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Mallet J.,Wissenschaftskolleg zu Berlin | Mallet J.,University College London
Ecological Entomology | Year: 2010

1. At first sight, it seems most unlikely that Heliconius warning colour races have evolved by means of stochastic peak shift or shifting balance. 2. Phase I, random local processes (including genetic drift and idiosyncratic selection), and phase III, interdemic selection are the most controversial phases of the shifting balance. Phase II consists of ordinary natural selection to a new adaptive peak within populations, and is uncontroversial. 3. Heliconius have bold patterns of iridescent blue, black, yellow, white, and red. These are clearly warning patterns, and near-perfect Müllerian mimicry has evolved among species, suggesting tight control by natural selection. Field experiments have also demonstrated strong selection (often s > 0.1 on single colour pattern loci), and the population structure of Heliconius is typically not conducive to phase I. Yet the colour patterns are clearly somewhat independent and incompatible signals of unpalatability. 4. There is empirical evidence in Heliconius for both controversial phases. For phase I, occasional and local polymorphisms of colour pattern in a number of species go against the generally expected (and generally observed) monomorphism for Müllerian mimics. 5. For phase III, one of the few colour pattern clines mapped in detail has been observed to move rapidly over a period of 20 years. There are also a number of curious 'leapfrog' geographical disjunctions in colour pattern races. Disjunctions are expected if successful races have spread from the centre of the range (e.g. the Amazonian rayed races) via phase III, in competition with earlier races that are now distributed in scattered places along the periphery of the range. 6. Evidence from the genomes of Heliconius may in the near future aid in understanding colour pattern 'supergenes' and to help test for origin and spread via shifting balance. © 2010 The Royal Entomological Society. Source

Renoult J.P.,Albert Ludwigs University of Freiburg | Courtiol A.,Wissenschaftskolleg zu Berlin | Courtiol A.,Leibniz Institute for Zoo and Wildlife Research | Schaefer H.M.,Albert Ludwigs University of Freiburg
Functional Ecology | Year: 2013

The overwhelming focus of studies on communication has been on interactions among conspecifics. However, communication is often selected by a complex network of disparate intended perceivers and eavesdroppers belonging to multiple species. Shifting towards a multiple-perceiver paradigm requires a framework to compare the perception of signals across the different community members. Here, we present the stimulation landscape, a generalist model that achieves this goal. A stimulation landscape consists of a multidimensional space describing every possible stimulus for a given signalling system, to which is added one dimension indicating for each stimulus its conspicuousness for a given perceiver. Random sampling of stimuli in the landscape then allows computing a reference distribution of conspicuousness, which is used to standardize the observed conspicuousness. The stimulation landscapes corresponding to the different perceivers participating in a communication system all have the same dimensionality and scaling. They can thus be combined to describe the amalgamation of the selective forces exerted on a signal by the distinct sensory systems of multiple perceivers. We detail the model in the context of colour signalling and apply it to the case of sexual communication in songbirds. Songbirds have a different visual system than their main predators, the birds of prey. We therefore asked whether songbirds evolved colour signals that can mediate the trade-off between sexual selection exerted by conspecifics and natural selection exerted by birds of prey. We show that yellow - not ultraviolet colours as previously thought - maximize the difference of conspicuousness to songbirds and to birds of prey, but that the perceptual similarities between these two groups generally hamper the evolution of private visual communication in songbirds. The stimulation landscape is a valuable tool to investigate the role of communication in structuring the large networks of interactions between species. We further show that the stimulation landscape is related to the evolutionary model of adaptive landscape. By explicitly addressing communication in a community context, the stimulation landscape contributes to bridge the current gap between evolution and ecology. © 2013 The Authors. Functional Ecology © 2013 British Ecological Society. Source

Wilkins A.S.,Wissenschaftskolleg zu Berlin
BioEssays | Year: 2010

This article proposes that cancers can be initiated by retrotransposon (RTN) activation through changes in the transcriptional regulation of nearby genes. I first detail the hypothesis and then discuss the nature of physiological stress(es) in RTN activation; the role of DNA demethylation in the initiation and propagation of new RTN states; the connection between ageing and cancer incidence and the involvement of activated RTNs in the chromosomal aberrations that feature in cancer progression. The hypothesis neither replaces nor invalidates other theories of cancer, in particular the somatic mutation theory, but helps clarify and unify much of the hitherto poorly integrated, complex phenomenology of cancer. © 2010 Wiley Periodicals, Inc. Source

Mallet J.,Wissenschaftskolleg zu Berlin | Mallet J.,Harvard University | Mallet J.,University College London
Biology and Philosophy | Year: 2010

Historians and philosophers of science agree that Darwin had an understanding of species which led to a workable theory of their origins. To Darwin species did not differ essentially from 'varieties' within species, but were distinguishable in that they had developed gaps in formerly continuous morphological variation. Similar ideas can be defended today after updating them with modern population genetics. Why then, in the 1930s and 1940s, did Dobzhansky, Mayr and others argue that Darwin failed to understand species and speciation? Mayr and Dobzhansky argued that reproductively isolated species were more distinct and 'real' than Darwin had proposed. Believing species to be inherently cohesive, Mayr inferred that speciation normally required geographic isolation, an argument that he believed, incorrectly, Darwin had failed to appreciate. Also, before the sociobiology revolution of the 1960s and 1970s, biologists often argued that traits beneficial to whole populations would spread. Reproductive isolation was thus seen as an adaptive trait to prevent disintegration of species. Finally, molecular genetic markers did not exist, and so a presumed biological function of species, reproductive isolation, seemed to delimit cryptic species better than character-based criteria like Darwin's. Today, abundant genetic markers are available and widely used to delimit species, for example using assignment tests: genetics has replaced a Darwinian reliance on morphology for detecting gaps between species. In the 150th anniversary of The Origin of Species, we appear to be returning to more Darwinian views on species, and to a fuller appreciation of what Darwin meant. © 2010 Springer Science+Business Media B.V. Source

Gourbiere S.,CNRS Host-Pathogen-Environment Interactions Laboratory | Mallet J.,Wissenschaftskolleg zu Berlin | Mallet J.,University College London
Evolution | Year: 2010

Under simple assumptions, the evolution of epistatic "Dobzhansky- Muller" incompatibilities between a pair of species should yield an accelerating decline of log overall reproductive compatibility - a "snowball" effect that might rapidly provide new species with "reality." Possible alternatives include: (1) simple exponential failure, giving a linear rate of log compatibility loss, and (2) "slowdown," likely during reinforcement in which mate choice evolves to prevent deleterious hybridization, yielding a decelerating log compatibility loss. In analyses of multiple datasets, we find little support for the snowball effect, except possibly in Lepidoptera hybrid viability. The snowball predicts a slow initial rate of incompatibility acquisition, with low initial variance; instead, highly variable compatibility is almost universally observed at low genetic distances. Another deviation from predictions is that reproductive isolation usually remains incomplete until long after speciation. These results do not disprove snowball compatibility decay, but can result if large deleterious effects are due to relatively few genetic changes, or if different types of incompatibility evolve at very different rates. On the other hand, data on Bacillus and Saccharomyces, as well as theories of chromosomal evolution, suggest that some kinds of incompatibility accumulate approximately linearly, without Dobzhansky-Muller effects. In microorganisms, linearity can result from direct negative effects of DNA sequence divergence on compatibility. Finally, a decelerating slowdown model is supported for sympatric Leptasterias starfish, and in Drosophila prezygotic isolation in sympatry but not allopatry, providing novel comparative evidence for reinforcement. © 2009 The Society for the Study of Evolution. Source

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