title: Pollination biology in the dioecious orchid Catasetum uncatum: How does floral scent influence the behaviour of pollinators?
abstract: Catasetum is a neotropical orchid genus that comprises about 160 dioecious species with a remarkable sexual dimorphism in floral morphology. Flowers of Catasetum produce perfumes as rewards, which are collected only by male euglossine bees. Currently, floral scents are known to be involved in the selective attraction of specific euglossine species. However, sexual dimorphism in floral scent and its eventual role in the pollination of Catasetum species have never been investigated. Here, we have investigated the pollination of Catasetum uncatum and asked: (1) Is floral scent a sexual dimorphic trait? (2) Does pollinarium removal/deposition affect scent emission? (3) Does sexual dimorphism in floral scent and changed scent emission have implications with regard to the behaviour of the pollinators? The frequency and behaviour of floral visitors were observed in non-manipulated flowers (both flower sexes) and in manipulated flowers (pistillate only) in which pollinaria were deposited. Scents of staminate and pistillate flowers (both manipulated and non-manipulated) were collected by using dynamic headspace methods and analysed chemically. Electrophysiological analyses were performed to detect compounds triggering antennal depolarisation in the euglossine species. C. uncatum is pollinated mainly by males of Euglossa nanomelanotricha. Pollinators were more frequent in pistillate than in staminate inflorescences. Bees approaching staminate flowers frequently flew away without visiting them, a behavioural pattern not observed in pistillate flowers. In the chemical analyses, we recorded 99 compounds, 31 of which triggered antennal depolarisation in pollinators. Multivariate analyses with the electrophysiological-active compounds did not detect differences between the scent composition of staminate and pistillate flowers. Pollinarium removal or deposition resulted in diminished scent emission within 24h in staminate and pistillate flowers, respectively. Surprisingly, bees discriminated pollinated from non-pollinated pistillate flowers as early as 2h after pollination. The rapid loss in the attractiveness of flowers following pollinarium removal/deposition can be interpreted as a strategy to direct pollinators to non-pollinated flowers. We have found no evidence that euglossine males discriminate staminate from pistillate flowers by means of floral scent. Instead, we speculate that bees use visual cues, such as sex dimorphic traits, to discriminate flowers of different sexes. Together, our results provide interesting insights into the evolution of floral signals in gender-dimorphic species and into its significance in plant reproductive biology.
authors.affiliation: Departamento de Química Fundamental, Universidade Federal de Pernambuco, Av. Prof. Moraes Rego, s/n, 50670-901 Recife, Brazil; Institute of Experimental Ecology, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany. Electronic address: miletpinheiro@hotmail.com.
authors.forename: Paulo
authors.initials: P
authors.lastname: Milet-Pinheiro
authors.affiliation: Departamento de Química Fundamental, Universidade Federal de Pernambuco, Av. Prof. Moraes Rego, s/n, 50670-901 Recife, Brazil.
authors.forename: Daniela Maria do Amaral Ferraz
authors.initials: DMDAF
authors.lastname: Navarro
authors.affiliation: Department of Organismic Biology, University of Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Dötterl
authors.affiliation: Departamento de Ciências Animais, Universidade Federal Rural do Semi-Árido, Avenida Francisco Mota 572, Mossoró, Rio Grande do Norte 59625-900, Brazil.
authors.forename: Airton Torres
authors.initials: AT
authors.lastname: Carvalho
authors.affiliation: Programa de Pós-Graduacão em Entomologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto-São Paulo 14040-901, Brazil.
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Pinto
authors.affiliation: Institute of Experimental Ecology, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Ayasse
authors.affiliation: Departamento de Botânica, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil.
authors.forename: Clemens
authors.initials: C
authors.lastname: Schlindwein
mesh_terms: D000818:Animals; D001516:Bees; D001938:Brazil; D035264:Flowers / Q000737:chemistry; D008297:Male; D015394:Molecular Structure; D029595:Orchidaceae / Q000737:chemistry*; D010476:Perfume / Q000032:analysis; D054817:Pollination / Q000502:physiology*; D013729:Terpenes / Q000737:chemistry* / Q000302:isolation & purification*; D055549:Volatile Organic Compounds / Q000032:analysis* / Q000737:chemistry
chemical_list: D010476:Perfume; D013729:Terpenes; D055549:Volatile Organic Compounds
keywords: Catasetum; Dioecy; Electrophysiological analyses; Euglossini; Perfume-producing orchids; Pollination; Volatile organic compounds (VOCs)