A genetically explicit model of speciation by sensory drive within a continuous population in aquatic environments

BACKGROUND: The sensory drive hypothesis predicts that divergent sensory adaptation in different habitats may lead to premating isolation upon secondary contact of populations. Speciation by sensory drive has traditionally been treated as a special case of speciation as a byproduct of adaptation to divergent environments in geographically isolated populations. However, if habitats are heterogeneous, local adaptation in the sensory systems may cause the emergence of reproductively isolated species from a single unstructured population. In polychromatic fishes, visual sensitivity might become adapted to local ambient light regimes and the sensitivity might influence female preferences for male nuptial color. In this paper, we investigate the possibility of speciation by sensory drive as a byproduct of divergent visual adaptation within a single initially unstructured population. We use models based on explicit genetic mechanisms for color vision and nuptial coloration. RESULTS: We show that in simulations in which the adaptive evolution of visual pigments and color perception are explicitly modeled, sensory drive can promote speciation along a short selection gradient within a continuous habitat and population. We assumed that color perception evolves to adapt to the modal light environment that individuals experience and that females prefer to mate with males whose nuptial color they are most sensitive to. In our simulations color perception depends on the absorption spectra of an individual's visual pigments. Speciation occurred most frequently when the steepness of the environmental light gradient was intermediate and dispersal distance of offspring was relatively small. In addition, our results predict that mutations that cause large shifts in the wavelength of peak absorption promote speciation, whereas we did not observe speciation when peak absorption evolved by stepwise mutations with small effect. CONCLUSION: The results suggest that speciation can occur where environmental gradients create divergent selection on sensory modalities that are used in mate choice. Evidence for such gradients exists from several animal groups, and from freshwater and marine fishes in particular. The probability of speciation in a continuous population under such conditions may then critically depend on the genetic architecture of perceptual adaptation and female mate choice.

Colonization history of the Swiss Rhine basin by the bullhead (Cottus gobio): inference under a Bayesian spatially explicit framework

The present distribution of freshwater fish in the Alpine region has been strongly affected by colonization events occurring after the last glacial maximum (LGM), some 20,000 years ago. We use here a spatially explicit simulation framework to model and better understand their colonization dynamics in the Swiss Rhine basin. This approach is applied to the European bullhead (Cottus gobio), which is an ideal model organism to study fish past demographic processes since it has not been managed by humans. The molecular diversity of eight sampled populations is simulated and compared to observed data at six microsatellite loci under an approximate Bayesian computation framework to estimate the parameters of the colonization process. Our demographic estimates fit well with current knowledge about the biology of this species, but they suggest that the Swiss Rhine basin was colonized very recently, after the Younger Dryas some 6600 years ago. We discuss the implication of this result, as well as the strengths and limits of the spatially explicit approach coupled to the approximate Bayesian computation framework.

Stress effects on working memory, explicit memory, and implicit memory for neutral and emotional stimuli in healthy men

Stress is a strong modulator of memory function. However, memory is not a unitary process and stress seems to exert different effects depending on the memory type under study. Here, we explored the impact of social stress on different aspects of human memory, including tests for explicit memory and working memory (for neutral materials), as well as implicit memory (perceptual priming, contextual priming and classical conditioning for emotional stimuli). A total of 35 young adult male students were randomly assigned to either the stress or the control group, with stress being induced by the Trier Social Stress Test (TSST). Salivary cortisol levels were assessed repeatedly throughout the experiment to validate stress effects. The results support previous evidence indicating complex effects of stress on different types of memory: A pronounced working memory deficit was associated with exposure to stress. No performance differences between groups of stressed and unstressed subjects were observed in verbal explicit memory (but note that learning and recall took place within 1 h and immediately following stress) or in implicit memory for neutral stimuli. Stress enhanced classical conditioning for negative but not positive stimuli. In addition, stress improved spatial explicit memory. These results reinforce the view that acute stress can be highly disruptive for working memory processing. They provide new evidence for the facilitating effects of stress on implicit memory for negative emotional materials. Our findings are discussed with respect to their potential relevance for psychiatric disorders, such as post traumatic stress disorder.

Implicit and explicit evaluations: a declaration of dependence

This section presents abstracts of three studies on how consumer choices can be influenced by the name letter effect of brands without decision makers being aware of this influence. The first paper examined whether making brand names similar to consumers' names increases the likelihood that consumers will choose the brand. One prediction is that people will prefer and be more likely to choose products or services whose names prominently feature the letters in their own first or last names. The results showed that subjects' preference rankings and evaluations of name letter matching brands were higher than those of non-name letter matching brands. The second paper tested the possibility of using subliminal priming to activate a concept that a persuasive communicator could take advantage of. To examine the idea, two experiments were presented. In the first experiment, participants' level of thirst were manipulated and then subliminally presented them with either thirst-related words or control words. While the manipulations had no effect on participants' self-reported, conscious ratings of thirst, there was a significant interactive effect of the two factors on how much of the drink provided in the taste test was consumed. In a second, follow up experiment, thirsty participants were subliminally presented with either thirst-related words or control words after which they viewed advertisements for two new sports beverages. In conclusion, the research demonstrates that under certain conditions, subliminal printing techniques can enhance persuasion. The third paper hypothesized that the lack of correlations between implicit and explicit evaluations is due to measurement error.

The implicit achievement motive predicts match performance and the explicit motive choices for goal distances in team sports

Motivational research over the past decade has provided ample evidence for the existence of two distinct motivational systems. Implicit motives are affect-based needs and have been found to predict spontaneous behavioral trends over time. Explicit motives in contrast represent cognitively based self-attributes and are preferably linked to choices. The present research examines the differentiating and predictive value of the implicit vs. explicit achievement motives for team sports performances. German students (N = 42) completed a measure of the implicit (Operant Motive Test) and the explicit achievement motive (Achievement Motive Scale-Sport). Choosing a goal distance is significantly predicted by the explicit achievement motive measure. By contrast, repeated performances in a team tournament are significantly predicted by the indirect measure. Results are in line with findings showing that implicit and explicit motive measures are associated with different classes of behavior.