Estrutura sexual e ecologia reprodutiva de Amaioua guianensis Aubl. (Rubiaceae), uma espécie dióica de formações florestais de cerrado

Abstract

-(Sexual structure and reproductive ecology of Amaioua guianensis Aubl. (Rubiaceae), a dioecious species of "cerrado" woody plant formations). The breeding biology of Amaioua guianensis was studied in a forest area at Parque do Sabiá in Uberlândia, MG, Brazil, between September 2003 and April 2005. Phenology, breeding system, flower morphology, pollinator and disperser's assemblages, and sexual structure of the reproductive individuals were investigated. Amaioua guianensis is a woody dioecious species common in Brazilian forest areas. Flowers are hexamerous, tubular, whitish and odoriferous, pollinated by relatively specialized vectors as large bees and hawkmoths. Pistilate flowers produced nectar earlier and in larger amounts than the staminate ones. Staminate flowers were produced in larger numbers per inflorescence and were significantly larger than the pistilate ones. Flowers were presented in terminal inflorescences, composite umbels in the staminate and simple ones in pistilate individuals. Both male and female flowers produced non-functional sexual structures of the opposite morph, but the style of male flowers act as a pseudo-stamen, a secondary pollen presentation mechanism which is common in the tribe Gardenieae but had not been described previously to the species. Sexual ratio was significantly male biased and gender was distributed contagiously in the area, probably due in both cases to vegetative multiplication and disturbance. Natural pollination was as high as 98.6% and fruit set was 75.7%. Apomictic fruit production was very low (3.4%). Fruits were dispersed by birds. Floral morphology and relatively specialized pollinator's fauna rendered efficient pollination service and fruit production in the species even in the relatively disturbed study area.

Biologia reprodutiva de Cordiera macrophylla (K. Schum.) Kuntze (Rubiaceae), espécie dioica da região sudoeste do Estado de Mato Grosso, Brasil

“…Alta viabilidade polínica foi observada em outras espécies dioicas, como Amaioua guianensis -Rubiaceae (Amorim & Oliveira, 2006), Schinus terebinthifoliusAnacardiaceae (Lenzi & Orth, 2004), Protium spruceanum -Burseraceae (Vieira et al, 2010), Jacaratia spinosa -Caricaceae (Piratelli et al, 1998), Trichilia sp.-Meliaceae (Morellato, 2004). O período prolongado de receptividade estigmática das flores pistiladas, acompanhado da alta viabilidade polínica e do prolongamento do tempo de liberação de pólen das flores estaminadas maximizam as chances de fecundação dos óvulos.…”

“…Amorim & Oliveira (2006) também observaram, em Amaioua guianensis (Rubiaceae), o desenvolvimento apomítico de frutos (11,16%), sendo que destes apenas 3,4% alcançaram maturação, porém eram menores e atrofiados. Baixa produção de frutos por apomixia foi relatada para outras espécies dioicas, como Tapirira guianensis-Anacardiaceae (Lenza & Oliveira, 2005), Jacaratia spinosa -Caricaceae (Piratelli et al, 1998).…”

Pollination of Pagamea duckei Standl. (Rubiaceae): a functionally dioecious species

“…In Psychotria, many species of bees, including those of Trigona and Euglossa, and some wasps, are efficient pollen vectors (Coelho & Barbosa 2003, Teixera & Machado 2004a. In Amaioua guianensis Aubl., large bees such as Bombus atratus (Franklin, 1913), Centris sp., Epicharis flava (Friese, 1900) and Eulema nigrita (Lepeletier, 1841), are the most efficient pollen vectors (Amorim & Oliveira 2006). Teixeira & Machado (2004b) recorded seven bee species on Sabicea cinerea Aubl., pointing out mainly individuals of Euglossa cordata (Linnaeus, 1758), Xylocopa suspecta (Moore & Camargo, 1988), Exaerete smaragdina (Guérin-Méneville, 1844), Trigona fulviventris (Guérin, 1835) and a species of Pseudaugochloropsis.…”

Sexual ratio and floral biology of the dioecious Neea theifera Oerst. (Nyctaginaceae) in a cerrado rupestre of central Brazil

“…Possible deviation from the expected 1:1 sex ratio was tested with the Chi-square test with Yates correction for the entire population and within each altitudinal gradient (Zar 1999). To test whether a gender spatial segregation (i.e., grouped distribution of sexes) occurs in the population we performed the Run test (Zar 1999according to Oliveira 1996Amorim & Oliveira 2006). Diff erential sexual maturation and mortality (plant performance) between sex morphs were estimated using values of plant basal area as a relative parameter to measure plant age (sensu Opler & Bawa 1978).…”

“…Besides diff erences in the sexual structures per se (i.e., fl owers), dioecious plants oft en show diff erences between genders in other features, such as fl oral display (fl ower quantity), fl oral rewards and demography (Freeman et al 1997;Lenza & Oliveira 2005;Amorim & Oliveira 2006). Individuals of diff erent sexes in dioecious plants present distinct patterns in resource allocation and consequently the resource requirements are not equal (Freeman et al 1997).…”