Pollination‐dependent female reproductive success in a self‐compatible outcrosser, Asphodelus aestivus Brot.

Abstract

SUMMARYExperiments were carried out, during three years , on a population oi Asphodelus aestivus Brot. (Liliaceae) in a semi-arid environment, to test whether seed production of plants was limited by quantity and/or quality of pollen supply. The natural pollinators are mainly solitary bees.The fraction of flowers setting fruits varied from 8 to 40 % between years. Fruit set of plants caged to exclude insects was less than 3%. Fruit set was increased by artificial pollination of flowers with their own pollen to 43-64%. This indicates that the plant is self-compatible, but due to the position of the anthers and stigma, insect visits are required for effective pollination. Cross-pollinated caged flowers set yet more fruits (59-82 °o) and much more (2-4 times) full seeds per fruit than self-pollinated flowers.The artificial addition of cross-pollen to flowers, in the natural environment, increased the mean number of full seeds per flower on the whole plant. Thus, natural reproduction was limited by insect pollination.A quantitative effect was indicated by a strong positive association between the number of pollen grams on a stigma and the probabilities of the flower maturing a fruit and of its ovules setting seeds. Furthermore, in 20-60 % of flowers in the population, stigma loads were less than 13 pollen grains, which indicated very low probability of fruit maturation.A qualitative response was shown by the positive effect of artificially added cross-pollen on the number of full vs. empty seeds, an effect similar to that of cross-vs. self-pollination in caged plants.The proportion of full seeds developing in a clone of Asphodelus m the natural population was inversely related to the proportion of inflorescences in its neighbourhood that belonged to the same clone, which suggests that fertility is limited by an excess of pollen from the same clone being supplied by insects.It is concluded that female reproductive success of Asphodelus aestivus in its natural environment depended on both the amount and origin of the pollen supplied by its pollinators.

Passive partner choice through exploitation barriers

“…This fitness function assumes that fruit set requires a minimum pollen load-abortion occurs if the number of fertilised seeds is below some threshold (Molau 1991;Hannan and Prucher 1996;Cruden 2000) and that about five pollen grains per ovule are required to maximise seed set (Murcia 1990;Schuster et al 1993). Equation 7 further incorporates the assumption that seed set will decrease with h j -due to interference processes, such as stigma clogging and allelopathy (Galen and Gregory 1989;Murphy and Aarssen 1995).…”

Influência dos Fatores Ambientais e da Quantidade de Néctar na Atividade de Forrageio de Abelhas em Flores de Adenocalymma bracteatum (Cham.) DC. (Bignoniaceae)

“…Contudo, a intensidade luminosa parece ser uma variável limitante ao forrageio das abelhas especialmente no início e no final do dia (kLeineRt et al 2009 dia, embora a maioria das correlações não tenha sido significativa (Tabela 3). Os recursos florais gradativamente vão se tornando limitados com o decorrer do dia, conforme são coletados pelos visitantes florais (Roubik 1989;sChusteR et al 1993 …”

Sistema reprodutivo de Sparattosperma leucanthum (Vell.) K. Schum. (Bignoniaceae)

“…A primeira leva em conta a insuficiente quantidade de pólen transportado ao estigma da flor (SCHUSTER et al, 1993), visto que nos testes reprodutivos foi transferida manualmente ao estigma grande quantidade de pólen. A mesma hipótese pode ser aplicada para a ausência de produção de frutos no teste de autopolinização natural, ocorrendo provavelmente pouca deposição de pólen no estigma das flores na ausência de visitantes florais.…”

“…A primeira hipótese corrobora Schuster et al (1993) A segunda hipótese, também de acordo com Schuster et al (1993), envolveria a baixa qualidade do pólen transportado ao estigma, devido a altas taxas de visitas geitonogâmicas realizadas pelas mamangavas. Freitas e Oliveira (2002) encontraram proporção de frutos maduros originados por polinização natural em Copaifera langsdorffii (Leguminosae) igual à deste estudo.…”

“…De acordo com Schuster et al (1993), embasado em resultados de pesquisas, a produção limitada de sementes associada com a polinização pode ser o resultado da baixa atividade do polinizador, quando, então, limita o suprimento de pólen ao estigma (quantidade insuficiente de pólen transferido), ou a deficiência na qualidade dos grãos de pólen (e.g. excessiva proporção de pólen da mesma planta em espécies autoincompatíveis) ou, ainda, ambos os casos.…”