OVULE DISCOUNTING IN AN OUTCROSSING, CRYPTICALLY DIOECIOUS TREE
Article first published online: 8 MAY 2007
Volume 60, Issue 10, pages 2056–2063, October 2006
How to Cite
Verdú, M., -Martínez, S. C. G., Montilla, A. I., Mateu, I. and Pannell, J. R. (2006), OVULE DISCOUNTING IN AN OUTCROSSING, CRYPTICALLY DIOECIOUS TREE. Evolution, 60: 2056–2063. doi: 10.1111/j.0014-3820.2006.tb01843.x
- Issue published online: 8 MAY 2007
- Article first published online: 8 MAY 2007
- Received April 20, 2006. Accepted July 16, 2006.
- cryptic dioecy;
- mating system;
- spatial genetic structure
Abstract Ovule discounting denotes the reduction in the number of ovules available for cross-fertilization due to the interference of inferior pollen. Traditionally, ovule discounting has been discussed solely from the perspective of compromised outcrossing opportunities as a result of selfing, but the principle is more general. Here, we extend its applicability beyond the simple contrast between selfing and outcrossing by showing that, in the cryptically dioecious tree species Fraxinus ornus, ovule discounting through frequent outcrossing with inferior fathers also constitutes a substantial cost of mating. In F. ornus, hermaphrodites produce pollen capable of siring offspring, but these offspring are less viable than those sired by males and are inferred to produce few, if any, surviving progeny. In this paper, we used microsatellite markers to analyze the mating system and paternity in a wild population of F. ornus. We found that the effective number of sires per mother was low (Nep= 2.93 to 4.95), and that paternity was correlated among progeny sampled from the same mother, but not among progeny sampled from neighboring mothers. Despite the existence of a local spatial genetic structure (up to 30 m), we found no evidence of biparental inbreeding. There was negligible selfing by hermaphrodites, but they sired approximately one fourth of the seeds produced by other hermaphrodites. Given that these progeny are not inferred to reach reproductive maturity, this constitutes a substantial cost of ovule discounting in the broad sense. We discuss the possible reasons for why hermaphrodites invest resources into inferior pollen.