Range limits in spatially explicit models of quantitative traits

In an influential paper, Kirkpatrick and Barton (Am Nat 150:1–23 1997) presented a system of diffusive partial differential equations modeling the joint evolution of population density and the mean of a quantitative trait when the trait optimum varies over a continuous spatial domain. We present a stability theorem for steady states of a simplified version of the system, originally studied in Kirkpatrick and Barton (Am Nat 150:1–23 1997). We also present a derivation of the system.     

Season of birth and chess expertise

The origin of talent and expertise is currently the subject of intense debate, with explanations ranging from purely biological to purely environmental. This report shows that the population of expert chess players in the northern hemisphere shows a seasonal pattern, with an excess of births in late winter and early spring. This effect remains when taking into account the distribution of births in the population at large, using statistics from the European Union member countries. A similar pattern has been found with schizophrenia, and the possible link between these two phenomena is discussed.     

Animal disease and the limits of local knowledge: dealing with ticks and tick‐borne diseases in South Africa

Some proponents of local knowledge, such as Paul Sillitoe, have expressed second thoughts about its capacity to effect development on the ‘revolutionary’ scale once predicted. Our argument in this article follows a similar route. Recent research into the management of livestock in South Africa makes clear that rural African livestock farmers experience uncertainty in relation to the control of stock diseases. State provision of veterinary services has been significantly reduced over the past decade. Both white and African livestock owners are to a greater extent left to their own devices. In some areas of animal disease management, African livestock owners have recourse to tried‐and‐tested local remedies, which are largely plant‐based. But especially in the critical sphere of tick control, efficacious treatments are less evident, and livestock owners struggle to find adequate solutions to high tickloads. This is particularly important in South Africa in the early twenty‐first century because land reform and the freedom to purchase land in the post‐apartheid context afford African stockowners opportunities to expand livestock holdings. Our research suggests that the limits of local knowledge in dealing with ticks is one of the central problems faced by African livestock owners. We judge this in relation not only to efficacy but also to the perceptions of livestock owners themselves. While confidence and practice vary, and there is increasing resort to chemical acaricides, we were struck by the uncertainty of livestock owners over the best strategies.     

Implicit and explicit features of paintings

Implicit features of the paintings are properties that are imposed by the observer (e.g. how pleasant, interesting, tense a painting appears), whereas explicit features refer to properties that can be directly perceived (form, color, depth, etc.). The aim of Experiments 1 and 2 was to investigate the underlying structure of implicit and explicit features of paintings using the factor analysis of elementary judgments. In the preliminary studies, representative sets of paintings and elementary implicit and explicit dimensions (in the form of bipolar scales) were selected. Four implicit factors were extracted: Regularity, Relaxation, Hedonic Tone and Arousal. Four explicit factors were extracted: Form, Color, Space and Complexity. The following significant correlations between implicit and explicit factors were obtained: Regularity-Form, Regularity-Space, Hedonic Tone-Form and Arousal-Complexity. In Experiment 3 the role of implicit and explicit factors in similarity-dissimilarity ratings was specified. Significant correlations between the position of paintings in MDS space and mean judgments of explicit factors Color, Space and Complexity and implicit factor Relaxation were obtained, suggesting that similarity ratings of paintings are primarily based on explicit features. The causal relation of explicit and implicit features is discussed.     

Temporally explicit habitat ecology and the coexistence of species

Habitats may have dynamics that exist independently of the population densities of species occupying the habitat. For example, ephemeral habitat patches may disappear regardless of whether a particular species is present or not. Such habitat dynamics are frequently modelled by ignoring age-related variation in patch turnover rates. This can be thought of as a temporally implicit approach. An alternative, temporally explicit approach involves using age-structured models in order to describe variations in habitat dynamics. Simple models of coexistence between competing species show that temporally implicit models may be misleading where there is age-related variation in patch dynamics. Changing the shape of the patch survivorship function but not the average patch survivorship can result in mutual extinction, monocultures or coexistence of an inferior and a superior competitor. An explicit treatment of habitat demography may therefore offer improved predictive models and alternative landscape management strategies.     

Evolutionary rescue and the limits of adaptation

Populations subject to severe stress may be rescued by natural selection, but its operation is restricted by ecological and genetic constraints. The cost of natural selection expresses the limited capacity of a population to sustain the load of mortality or sterility required for effective selection. Genostasis expresses the lack of variation that prevents many populations from adapting to stress. While the role of relative fitness in adaptation is well understood, evolutionary rescue emphasizes the need to recognize explicitly the importance of absolute fitness. Permanent adaptation requires a range of genetic variation in absolute fitness that is broad enough to provide a few extreme types capable of sustained growth under a stress that would cause extinction if they were not present. This principle implies that population size is an important determinant of rescue. The overall number of individuals exposed to selection will be greater when the population declines gradually under a constant stress, or is progressively challenged by gradually increasing stress. In gradually deteriorating environments, survival at lethal stress may be procured by prior adaptation to sublethal stress through genetic correlation. Neither the standing genetic variation of small populations nor the mutation supply of large populations, however, may be sufficient to provide evolutionary rescue for most populations.     

Brain networks of explicit and implicit learning

Are explicit versus implicit learning mechanisms reflected in the brain as distinct neural structures, as previous research indicates, or are they distinguished by brain networks that involve overlapping systems with differential connectivity? In this functional MRI study we examined the neural correlates of explicit and implicit learning of artificial grammar sequences. Using effective connectivity analyses we found that brain networks of different connectivity underlie the two types of learning: while both processes involve activation in a set of cortical and subcortical structures, explicit learners engage a network that uses the insula as a key mediator whereas implicit learners evoke a direct frontal-striatal network. Individual differences in working memory also differentially impact the two types of sequence learning.     

The limits and relationships of the acanthomorph teleosts

The phylogenetic status of the speciose euteleostean assemblage, the Acanthomorpha, is investigated. For the purposes of cladistic analysis attention is centred upon an examination of euteleostean buccal ligament systems, the occipital and ethmoid regions of the neurocranium, and the posttemporal/neurocranial association.
In this study four derived morphological features are identified which support the monophyly of the Acanthomorpha, and the previously 'problematical' genus Polymixia is determined to be the sistergroup of all the remaining acanthomorphs. The phylogenetic integrity of the sistergroup of the entire Acanthomorpha, the Myctophiformes (sensu Rosen, 1973), is attested by the presence of four derived features, and the monophyly of its major subdivisions (the Myctophidae and Neoscopelidae) is resolved.
Additional problems of euteleostean systematics and systematic methodology are discussed.     

Color perception and the limits of color constancy

Summary A summary of colorimetry is given and the limits of color constancy mechanism under changing illuminations are discussed.