INBREEDING EFFECTS IN CLARKIA TEMBLORIENSIS (ONAGRACEAE) POPULATIONS WITH DIFFERENT NATURAL OUTCROSSING RATES

Area of Science:

• Evolutionary Biology
• Plant Reproduction
• Population Genetics

Background:

• Inbreeding depression, the reduced fitness of offspring from related parents, is common in natural populations.
• It is hypothesized that self-pollinating species experience less inbreeding depression than outcrossing species.
• Understanding mating systems is crucial for predicting inbreeding depression effects.

Purpose of the Study:

• To test the hypothesis that inbreeding depression is less pronounced in self-pollinating plant populations compared to outcrossing ones.
• To investigate the relationship between natural outcrossing rates and the severity of inbreeding depression.
• To compare the performance of selfed versus outcrossed progeny across populations with varying mating systems.

Main Methods:

• Estimating outcrossing rates and inbreeding coefficients using isozyme polymorphisms as genetic markers.
• Conducting artificial self- and cross-pollinations in three plant populations with distinct estimated outcrossing rates (0.03, 0.26, 0.58).
• Analyzing germination, survival, fecundity traits (fruit number, seed weight), and estimated lifetime fitness of progeny.

Main Results:

• Selfed and outcrossed seeds showed equal germination and survival rates across all populations.
• Inbreeding depression was evident in fecundity traits (fewer fruits, less seed weight) for self-pollinated plants in all populations.
• The severity of inbreeding effects on reproductive yield was highest in the most outcrossing population and lowest in the most self-fertilizing population.

Conclusions:

• Contrary to hypothesis, inbreeding depression affects fecundity even in highly self-pollinating populations.
• Biparental inbreeding, in addition to self-fertilization, contributes to homozygosity and influences inbreeding depression.
• While lifetime fitness showed no detectable inbreeding depression, reproductive yield is significantly impacted, particularly in outcrossing populations.