Abstract
Males of many insects eclose with their entire lifetime sperm supply and have to allocate their ejaculates at mating prudently. In polyandrous species, ejaculates of rival males overlap, creating sperm competition. Recent models suggest that males should increase their ejaculate expenditure when experiencing a high risk of sperm competition. Ejaculate expenditure is also predicted to vary in relation to sperm competition intensity. During high intensity, where several ejaculates compete for fertilization of the female's eggs, ejaculate expenditure is expected to be reduced. This is because there are diminishing returns of providing more sperm. Additionally, sperm numbers will depend on males' ability to assess female mating status. We investigate ejaculate allocation in the polyandrous small white butterfly Pieris rapae (Lepidoptera). Males have previously been found to ejaculate more sperm on their second mating when experiencing increased risk of sperm competition. Here we show that males also adjust the number of sperm ejaculated in relation to direct sperm competition. Mated males provide more sperm to females previously mated with mated males (i.e. when competing with many sperm) than to females previously mated to virgin males (competing with few sperm). Virgin males, on the other hand, do not adjust their ejaculate in relation to female mating history, but provide heavier females with more sperm. Although virgin males induce longer non-receptive periods in females than mated males, heavier females remate sooner. Virgin males may be responding to the higher risk of sperm competition by providing more sperm to heavier females. It is clear from this study that males are sensitive to factors affecting sperm competition risk, tailoring their ejaculates as predicted by recent theoretical models.
Full Text
The Full Text of this article is available as a PDF (146.7 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Baker A. M., Trimm J. R., Sikora F. J. Availability of phosphorus in bone meal. J Assoc Off Anal Chem. 1989 Sep-Oct;72(5):867–869. [PubMed] [Google Scholar]
- Ball M. A., Parker G. A. Sperm competition games: a general approach to risk assessment. J Theor Biol. 1998 Sep 21;194(2):251–262. doi: 10.1006/jtbi.1998.0756. [DOI] [PubMed] [Google Scholar]
- Ball M. A., Parker G. A. Sperm competition games: external fertilization and "adaptive"' infertility. J Theor Biol. 1996 May 21;180(2):141–150. doi: 10.1006/jtbi.1996.0090. [DOI] [PubMed] [Google Scholar]
- Ball M. A., Parker G. A. Sperm competition games: inter- and intra-species results of a continuous external fertilization model. J Theor Biol. 1997 Jun 21;186(4):459–466. doi: 10.1006/jtbi.1997.0406. [DOI] [PubMed] [Google Scholar]
- Gurdon J. B. Nuclear transplantation in Xenopus. Methods Cell Biol. 1991;36:299–309. doi: 10.1016/s0091-679x(08)60284-8. [DOI] [PubMed] [Google Scholar]
- Harcourt A. H., Harvey P. H., Larson S. G., Short R. V. Testis weight, body weight and breeding system in primates. Nature. 1981 Sep 3;293(5827):55–57. doi: 10.1038/293055a0. [DOI] [PubMed] [Google Scholar]
- Mossey J. M., Shapiro E. Physician use by the elderly over an eight-year period. Am J Public Health. 1985 Nov;75(11):1333–1334. doi: 10.2105/ajph.75.11.1333. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Nakatsuru K., Kramer D. L. Is sperm cheap? Limited male fertility and female choice in the lemon tetra (pisces, characidae). Science. 1982 May 14;216(4547):753–755. doi: 10.1126/science.216.4547.753. [DOI] [PubMed] [Google Scholar]
- doi: 10.1098/rspb.1997.0065. [DOI] [PMC free article] [Google Scholar]
- doi: 10.1098/rspb.1997.0166. [DOI] [PMC free article] [Google Scholar]
- doi: 10.1098/rspb.1998.0340. [DOI] [PMC free article] [Google Scholar]
- Parker G. A., Ball M. A., Stockley P., Gage M. J. Sperm competition games: a prospective analysis of risk assessment. Proc Biol Sci. 1997 Dec 22;264(1389):1793–1802. doi: 10.1098/rspb.1997.0249. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Parker G. A. Sperm competition games: sperm size and sperm number under adult control. Proc Biol Sci. 1993 Sep 22;253(1338):245–254. doi: 10.1098/rspb.1993.0110. [DOI] [PubMed] [Google Scholar]
- Parker G. A. Why are there so many tiny sperm? Sperm competition and the maintenance of two sexes. J Theor Biol. 1982 May 21;96(2):281–294. doi: 10.1016/0022-5193(82)90225-9. [DOI] [PubMed] [Google Scholar]
- Wedell N. Sperm protection and mate assessment in the bushcricket Coptaspis sp. 2. Anim Behav. 1998 Aug;56(2):357–363. doi: 10.1006/anbe.1998.0834. [DOI] [PubMed] [Google Scholar]