MEASURES OF PHENOTYPIC SELECTION ARE BIASED BY PARTIAL INBREEDING

Area of Science:

• Evolutionary Biology
• Quantitative Genetics
• Plant Science

Background:

• Partial inbreeding, arising from population structure or mixed mating systems, creates individual variation in inbreeding history.
• This heterogeneity complicates the interpretation of quantitative genetic variability and inbreeding depression.
• Partial inbreeding can bias measures of phenotypic selection, potentially overestimating directional and stabilizing selection.

Purpose of the Study:

• To investigate the impact of partial inbreeding on quantitative genetic variability and phenotypic selection in Mimulus guttatus.
• To determine if inbreeding history affects trait expression and seed production.
• To assess the bias introduced by partial inbreeding on the detection of natural selection.

Main Methods:

• Conducted inbreeding experiments on two partially selfing Mimulus guttatus populations.
• Measured morphological and phenological traits in inbred and outcrossed individuals.
• Performed phenotypic selection analyses using linear regressions of relative seed production on traits.

Main Results:

• Inbreeding significantly affected the means of many measured morphological and phenological traits.
• Estimates of heritabilities and additive genetic covariances may not accurately reflect adaptive potential.
• Selection analyses revealed that a portion of the observed selection was attributable to the mating system, not solely to trait-fitness correlations.

Conclusions:

• Partial inbreeding complicates the interpretation of genetic variability and can inflate estimates of directional and stabilizing selection.
• Inbred individuals exhibit reduced seed production and altered trait values compared to outcrossed individuals.
• The apparent strength of natural selection in partially inbred species may be overestimated; actual selection could be weaker.