POLLINATION OF PHILODENDRON ACUTATUM (ARACEAE) IN THE ATLANTIC FOREST OF NORTHEASTERN BRAZIL: A SINGLE SCARAB BEETLE SPECIES GUARANTEES HIGH FRUIT SET Artur Campos Da ´lia Maia, 1, * Clemens Schlindwein, y Daniela Maria Almeida Ferraz Navarro, z and Marc Gibernau§ *Universidade Federal da Paraı ´ba, Programa de Po ´ s-Graduac ¸a ˜o em Cie ˆncias Biolo ´ gicas, Cidade Universita ´ria, 58059-900 Joa ˜o Pessoa, Brazil, and Universite ´ Paul Sabatier, Ba ˆtiment 4R3-B2, 31062 Toulouse Cedex 9, France; y Universidade Federal de Pernambuco, Departamento de Bota ˆnica, Avenida Professor Morais Re ˆgo, s/n Cidade Universita ´ria, 50670-901 Recife, Brazil; z Universidade Federal de Pernambuco, Departamento de Quı ´mica Fundamental, Avenida Professor Morais Re ˆgo, s/n Cidade Universita ´ria, 50670-901 Recife, Brazil; and §Centre National de la Recherche Scientifique, Ecologie des Fore ˆts de Guyane (Unite ´ Mixte de Recherche 8172), Campus Agronomique BP709, 97387 Korou Cedex, France Philodendron acutatum (Araceae) is a hemiepiphyte common to the Atlantic Forest of northeastern Brazil. In two localities, we studied the species’ breeding system and associations with flower-visiting insects, along with an analysis of its floral scent composition. The fruit set of self-incompatible P. acutatum was high, more than 90%, and inflorescences were exclusively pollinated by one species of scarab beetle, Cyclocephala celata (Scarabaeidae, Dynastinae). Pollinators are drawn toward the inflorescences at dusk by strong floral fragrances given off during the female phase of anthesis, along with endogenous heating of the spadix, whose temperatures were recorded at more than 11°C above ambient air. Two other species of flower-visiting Cyclocephala were also consistently recovered in blacklight trappings during the flowering period of P. acutatum. The fact that only C. celata was found in association with P. acutatum suggests a local reproductive dependence of the plant to this scarab beetle species. Dihydro-b-ionone and 2-hydroxy-5-methyl-3-hexanone, a rare volatile molecule so far unreported as a floral compound, together accounted for more than 97% of the unique scent composition of P. acutatum and might be involved in specific attraction of C. celata. Keywords: Cyclocephala, floral volatiles, pollination specificity, reproductive success, thermogenesis. Introduction Scarab beetles (Coleoptera, Scarabaeidae) constitute an un- usual group of pollinating insects (Barth 1991; Endress 1996; Richards 1997; Gottsberger and Silberbauer-Gottsberger 2006). Morphological adaptations toward anthophily—readily rec- ognizable among many bees, flies, butterflies, moths, birds, and bats (Mu ¨ller 1873; Vogel 1954)—are apparently absent in these insects. Thus, it has frequently been concluded that they are unspecialized pollinators and that if they do effec- tively pollinate a plant species, it is only by chance, since they indiscriminately visit flowers to feed on pollen and/or fertile floral tissues (Buchmann and Nabham 1996). Nevertheless, in tropical and subtropical ecosystems, several Magnoliaceae, Annonaceae, Cyclanthaceae, Arecaceae, Nymphaeaceae, and Araceae rely solely on scarab beetles (Dynastinae, Cyclo- cephalini) as their effective pollinators (Gottsberger 1986; Bernhardt 2000). According to Schatz (1990), the diverse cy- clocephaline scarabs (>500 species) are pollinators of more than 900 plant species in the Neotropics alone. Although not all of the 14 known genera exhibit flower-visiting species, Cy- clocephala (>350 species), Erioscelis (5 species), and Rutero- lyctes (2 species) are predominantly anthophilous (Endro ¨ di 1985). Angiosperms pollinated by cyclocephaline scarabs show specialized floral assembly and physiology, generally under- stood as the result of convergent evolution (Gottsberger 1990; Bernhardt 2000). Their flowers present nocturnal an- thesis and are protogynous, which render them functionally self-incompatible as a result of a rigorous temporal partition- ing of stigma receptivity (female phase) and pollen release (male phase; Grayum 1990; Mayo et al. 1997). Floral struc- tures are robust and often modified into floral chambers, which function as shelter and mating aggregation sites for the beetles (Gottsberger and Amaral 1984; Bernhardt 2000). Food rewards are available in the form of abundant pollen, nutritious sterile floral tissues (e.g., petals and staminodes) and floral exudates, which entice a prolonged stay of the pol- linators and ensure effective pollen transfer (Bernhardt 2000). The large flowers of the Annonaceae and the funnel- shaped inflorescences of the Araceae may host dozens, some- times hundreds of night-active cyclocephaline scarabs at a time, attracted by floral scents given off during anthesis (Gottsberger 1986). These fragrances are strong and their dispersion is facilitated by flower thermogenicity, a physiolog- ical process during which carbohydrates or lipids stored in specific floral tissues are burnt to raise their temperatures above that of the surrounding air, thus enhancing volatilization (Seymour et al. 1983; Gottsberger 1990). Endogenous tem- peratures of some thermogenic flowers are the highest ever recorded in plants and exceed 45°C (Gottsberger and Amaral 1984; Seymour 1999). 1 Author for correspondence; e-mail: artur_campos_maia@yahoo .com.br. Manuscript received March 2010; revised manuscript received April 2010. 740 Int. J. Plant Sci. 171(7):740–748. 2010. Ó 2010 by The University of Chicago. All rights reserved. 1058-5893/2010/17107-0003$15.00 DOI: 10.1086/654846