Experimental analysis of sperm competition mechanisms in a wild bird population.
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.
Michl
Gábor
G
Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös University, H-1117, Pázmány P. Sétány 1/C, Budapest, Hungary.
Török
János
J
Griffith
Simon C
SC
Sheldon
Ben C
BC
D000818:Animals; D005260:Female; D005306:Fertilization / Q000502:physiology*; D008297:Male; D010063:Ovum / Q000502:physiology; D012726:Sexual Behavior, Animal; D020308:Songbirds; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000166:cytology* / Q000378:metabolism; D013997:Time Factors