Selection in a cycling population: differential response among skeletal traits

Area of Science:

• Ecology and Evolutionary Biology
• Population Genetics
• Mammalian Biology

Background:

• Population density cycles are known to influence phenotypic evolution.
• Density-dependent selection and genetic drift are key mechanisms.
• Understanding trait-specific responses to these cycles is crucial.

Purpose of the Study:

• To investigate how various phenotypic traits of the yellow-necked mouse (Apodemus flavicollis) respond to population density cycles.
• To analyze changes in nonmetric skull traits, skull and mandible size/shape, and transferrin allele frequencies.

Main Methods:

• Studied a population of yellow-necked mice in Białowieza National Park over seven years.
• Examined nonmetric skull traits, skull and mandible dimensions, and transferrin allele frequencies.
• Utilized Q(ST)/F(ST) analysis to assess selective pressures on different traits.

Main Results:

• All examined phenotypic traits showed significant changes over the study period.
• Mandible size and nonmetric traits changed most during increasing density; shape changes correlated with density fluctuations.
• Transferrin allele frequencies shifted most during density declines.
• Nonmetric traits appeared selectively neutral, while mandible and skull shape showed strong selection; skull size showed weak selection.

Conclusions:

• Phenotypic traits exhibit diverse evolutionary responses to population density cycles.
• Different traits are influenced by distinct mechanisms (selection vs. drift) under varying density conditions.
• Observed changes in several traits exceeded neutral model expectations, suggesting significant evolutionary forces at play.