Abstract
Adjustment of offspring sex ratios should be favoured by natural selection when parents are capable of facultatively altering brood sex ratios and of recognizing the circumstances that predict the probable fitness benefit of producing sons and daughters. Although experimental studies have shown that female birds may adjust offspring sex ratios in response to changes in their own condition and in the external appearance of their mate, and male attributes other than his external morphology are also thought to act as signals of male quality, it is not known whether females will respond to changes in such signals, in the absence of any change in the appearance of the male himself. Here, we experimentally manipulated a male courtship display, the green plants carried to the nest by male spotless starlings (Sturnus unicolor), without changing any physical attributes of the male himself, and examined whether this influenced female decisions on offspring sex ratio. We found that in an environment in which female starlings were producing more daughters than sons, experimental enhancement of the green nesting material caused females to significantly increase the number of male eggs produced and thereby removed the female bias. This effect was consistent in 2 years and at two localities. This demonstrates that the green material, whose function has long puzzled biologists, conveys important information to the female and that she facultatively adjusts offspring production accordingly.
Full Text
The Full Text of this article is available as a PDF (111.1 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Aparicio J. M., Cordero P. J. The effects of the minimum threshold condition for breeding on offspring sex-ratio adjustment in the lesser kestrel. Evolution. 2001 Jun;55(6):1188–1197. doi: 10.1111/j.0014-3820.2001.tb00638.x. [DOI] [PubMed] [Google Scholar]
- Duffy Deborah L., Ball Gregory F. Song predicts immunocompetence in male European starlings (Sturnus vulgaris). Proc Biol Sci. 2002 Apr 22;269(1493):847–852. doi: 10.1098/rspb.2002.1956. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Griffiths R., Double M. C., Orr K., Dawson R. J. A DNA test to sex most birds. Mol Ecol. 1998 Aug;7(8):1071–1075. doi: 10.1046/j.1365-294x.1998.00389.x. [DOI] [PubMed] [Google Scholar]
- Gwinner H, Oltrogge M, Trost L, Nienaber U. Green plants in starling nests: effects on nestlings. Anim Behav. 2000 Feb;59(2):301–309. doi: 10.1006/anbe.1999.1306. [DOI] [PubMed] [Google Scholar]
- Nager R. G., Monaghan P., Griffiths R., Houston D. C., Dawson R. Experimental demonstration that offspring sex ratio varies with maternal condition. Proc Natl Acad Sci U S A. 1999 Jan 19;96(2):570–573. doi: 10.1073/pnas.96.2.570. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Patricelli Gail L., Uy J. Albert C., Borgia Gerald. Multiple male traits interact: attractive bower decorations facilitate attractive behavioural displays in satin bowerbirds. Proc Biol Sci. 2003 Nov 22;270(1531):2389–2395. doi: 10.1098/rspb.2003.2530. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pienaar J., Greeff J. M. Maternal control of offspring sex and male morphology in the Otitesella fig wasps. J Evol Biol. 2003 Mar;16(2):244–253. doi: 10.1046/j.1420-9101.2003.00522.x. [DOI] [PubMed] [Google Scholar]
- Pinxten Rianne, De Ridder Elke, Balthazart Jacques, Eens Marcel. Context-dependent effects of castration and testosterone treatment on song in male European starlings. Horm Behav. 2002 Nov;42(3):307–318. doi: 10.1006/hbeh.2002.1824. [DOI] [PubMed] [Google Scholar]
- Soler JJ, Cuervo JJ, Møller AP, De lope F Nest building is a sexually selected behaviour in the barn swallow. Anim Behav. 1998 Dec;56(6):1435–1442. doi: 10.1006/anbe.1998.0938. [DOI] [PubMed] [Google Scholar]
- Thuman Katherine A., Widemo Fredrik, Griffith Simon C. Condition-dependent sex allocation in a lek-breeding wader, the ruff (Philomachus pugnax). Mol Ecol. 2003 Jan;12(1):213–218. doi: 10.1046/j.1365-294x.2003.01717.x. [DOI] [PubMed] [Google Scholar]
- Trivers R. L., Willard D. E. Natural selection of parental ability to vary the sex ratio of offspring. Science. 1973 Jan 5;179(4068):90–92. doi: 10.1126/science.179.4068.90. [DOI] [PubMed] [Google Scholar]
- Veiga José P., Viñuela Javier, Cordero Pedro J., Aparicio José M., Polo Vicente. Experimentally increased testosterone affects social rank and primary sex ratio in the spotless starling. Horm Behav. 2004 Jun;46(1):47–53. doi: 10.1016/j.yhbeh.2004.01.007. [DOI] [PubMed] [Google Scholar]