The evolutionary significance of introgression has been discussed for decades. Questions about potential impacts of transgene flow into wild and weedy populations brought renewed attention to the introgression of crop alleles into those populations. In the past two decades, the field has advanced with considerable descriptive, experimental, and theoretical activity on the dynamics of crop gene introgression and its consequences. As illustrated by five case studies employing an array of different approaches, introgression of crop alleles has occurred for a wide array of species, sometimes without significant consequence, but on occasion leading to the evolution of increased weediness. A new theoretical context has emerged for analyzing empirical data, identifying factors that influence introgression, and predicting introgression's progress. With emerging molecular techniques and analyses, research on crop allele introgression into wild and weedy populations is positioned to make contributions to both transgene risk assessment and reticulate evolution.

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Bacteria have developed an impressive ability to survive and propagate in highly diverse and changing environments by evolving phenotypic heterogeneity. Phenotypic heterogeneity ensures that a subpopulation is well prepared for environmental changes. The expression bet hedging is commonly (but often incorrectly) used by molecular biologists to describe any observed phenotypic heterogeneity. In evolutionary biology, however, bet hedging denotes a risk‐spreading strategy displayed by isogenic populations that evolved in unpredictably changing environments. Opposed to other survival strategies, bet hedging evolves because the selection environment changes and favours different phenotypes at different times. Consequently, in bet hedging populations all phenotypes perform differently well at any time, depending on the selection pressures present. Moreover, bet hedging is the only strategy in which temporal variance of offspring numbers per individual is minimized. Our paper aims to provide a guide for the correct use of the term bet hedging in molecular biology.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. SUMMARY(1) In this paper, the relation between the tendency to leave a patch and the experience in that patch is studied, from a functional point of view.(2) The study is based on empirical data rather than the usual a priori modelling. The relative effects of several factors on patch-leaving decisions are estimated from the data and it is tested which factors have significant effects. Afterwards, we discuss the implications of the effects that were found in a functional context.(3) This approach is an important extension to a priori modelling, since it can indicate the relative importance of several aspects of the natural environment in determining the foraging strategy.(4) Experiments were done with the parasitic wasp Leptopilina heterotoma. In the trials, wasps were deposited in a Petri dish containing a patch of yeast with Drosophila larvae. Their behaviour was continuously recorded until they left the patch for more than 60 s.(5) The data were analysed by means of the proportional hazards model (Cox 1972) for factors affecting the leaving tendency of the parasitoids, i.e. the chance per unit of time that the patch was left.(6) It was found that the leaving tendency decreases with the number of ovipositions.(7) Oviposition rates experienced in the patch also have a strong influence on the tendency of the wasps to leave. As expected, the most recently experienced oviposition rates have the strongest effect. Long foraging times between recent ovipositions produce a high leaving tendency.(8) The number of times the patch has been left before, during periods shorter than 60 s, also strongly influences the tendency to leave.(9) Rejection rates with parasitized hosts do not affect the leaving tendency significantly.(10) These findings suggest that the behaviour of the wasps is strongly adapted to a clumped distribution of hosts over patches.Information processing by foragers empirical data. The best known theorem about optimization of patch residence times is Charnov's (1976) marginal value theorem. This theorem is based on the assumptions that a forager maximizes average intake rate, knows all relevant environmental characteristics (i.e. inter-patch travel times and patch depletion rates) and is unconstrained. Of course, these assumptions are not met in practice. Therefore, many authors have sought to make them more realistic. In particular, the assumption of an omniscient forager has been dropped by, e.g. Iwasa, Higashi & Yamamura (1981), McNair (1982), McNamara & Houston (1987a) and Green (1987). All these authors derive optimal strategies for hypothetical...

Biology takes a special place among the other natural sciences because biological units, be they pieces of DNA, cells or organisms, reproduce more or less faithfully. As for any other biological processes, reproduction has a large random component. The theory of branching processes was developed especially as a mathematical counterpart to this most fundamental of biological processes. This active and rich research area allows us to make predictions about both extinction risks and the development of population composition, and also uncovers aspects of a population's history from its current genetic composition. Branching processes play an increasingly important role in models of genetics, molecular biology, microbiology, ecology and evolutionary theory. This book presents this body of mathematical ideas for a biological audience, but should also be enjoyable to mathematicians.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. This paper considers the effects of intra-patch experiences, such as contact with kairomone, ovipositions and rejections on the searching behaviour of individual female parasitoids of the species Leptopilina clavipes. 2. Behavioural records were analysed by means of the proportional hazards model (Cox 1972) taking effects of fixed as well as time-varying covariates into account. 3. Analyses were carried out at three levels of resolution: (i) patch leaving and return tendencies; (ii) tendencies to stop and start searching while on the patch; and (iii) the encounter rate during search bouts. 4. Due to the large rnumber of censored observations no conclusions can be drawn about the effect of 'presence of kairomone' on the patch return tendency. 'Number of times off patch' has no effect on the patch return tendency. However, the experienced number of ovipositions or rejections and the 'latest experienced oviposition rate' have a joint effect on this tendency. The 'latest experienced oviposition rate' and one rejection, one oviposition or two ovipositions increase the patch-return tendency. 5. 'Presence of kairomone' decreases the patch-leaving tendency. 'Number of times off patch' also affects the patch-leaving tendency. When the first encounter is with a parasitized host the leaving tendency increases and after one or two ovipositions this tendency decreases. 6. Ovipositions affect the tendencies to stop and start searching such that a proportionally larger part of time on the patch is allocated to searching. Rejections have an opposite effect. 7. The encounter rate per unit search time increases during a patch visit when ovipositions have occurred. 8. The results of the analysis are discussed in a functional context. Our result (7) indicates that models for optimization should take into account that the searching efficiency is affected by intra-patch experiences.