Slow fertilization of stickleback eggs: the result of sexual conflict?
1 Institute for Evolutionary Biology and Ecology, University of Bonn, An der Immenburg 1, D-53121 Bonn, Germany
2 Institut für Klinische Chemie IKC, Inselspital, University of Bern, CH-3010 Bern, Switzerland
3 Swiss National Science Foundation, Division Biology and Medicine, Wildhainweg 3, P.O. Box 8232, CH-3001 Bern, Switzerland
BMC Ecology 2006, 6:7 doi:10.1186/1472-6785-6-7Published: 19 May 2006
The fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm. The time delay between sequential ejaculations may further influence the outcome of sperm competition. Such a time interval can load the raffle over fertilization if fertilization takes place very fast. Short fertilization times are generally assumed for externally fertilizing fish such as the three-spined stickleback (Gasterosteus aculeatus). In this pair-spawning fish, territorial males often try to steal fertilizations in nests of neighbouring males. This sneaking behaviour causes sperm competition. Sneakers will only get a share of paternity when eggs are not fertilized immediately after sperm release. Contrary to males, females may be interested in multiple paternity of their clutch of eggs. There thus may be a sexual conflict over the speed of fertilization.
In this study we used two different in vitro fertilization experiments to assess how fast eggs are fertilized in sticklebacks. We show that complete fertilization takes more than 5 min which is atypically long for externally fertilizing fishes.
This result suggests that the time difference does not imply high costs to the second stickleback male to ejaculate. Slow fertilization (and concomitant prolonged longevity of sperm) may be the result of sexual conflict in which females aimed at complete fertilization and/or multiple paternity.