SEXUAL SELECTION IN THE BARN SWALLOW (HIRUNDO-RUSTICA) .4. PATTERNS OF FLUCTUATING ASYMMETRY AND SELECTION AGAINST ASYMMETRY

The patterns of variation in fluctuating asymmetry were studied in fou r morphological characters of the barn swallow Hirundo rustica. The le vel of absolute and relative asymmetry was larger in the secondary sex ual character ''outer tail length'' than in three nonsexual morphologi c;tl traits (wing, central tail, and tarsus length). The extent of ind ividual asymmetry in outer tail length was negatively correlated with tail-ornament size, whereas the relationship between asymmetry of all other morphological characters and their size was flat or U-shaped. As ymmetry in outer tail length was unrelated to asymmetry in other morph ological characters, whereas asymmetries in the length of wing, centra l tail, and tarsus were positively correlated. Male barn swallows exhi bited larger asymmetry in outer tail length than females. Asymmetry of most morphological traits exhibited intermediate repeatabilities betw een years, with the exception of male and female outer tail length, wh ich were highly repeatable. Tail asymmetry of offspring weakly, though significantly, resembled that of their parents. Asymmetry in wing and outer tail length was also significantly related to several fitness c omponents. Male barn swallows that acquired a mate were less asymmetri c in wing and outer tail length than unmated males. Females with more asymmetrical tails laid eggs significantly later. Annual reproductive success was unrelated to fluctuating asymmetry. Male barn swallows tha t survived were less asymmetric in wing and outer tail length than non survivors, whereas female survivors were less asymmetric in outer tail length than nonsurvivors. These results suggest that levels of fluctu ating asymmetry in barn swallows are associated with differences in fi tness.