Glover's rule in North American barn owls

Studying the geographic variation of phenotypic traits can provide key information about the potential adaptive function of alternative phenotypes. Gloger's rule posits that animals should be dark-vs. light-colored in warm and humid vs. cold and dry habitats, respectively. The rule is based on the assumption that melanin pigments and/or dark coloration confer selective advantages in warm and humid regions. This rule may not apply, however, if genes for color are acting on other traits conferring fitness benefits in specific climes. Covariation between coloration and climate will therefore depend on the relative importance of coloration or melanin pigments and the genetically correlated physiological and behavioral processes that enable an animal to deal with climatic factors. The Barn Owl (Tyto alba) displays three melanin-based plumage traits, and we tested whether geographic variation in these traits at the scale of the North American continent supported Gloger's rule. An analysis of variation of pheomelanin-based reddish coloration and of the number and size of black feather spots in 1,369 museum skin specimens showed that geographic variation was correlated with ambient temperature and precipitation. Owls were darker red in color and displayed larger but fewer black feather spots in colder regions. Owls also exhibited more and larger black spots in regions where the climate was dry in winter. We propose that the associations between pigmentation and ambient temperature are of opposite sign for reddish coloration and spot size vs. the number of spots because selection exerted by climate (or a correlated variable) is plumage trait-specific or because plumage traits are genetically correlated with different adaptations.

On the Definition of Public Goods. Assessing Richard A. Musgrave's contribution

This paper provides an explanation of the emergence of the standard textbook definition of public goods in the middle of the 20th century. It focuses on Richard Musgrave's contribution in defining public goods as non-rival and non-excludable - from 1939 to 1969. Although Samuelson's mathematical definition is generally used in models of public goods, the qualitative understanding of the specificity of pure public goods owes more to Musgrave's emphasis on the impossibility of exclusion. This paper also highlights the importance of the size of the group to which benefits of a public good accrue. This analysis allow for a reassessment of the Summary table of goods which first appeared in Musgrave and Musgrave (1973) textbook.