Does seed size respond to selection on blossom size? - An artificial selection experiment on Dalechampia scandens

Abstract

1. Within populations variation in seed size may result from phenotypic correlation between seed size and flower size, a hypothesis originally suggested by Primack (1987). Such phenotypic correlation can be generated either by environmental or genetic covariation among traits. If phenotypic correlation between seed size and flower size results from genetic covariance, this may strongly affect the evolution of both traits. 2. I investigated the correlation between seed size and flower size using an artificial selection experiment performed on two populations of Dalechampia scandens selecting for larger and smaller blossoms for 4 generations. In the last generation, blossoms and seeds were measured in order to estimate the direct and correlated response to selection and infer the genetic regression of seed size on blossom size. In order to estimate the coefficient of variance, seeds and blossoms were measured in the control line 3. Seed size increased by 0.20% and 0.14% per percent increase in blossom size due to selection, in the two populations. The coefficient of variance was considerably lower for seed size compared to blossom size. 4. Because seed size responded little to selection on blossom size, and because seed size varies considerably less than size of floral structures, I consider seed size to be genetically canalized.