If you had to be a pig, would you rather be a strong pig or a weak pig? Sometimes it pays to be weak. The biologist John Maynard Smith reports an experiment where two pigs are kept in a box with a lever at one end and a food dispenser at the other. When the lever is pushed, food appears at the dispenser. If the weak pig pushes the lever, the strong pig waits by the dispenser and eats all the food. Even if the weak pig races to the dispenser and arrives before the food is gone, the strong pig pushes the weak pig away. The weak pig is smart enough to figure this out, so it never bothers pressing the lever in the first place. On the other hand, if the strong pig pushes the lever, the weak pig waits by the dispenser and gets most of the food. But the strong pig can race to the dispenser and shove the weak pig aside before it has entirely finished eating and then help itself to the leftovers. This makes it worthwhile for the strong pig to push the lever. The outcome is that the strong pig does all of the work, and the weak pig does most of the eating. Strategic situations can yield surprising outcomes. The Prisoner’s Dilemma of Chapter 11 provides one example; the pigs in a box provide another. In this chapter, we will study the theory of games (or game theory for short), which allows us to catalog many of those outcomes and to discuss both their positive and their normative aspects.

Acoustic ecologist Bernie Krause hypothesized that rich soundscapes in mature ecosystems are generated by sound communication between different species with differentiating acoustic niches. This hy...

EvolutionVolume 37, Issue 4 p. 872-873 Book ReviewFree Access THE ECONOMICS OF SEX† John Maynard Smith, John Maynard Smith Department of Biology, The University of Sussex, Falmer, Brighton, Sussex, BN1 9QG EnglandSearch for more papers by this author John Maynard Smith, John Maynard Smith Department of Biology, The University of Sussex, Falmer, Brighton, Sussex, BN1 9QG EnglandSearch for more papers by this author First published: July 1983 https://doi.org/10.1111/j.1558-5646.1983.tb05615.xCitations: 1 †The Theory of Sex Allocation. Eric L. Charnov. Princeton University Press, Princeton, New Jersey, 1982. x + 355 pp. $40.00 cloth, $12.95 paper. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume37, Issue4July 1983Pages 872-873 RelatedInformation

Inevitably, much of this reply will concern points on which I disagree with one or other of the commentators. I should start, therefore, by saying that I am delighted to find that their thinking is in many ways similar to my own, and that a serious attempt is under way to clarify the concept of information in biology.

We test the assumption that preferences are unchanged throughout a strategic game in the absence of feedback. To do so, we study the relationship between the strategic nature of a game and players'identi…cation in social groups. We present evidence that the strategic nature of the game aects the strength of identity. We also show when the change in identity occurs and what causes this change. In our experiment, the subjects play one of two versions of the Prisoner's Dilemma game where the attractiveness of the uncooperative action is manipulated. We refer to the version with a relatively attractive uncooperative action as the "Mean Game" and the other as the "Nice Game." We place each subject into one of two groups. Throughout the experimental procedure we measure identity, as standard in the psychology literature, in order to assess the extent to which subjects identify with their group. First, we …nd evidence of an interaction between the strategic nature of the game and the action selected in the game as aecting the identity of the subject. We …nd that in the Mean Game, there is little dierence in the change in identi…cation of those playing cooperatively against an ingroup member and those playing uncooperatively. However, in the Nice Game, those playing cooperatively against an ingroup member exhibit a signi…cantly stronger change in identi…cation than those playing uncooperatively. We …nd that the opposite is true for outgroup matches. Also, we show that the change in identity does not occur after initial inspection of the game but rather largely after the action choice has been made. Finally, we present evidence of an explanation of the eect: identity is enhanced by actions which are perceived to be less competitive and more cooperative.

The aim of this department is to give the reader brief indications of the character, the content, and the value of new books in the various fields of Biology. In addition, there will occasionally appear one longer critical review of a book of special significance. Authors and publishers of biological books should bear in mind that THE QUARTERLY REVIEW OF BIOLOGY can notice in this department only such books as come to the office of the editor. The absence of a book, therefore, from the following and subsequent lists only means that we have not received it. All material for notice in this department should be addressed to H. B. Glass, Editor of THE QUARTERLY REVIEW OF BIOLOGY, Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218, U. S. A.

A phylogeny of the Mycobacterium tuberculosis complex has recently shown that the animal-adapted strains are found in a single lineage marked by the deletion of chromosomal region 9 (RD9) [Brosch et al., 2002. A new evolutionary scenario for the Mycobacterium tuberculosis complex. Proc. Natl Acad. Sci. USA 99 (6), 3684-3689]. We have obtained the spoligotype patterns of the RD9 deleted strains used to generate this new evolutionary scenario and we show that the presence of spoligotype spacers 3, 9, 16, 39, and 40-43 is phylogenetically informative in this lineage. We have used the phylogenetically informative spoligotype spacers to screen a database of spoligotype patterns and have identified further members of a group of strains apparently host-adapted to antelopes. The presence of the spoligotype spacers is congruent with the phylogeny generated by chromosomal deletions, suggesting that recombination is rare or absent between strains of this lineage. The phylogenetically informative spacers, in concert with the previously identified single nucleotide mutations and chromosomal deletions, can be used to identify a series of clades in the RD9 deleted lineage each with a separate host preference. Finally, we discuss the application of the ecotype concept to this series of clades and suggest that the M. tuberculosis complex may best be described as a series of host-adapted ecotypes.

The ratio of non-synonymous (dN) to synonymous (dS) changes between taxa is frequently computed to assay the strength and direction of selection. Here we note that for comparisons between closely related strains and/or species a second parameter needs to be considered, namely the time since divergence of the two sequences under scrutiny. We demonstrate that a simple time lag model provides a general, parsimonious explanation of the extensive variation in the dN/dS ratio seen when comparing closely related bacterial genomes. We explore this model through simulation and comparative genomics, and suggest a role for hitch-hiking in the accumulation of non-synonymous mutations. We also note taxon-specific differences in the change of dN/dS over time, which may indicate variation in selection, or in population genetics parameters such as population size or the rate of recombination. The effect of comparing intra-species polymorphism and inter-species substitution, and the problems associated with these concepts for asexual prokaryotes, are also discussed. We conclude that, because of the critical effect of time since divergence, inter-taxa comparisons are only possible by comparing trajectories of dN/dS over time and it is not valid to compare taxa on the basis of single time points.

The eggs laid by outbred females have been collected from the time of mating until the death of the females, and the proportion of eggs hatching recorded. Initially oyer 99 % of the eggs hatch after mating to outbred males; after about 30 days the quantity of sperm in the ventral receptacle is inadequate to ensure fertilization, and few or no eggs hatch. After mating to inbred males, the initial hatch varied from 43 to 84%, and a sharp decline in the proportion hatching occurred after about 10 days. Thus inbred males are inferior both in the quality and quantity of sperm produced.

Abstract This chapter discusses a number of ideas that are only rather distantly related to one another, but which have in common that they were stimulated in the first place by the study of primates, and by a comparison of human and primate signalling: Section 7.2, we discuss the role of signals in the wild, using Vervet Monkeys as our main example. In Section 7.3, still using Vervets as our main example, we discuss the development of the ability to produce a signal in the appropriate circumstances, and to respond appropriately. It turns out that there is no simple answer to the question whether these abilities are learnt or innate: there is certainly an innate component, but competence is improved by experience. However, in Vervets and other primates there is little sign of teaching by parents. We compare the roles of nature and nurture in the acquisition of signalling ability in monkeys with their roles in the acquisition of species-specific song in songbirds.

ABSTRACT Staphylococcus aureus is an important human pathogen and represents a growing public health burden owing to the emergence and spread of antibiotic-resistant clones, particularly within the hospital environment. Despite this, basic questions about the evolution and population biology of the species, particularly with regard to the extent and impact of homologous recombination, remain unanswered. We address these issues through an analysis of sequence data obtained from the characterization by multilocus sequence typing (MLST) of 334 isolates of S . aureus , recovered from a well-defined population, over a limited time span. We find no significant differences in the distribution of multilocus genotypes between strains isolated from carriers and those from patients with invasive disease; there is, therefore, no evidence from MLST data, which index variation within the stable “core” genome, for the existence of hypervirulent clones of this pathogen. Examination of the sequence changes at MLST loci during clonal diversification shows that point mutations give rise to new alleles at least 15-fold more frequently than does recombination. This contrasts with the naturally transformable species Neisseria meningitidis and Streptococcus pneumoniae , in which alleles change between 5- and 10-fold more frequently by recombination than by mutation. However, phylogenetic analysis suggests that homologous recombination does contribute toward the evolution of this species over the long term. Finally, we note a striking excess of nonsynonymous substitutions in comparisons between isolates belonging to the same clonal complex compared to isolates belonging to different clonal complexes, suggesting that the removal of deleterious mutations by purifying selection may be relatively slow.

Mitochondrial DNA is the primary tool in the investigation of recent evolutionary history, particularly for uncovering human origins and expansion. Maternal inheritance of mitochondria enables models of population history to be much simpler that those needed for the analysis of nuclear DNA. The recent report of a man with his father's mitochondria suggests a rethink of mitochondrial evolutionary dynamics in humans might be necessary.

We have analyzed 11,500 isolates of Mycobacterium bovis (the cause of tuberculosis in cattle and other mammals) isolated in Great Britain (England, Wales and Scotland)] and characterized by spoligotype. Genetic exchange between cells is rare or absent in strains of the Mycobacterium tuberculosis complex so that, by using spoligotypes, it is possible to recognize “clones” with a recent common ancestor. The distribution of variable numbers of tandem repeats types in the most common clone in the data set is incompatible with random mutation and drift. The most plausible explanation is a series of “clonal expansions,” and this interpretation is supported by the geographical distribution of different genotypes. We suggest that the clonal expansion of a genotype is caused either by the spread of a favorable mutation, together with all other genes present in the ancestral cell in which the mutation occurred, or by the invasion of a novel geographical region by a limited number of genotypes. A similar pattern is observed in M. tuberculosis (the main cause of tuberculosis in humans). The significance of clonal expansion in other bacteria that have recombination is discussed.

Staphylococcus aureus is a major cause of severe infection in humans and yet is carried without symptoms by a large proportion of the population. We used multilocus sequence typing to characterize isolates of S. aureus recovered from asymptomatic nasal carriage and from episodes of severe disease within a defined population. We identified a number of frequently carried genotypes that were disproportionately common as causes of disease, even taking into account their relative abundance among carriage isolates. The existence of these ecologically abundant hypervirulent clones suggests that factors promoting the ecological fitness of this important pathogen also increase its virulence.