Selection on early survival does not explain germination rate clines in Mimulus cardinalis

Area of Science:

• Evolutionary Biology
• Quantitative Genetics
• Plant Ecology

Background:

• Phenotypic traits often vary along environmental gradients, forming clines.
• Local adaptation can generate these clines, but nonadaptive processes are also possible.
• Quantifying genetic variance in traits like germination rate has been challenging.

Purpose of the Study:

• To test if a germination rate cline in Mimulus cardinalis is a signature of local adaptation.
• To investigate the covariation between germination rate and early survival as a fitness component.
• To develop a novel statistical model for estimating genetic variance in germination rate.

Main Methods:

• Employed quantitative genetics and reciprocal transplant experiments.
• Measured genotypic and population-level covariation between germination rate and early survival.
• Developed and utilized a discrete log-normal model for genetic variance estimation.

Main Results:

• Found no evidence that genetic variation in germination rate influenced early survival.
• Southern populations, in both transplant gardens, showed earlier germination and higher survival rates.
• Higher early survival in southern populations was not attributable to faster germination.

Conclusions:

• The observed phenotypic cline in germination rate is likely driven by nonadaptive forces.
• Local adaptation may not be the primary driver of this specific germination cline.
• Further research is needed to explore selection at other life stages and apply the statistical framework to other traits.