations. The R and S enantiomers of alpha-methyldecanoic acid ester served as substrates for the wild-type lipase from Pseudomonas aeruginosa and nine selected mutants. After suitable preparation of initial structures from an available wild-type crystal structure, each system was subjected to 1 ns CHARMM force-field molecular dynamics simulations. The resulting geometric and energetic changes allow interpretation of some experimentally observed effects of mutations, particularly with regard to the "hot spots" at residues 155 and 162. The replacement S155F enhances S enantiopreference through a steric relay involving Leu162. The double mutation S53P + L162G improves S enantioselectivity by creating a new binding pocket for the S enantiomer with an additional stabilizing hydrogen bond to His83. The simulations provide insight into remote and cooperative effects of mutations.

Catalysis↗
PubMed2002

Breeding together: kin selection and mutualism in cooperative vertebrates.

In cooperatively breeding vertebrates, nonbreeding helpers raise young produced by dominant breeders. Although the evolution of cooperative breeding has often been attributed primarily to kin selection (whereby individuals gain "indirect" benefits to their fitness by assisting collateral relatives), there is increasing evidence that helpers can be unrelated to the young they are raising. Recent studies also suggest that the indirect benefits of cooperative behavior may often have been overestimated while the direct benefits of helping to the helper's own fitness have probably been underestimated. It now seems likely that the evolutionary mechanisms maintaining cooperative breeding are diverse and that, in some species, the direct benefits of helping may be sufficient to maintain cooperative societies. The benefits of cooperation in vertebrate societies may consequently show parallels with those in human societies, where cooperation between unrelated individuals is frequent and social institutions are often maintained by generalized reciprocity.

Altruism↗
PubMed2002

The stability of cooperation involving variable investment.

In this paper, we attempt to reconcile the results of several studies which have investigated the evolution of cooperation between non-relatives in systems where investment in partners can vary. In contrast to previous proposals, we show for the first time that variable-investment cooperation can be readily maintained in inter-species mutualistic relationships even in the absence of spatial structure, but that the stability of this interaction is dependent on the particular investment-response rule that is employed. By allowing the evolution of investment-response parameters in both inter- and intra-specific versions of the continuous variable-investment Prisoners' Dilemma we show that, in the absence of further factors, the raise-the stakes (RTS) strategy is likely to evolve into a simpler, variable investment form of Give-as-Good-as-you-Get that initially offers a high fixed amount and subsequently matches its partner's investment. Nevertheless, we demonstrate that genuine RTS-like strategies will still be selected if two intuitively reasonable conditions hold: if individuals are limited in terms of the total they can invest in cooperative actions over their lifetimes, and if there are always some individuals in a population that cannot cooperate.

Animals↗
PubMed1996

Evolving cooperation: the role of individual recognition.

To evaluate the role of individual recognition in the evolution of cooperation, we formulated and analyzed genetic algorithm model (EvCo) for playing the Iterated Prisoner's Dilemma (IPD) game. Strategies compete against each other during each generation, and successful strategies contribute more of their attributes to the next generation. Each strategy is encoded on a 'chromosome' that plays the IPD, responding to the sequences of most recent responses by the interacting individuals (chromosomes). The analysis reported in this paper considered different memory capabilities (one to five previous interactions), pairing continuities (pairs of individuals remain together for about one, two, five, or 1000 consecutive interactions), and types of individual recognition (recognition capability was maximal, nil, or allowed to evolve between these limits). Analysis of the results focused on the frequency of mutual cooperation in pairwise interactions (a good indicator of overall success in the IPD) and on the extent to which previous responses by the focal individual and its partner were associated with the partner's identity (individual recognition). Results indicated that a fixed, substantial amount of individual recognition could maintain high levels of mutual cooperation even at low pairing continuities, and a significant but limited capability for individual recognition evolved under selection. Recognition generally increased mutual cooperation more when the recent responses of individuals other than the current partner were ignored. Titrating recognition memory under selection using a fitness cost suggested that memory of the partner's previous responses was more valuable than memory of the focal's previous responses. The dynamics produced to date by EvCo are a step toward understanding the evolution of social networks, for which additional benefits associated with group interactions must be incorporated.

Algorithms↗
PubMed2002

Simple adaptive strategy wins the prisoner's dilemma.

The prisoner's dilemma has become the leading paradigm to explain the evolution of cooperation among selfish individuals. Here, we present an adaptive strategy that implements new mechanisms to process information about past encounters. The history of moves is summarized in an internal state which then determines the subsequent move. This enables the strategy to adjust its decisions to the character of the current opponent and to adapt the most promising strategic behavior. For this reason, we call such strategies Adaptor. Through evolutionary simulations, we demonstrate that the concept of Adaptor leads to strategic patterns that are (a) highly cooperative when playing against kin, (b) stable in a sense that goes far beyond the concept of evolutionary stability, (c) robust to environmental changes, i.e. variations of the parameter values and finally (d) superior in performance to the most prominent strategies in the literature.

Adaptation, Psychological↗
PubMed2003

Kin selection may inhibit the evolution of reciprocation.

Kin selection and reciprocal cooperation provide two candidate explanations for the evolution of cooperation. Models of the evolution of cooperation have typically focussed on one or the other mechanism, despite claims that kin selection could pave the way for the evolution of reciprocal cooperation. We describe a computer simulation model that explicitly supports both kin selection and reciprocal cooperation. The model simulates a viscous population of discrete individuals with social interaction taking the form of the Prisoner's Dilemma and selection acting on performance in these interactions. We recount how the analytical and empirical study of this model led to the conclusion that kin selection may actually inhibit the evolution of effective strategies for establishing reciprocal cooperation.

Altruism↗
PubMed2001

Dispersal costs set the scene for helping in an atypical avian cooperative breeder.

The ecological constraints hypothesis is suggested to explain the evolution of cooperative breeding in birds. This hypothesis predicts that the scene for cooperative breeding is set when ecological factors constrain offspring from dispersal. This prediction was tested in the atypical cooperative breeding system of the long-tailed tit, Aegithalos caudatus, by comparing the degree of philopatry and cooperation in an isolated and a contiguous site whilst experimentally controlling for confounding aspects of reproduction. No difference was found between the two sites in the survival of offspring but a greater proportion were found to remain philopatric in the isolated site. This difference was caused by greater philopatry of normally dispersive females suggesting, as predicted, that dispersal costs were greater from this site. Furthermore, a greater proportion of males and females cooperated following breeding failure in the isolated site than in the contiguous site. Thus, as has been suggested for typical avian cooperative breeders, dispersal costs, relative to philopatric benefits, appear to set the scene for cooperative breeding in long-tailed tits.

Animals↗
PubMed1995

The spatial struggle of tit-for-tat and defect.

The pioneering work by Trivers (1971), Axelrod (1984) and Axelrod & Hamilton (1981) has stimulated continuing interest in explaining the evolution of cooperation by game theory, in particular, the iterated prisoner's dilemma and the strategy of tit-for-tat. However these models suffer from a lack of biological reality, most seriously because it is assumed that players meet opponents at random from the population and, unless the population is very small, this excludes the repeated encounters necessary for tit-for-tat to prosper. To meet some of the objections, we consider a model with two types of players, defectors (D) and tit-for-tat players (T), in a spatially homogeneous environment with player densities varying continuously in space and time. Players only encounter neighbours but move at random in space. The analysis demonstrates major new conclusions, the three most important being as follows. First, stable coexistence with constant densities of both players is possible. Second, stable coexistence in a pattern (a spatially inhomogeneous stationary state) may be possible when it is impossible for constant distributions (even unstable ones) to exist. Third, invasion by a very small number of T-players is sometimes possible (in contrast with the usual predictions) and so a mutation to tit-for-tat may lead to a population of defectors being displaced by the T-players.

Animals↗
PubMed2004

The evolution of strong reciprocity: cooperation in heterogeneous populations.

How do human groups maintain a high level of cooperation despite a low level of genetic relatedness among group members? We suggest that many humans have a predisposition to punish those who violate group-beneficial norms, even when this imposes a fitness cost on the punisher. Such altruistic punishment is widely observed to sustain high levels of cooperation in behavioral experiments and in natural settings. We offer a model of cooperation and punishment that we call STRONG RECIPROCITY: where members of a group benefit from mutual adherence to a social norm, strong reciprocators obey the norm and punish its violators, even though as a result they receive lower payoffs than other group members, such as selfish agents who violate the norm and do not punish, and pure cooperators who adhere to the norm but free-ride by never punishing. Our agent-based simulations show that, under assumptions approximating likely human environments over the 100000 years prior to the domestication of animals and plants, the proliferation of strong reciprocators when initially rare is highly likely, and that substantial frequencies of all three behavioral types can be sustained in a population. As a result, high levels of cooperation are sustained. Our results do not require that group members be related or that group extinctions occur.

Altruism↗