Morfo-anatomia floral e biologia reprodutiva de Selenicereus setaceus (Salm-Dyck) Berger (Cactaceae) em São Thomé das Letras, Minas Gerais, Brasil
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Data
2022-08-24
Autores
Sampaio, Paulo de Salles Penteado
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Universidade Estadual Paulista (Unesp)
Resumo
Cactos epífitos, hemiepífitos e escandentes compreendem cerca de 10% do total de espécies de Cactaceae e são o grupo menos estudado nesta família, sendo que a flor das cactáceas apresenta características estruturais importantes para compreender a taxonomia e filogenia da família. A evolução de um hipanto de origem receptacular levou a possibilidade do desenvolvimento de um tubo floral longo nos grupos mais derivados, uma inovação chave que permitiu uma maior diversidade de polinizadores. Estudos sobre a biologia reprodutiva, morfologia, anatomia e ontogenia floral de Selenicereus são escassos e a maioria deles tem um viés agrícola, com foco nas pitaias comerciais, nenhum deles abordando o Selenicereus setaceus, o que limita o entendimento da diversidade morfológica das estruturas florais, bem como a evolução destas não somente no gênero Selenicereus como em Cactaceae. Assim, o objetivo desta tese foi descrever a morfologia, ontogenia e anatomia floral do cacto epífito/escandente Selenicereus setaceus, utilizando técnicas tradicionais de histologia vegetal e compreender, também, a biologia reprodutiva desta espécie estudando seu ciclo floral, fenologia reprodutiva, produção de néctar, visitantes florais, polinizadores potenciais e seu sistema reprodutivo. Experimentos com métodos de exclusão foram realizados para monitorar o sucesso reprodutivo e determinar quais visitantes florais eram polinizadores potenciais e tratamentos de polinização foram realizados para determinar seu sistema reprodutivo. A morfologia floral do S. setaceus segue o padrão da Tribo Hylocereeae, gênero Selenicereus e também está de acordo com o padrão morfológico para flores de Cactaceae esfingófilas. O ovário é sincárpico unilocular, apresenta uma epiderme interna com tricomas, os funículos são ramificados com um tronco central ligado a placenta portando óvulos circinótropos, bitegumentados, em número médio de 2.763 óvulos. O androceu apresenta cerca de 390 estames com anteras bitecas, basifixas com quatro sacos polínicos apresentando muitos grãos de pólen por flor com uma média de 521.690 grãos apresentados em mônades, grandes (86-96,3 µm), 3 colpados com exina espinulosa e perfurada. O néctar floral é produzido em uma câmara nectarífera onde o néctar é produzido e acumulado em uma região localizada acima do ovário, expandida e alongada ocupando grande extensão no tubo floral, sendo do tipo difusa. A ontogenia mostrou que os primórdios de androceu e gineceu surgem já nos primeiros estágios do desenvolvimento do botão floral; em um mesmo eixo num plano horizontal, sendo que o androceu possui um padrão centrífugo de desenvolvimento e o gineceu apresentando somente uma cavidade e primórdios de carpelos já unidas neste estágio de desenvolvimento inicial; comprovando então uma fusão congenital e não ontogenética. A formação do tubo floral com a cavidade nectarífera em seu interior e o crescimento em extensão destas estruturas só ocorre faltando metade do tempo para a antese; os tricomas da epiderme nectarífera se apresentam desenvolvidos somente na pre-antese faltando dois dias para a antese; já os tricomas do canal estilar e lobos do estigma estão bem desenvolvidos faltando 10 dias para a antese. O botão floral leva 41 dias para atingir a antese e a maturação dos frutos 63 dias. Os horários de início da antese ocorrem por volta das 16h, 2h antes do pôr do sol, e a flor está totalmente aberta por volta das 20h30, com 30 cm de comprimento e 29 cm de diâmetro e o término da antese ocorre por volta das 11h. O néctar apresentou uma concentração média de soluto de 28,3% e volume médio de 133 µL. As abelhas Apis mellifera foram os visitantes mais frequentes e os principais polinizadores das flores de S. setaceus, principalmente no período entre 05h00-06h00 quando foi observada a maior frequência e número de visitas; sendo que os visitantes noturnos foram muito escassos, com apenas uma visita registrada para a mariposa Manduca rustica, outro polinizador potencial. A polinização natural teve alta taxa de frutificação (89,8%); a população estudada é autocompatível; e frutifica através de autopolinização manual e espontânea que ocorre através do contato físico entre as anteras e os lobos do estigma durante o fechamento das flores. Este estudo comprovou que o Selenicereus setaceus apesar de se enquadrar na síndrome da esfingofilia com uma flor fenotipicamente especializada, possui uma polinização natural ocorrendo, principalmente, pela extensão da antese floral até às 11h do dia seguinte e visitação diurna realizada por Apis mellifera, além da autopolinização espontânea. A população do S. setaceus está mudando seu sistema de polinização devido à escassez do polinizador noturno e apresentando um sistema de polinização generalista com diferentes mecanismos de transporte de pólen, ou seja, a autopolinização e a polinização cruzada realizada pelas abelhas, a autopolinização e a polinização cruzada por mariposas e a autopolinização espontânea estão garantindo a produção de frutos e sementes no S. setaceus em São Thomé das Letras. A autopolinização espontânea ou realizada pelas Apis mellifera é uma garantia para a segurança reprodutiva e manutenção da espécie no local de estudo, como indicado pela baixa taxa de fertilização dos óvulos disponíveis nas flores fenotipicamente especializadas, devido à raridade local da mariposa esfingídea.
Epiphytic, hemiepiphytic and scandent cacti comprise about 10% of the total species of Cactaceae and are the least studied group in this family, the cactus flower presents important structural characteristics to understand the taxonomy and phylogeny of the family. The evolution of a hypanthium of receptacular origin led to the possibility of the development of a long floral tube in the more derived groups, a key innovation that allowed for a greater diversity of pollinators. Studies on the reproductive biology, morphology, anatomy and floral ontogeny of Selenicereus are scarce and most of them have an agricultural bias, focusing on commercial pitayas, none of them addressing Selenicereus setaceus, which limits the understanding of the morphological diversity of floral structures, as well as their evolution not only in the genus Selenicereus but also in Cactaceae. Thus, the objective of this thesis was to describe the morphology, ontogeny and floral anatomy of the epiphytic/scandent cactus Selenicereus setaceus, using traditional techniques of plant histology and also to understand the reproductive biology of this species by studying its floral cycle, reproductive phenology, nectar production, floral visitors, potential pollinators and their reproductive system. Experiments with exclusion methods were performed to monitor reproductive success and determine which floral visitors were potential pollinators, and pollination treatments were performed to determine their reproductive system. The floral morphology of S. setaceus follows the pattern of the Tribe Hylocereeae, genus Selenicereus and is also in accordance with the morphological pattern for sphingophilous Cactaceae flowers. The ovary is unilocular syncarpic, presents an internal epidermis with trichomes, the funiculi are branched with a central trunk connected to the placenta carrying circinotropous, bitegmic ovules, with an average number of 2,763 ovules. The androecium presents about 390 stamens with bitec anthers, basifixes with four pollen sacs presenting many pollen grains per flower with an average of 521,690 grains presented in monads, large (86-96.3 µm), 3 colpate with spinulose and perforated exine . The floral nectar is produced in a nectariferous chamber where the nectar is produced and accumulated in a region located above the ovary, expanded and elongated, occupying a large extension in the floral tube, being of the diffuse type. Ontogeny showed that the beginnings of androecium and gynoecium appear in the first stages of flower bud development; on the same axis in a horizontal plane, with the androecium having a centrifugal pattern of development and the gynoecium presenting only one cavity and primordia of carpels already united at this early stage of development; thus proving a congenital and not ontogenetic fusion. The formation of the floral tube with the nectariferous cavity in its interior and the extension growth of these structures only occurs with half the time for anthesis; the trichomes of the nectariferous epidermis are developed only in the pre-anthesis, with two days before the anthesis; on the other hand, the trichomes of the stylar canal and stigma lobes are well developed, 10 days before anthesis. The flower bud takes 41 days to reach anthesis and fruit maturation 63 days. Anthesis start times are around 4 pm, 2 hours before sunset, and the flower is fully open around 8h30 pm, 30 cm long and 29 cm in diameter, and anthesis ends around 11 am . The nectar had an average solute concentration of 28.3% and an average volume of 133 µL. Apis mellifera bees were the most frequent visitors and the main pollinators of S. setaceus flowers, mainly in the period between 05h00-06h00 am, when the highest frequency and number of visits was observed; and nocturnal visitors were very scarce, with only one recorded visit for the Manduca rustica moth, another potential pollinator. Natural pollination had a high fruiting rate (89.8%); the population studied is self-compatible; and fruit through manual and spontaneous self-pollination that occurs through physical contact between the anthers and the stigma lobes during the closing of the flowers. This study proved that Selenicereus setaceus, despite being part of the sphingophilous syndrome with a phenotypically specialized flower, has a natural pollination occurring mainly by the extension of floral anthesis until 11:00 am the following day and daytime visitation by Apis mellifera, in addition to the spontaneous self-pollination. The population of S. setaceus is changing its pollination system due to the scarcity of the nocturnal pollinator and presenting a generalist pollination system with different pollen transport mechanisms, that is, self-pollination and cross-pollination performed by bees, self-pollination and cross-pollination by moths and spontaneous self-pollination are guaranteeing the production of fruits and seeds in São Thomé das Letras. Spontaneous self-pollination or self-pollination by Apis mellifera is a guarantee for the reproductive safety and maintenance of the species at the study site, as indicated by the low fertilization rate of the eggs available in the phenotypically specialized flowers, due to the local rarity of the sphingid moth.
Epiphytic, hemiepiphytic and scandent cacti comprise about 10% of the total species of Cactaceae and are the least studied group in this family, the cactus flower presents important structural characteristics to understand the taxonomy and phylogeny of the family. The evolution of a hypanthium of receptacular origin led to the possibility of the development of a long floral tube in the more derived groups, a key innovation that allowed for a greater diversity of pollinators. Studies on the reproductive biology, morphology, anatomy and floral ontogeny of Selenicereus are scarce and most of them have an agricultural bias, focusing on commercial pitayas, none of them addressing Selenicereus setaceus, which limits the understanding of the morphological diversity of floral structures, as well as their evolution not only in the genus Selenicereus but also in Cactaceae. Thus, the objective of this thesis was to describe the morphology, ontogeny and floral anatomy of the epiphytic/scandent cactus Selenicereus setaceus, using traditional techniques of plant histology and also to understand the reproductive biology of this species by studying its floral cycle, reproductive phenology, nectar production, floral visitors, potential pollinators and their reproductive system. Experiments with exclusion methods were performed to monitor reproductive success and determine which floral visitors were potential pollinators, and pollination treatments were performed to determine their reproductive system. The floral morphology of S. setaceus follows the pattern of the Tribe Hylocereeae, genus Selenicereus and is also in accordance with the morphological pattern for sphingophilous Cactaceae flowers. The ovary is unilocular syncarpic, presents an internal epidermis with trichomes, the funiculi are branched with a central trunk connected to the placenta carrying circinotropous, bitegmic ovules, with an average number of 2,763 ovules. The androecium presents about 390 stamens with bitec anthers, basifixes with four pollen sacs presenting many pollen grains per flower with an average of 521,690 grains presented in monads, large (86-96.3 µm), 3 colpate with spinulose and perforated exine . The floral nectar is produced in a nectariferous chamber where the nectar is produced and accumulated in a region located above the ovary, expanded and elongated, occupying a large extension in the floral tube, being of the diffuse type. Ontogeny showed that the beginnings of androecium and gynoecium appear in the first stages of flower bud development; on the same axis in a horizontal plane, with the androecium having a centrifugal pattern of development and the gynoecium presenting only one cavity and primordia of carpels already united at this early stage of development; thus proving a congenital and not ontogenetic fusion. The formation of the floral tube with the nectariferous cavity in its interior and the extension growth of these structures only occurs with half the time for anthesis; the trichomes of the nectariferous epidermis are developed only in the pre-anthesis, with two days before the anthesis; on the other hand, the trichomes of the stylar canal and stigma lobes are well developed, 10 days before anthesis. The flower bud takes 41 days to reach anthesis and fruit maturation 63 days. Anthesis start times are around 4 pm, 2 hours before sunset, and the flower is fully open around 8h30 pm, 30 cm long and 29 cm in diameter, and anthesis ends around 11 am . The nectar had an average solute concentration of 28.3% and an average volume of 133 µL. Apis mellifera bees were the most frequent visitors and the main pollinators of S. setaceus flowers, mainly in the period between 05h00-06h00 am, when the highest frequency and number of visits was observed; and nocturnal visitors were very scarce, with only one recorded visit for the Manduca rustica moth, another potential pollinator. Natural pollination had a high fruiting rate (89.8%); the population studied is self-compatible; and fruit through manual and spontaneous self-pollination that occurs through physical contact between the anthers and the stigma lobes during the closing of the flowers. This study proved that Selenicereus setaceus, despite being part of the sphingophilous syndrome with a phenotypically specialized flower, has a natural pollination occurring mainly by the extension of floral anthesis until 11:00 am the following day and daytime visitation by Apis mellifera, in addition to the spontaneous self-pollination. The population of S. setaceus is changing its pollination system due to the scarcity of the nocturnal pollinator and presenting a generalist pollination system with different pollen transport mechanisms, that is, self-pollination and cross-pollination performed by bees, self-pollination and cross-pollination by moths and spontaneous self-pollination are guaranteeing the production of fruits and seeds in São Thomé das Letras. Spontaneous self-pollination or self-pollination by Apis mellifera is a guarantee for the reproductive safety and maintenance of the species at the study site, as indicated by the low fertilization rate of the eggs available in the phenotypically specialized flowers, due to the local rarity of the sphingid moth.
Descrição
Palavras-chave
Selenicereus setaceus, Hylocereeae, Cactaceae, Apis mellifera, Biologia reprodutiva, Ontogenia, Anatomia, Manduca rustica, Polinizador potencial, Antese noturna, Morfologia, Breeding system, Ontogeny, Anatomy, Morphology, Potential pollinator, Nocturnal anthesis, Diurnal floral visitors