Document: CHR-3-36-2

Phenotypic selection on floral traits of Lobelia cardinalis and Lobelia siphilitica: Interspecific and interpopulation variation.

CARUSO, C.M.*

Grinnell College, Grinnell, Iowa 50112 USA ¹

Abstract:
The diversity of floral displays observed in nature has been attributed to variation in the identity of pollinators visiting different plant species. If this is so, then selection on and correlations among floral traits should consistently differ between species based on pollinator identity. I measured phenotypic selection and phenotypic correlations for the same eight floral traits of L. cardinalis and L. siphilitica, sister species that have similar life history and vegetative characteristics but whose flowers are specialized to different pollinators (hummingbirds and bees, respectively). Contrary to expectations, selection on floral traits varied more between L. siphilitica populations than between species. Selection on corolla length, stigma-nectary distance, stigma exertion, and flower number differed significantly between L. siphilitica populations, while selection on only one trait (plant height) differed between species. These data suggest that the strength of selection on floral traits may be influenced more by environmental variation than by pollinator identity. For example, the L. siphilitica population that experienced the strongest selection had the lowest fruit:flower ratio, suggesting that its reproduction may have been more pollen- or resource-limited. In contrast, phenotypic correlations among floral traits varied more between species than between L. siphilitica populations. The weak interspecific differences in selection suggest that these differences in phenotypic correlations may reflect past selection on floral traits.

Keywords: natural selection; pollination; Lobelia cardinalis ; Lobelia siphilitica

This abstract is being presented at: 3:30 PM in session:
REPRODUCTIVE ECOLOGY