Ovule discounting in an outcrossing, cryptically dioecious tree

Area of Science:

• Plant reproductive biology
• Evolutionary ecology
• Population genetics

Background:

• Ovule discounting traditionally focuses on selfing, but applies more broadly to mating costs.
• Fraxinus ornus exhibits cryptic dioecy, with hermaphrodites producing less viable pollen.

Purpose of the Study:

• To investigate ovule discounting as a mating cost in Fraxinus ornus.
• To analyze the mating system and paternity in a wild population using microsatellite markers.

Main Methods:

• Microsatellite marker analysis to determine mating system and paternity.
• Population genetic structure analysis.

Main Results:

• Low effective number of sires (N(ep) = 2.93–4.95) per mother.
• Paternity correlation among progeny from the same mother, but not neighboring mothers.
• Hermaphrodites sired ~25% of seeds from other hermaphrodites, with low inferred offspring viability.

Conclusions:

• Ovule discounting via outcrossing with inferior pollen is a substantial mating cost in F. ornus.
• Hermaphrodites contribute significantly to ovule discounting through inferior pollen.
• Further research is needed on resource allocation to inferior pollen production.