title: Integration and macroevolutionary patterns in the pollination biology of conifers.
abstract: Integration influences patterns of trait evolution, but the relationship between these patterns and the degree of trait integration is not well understood. To explore this further, we study a specialized pollination mechanism in conifers whose traits are linked through function but not development. This mechanism depends on interactions among three characters: pollen that is buoyant, ovules that face downward at pollination, and the production of a liquid droplet that buoyant grains float through to enter the ovule. We use a well-sampled phylogeny of conifers to test correlated evolution among these characters and specific sequences of character change. Using likelihood models of character evolution, we find that pollen morphology and ovule characters evolve in a concerted manner, where the flotation mechanism breaks down irreversibly following changes in orientation or drop production. The breakdown of this functional constraint, which may be facilitated by the lack of developmental integration among the constituent traits, is associated with increased trait variation and more diverse pollination strategies. Although this functional "release" increases diversity in some ways, the irreversible way in which the flotation mechanism is lost may eventually result in its complete disappearance from seed plant reproductive biology.
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, 06511.|Current Address: Department of Ecology and Evolutionary Biology, Brown University, Box G-W, 80 Waterman Street, Providence, Rhode Island, 02912.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Leslie
authors.affiliation: National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, Tennessee, 37996.
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Beaulieu
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, 06511.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Crane
authors.affiliation: Botanischer Garten Rombergpark, Dortmund, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Knopf
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, 06520.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Donoghue
mesh_terms: D005075:Biological Evolution; D001696:Biomechanical Phenomena; D016013:Likelihood Functions; D056771:Ovule / Q000033:anatomy & histology* / Q000502:physiology*; D010802:Phylogeny; D011058:Pollen / Q000033:anatomy & histology* / Q000502:physiology*; D054817:Pollination / Q000502:physiology*; D064028:Tracheophyta / Q000502:physiology*
keywords: Character correlation; integration; pollination biology; saccate pollen