Pollination and Herbivore Ecology of an African Dalechampia (Euphorbiaceae): Comparisons with New World Species

Abstract

Dalechampia cf. parvifolia is a common vine in parts of northern Tanzania. It is similar in floral morphology and many aspects of pollination ecology to New World species of Dalechampia. The inflorescence gland secretes a sticky resin which attracts female Heriades aff. spiniscutis (Hymenoptera: Megachilidae). These bees regularly pollinate the flowers when collecting the resin or pollen. D. cf. parvifolia, like New World species, is self-compatible and capable of self-pollination in the absence of pollinators. The leaves and flowers of D. cf. parvifolia are eaten by several generalist insect herbivores and at least two suspected specialists, Neptidopsis aff. ophione and Byblia aff. acheloin (Lepidoptera: Nymphalidae). These two butterfly genera appear to be related to the specialist herbivores on Dalechampia in the New World. This observation, together with other circumstantial information, supports the hypothesis that Dalechampia and its associated specialist butterfly herbivores were dispersed together throughout the neotropics and western paleotropics either by continental drift in the Cretaceous or by migration across higher latitudes in the Tertiary. Subsequent extinctions in Africa and more recent dispersal of certain advanced Dalechampia species (including the ancestor of D. cf. parvifolia) may account for the present geographic patterns of distribution and diversity of Dalechampia and its herbivores. MEMBERS OF THE GENUS DALECHAMPIA are found throughout the lowland neotropics and the paleotropics west of Australia (Fig. 1; Pax & Hoffmann 1919). Over threequarters of the 100 or more species are found in South and Central America. Fewer than 20 species occur in the paleotropics; of these 6 are found in continental Africa and 7 in Madagascar. Most species of Dalechampia are twining vines, often growing in scrubby or secondary habitats. The leaves are usually covered with urticating, crystaliferous trichomes (Webster & Webster 1972). Current systematic and evolutionary studies suggest that there have been at least two evolutionary radiations in the genus Dalechampia (W. S. Armbruster, pers. obs.). One burst of diversification appears to have occurred fairly early in the evolutionary history of the genus, and the second appears to have occurred much later. Preliminary morphological studies indicate that the most primitive species now occur in South America; several very primitive species also occur in Madagascar. In contrast, all known African species are advanced, i.e., the result of the latter radiation (W. S. Armbruster, pers. obs.). Morphological, ecological and evolutionary investigations have been conducted primarily on Neotropical species of Dalechampia. Most Neotropical species have pseudanthial inflorescences, each containing a cymule of three pistillate flowers and a cymule of 5-13 staminate flowers and modified secretory bractlets. The staminate and pistillate flowers of each pseudanthium (blossom) are subtended by 2 involucral bracts (Webster & Webster 1972; W. S. Armbruster, pers. obs.). The group of secretory bractlets associated with the staminate flowers has been referred to as a gland and, when present, produces the pollinator reward (Armbruster & Webster 1979). In most species the reward is a triterpenoid resin which attracts female euglossine bees (Euglossa, Eufriesea, Eulaema), megachilid bees (Hypanthidium), or stingless bees (Trigona); all of these bees collect the resin for nest construction (Armbruster 1984). A few species produce volatile fragrance rewards to attract male euglossine bees (Eulaema or Euglossa) that collect the fragrances, perhaps for use as precursors in pheromone synthesis (Armbruster & Webster 1979, Webster & Armbruster 1982, Williams & Whitten 1983, Whitten et al., 1986). In the process of collecting the reward, bees pick up pollen from the staminate flowers and/or deposit pollen on the stigmas of pistillate flowers (Armbruster & Webster 1979, Armbruster & Herzig 1984). Some work has been conducted on herbivorous insects that feed on Neotropical Dalechampia. The lepidopteran fauna has perhaps received the most attention. The larvae of members of the moderately large genus of common nymphalid butterflies Hamadryas feed almost exclusively on the leaves of various Dalechampia species (Friihstorfer I Received 2 July 1984, revision accepted 24 October 1985. 64 BIOTROPICA 19(1): 64-73 1987 This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:37:51 UTC All use subject to http://about.jstor.org/terms 14 o,u,u, _ _ _ /X\5/ iSsp -