Harmful self-pollination drives gynodioecy in European chestnut, a self-incompatible tree

Area of Science:

• Evolutionary Biology
• Plant Reproduction
• Sexual Systems

Background:

• Gynodioecy, a rare sexual system with cosexuals and females, requires females to compensate for reduced reproductive success.
• European chestnut (Castanea sativa) exhibits self-pollination issues in cosexual individuals due to self-incompatibility and inbreeding depression.

Purpose of the Study:

• Investigate the role of sexual conflict and self-pollination in the maintenance of gynodioecy in European chestnut.
• Compare fruit set and female fitness components between cosexual and female chestnut trees.

Main Methods:

• Studied gender variation in wild European chestnut populations.
• Compared fruit set and reproductive allocation between genders.
• Conducted emasculation experiments on cosexual trees by removing male inflorescences.

Main Results:

• Observed a variable proportion of female (male-sterile) individuals in wild populations.
• Cosexual and female trees showed similar size and flower density, but differing fruit set.
• Removing male inflorescences increased fruit set in cosexual trees, but not in female trees.

Conclusions:

• Self-pollination negatively impacts fruit set in cosexual European chestnut trees.
• Female trees bypass self-pollination issues and achieve higher fruit set by attracting pollinators with sterile male-inflorescences.
• These findings highlight the evolutionary advantage of avoiding self-pollination, potentially driving the evolution of unisexuality in outcrossing plants.