REPRODUCTIVE CONSEQUENCES OF BILATERAL ASYMMETRY FOR INDIVIDUAL MALE RED-WINGED BLACKBIRDS

We used morphological and breeding data from a 2-year field study of r ed-winged blackbirds (Agelaius phoeniceus) to test the hypothesis that males characterized by low levels of bilateral asymmetry (i.e., high developmental competence) realize a reproductive advantage. Specifical ly, we evaluated each of several distinct components of male reproduct ive success relative to asymmetry measures made on five bilaterally pa ired characters. Results of a male removal experiment generally failed to support the prediction that symmetry would be associated with succ ess in competition for access to breeding territories: established ter ritory owners and nonterritorial replacement males were effectively in distinguishable in this regard. Similarly, there was no indication tha t symmetrical males were more likely to establish territories in high- quality marsh habitat than in marginal upland field habitat. Finally, monitoring of breeding activity in high-quality habitat revealed that male symmetry was generally unrelated to recruitment of social mates ( i.e., harem size), the productivity of those mates (average female rep roductive success), within-pair paternity (assessed using DNA-based an alysis of parentage), or extrapair mating success. Collectively, these results indicate that symmetry is not an important determinant of rep roductive success among individual male red-winged blackbirds. This ob servation, in combination with the results of several other recent inv estigations, suggests that the fitness consequences of subtle departur es from perfect symmetry may be less significant and/or less ubiquitou s than initially suggested.