Abstract
The loss of traits that no longer contribute to fitness is widespread; however, the causative evolutionary mechanisms are poorly understood. Vestigialization could proceed through the fixation of selectively neutral degenerative mutations via genetic drift. Alternatively, selection may facilitate vestigialization if trait loss results in enhanced fitness. We tested these hypotheses using Decodon verticillatus, a clonal plant in which sexual sterility has arisen repeatedly in populations across the northern geographical range limit. We compared growth and survival of replicated genotypes from 7 sexually fertile and 18 sterile populations, over 3 years in a common environment. Survival of sterile genotypes was 53% greater than for fertile genotypes, but there was no difference in biomass accumulation. Almost all mortality, and hence increased performance of sterile genotypes, occurred during simulated overwinter dormancy. These observations suggest that selection has facilitated the vestigialization of sex, and thus do not support the neutral mutation hypothesis. The selective mechanism probably involves the relaxation of a genetic trade-off between sexual reproduction and survival: alleles that increase vegetative performance at the expense of sexual fertility are selected in geographically peripheral populations where sexual reproduction is suppressed by adverse environmental conditions.
Full Text
The Full Text of this article is available as a PDF (135.8 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Borowsky R., Wilkens H. Mapping a cave fish genome: polygenic systems and regressive evolution. J Hered. 2002 Jan-Feb;93(1):19–21. doi: 10.1093/jhered/93.1.19. [DOI] [PubMed] [Google Scholar]
- Bradshaw A. D. The Croonian Lecture, 1991. Genostasis and the limits to evolution. Philos Trans R Soc Lond B Biol Sci. 1991 Aug 29;333(1267):289–305. doi: 10.1098/rstb.1991.0079. [DOI] [PubMed] [Google Scholar]
- Conner Jeffrey K. Genetic mechanisms of floral trait correlations in a natural population. Nature. 2002 Nov 28;420(6914):407–410. doi: 10.1038/nature01105. [DOI] [PubMed] [Google Scholar]
- Jeffery W. R. Cavefish as a model system in evolutionary developmental biology. Dev Biol. 2001 Mar 1;231(1):1–12. doi: 10.1006/dbio.2000.0121. [DOI] [PubMed] [Google Scholar]
- Kaltz Oliver, Bell Graham. The ecology and genetics of fitness in Chlamydomonas. XII. Repeated sexual episodes increase rates of adaptation to novel environments. Evolution. 2002 Sep;56(9):1743–1753. doi: 10.1111/j.0014-3820.2002.tb00188.x. [DOI] [PubMed] [Google Scholar]
- MULLER H. J. The Darwinian and modern conceptions of natural selection. Proc Am Philos Soc. 1949 Dec 29;93(6):459–470. [PubMed] [Google Scholar]
- Schwaegerle K. E., McIntyre H., Swingley C. Quantitative genetics and the persistence of environmental effects in clonally propagated organisms. Evolution. 2000 Apr;54(2):452–461. doi: 10.1111/j.0014-3820.2000.tb00048.x. [DOI] [PubMed] [Google Scholar]
- van Kleunen Mark, Fischer Markus, Schmid Bernhard. Experimental life-history evolution: selection on the allocation to sexual reproduction and its plasticity in a clonal plant. Evolution. 2002 Nov;56(11):2168–2177. [PubMed] [Google Scholar]