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.

The Swiss Schools have been Governed by Local Lay Authorities

After the introduction of the liberal-democratic constitutions in the Swiss cantons in the first half of the 1830ies the grid of existing schools has been systemized and broadly expanded. The school systems have ever since been characterized by one key element: a special local authority type called „Schulkommission“ or „Schulpflege“. They take the form of committees consisting of laymen that are appointed by democratic elections like all the other executive bodies on the different federal levels in Switzerland. When it comes to their obligations and activities these community level school committees conform very much to the school boards in the American and Canadian school systems. They are accountable for the selection and supervision of the teachers. They approve decisions about the school careers of pupils and about curricular matters like the choice of school books. Normally their members are elected by the local voters for four year terms of office (reelection remains possible) and with regard to pedagogics they normally are non-professionals. The board members are responsible for classes and teachers assigned to them and they have to go to see them periodically. These visitations and the board meetings each month together with the teachers enable the board members to attain a deep insight into what happens in their schools over the course of their term of office. But they are confronted as laymen with a professional teaching staff and with educational experts in the public administration. Nevertheless this form of executive power by non-professionals is constitutive for the state governance in the Swiss as well as in other national political environments. It corresponds to the principles of subsidiarity and militia and therefore allows for a strong accentuation of liberty and the right of self-determination, two axioms at the very base of democratic federalist ideology. This governance architecture with this strong accent on local anchorage features substantial advantages for the legitimacy and acceptability of political and administrative decisions. And this is relevant especially in the educational area because the rearing of the offspring is a project of hope and, besides, quite costly. In the public opinion such supervision bodies staffed by laymen seem to have certain credibility advances in comparison with the professional administration. They are given credit to be capable of impeding the waste of common financial resources and of warranting the protection and the fostering of the community’s children at once. Especially because of their non-professional character they are trusted to be reliably immune against organizational blindness and they seem to be able to defend the interests of the local community against the standardization and centralization aspirations originating from the administrational expertocracy. In the paper these common rationales will be underpinned by results of a comprehensive historical analysis of the Session protocols of three Bernese school commissions from 1835 to 2005.

Local adaptations in populations of rock-dwelling haplochromines (Pisces:Cichlidae) from southern Lake Victoria

The radiation of cichlid fishes in the African great lakes is often described as adaptive, because, at a superficial level, cichlid fishes seem adapted to the ecological niches they occupy. However, adaptiveness has rarely been studied. We investigated to what extent island populations of three species of the rock-dwelling genus Neochromis, endemic to Lake Victoria, are adapted anatomically to exploit locally abundant resources. Specifically, we asked whether different resource environments were reflected in differences in the feeding apparatus, both within species and between species. In populations of two specialized biters, the algae scrapers N. rufocaudalis and N. omnicaeruleus, the biting force of the lower jaw increased with increasing amount of items that require biting in the diet. N. greenwoodi is a less specialized biter; we found differences between two populations in the hyoid position and in the premaxilla that enhance suction feeding. These adaptations were related to the amount of items requiring suction. Comparing across three sympatric pairs of species, in each case different diets were reflected in differences in anatomy.