Germination Timing Influences Natural Selection on Life-history Characters in Arabidopsis Thaliana

An experimental manipulation of germination timing was conducted to test whether germination timing influences the phenotypic expression of postgermination lifehistory characteristics and whether it alters natural selection on those characters. Seeds collected from five natural populations of Arabidopsis thaliana in Kentucky were forced to germinate in early November, early December, and early March. Life-history characters such as timing of reproduction, size at reproduction, and size at senescence were measured, and fruit production and mortality were monitored. Germination timing significantly altered subsequent life-history characters and reproduction. November germinants were larger than December germinants when they began reproducing, and they commenced reproduction sooner. All spring germinants died before reproducing. Germination timing also influenced natural selection on life-history characters. December germinants were more strongly selected to be large at the time of reproduction than November germinants, indicating stronger selection for a faster growth rate in December germinants. Stabilizing selection on timing of reproduction was detected in December germinants but not in November germinants. Therefore, variation in germination timing influenced fitness, modified the phenotypic expression of important life-history characters, and altered the strength and mode of natural selection on them.