S A West

..We also reconsider experimental data collected on Chlamydomonas moewussi using two of the three methods. Finally, we suggest how the test could be applied to diploid species...

..Recent theoretical work has clarified the processes and selective forces underlying this effect and has demonstrated the generality of the effect of competition between relatives...

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..However, it should be pointed out that: (1) there are theoretical and empirical problems for his alternative hypotheses; and (2) existing empirical data support the application of sex ratio theory to these parasites, not its rejection...

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..We draw examples from all areas, but especially recent work on humans and microbes...

..Overall, our analyses suggest that sex-allocation theory needs to consider simultaneously the influence of variable selection pressures and variable constraints when applying general theory to specific cases...

..Over the last 40 years, biologists have developed a theoretical framework that can explain cooperation at all these levels. Here, we summarise this theory, illustrate how it may be applied to real organisms and discuss future directions...

..The implications for different agricultural practices and mutualism stability in general are discussed...

..Specifically, why do different organisms show so much variation in the amount and precision with which they adjust their offspring sex ratios?..

..Moreover, inbreeding rates can be estimated from gametocyte sex ratios. The sex ratio is also an excellent model trait for testing the validity of important components of what is being marketed as 'Darwinian medicine'...

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..In addition, the Wolbachia strains observed in five leaf-mining species from the same genus were not closely related, indicating that transfer between species has not occurred due to a shared feeding niche or cospeciation...

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..As predicted, data from four adeleorin species showed sex ratios not significantly different from 0.5...

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..In a Perspective, Stuart West and colleagues discuss what sex allocation tells us about evolution by natural selection and how sex allocation can be applied to understanding the mating structure of parasitic protozoans...

..Our results show that interactions between the two types of fertility insurance reduce the extent of female bias predicted in the sex ratio, suggesting that fertility insurance may be more important than has previously been assumed...

..This confirms that RC per se, as opposed to increased relatedness, has driven the observed increase in bacterial cooperation...

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..More generally, our results show that multiple constraints may determine the precision of adaptation...

..We found one clutch size QTL on chromosome 1, and six weaker QTL across chromosomes 2, 3 and 5, with some overlap to regions associated with sex ratio. The results suggest rather limited scope for pleiotropy between these traits...

..Wilsonian); (iv) local competition can enhance the spread of spiteful greenbeards; and (v) the theory makes testable predictions for how the extent of spite should vary dependent upon population structure and average relatedness...

..We found that although parasites were capable of causing synergistic epistasis between mutations in their hosts, these effects were dependent upon an interaction between parasite genotype and temperature...

..Our results also question some intuitive hypotheses concerning the evolution of threshold traits and confirm how neural processing may constrain adaptive behaviour...

..This suggests that females of N. vitripennis cannot discriminate between kin and nonkin. The implications of our results for the understanding of sex ratio and social evolution are discussed...

..More generally, our results illustrate the caution that must be exercised when interpreting the evolutionary implications of economic experiments, especially the absolute level of cooperation in a particular treatment...

..Our work adds to the evidence that nonadditive genetic effects may influence the evolution of mating behaviour in Nasonia vitripennis, and the evolution of polyandry more generally...

..The mortality rate was significantly higher for female gametocytes, with an average half-life of 8 h for female gametocytes and 16 h for male gametocytes...

..Consequently, our results do not support the hypothesis that there is an advantage to producing larger eggs when food is limited. In contrast, data from the literature support the importance of a lower boundary on egg size...

..More generally, our results clarify the links between persistence and other bet-hedging or social behaviours...

..This result provides a possible explanation for the observed variation in N. vitripennis sex ratios. More generally, it confirms the need to consider the mechanistic basis of a behavior to understand fully its adaptive value...

..Furthermore, as assumed by theory, we show that this occurs because cheats are better able to exploit the cooperative siderophore production of other cells when they are physically closer to them...

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..e., pleiotropy), as has been argued to be the case more generally...

..Animals should benefit from the ability to recognise their kin, yet curiously this faculty is often absent. New theory confirms that genetic kin recognition is inherently unstable, explaining its rarity...

..A recent study suggests that aggression between wasps depends upon the costs and benefits of fighting, as determined by the position of individuals in a dominance hierarchy...

..We found support for the first and third predictions across all species. The second prediction was supported within the protogynous species (mainly fish), but not the protandrous species (mainly invertebrates)...

..This emphasizes how biological details can fundamentally alter the qualitative nature of theoretical predictions made by models of parasite virulence...

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..These results suggest a general role for kin selection and that the relative importance of kin selection varies across species, as predicted by Hamilton's rule...

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..chabaudi increases investment in sexual stages, whereas P. vinckei produces a less female biased sex ratio. We suggest that these different transmission strategies may be due to marked differences in host cell preference...

..Recent work on ants shows both extraordinary patterns of reproduction and a new type of sexual conflict, leading to the remarkable scenario where females have no father and males have no mother...

..The following question arises from our analysis: How do we identify an invariant?..

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..Consistent with this, we found that mean egg volume decreased with increasing clutch size...

..We examine two components of fitness, both of which are thought to be important in natural populations of parasitic wasps: longevity and egg production. Our results show synergistic epistasis for longevity, but not for egg production...

..Our study demonstrates that phenotypic plasticity in a cooperative trait as a response to changes in the environment occurs in even the simplest of organisms, a bacterium...

..We suggest that exchange may be mediated by the generalist parasitoids common in oak galls...

..Variable selection on sex ratio adjustment may thus explain variable empirical findings...

..ratti using its natural host Rattus norvegicus. Host strain influenced the pattern of larval production. The results were qualitatively the same for 2 S. ratti lines of North American and Japanese origin...

..Furthermore, our results suggest some very broad generalities in how male fitness varies with size and age across fish species with different mating systems...

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..Fourth, cooperative pyoverdin production is also shown to be favoured by kin selection in vivo (caterpillars), and results in more virulent infections. Finally, we briefly outline ongoing and future work using this experimental system...

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..More generally, such sanctions by one or both partners may be important in stabilizing a wide range of mutualistic symbioses...

..We discuss how our results: (a) can be applied to recent empirical work in different lepidopteran species and (b) predict an important role of learning in lepidopteran agricultural pests...

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..These results show that the problem of exploitation, which has been the focus of considerable attention in animal communication, also arises in bacteria...

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