EFFECTS OF POPULATION STRUCTURE AND CONE PRODUCTION ON OUTCROSSING RATES IN ENGELMANN SPRUCE AND SUBALPINE FIR.

Area of Science:

• Forest ecology
• Plant reproductive biology
• Population genetics

Background:

• Mating systems are crucial for plant population dynamics and genetic diversity.
• Understanding variation in outcrossing rates is key to predicting forest resilience.
• Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) are ecologically important Western North American conifers.

Purpose of the Study:

• To investigate the variation in mating systems of Engelmann spruce and subalpine fir.
• To identify factors influencing outcrossing rates in these species.
• To compare outcrossing rates between the two species and within subpopulations.

Main Methods:

• Estimation of multilocus outcrossing rates using allozyme variation.
• Analysis of embryo and megagametophyte tissue.
• Grouping of trees by age, size, spatial distribution, maternal heterozygosity, cone production, and year of sampling.

Main Results:

• Overall multilocus outcrossing rate for spruce (0.93) was higher than for fir (0.89).
• Outcrossing rates varied significantly based on factors like male-cone production and spatial distribution.
• Trees with higher male-cone production and clumped distribution exhibited lower outcrossing rates.

Conclusions:

• Male cone production and spatial distribution are primary drivers of outcrossing levels in these wind-pollinated species.
• Temporal variation in outcrossing rates was less significant than variation between subpopulations.
• Optimal outcrossing rates are associated with medium to large-sized trees, not necessarily the largest.