Abstract : The male fitness (reproductive success) means by mating number and offspring obtained by mate (Dewsbury, 1982; Simmons, 2001). It depends on the number of spermatozoa that succeed in egg fertilization. In competition, a male should optimize his reproductive success according to rivals. Through multiple mating of a female insect, sperm competition may occur between ejaculates of different males in female sperm store(s). Study tool of sperm competition is mainly the determination of offspring paternity. A recessive mutant of eye colour (red eyes) was used to investigate the differences in male mating capacity and fertilization success in the parasitoid wasp Anisopteromalus calandrae (Hymenoptera, Chalcidoidea, Pteromalidae). This work concerned the study of male reproductive success in relation to their available sperm supplies. First, the quantification of male sperm supply was performed in function of male life history (age or mating history) and phenotype. Second, the relationship between male reproductive success and sperm supply was examined through single mating, multiple mating and after competition between two males. Consequences of female double matings on the offspring paternity of males having different statuses (either young, aged, or with sexual experience) was measured by the use of this paternity genetic marker (eye colour).

Experimentally, results showed that (1) red-eyed (R) and wild-eyed (W) males are different in mating capacity but females mate normally with males of both phenotypes. (2) Sperm count in seminal vesicles evidenced that one-day-old R virgin males have more sperm than W ones (approximately 1.46 times greater, 4545 vs 3116 spermatozoa). Experienced males have only 15% to 25% from the initial sperm store of virgin males. 21-days-old virgin males have 1.8 times more sperm than one-day-old ones in both morphs. (3) The number of sperm stored by females in spermatheca after one mating does not differ (143 spermatozoa in average). (4) Double-mated females increase neither sperm storage (193 spermatozoa after double mating vs 161 after single) nor fecundity (respectively 130 vs 108 offspring). (5) One mating ensures life-time fecundity of females, and offspring sex ratio is anyway female-biased (about 0.79). Double mated females with two males of different phenotypes produce offspring of both phenotypes, whatever the mating order of males. (6) In competition of two males, any mating pattern always produce more offspring of the male having more sperm in seminal vesicles, whatever the male phenotype, age or mating history. In Anisopteromalus calandrae, offspring paternity distribution (after female double matings) is consistent with a fair raffle process of sperm from both donors, proposed by Parker in 1990. (7) Finally, results do prove neither augmentation nor diminution of transferred sperm quantity by males to females, opposed to sperm competition risk or intensity theories.
Document type :
Ecologie, Environnement. Université François Rabelais - Tours, 2005. Français
Contributor : Christine Besse <>
Submitted on : Tuesday, October 10, 2006 - 1:52:24 PM
Last modification on : Tuesday, October 10, 2006 - 9:17:01 PM
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UN MODÈLE POUR L'ÉTUDE DU SUCCÈS REPRODUCTEUR DES MÂLES. Ecologie, Environnement. Université François Rabelais - Tours, 2005. Français. <tel-00105131>



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