Natural selection in a postglacial range expansion: the case of the colour cline in the European barn owl.

Gradients of variation-or clines-have always intrigued biologists. Classically, they have been interpreted as the outcomes of antagonistic interactions between selection and gene flow. Alternatively, clines may also establish neutrally with isolation by distance (IBD) or secondary contact between previously isolated populations. The relative importance of natural selection and these two neutral processes in the establishment of clinal variation can be tested by comparing genetic differentiation at neutral genetic markers and at the studied trait. A third neutral process, surfing of a newly arisen mutation during the colonization of a new habitat, is more difficult to test. Here, we designed a spatially explicit approximate Bayesian computation (ABC) simulation framework to evaluate whether the strong cline in the genetically based reddish coloration observed in the European barn owl (Tyto alba) arose as a by-product of a range expansion or whether selection has to be invoked to explain this colour cline, for which we have previously ruled out the actions of IBD or secondary contact. Using ABC simulations and genetic data on 390 individuals from 20 locations genotyped at 22 microsatellites loci, we first determined how barn owls colonized Europe after the last glaciation. Using these results in new simulations on the evolution of the colour phenotype, and assuming various genetic architectures for the colour trait, we demonstrate that the observed colour cline cannot be due to the surfing of a neutral mutation. Taking advantage of spatially explicit ABC, which proved to be a powerful method to disentangle the respective roles of selection and drift in range expansions, we conclude that the formation of the colour cline observed in the barn owl must be due to natural selection.

Casado Rigalt, Daniel, 2009: El arqueólogo enamorado. Historia oculta de la arqueología española: de los hallazgos fortuitos a los falsificadores de tesoros. La esfera de los libros, Madrid, 275 pp.

Pyrenae acoge la reseña de una obra divulgativa, que debe ser valorada dentro de ese género. No obstante, su lectura también será útil para cualquier profesional que quiera abrir una cata en el estado de la arqueología peninsular de finales de la primera década del siglo XXI, puesto que la firma un doctor en la materia y no un divulgador procedente de otro campo. El arqueólogo enamorado va precedido de un prólogo escrito con amor por Carmen Rigalt, periodista y madre del autor. Bajo el subtítulo Historia oculta de la arqueología española: de los hallazgos fortuitos a los falsificadores de tesoros, se plantea un proyecto elogiable, que aspira a ofrecer un panorama completo del pasado hispánico, desde la más remota prehistoria a los visigodos, haciendo cuadrar, de forma bastante equilibrada, la amplia geografía peninsular en 14 capítulos y una introducción.