No evidence for adjustment of sex allocation in relation to paternal ornamentation and paternity in barn swallows

Sex allocation theory predicts that parents should adjust investment in son s and daughters according to relative fitness of differently sexed offsprin g. In species with female preference for highly ornamented males, one advan tage potentially accruing to parents from investing more in Sons of the mos t ornamented males is that male offspring will inherit characters ensuring sexual attractiveness or high-quality genes, if ornaments honestly reveal m ale genetic quality. Furthermore, in species where extra-pair fertilization s occur, offspring sired by an extra-pair male are expected to more frequen tly be male than those of the legitimate male if the latter is of lower qua lity than the extra-pair male. We investigated adjustment of sex ratio of o ffspring in relation to ornamentation of the extra-pair and the social mate of females by direct manipulation of tails of male barn swallows Hirundo r ustica. Molecular sexing of the offspring was performed using the W chromos ome-linked avian chromo-helicase-DNA-binding protein (CHD) gene while pater nity assessment was conducted by typing of hypervariable microsatellite loc i. Extra-pair offspring sex ratio was not affected by ornamentation of thei r biological fathers relative to the experimental ornamentation of the pare ntal male. Experimental ornamentation of the parental males did not affect the sex ratio of nestlings in their broods. Female barn swallows might be u nable to bias offspring sex ratio at hatching according to the quality of t he biological father. Alternatively, fitness benefits in terms of sexual at tractiveness of sons might be balanced by the cost of compensating for litt le parental care provided by highly ornamented parental males, if sons are more costly to rear than daughters, or the advantage of producing more daug hters, if males with large ornaments contribute differentially more to the viability of daughters than sons.