2,330 research outputs found
Prospects for locating adaptive genes in lepidopteran genomes: A case study of butterfly colour patterns
No full textThe Lepidoptera is a diverse clade that has long attracted the attention of biologists interested in ecological and evolutionary processes. This dates back to classic evolutionary genetic studies of natural populations, which have contributed significantly to our current understanding of the natural world (Clarke and Sheppard 1960; Kettlewell 1973; Ford 1975). Nonetheless, such studies were limited by the fact that the link between genotype and phenotype was essentially an intractable “black box.” In contrast, we are now in an era in which it is becoming increasingly feasible to clone genes with major phenotypic effects in even the most poorly studied genomes, offering an unprecedented opportunity to understand phenotypic evolution at a molecular level (Feder and Mitchell-Olds 2003). Consequently, there is now considerable recent research interest in identifying genes controlling major phenotypic traits in the Lepidoptera, and several recent studies have made significant progress in documenting the genetic basis of phenotypic traits ranging from insecticide resistance, through dispersal ability, to morphological traits such as color pattern (Gahan, Gould, and Heckel 2001; Daborn et al. 2002; Hanski and Saccheri 2006; Joron et al. 2007).S.W. Baxter, O. McMillan, N. Chamberlain, R.H. ffrench-Constant, and C. D. Jiggin
Non-constant discounting in finite horizon: The free terminal time case
No full textThis paper derives the HJB (Hamilton-Jacobi-Bellman) equation for sophisticated agents in a finite horizon dynamic optimization problem with non-constant discounting in a continuous setting, by using a dynamic programming approach. A simple example is used in order to illustrate the applicability of this HJB equation, by suggesting a method for constructing the subgame perfect equilibrium solution to the problem. Conditions for the observational equivalence with an associated problem with constant discounting are analyzed. Special attention is paid to the case of free terminal time. Strotzs model (an eating cake problem of a nonrenewable resource with non-constant discounting) is revisited.naive and sophisticated agents, observational equivalence, non-constant discounting, free terminal time
Drosophila embryos as model systems for monitoring bacterial infection in real time
No full textDrosophila embryos are well studied developmental microcosms that have been used extensively as models for early development and more recently wound repair. Here we extend this work by looking at embryos as model systems for following bacterial infection in real time. We examine the behaviour of injected pathogenic (Photorhabdus asymbiotica) and non-pathogenic (Escherichia coli) bacteria and their interaction with embryonic hemocytes using time-lapse confocal microscopy. We find that embryonic hemocytes both recognise and phagocytose injected wild type, non-pathogenic E. coli in a Dscam independent manner, proving that embryonic hemocytes are phagocytically competent. In contrast, injection of bacterial cells of the insect pathogen Photorhabdus leads to a rapid ‘freezing’ phenotype of the hemocytes associated with significant rearrangement of the actin cytoskeleton. This freezing phenotype can be phenocopied by either injection of the purified insecticidal toxin Makes Caterpillars Floppy 1 (Mcf1) or by recombinant E. coli expressing the mcf1 gene. Mcf1 mediated hemocyte freezing is shibire dependent, suggesting that endocytosis is required for Mcf1 toxicity and can be modulated by dominant negative or constitutively active Rac expression, suggesting early and unexpected effects of Mcf1 on the actin cytoskeleton. Together these data show how Drosophila embryos can be used to track bacterial infection in real time and how mutant analysis can be used to genetically dissect the effects of specific bacterial virulence factors
A molecular diagnostic for endosulfan insecticide resistance in the coffee berry borer Hypothenemus hampei (Coleoptera : Scolytidae)
No full textDiscounting Arduousness
No full textThere is a growing literature considering deviations from standard constant discounting. In this paper we combine time-inconsistent (non-constant discounting) preferences with recursive utilities. We apply this setting to the demand side properties of what we call arduous goods. The rational for a non-standard discounting is that production and consumption are not separable in these kinds of goods. The necessary effort implies that individuals discount consumption of these goods in a special way: both biased preferences and dynamic recursive adjustment are present. In this way, willingness to make an effort, modeled as a discount factor, becomes endogenous.time-consistent solution, arduous and easy goods, non-constant discounting, continuous-time, recursive utility
A conserved supergene locus controls colour pattern diversity in Heliconius butterflies
No full textWe studied whether similar developmental genetic mechanisms are involved in both convergent and divergent evolution. Mimetic insects are known for their diversity of patterns as well as their remarkable evolutionary convergence, and they have played an important role in controversies over the respective roles of selection and constraints in adaptive evolution. Here we contrast three butterfly species, all classic examples of Müllerian mimicry. We used a genetic linkage map to show that a locus, Yb, which controls the presence of a yellow band in geographic races of Heliconius melpomene, maps precisely to the same location as the locus Cr, which has very similar phenotypic effects in its co-mimic H. erato. Furthermore, the same genomic location acts as a “supergene”, determining multiple sympatric morphs in a third species, H. numata. H. numata is a species with a very different phenotypic appearance, whose many forms mimic different unrelated ithomiine butterflies in the genus Melinaea. Other unlinked colour pattern loci map to a homologous linkage group in the co-mimics H. melpomene and H. erato, but they are not involved in mimetic polymorphism in H. numata. Hence, a single region from the multilocus colour pattern architecture of H. melpomene and H. erato appears to have gained control of the entire wing-pattern variability in H. numata, presumably as a result of selection for mimetic “supergene” polymorphism without intermediates. Although we cannot at this stage confirm the homology of the loci segregating in the three species, our results imply that a conserved yet relatively unconstrained mechanism underlying pattern switching can affect mimicry in radically different ways. We also show that adaptive evolution, both convergent and diversifying, can occur by the repeated involvement of the same genomic regions
Heterogeneous discounting in consumption-investment problems. Time consistent solutions
No full textIn this paper we analyze a stochastic continuous time model in finite horizon in which agents discount the instantaneous utility function and the final function at constant but different instantaneous discount rates of time preference. Within this context we can model problems in which, when the time t approaches to the final time, the valuation of the final function increases compared with previous valuations in a way that cannot be explained by using a unique constant or a variable discount rate. We derive a dynamic programming equation whose solutions are time-consistent Markov equilibria. For this class of time preferences, we study the classical consumption and portfolio rules model (Merton, 1971) for CRRA and CARA utility functions for time- consistent agents, and we compare the different equilibria with the time-inconsistent solutions. The introduction of stochastic terminal time is also discussed.dynamic programming, consumption and portfolio rules, heterogeneous discounting, time consistency
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