Female barn owls (Tyto alba) advertise good genes

Abstract

The good genes hypothesis of sexual selection postulates that ornamentation signals superior genetic quality to potential mates. Support for this hypothesis comes from studies on male ornamentation only, while it remains to be shown that female ornamentation may signal genetic quality as well. Female barn owls (Tyto alba) display more black spots on their plumage than males. The expression of this plumage trait has a genetic basis and it has been suggested that males prefer to mate with females displaying more black spots. Given the role of parasites in the evolution of sexually selected traits and of the immune system in parasite resistance, we hypothesize that the extent of female plumage`spottiness' re£ects immunological defence. We assessed the genetic variation in speci¢c antibody production against a non-pathogenic antigen among cross-fostered nestlings and studied its covariation with the plumage spottiness of genetic parents. The magnitude of the antibody response was positively correlated with the plumage spottiness of the genetic mother but not of the genetic father. Our study thereby provides the ¢rst experimental support, to our knowledge, for the hypothesis that female ornamentation signals genetic quality.

Genetic and environmental components of variation in eumelanin and phaeomelanin sex-traits in the barn owl

“…In Switzerland, darker reddishbrown males were observed to produce more offspring per breeding attempt and to sustain higher feeding rates, suggesting that these males invest more effort per breeding attempt (Roulin et al, 2001a). If we turn to the other trait, plumage spottiness, heavily spotted females produced offspring that were more immunocompetent towards an artificially administrated antigen (Roulin et al, 2000), resistant to ectoparasites (Roulin et al, 2001b) and developmentally stable (Roulin et al, 2003). These results suggest that eu-and phaeomelanin plumage traits signal different qualities.…”

“…Similarly, we can wonder why the phenotypic correlation between the two plumage traits is more intense in males than females. Female plumage spottiness has been shown to signal immunocompetence towards an artificially administrated antigen (Roulin et al, 2000), ectoparasite resistance of offspring (Roulin et al, 2001a) and offspring developmental homeostasis (Roulin et al, 2003), whereas female plumage coloration was correlated with laying date (lighter coloured females bred earlier, Roulin et al, 2001b). Therefore, if immunocompetence/parasite resistance/ developmental homeostasis and an early initiation of breeding activities are qualities that rely on different phenotypic or genotypic characteristics, these qualities may be signalled with traits that are not correlated.…”

Brightness variability in the white badge of the eagle owl Bubo bubo

“…Along the same line, recent researches on another owl species, the barn owl Tyto alba , showed how plumage coloration (number of black spots) was positively correlated to female quality in terms of immuno-competence (Roulin et al 2001a,b). The same authors suggest that the trait would be under intersexual selection (male mate choice) because: (a) males mated to highly spotted females obtain more immune-competent offspring (Roulin et al 2000), (b) males consistently choose to mate with such females in different breeding seasons, and (c) their male offspring also preferred highly spotted females as mates (Roulin 1999).…”

“…In fact, in some monogamous species with biparental care, males seem to discriminate their mate in the same way that females do, the fitness of the former also being affected by female quality (e.g. Jones and Hunter 1993, Roulin 1999, Roulin et al 2000; but see Smiseth and Amundsen 2000).…”

Evolution of human mate choice

“…Although the research in this area is less extensive, there is evidence that similar mechanisms may operate in species in which males parent or females vary greatly in their reproductive success. In these species, males tend to be choosy when it comes to mates and females often have exaggerated traits (Roulin, 1999;Roulin, Jungi, Pfister, & Dijkstra, 2000;Szykman et al, 2001). …”