BERNARDELLO, L., GALETTO, L. & RODRIGUEZ, I. G., 1994. Reproductive biology, variability of nectar features and pollination of Combretumfmticosum (Combretaceae) in Argentina. Flower morphology, nectary structure, nectar features (chemical composition, secretion pattern, standing crop, removal effects) and flower visitors are analysed in an Argentinian population of Combretum fruticosurn. The variability of these data was examined throughout the flower lifetime. Nectar is hexose dominant. Its chemical composition and concentration are constant for all flowering stages. Nectar volume varies as a function of flower age due to a combination of nectar secretion, cessation and resorption periods. The overall sugar production is decreased by nectar removal. The plant is self-incompatible and xenogamous. Only 16.2% of the flowers set seeds. Inflorescences with green flowers were exclusively visited by two hummingbird and three perching bird species which transfer the pollen. A clear link was observed among nectar production pattern, standing crop of nectar, and visitors' behaviour.
The hybrid nature of Lyciurn ciliaturn x cestroides Hieron. is supported through experimental crosses. Using L. ciliaturn Schlecht. as a female parent, 57% of crosses set fruit with hybrid seeds, whereas reciprocal crosses were unsuccessful. Seeds had a high germination rate (76%). F, plants obtained agree with the herbarium specimens previously cited as putative hybrid and with a living plant we found in C6rdoba (Argentina). Leaf, stem, and flower anatomy, karyotype composition, and chemical nectar composition were analyzed in the artificial and the natural hybrid. Results were . compared with similar data on the parental species. Most of the studied features were intermediate between those of the parental species, as supported by principal component analysis. The origin of this hybrid may be due to pollen transfer mediated by bumblebees that occasionally visit both parental species. The distribution of the parental species overlaps in a wide Chaco region showing no spatial, environmental, or external reproductive isolating mechanisms. Results indicate there is a hybrid breakdown in the progeny of the hybrid that would restrict the natural interspecific gene flow.RCsumC : Des croisements expkrimentaux confirment la nature hybride du Lyciurn ciliaturn x cestroides Hieron. En utilisant le L. ciliaturn Schlecht. comme parent femelle, 57% des croisements foment des fruits avec des graines hybrides alors que les croisements rCciproques ne fonctionnent pas. Les graines ont un pouvoir germinatif ClevC (76%). Les plantes F, obtenues concordent avec les specimens d'herbier prealablement cites comme prCsumCs hybrides, et avec une plante vivante trouvCe ti Cordoba (Argentine).L'anatomie des feuilles, des tiges et des fleurs, la composition karyotypique, et la composition chimique du nectar ont Ct C analysCes chez l'hybride naturel et artificiel. Les rCsultats ont Ct C comparCs avec des donnCes de m&me nature sur les espbces parentales. La plupart des caractbres CtudiCs sont intermkdiaires entre ceux des espbces parentales, avec confirmation par analyse en composantes principales. L'origine de cet hybride pourrait provenir du transfer? de pollen par les bourdons, qui visitent occasionnellement et consCcutivement les deux espbces parentales. La distribution de ces deux espbces se recouvre dans une vaste rCgioin de Chaco et ne montrent pas de mCcanismes d'isolement reproductifs spatial, environnemental ou externe. Les rksultats indiquent l'existence d'une rupture hybride dans la descendance de l'hybride, laquelle restreindrait le flux gCnique interspkcifique naturel.
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