Experimental Analysis of Sperm Competition Mechanisms in a Wild Bird Population

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 99; no. 8; pp. 5466 - 5470
• Main Authors: Michl, Gábor, Török, János, Griffith, Simon C., Sheldon, Ben C.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 16.04.2002; National Acad Sciences
• Subjects: Animal behavior; Animal reproduction; Animals; Biological Sciences; Birds; Female; Female animals; Fertile period; Fertilization; Fertilization - physiology; Ficedula albicollis; Flycatchers; Insemination; Male; Male animals; Mating behavior; Ova; Ovum - physiology; Sexual Behavior, Animal; Songbirds; Sperm competition; Sperm-Ovum Interactions - physiology; Spermatozoa; Spermatozoa - cytology; Spermatozoa - metabolism; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.082036699

Recent work on wild birds has revealed the importance of sperm competition as a source of sexual selection, but behavioral and paternity studies have previously provided only indirect evidence for mechanisms of sperm competition in wild birds. In a field study of collared flycatchers Ficedula albicollis we used a previously uncharacterized method to determine the frequency and timing of extra-pair inseminations. By counting the number of sperm trapped on the perivitelline layer of eggs, we determined the timing of inseminations and estimated, on a day-to-day basis, the amount of sperm females stored. Our results showed that female collared flycatchers preferentially engaged in extra-pair copulations when mated to an unattractive male with a small white forehead patch. These copulations were timed for the middle part of their fertile period, at least 2 days after the last within-pair insemination. Although the mean number of extra-pair insemination events was only 1.33 per cuckolding female, the ratio between the number of sperm from extra-pair and pair inseminations was at least 5 to 1. Thus a single, well timed extra-pair insemination caused by female behavior could greatly bias fertilization probability in favor of an attractive extra-pair male. Our results suggest a possible behavioral mechanism for female control of sperm competition.