EARLY EVOLUTION OF DALECHAMPIA (EUPHORBIACEAE) - INSIGHTS FROM PHYLOGENY, BIOGEOGRAPHY, AND COMPARATIVE ECOLOGY

Dalechampia contains over 120 species arid occurs throughout the lowland tropics of Asia, Africa, and the New World. Most species in both the Old and the New World secrete terpenoid resin from large glandlike aggregations of bractlets in the pseudanthial inflorescences (blossorns) and are pollinated by bees that collect resin for use in nest construction. Using comparative chemical, morphological, and ecological data and phylogenetic analyses, I attempt to ascertain the early evolutionary and biogeographic events that led to the present distribution of species, character states, and pollinatioii systems throughout the tropics. Available evidence suggests the genus originated in western Gondwana or South America in the iiiid Cretaceous or early Tertiary, respectively, and spread throughout the tropics by the rafting of land masses, or by migration across higher latitudes when they bad subtropical climates, or both. There is some evidence for two migrational events between the Old and New Worlds. The original pollination system may have involved pollination by pollen-collecting insects or bv fragrance-collecting male euglossine bees, The origin of pollination by resin-collecting bees appears to have been a consequence of a preadaptation (exaptation): the earliest Dalechampia apparently used triterpene resins to defend flower parts against attack by herbivores and/or microbes, and resiri secondarily assumed the role of pollinator reward. The mutualistic relationship with resin-collecting bees may have originated independently in the Old and New Worlds.