Performance of human groups in social foraging: the role of communication in consensus decision making

Early hominids searched for dispersed food sources in a patchy, uncertain environment, and modern humans encounter equivalent spatial-temporal coordination problems on a daily basis. A fundamental, but untested assumption is that our evolved capacity for communication is integral to our success in such tasks, allowing information exchange and consensus decisions based on mutual consideration of pooled information. Here we examine whether communication enhances group performance in humans, and test the prediction that consensus decision-making underlies group success. We used bespoke radio-tagging methodology to monitor the incremental performance of communicating and non-communicating human groups (small group sizes of two to seven individuals), during a social foraging experiment. We found that communicating groups (n = 22) foraged more effectively than non-communicating groups (n = 21) and were able to reach consensus decisions (an 'agreement' on the most profitable foraging resource) significantly more often than non-communicating groups. Our data additionally suggest that gesticulations among group members played a vital role in the achievement of consensus decisions, and therefore highlight the importance of non-verbal signalling of intentions and desires for successful human cooperative behaviour.     

Mechanistic constraints and the unlikely evolution of reciprocal cooperation

Social evolution theory faces a puzzle: a gap between theoretical and empirical results on reciprocity. On the one hand, models show that reciprocity should evolve easily in a wide range of circumstances. On the other hand, empirically, few clear instances of reciprocity (even in a broad sense) have been found in nonhuman animals. In this paper, I aim to suggest and evaluate a novel reason concurring to solve this puzzle. I propose that it is difficult for reciprocity to evolve because it raises an evolutionary problem of bootstrapping: it requires that two complementary functions: (i) the ability to cooperate and (ii) the ability to respond conditionally to the cooperation of others, arise together and reach a significant frequency, whereas neither of them can be favoured in the absence of the other. I develop analytical models and simulations showing that, for this reason, the evolutionary emergence of reciprocal cooperation is highly unlikely. I then discuss the consequences of this result for our understanding of cooperation.     

The evolution of conformity-enforcing behaviour in cultural communication systems

Conformity is an important aspect of many communication systems in which signals are culturally transmitted. We suggest that one reason for it to evolve is if nonconforming individuals are discriminated against, and we therefore investigated how this might arise. We designed a spatial simulation, in which individuals occupied a territory on a lattice, and played a territorial game with their neighbours in which one individual could challenge another and, if successful, obtain some of the latter's resources. We then examined the relative success of pairs of strategies. We found that aggression targeted towards nonconformers (conformity-enforcing behaviour) was more successful than randomly targeted aggression in both a simple model and a more complicated one in which the conditions were based on the specific case of song sharing between songbirds. The reason for this result is that individuals could use patterns of vocal sharing to gang up on neighbours with locally uncommon song types, increasing their own chances of success. In both models, a critical parameter was how the number of contests an individual was previously involved in altered the chance of winning: conformity-enforcing behaviour was the most successful strategy only if the more contests an individual had been involved in, the less likely it was to win. Our results may explain the origin of conformity-enforcing behaviour and discrimination in nonhuman animals and may have relevance to similar behaviour in humans.     

Explaining Dog Wolf Differences in Utilizing Human Pointing Gestures: Selection for Synergistic Shifts in the Development of Some Social Skills

Background

The comparison of human related communication skills of socialized canids may help to understand the evolution and the epigenesis of gesture comprehension in humans. To reconcile previously contradicting views on the origin of dogs'' outstanding performance in utilizing human gestures, we suggest that dog-wolf differences should be studied in a more complex way.

Methodology/Principal Findings

We present data both on the performance and the behaviour of dogs and wolves of different ages in a two-way object choice test. Characteristic behavioural differences showed that for wolves it took longer to establish eye contact with the pointing experimenter, they struggled more with the handler, and pups also bit her more before focusing on the human''s signal. The performance of similarly hand-reared 8-week-old dogs and wolves did not differ in utilizing the simpler proximal momentary pointing. However, when tested with the distal momentary pointing, 4-month-old pet dogs outperformed the same aged hand reared wolves. Thus early and intensive socialisation does not diminish differences between young dogs and wolves in behaviour and performance. Socialised adult wolves performed similarly well as dogs in this task without pretraining. The success of adult wolves was accompanied with increased willingness to cooperate.

Conclusion/Significance

Thus, we provide evidence for the first time that socialised adult wolves are as successful in relying on distal momentary pointing as adult pet dogs. However, the delayed emergence of utilising human distal momentary pointing in wolves shows that these wild canines react to a lesser degree to intensive socialisation in contrast to dogs, which are able to control agonistic behaviours and inhibition of actions in a food related task early in development. We suggest a “synergistic” hypothesis, claiming that positive feedback processes (both evolutionary and epigenetic) have increased the readiness of dogs to attend to humans, providing the basis for dog-human communication.     

Cooperation among non-relatives evolves by state-dependent generalized reciprocity

For decades, attempts to understand cooperation between non-kin have generated substantial theoretical and empirical interest in the evolutionary mechanisms of reciprocal altruism. There is growing evidence that the cognitive limitations of animals can hinder direct and indirect reciprocity because the necessary mental capacity is costly. Here, we show that cooperation can evolve by generalized reciprocity (help anyone, if helped by someone) even in large groups, if individuals base their decision to cooperate on a state variable updated by the outcome of the last interaction with an anonymous partner. We demonstrate that this alternative mechanism emerges through small evolutionary steps under a wide range of conditions. Since this state-based generalized reciprocity works without advanced cognitive abilities it may help to understand the evolution of complex social behaviour in a wide range of organisms.     

The origin of new genes: glimpses from the young and old

Genome data have revealed great variation in the numbers of genes in different organisms, which indicates that there is a fundamental process of genome evolution: the origin of new genes. However, there has been little opportunity to explore how genes with new functions originate and evolve. The study of ancient genes has highlighted the antiquity and general importance of some mechanisms of gene origination, and recent observations of young genes at early stages in their evolution have unveiled unexpected molecular and evolutionary processes.     

The proper place of hopeful monsters in evolutionary biology

Hopeful monsters are organisms with a profound mutant phenotype that have the potential to establish a new evolutionary lineage. The Synthetic Theory of evolutionary biology has rejected the evolutionary relevance of hopeful monsters, but could not fully explain the mechanism and mode of macroevolution. On the other hand, several lines of evidence suggest that hopeful monsters played an important role during the origin of key innovations and novel body plans by saltational rather than gradual evolution. Homeotic mutants are identified as an especially promising class of hopeful monsters. Examples for animal and plant lineages that may have originated as hopeful monsters are given. Nevertheless, a brief review of the history of the concept of hopeful monsters reveals that it needs refinements and empirical tests if it is to be a useful addition to evolutionary biology. While evolutionary biology is traditionally zoocentric, hopeful monsters might be more relevant for plant than for animal evolution. Even though during recent years developmental genetics has provided detailed knowledge about how hopeful monsters can originate in the first place, we know almost nothing about their performance in natural populations and thus the ultimate difference between hopeful and hopeless. Studying the fitness of candidate hopeful monsters (suitable mutants with profound phenotype) in natural habitats thus remains a considerable challenge for the future.     

Specialization in multi-agent systems through learning

Specialization is a common feature in animal societies that leads to an improvement in the fitness of the team members and to an increase in the resources obtained by the team. In this paper we propose a simple reinforcement learning approach to specialization in an artificial multi-agent system. The system is composed of homogeneous and non-communicating agents. Because there is no communication, the number of agents in the team can easily scale up. Agents have the same initial functionalities, but they learn to specialize and so cooperate to achieve a complex gathering task efficiently. Simulation experiments show how the multi-agent system specializes appropriately so as to reach optimal (or near-to-optimal) performance in unknown and changing environments. Received: 12 September 1996 / Accepted in revised form: 5 February 1997     

Correlated evolution of the association between aphids and ants and the association between aphids and plants with extrafloral nectaries

The evolution of extrafloral nectaries (EFN) and the evolution of ant-aphid associations may have influenced each other. Published records allowed me to determine whether aphid species are associated with ants and whether they are associated with host plant species with EFNs. On the basis of these results a comparative phylogenetic study was conducted on a subgroup of monoeocious aphid species living above the soil surface. As aphid phylogeny was unresolved below the family level, I analysed two families – Aphididae and Drepanosiphidae – separately. Within each family, a large number of random phylogenies were generated and each random tree was analysed with a standard phylogenetic approach. The results suggest, on the one hand, that being tended by ants increases the likelihood that an aphid species will evolve an association with host plants that produce EFNs, or on the other hand, that aphid species associated with host plants carrying EFNs were more likely than other species to evolve an association with ants. I present two new hypotheses – the host-selection hypothesis and the host-sharing hypothesis – to explain these evolutionary patterns. The hypothesis that ant-attended homopterans may function as EFNs is rejected by the evolutionary patterns found in this study.     

Evolving communicative complexity: insights from rodents and beyond

Social living goes hand in hand with communication, but the details of this relationship are rarely simple. Complex communication may be described by attributes as diverse as a species' entire repertoire, signallers' individualistic signatures, or complex acoustic phenomena within single calls. Similarly, attributes of social complexity are diverse and may include group size, social role diversity, or networks of interactions and relationships. How these different attributes of social and communicative complexity co-evolve is an active question in behavioural ecology. Sciurid rodents (ground squirrels, prairie dogs and marmots) provide an excellent model system for studying these questions. Sciurid studies have found that demographic role complexity predicts alarm call repertoire size, while social group size predicts alarm call individuality. Along with other taxa, sciurids reveal an important insight: different attributes of sociality are linked to different attributes of communication. By breaking social and communicative complexity down to different attributes, focused studies can better untangle the underlying evolutionary relationships and move us closer to a comprehensive theory of how sociality and communication evolve.     

Task partitioning in a robot swarm: a study on the effect of communication

Task partitioning consists in dividing a task into sub-tasks that can be tackled separately. Partitioning a task might have both positive and negative effects: On the one hand, partitioning might reduce physical interference between workers, enhance exploitation of specialization, and increase efficiency. On the other hand, partitioning may introduce overheads due to coordination requirements. As a result, whether partitioning is advantageous or not has to be evaluated on a case-by-case basis. In this paper we consider the case in which a swarm of robots must decide whether to complete a given task as an unpartitioned task, or utilize task partitioning and tackle it as a sequence of two sub-tasks. We show that the problem of selecting between the two options can be formulated as a multi-armed bandit problem and tackled with algorithms that have been proposed in the reinforcement learning literature. Additionally, we study the implications of using explicit communication between the robots to tackle the studied task partitioning problem. We consider a foraging scenario as a testbed and we perform simulation-based experiments to evaluate the behavior of the system. The results confirm that existing multi-armed bandit algorithms can be employed in the context of task partitioning. The use of communication can result in better performance, but in may also hinder the flexibility of the system.     

Interspecific interactions drive cultural co-evolution and acoustic convergence in syntopic species

1.?Antagonistic interactions have been favourite subjects of studies on species co-evolution, because coexistence among competing species often results in quantifiable character displacement. A common output for competitive interactions is trait divergence, although the opposite phenomenon, convergence, has been proposed to evolve in some instances, for example in the communication behaviour of species that maintain mutually exclusive territories. 2.?I use here experimental and observational evidence to study how species interactions drive heterospecific signal convergence and analyse how convergence feeds back to the interaction itself, in the form of aggressive behaviour. I recorded the learned territorial signals of two non-hybridizing larks, Galerida cristata and G.?theklae, and used allopatric populations as controls for evaluating acoustic convergence in syntopy. Acoustic variation was analysed with respect to social conditions controlling for other potential agents of natural selection, habitat and climate. 3.?Interspecific convergence of Galerida calls peaked in syntopy. Although call acoustic structure was affected by climate and habitat, it matched gradients of density and proximity to congeners even at small local scales. The process of cultural transmission, in which individuals may acquire components of behaviour by copying neighbours, enhances the correlation between call acoustics and the local social milieu. 4.?Territories were defended against both species, but playback stimuli of convergent congener calls elicited a stronger aggressive reaction than congener calls from allopatric locations. 5.?This study shows that learned behaviours may co-evolve as a consequence of antagonistic interactions, determining reciprocal cultural evolution or cultural co-evolution. As for (biological) co-evolution, the distribution of competing species influences whether a particular area becomes a syntopic environment in which convergence is occurring, or an allopatric environment lacking interactions and reciprocal change. Because of their plastic nature, cultural coadaptations may rapidly shift in response to fluctuating social selection, thus propelling dynamic interactions and fine adjustments to the local environment.     

Phylogenetic tests of the sensory exploitation model of sexual selection

The diverse characteristics among closely related species are often involved in communication between the sexes. The traditional view that intersexual communication behaviors evolve in a complementary way is called into question by the sensory exploitation hypothesis. By predicting a lack of coordinated evolution between signals and preferences, the sensory exploitation hypothesis is distinct from other mechanisms of sexual selection. Tests of sensory exploitation have taken a multi-disciplinary approach, with insights from sensory physiology, behavior and phylogenetic comparisons. By demonstrating that signals and receivers are not closely coupled, and that signal preference pre-dates signal origin, proponents of the model argue that sensory exploitation is an evolutionary force responsible for the diversification of intersexual communication signals.     

Conflict theory of genomic imprinting in mammals

In mammals, some embryonic genes are expressed differently depending on whether they are inherited from the sperm or egg, a phenomenon known as genomic imprinting. The information on the parental origin is transmitted by an epigenetic mark. Both the molecular mechanisms and evolutionary processes of genomic imprinting have been studied extensively. Here, I illustrate the simplest evolutionary dynamics of imprinting evolution based on the “conflict theory,” by considering the evolution of a gene encoding an embryonic growth factor controlling the maternal resource supply. It demonstrates that (a) the autosomal genes controlling placenta development to modify maternal resource acquisition may evolve a strong asymmetry of gene expression, provided the mother has some chance of accepting multiple males. (b) The genomic imprinting may not evolve if there is a small fraction of recessive deleterious mutations on the gene. (c) The growth-enhancing genes should evolve to paternally expressed, while the growth-suppressing genes should evolve to maternally expressed. (d) The X-linked genes also evolve genomic imprinting, but the main evolutionary force is the sex difference in the optimal embryonic size. I discuss other aberrations that can be explained by the modified versions of the basic model.     

Human infants and baboons show the same pattern of handedness for a communicative gesture

To test the role of gestures in the origin of language, we studied hand preferences for grasping or pointing to objects at several spatial positions in human infants and adult baboons. If the roots of language are indeed in gestural communication, we expect that human infants and baboons will present a comparable difference in their pattern of laterality according to task: both should be more right-hand/left-hemisphere specialized when communicating by pointing than when simply grasping objects. Our study is the first to test both human infants and baboons on the same communicative task. Our results show remarkable convergence in the distribution of the two species' hand biases on the two kinds of tasks: In both human infants and baboons, right-hand preference was significantly stronger for the communicative task than for grasping objects. Our findings support the hypothesis that left-lateralized language may be derived from a gestural communication system that was present in the common ancestor of baboons and humans.     

Evolution of a conspicuous melanin‐based ornament in gulls Laridae

Melanin‐ and carotenoid‐based ornaments often signal different aspects of individual quality or similar components of quality under different environmental conditions and, thus, they may become evolutionarily integrated into a composite sexual trait. On the other hand, functionally and developmentally different characters (e.g. coloration characters of different developmental origin) are more likely to evolve independently from each other than more similar traits. Here, we examined evolutionary correlations between the occurrence of a conspicuous melanin‐based ornament (hood) and carotenoid‐based bare‐part ornaments within gull family. We also aimed to identify major ecological, life‐history and biogeographical predictors of hood occurrence and reconstruct evolutionary history of this ornament. We found that hood occurrence was associated with red or dark coloration of unfeathered traits (bill and legs), whereas combinations of hood with yellow carotenoid‐based coloration of integument were evolutionarily avoided. Also, hood occurrence correlated negatively with the occurrence of other melanin‐based plumage character (mantle). Breeding latitude and habitat were identified as major predictors of hood occurrence in gulls, as hoods were recorded more frequently in low‐latitude and inland (rather than marine) species. Finally, our analysis provided support for evolutionary lability in hood occurrence, with a dominance of transitions towards hood loss in the evolutionary history of gulls. The results of our study provide one of the first evidence for a correlated evolution of melanin‐ and carotenoid‐based ornaments in an avian lineage, which supports evolutionary modularity of developmentally and functionally different coloration traits.     

Sex ratio polymorphism: The impact of mutation and drift on evolution

This paper addresses the question, which sex ratio will evolve in a population that is subject to mutation and drift. The problem is analyzed using a simulation model as well as analytical methods. A detailed simulation model for the evolution of a population's allele distribution shows that for the sex ratio game a wide spectrum of different population states may evolve from on the one hand a monomorphic state with one predominant allele and with all other alleles suppressed by the forces of selection, to on the other hand a polymorphism determined by recurrent mutations. Which of these states will evolve depends on the population size, the mating system and the rate of mutations. For the sex ratio game the evolutionary stable strategy (ESS), as defined by evolutionary game theory, can only predict the population sex ratio but not the underlying stable population state. A comparison of different approaches to the problem shows that false predictions of the stable population states might result from two simplifying assumptions that are fairly common in evolutionary biology: a) it is assumed that mutations are rare events and there is never more than one mutant gene present in a population at any one time; b) a deterministic relationship is assumed between the fitness assigned to an individual's strategy and the individual's contribution to the gene pool of future generations.     

Biogeographic differences in plant–soil biota relationships contribute to the exotic range expansion of Verbascum thapsus

1. Exotic plant species can evolve adaptations to environmental conditions in the exotic range. Furthermore, soil biota can foster exotic spread in the absence of negative soil pathogen–plant interactions or because of increased positive soil biota–plant feedbacks in the exotic range. Little is known, however, about the evolutionary dimension of plant–soil biota interactions when comparing native and introduced ranges.
2. To assess the role of soil microbes for rapid evolution in plant invasion, we subjected Verbascum thapsus, a species native to Europe, to a reciprocal transplant experiment with soil and seed material originating from Germany (native) and New Zealand (exotic). Soil samples were treated with biocides to distinguish between effects of soil fungi and bacteria. Seedlings from each of five native and exotic populations were transplanted into soil biota communities originating from all populations and subjected to treatments of soil biota reduction: application of (a) fungicide, (b) biocide, (c) a combination of the two, and (d) control.
3. For most of the investigated traits, native populations showed higher performance than exotic populations; there was no effect of soil biota origin. However, plants developed longer leaves and larger rosettes when treated with their respective home soil communities, indicating that native and exotic plant populations differed in their interaction with soil biota origin. The absence of fungi and bacteria resulted in a higher specific root length, suggesting that V. thapsus may compensate the absence of mutualistic microbes by increasing its root–soil surface contact.
4. Synthesis. Introduced plants can evolve adaptations to soil biota in their new distribution range. This demonstrates the importance of biogeographic differences in plant–soil biota relationships and suggests that future studies addressing evolutionary divergence should account for differential effects of soil biota from the home and exotic range on native and exotic populations of successful plant invaders.

     

Genome-wide effects of postglacial colonization in Arabidopsis lyrata

The perennial outcrossing Arabidopsis lyrata is becoming a plant model species for molecular ecology and evolution. However, its evolutionary history, and especially the impact of the climatic oscillations of the Pleistocene on its genetic diversity and population structure, is not well known. We analyzed the broad-scale population structure of the species based on microsatellite variation at 22 loci. A wide sample in Europe revealed that glaciations and postglacial colonization have caused high divergence and high variation in variability between populations. Colonization from Central Europe to Iceland and Scandinavia was associated with a strong decrease of genetic diversity from South to North. On the other hand, the Russian population included in our data set may originate from a different refugium probably located more to the East. These genome-wide patterns must be taken into account in studies aiming at elucidating the genetic basis of local adaptation. As shown by sequence data, most of the loci used in this study do not evolve like typical microsatellite loci and show variable levels of homoplasy: this mode of evolution makes these markers less suitable to investigate the between-continent divergence and more generally the worldwide evolution of the species. Finally, a strong negative correlation was detected between levels of within-population diversity and indices of differentiation such as F(ST). We discuss the causes of this correlation as well as the potential bias it induces on the quantification and interpretation of population structure.