Selection for independence of floral and vegetative traits: evidence from correlation patterns in five species

Abstract

Underlying developmental and genetic relationships cause positive correlations among the sizes of a variety of plant traits. Selection for functional independence among traits, however, can reduce these correlations over evolutionary time. In 1960, R.L. Berg hypothesized that the sizes of flowers in insect-pollinated plants should be selected to remain constant regardless of the size of vegetative structures, so that flowers match the sizes of their pollinators for effective pollination. This hypothesis of functional independence of floral sizes from the size of the rest of the plant predicts that correlations between floral and vegetative traits should be reduced relative to correlations within trait groups. We measured correlations in five species of insect-pollinated plants, including four Brassicaceae and Phlox divaricata. Our results support the hypothesis. The correlations among floral traits and the correlations among vegetative traits were significantly greater than the correlations across these two groups of traits in all five species. Keywords: phenotypic correlations, natural selection, functional independence, pollination, floral evolution.