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Reproductive effort and costs of reproduction do not explain female-biased sex ratios in the moss Pseudocalliergon trifarium (Amblystegiaceae)¹

²Swedish Museum of Natural History, Research Division, Directorate, Box 50007, SE–104 05 Stockholm, Sweden; ³Department of Botany, University of Stockholm, SE–106 91 Stockholm, Sweden; ⁴Swedish Museum of Natural History, Department of Cryptogamic Botany, Box 50007, SE–104 05 Stockholm, Sweden

ABSTRACT

A fundamental assumption in life-history theory is that reproduction is costly. Higher reproductive investment for fruits than for flowers may result in larger costs of reproduction in females than in males, which is often used to explain male-skewed sex ratios in unisexual seed plants. In contrast, bryophytes have predominantly female-biased sex ratios, suggested to be a product of a higher average cost of sexual reproduction in males. Empirical evidence to support this notion is largely lacking. We investigated sex-specific reproductive effort and costs in the unisexual moss Pseudocalliergon trifarium that has a female-dominated expressed sex ratio and rarely produces sporophytes. Annual vegetative segment mass did not differ among male, female, and non-expressing individuals, indicating that there was no threshold-size for sex expression. Mean and annual mass of sexual branches were higher in females than in males, but branch number per segment did not differ between sexes. Prefertilization reproductive effort for females was significantly greater (11.2%) than for males (8.6%). No cost for sexual branch production in terms of reduced relative vegetative growth or decreased investment in reproductive structures in consecutive years was detected. A higher realized reproductive cost in males cannot explain the unbalanced sex ratio in the study species.

Key Words: Amblystegiaceae • bryophyte • prefertilization reproductive effort and costs • resource allocation • sex ratio • sexual branches • Sweden

This article has been cited by other articles:

				H. Korpelainen, I. Bisang, L. Hedenas, and J. Kolehmainen The First Sex-Specific Molecular Marker Discovered in the Moss Pseudocalliergon trifarium J. Hered., July 24, 2008; (2008) esn036v3. [Abstract] [Full Text] [PDF]