Fenologia, ecologia reprodutiva e razão sexual de Zamia boliviana (Brongn.) A. DC. (Cycadales, Zamiaceae): uma cicada tropical rara e ameaçada
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2020-06-03
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Universidade Estadual Paulista (Unesp)
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Cicadáceas são plantas que ocupam um lugar especial na botânica. A valoração biológica, social e cultural deriva do antigo registro fóssil, que remontam mais de 250 milhões de anos e dos atributos cênicos e harmônicos que elas representam. As cicadáceas são predominantemente dioicas, com cruzamentos e sincronismos fenológicos obrigatórios. A ausência desses mecanismos torna indivíduos efetivamente estéreis. No curso de sua evolução, tais plantas desenvolveram interações com agentes bióticos, algumas indissociáveis como os mutualismos envolvidos na polinização, os serviços de dispersão de sementes e os antagonismos, como a herbivoria. Nesta tese elegemos Zamia boliviana, uma cicadácea do Cerrado, para descrever a fenologia reprodutiva, a razão sexual e as interações mutualísticas e antagônicas de suas populações no ambiente natural. Avaliamos o desempenho reprodutivo, mostrado pelo padrão da vida útil de estróbilos e da análise do padrão fenológico e da razão sexual, bem como, a natureza das interações cicadácea-insetos. Discorremos sobre como podemos associar as descobertas ao entendimento e conservação deste sistema biológico, à luz do sucesso ancestral da planta e do regime dos ecossistemas contemporâneos em que se desenvolve. Argumentamos que as condições bioclimáticas do Cerrado e as interações bióticas envolvidas com a cicadácea, têm sido primordiais para sua sobrevivência. A abrangência de atributos funcionais desses habitats permite que essa espécie persista como "gimnospermas em meio à indubitável diversidade de angiospermas" tropicais (Forzza et al. 2010; BFG, 2015), em ecossistemas impulsionados por processos determinísticos, efeitos fundadores e estocásticos. Em uma revisão de literatura da família Zamiaceae (Capítulo I), descobrimos que o número de publicações dobrou no século XXI, concentrando-se principalmente em genética, taxonomia e sistemática, morfologia, interações ecológicas e um interesse crescente em ecologia e conservação populacional. Investigações sobre esses tópicos e estratégias de conservação, especialmente para espécies de Zamia na América do Sul, foram apontadas como necessárias. No estudo fenológico (Capítulo II), identificamos padrão reprodutivo sazonalmente sincrônico, com sobreposição predominante das fases de emergência, derramamento de pólen e receptividade dos estróbilos, igualmente compatíveis entre os sexos, populações e anos subsequentes. A vida útil dos estróbilos é semelhante a distinção morfológica e temporal típica de Zamia spp., com marcada diferença no desenvolvimento de estróbilos ovulíferos, em relação aos poliníferos. O estudo de razão sexual (Capítulo III), mostrou viés predominantemente masculino para a maioria das populações examinadas. Esse resultado foi atribuído, principalmente, aos custos diferenciais dos sexos. Interações antagônicas especializadas e obrigatórias são típicas das cicadáceas em todo o mundo, como as de Eumaeus minyas Hübn. (Lepidoptera: Lycaenidae) (Capítulo IV) e também foram registradas para Z. boliviana. Observações periódicas em populações da cicadácea e a condução de experimentos no ambiente natural mostraram insetos visitantes (visitantes sazonais e oportunisticamente não confiáveis), seu comportamento e eficiência como vetores de polinização (Capítulo V). Os resultados evidenciaram que o vento não é necessário para a polinização dessa cicadácea. Por outro lado, revelamos a existência de mutualismo obrigatório e especializado envolvendo uma espécie de besouro e essa cicadácea, um mecanismo também conhecido para outras Zamia spp.. A cicadácea hospedeira é polinizada por uma nova espécie de Pharaxonotha (Coleoptera: Erotylidae), descrita no decorrer desta tese. Pharaxonotha cerradensis Skelley and Segalla mantém seu ciclo de vida em associação com as estruturas reprodutivas de Z. boliviana e a sazonalidade bioclimática do Cerrado. Provavelmente, a combinação de fatores físicos, químicos e biológicos (e. eg.: bioclimáticos, morfológicos, adaptativos, defensivos e interações) permitiu que essa e outras Zamia spp. tenham sobrevivido a outras plantas sub-históricas. Nossa pesquisa mostra e corrobora estudos anteriores sobre a biologia e ecologia de Zamia spp. e aponta para a necessidade de pesquisas com espécies dioicas e suas interações na América do Sul. Esse conhecimento é fundamental para entender e conservar sistemas biológicos co-dependentes de espécies endêmicas, raras e de vida longa, como as linhagens relíquias e ecologicamente restritas de Zamia spp..
Cycads are plants that occupy a special place in botany. The biological, social and cultural relevance derive from the ancient fossil record, which dates back more than 250 million years and the scenic and harmonic attributes that represent. Cycads are predominantly dioecious, with obligate outcrossing and phenological synchronism. In the absence of such mechanisms, individuals become effectively sterile. During their evolution, cycads have developed interactions with biotic agents, including some inextricable relationships such as mutualisms involved in pollination, seed dispersal services and antagonisms, such as herbivory. In this dissertation, we chose Zamia boliviana, a cycad from the Cerrado, to describe the reproductive phenology, sex ratio and mutualistic and antagonistic interactions of Zamia populations in the natural environment. We evaluated Zamia reproductive performance, including the lifespan pattern of strobili, the phenological pattern and sex ratio, as well as the nature of cycad-insect interactions. We discussed how we could associate our findings with the current understanding and conservation of this biological system, taking into consideration the past success of the plant and the contemporary ecosystem regime in which it develops. We argue that the bioclimatic conditions of the Cerrado ecosystem and the biotic interactions involved in cycad development have been essential for its survival. The range of functional attributes of these habitats allows this species to persist as "gymnosperms amid the undoubted diversity of tropical angiosperms" (Forzza et al. 2010; BFG, 2015) in ecosystems driven by deterministic process and founding and stochastic effects. In a literature review about the Zamiaceae family (Chapter one), we found that the number of publications doubled in the 21st century, and they were mostly focused on genetics, taxonomy and systematics, morphology, ecological interactions, with an increasing interest in population ecology and conservation. Investigation about these topics and conservation strategies, especially for South America species of Zamia, were pointed out as necessary. In the phenological study (Chapter two), we identified a seasonally synchronous reproductive pattern, with predominance of emergence stage, pollen release and strobili receptivity, which were equally compatible between sexes, populations and subsequent years. The lifespan of strobili resembles the morphological and temporal distinction typical of Zamia spp., with a marked difference in the development of ovuliferous strobili in comparison to polleniferous strobili. The sex ratio study (Chapter three) showed a predominantly male bias for most of the populations examined. This result was mainly attributed to differences in reproductive costs. Specialized and obligate antagonistic interactions are typical of cycads around the world, such as those of Eumaeus minyas Hübner (Lepidoptera: Lycaenidae) (Chapter four) and those registered for Z. boliviana. Periodic observations of cycad populations and the conduct of experiments in the natural environment revealed insect visitors (seasonal visitors and opportunistically unreliable visitors), their behavior and the efficiency as vectors of pollination (Chapter five). The results demonstrated that wind is not necessary for pollination of this cycad. On the other hand, we revealed the existence of obligate and specialized mutualism between a species of beetle and this cycad, which is a mechanism also known in other Zamia spp. The host cycad is pollinated by a new species of Pharaxonotha (Coleoptera: Erotylidae) as described in this dissertation. Pharaxonotha cerradensis Skelley and Segalla maintains its life cycle in association with the reproductive structures of Z. boliviana and the bioclimatic seasonality of the Cerrado. It is likely that the combination of physical, chemical and biological factors (e.g., bioclimatic, morphological, adaptive, defensive and interactions) allowed the survival of this and other Zamia spp. to other understory plants. Our research corroborates previous studies on the biology and ecology of Zamia spp. and points to the need for research with dioecious species and their interactions in South America. This knowledge is essential to understand and conserve biological systems co-dependent on endemic, rare and long-lived species, such as the relic and ecologically restricted populations of Zamia spp.
Cycads are plants that occupy a special place in botany. The biological, social and cultural relevance derive from the ancient fossil record, which dates back more than 250 million years and the scenic and harmonic attributes that represent. Cycads are predominantly dioecious, with obligate outcrossing and phenological synchronism. In the absence of such mechanisms, individuals become effectively sterile. During their evolution, cycads have developed interactions with biotic agents, including some inextricable relationships such as mutualisms involved in pollination, seed dispersal services and antagonisms, such as herbivory. In this dissertation, we chose Zamia boliviana, a cycad from the Cerrado, to describe the reproductive phenology, sex ratio and mutualistic and antagonistic interactions of Zamia populations in the natural environment. We evaluated Zamia reproductive performance, including the lifespan pattern of strobili, the phenological pattern and sex ratio, as well as the nature of cycad-insect interactions. We discussed how we could associate our findings with the current understanding and conservation of this biological system, taking into consideration the past success of the plant and the contemporary ecosystem regime in which it develops. We argue that the bioclimatic conditions of the Cerrado ecosystem and the biotic interactions involved in cycad development have been essential for its survival. The range of functional attributes of these habitats allows this species to persist as "gymnosperms amid the undoubted diversity of tropical angiosperms" (Forzza et al. 2010; BFG, 2015) in ecosystems driven by deterministic process and founding and stochastic effects. In a literature review about the Zamiaceae family (Chapter one), we found that the number of publications doubled in the 21st century, and they were mostly focused on genetics, taxonomy and systematics, morphology, ecological interactions, with an increasing interest in population ecology and conservation. Investigation about these topics and conservation strategies, especially for South America species of Zamia, were pointed out as necessary. In the phenological study (Chapter two), we identified a seasonally synchronous reproductive pattern, with predominance of emergence stage, pollen release and strobili receptivity, which were equally compatible between sexes, populations and subsequent years. The lifespan of strobili resembles the morphological and temporal distinction typical of Zamia spp., with a marked difference in the development of ovuliferous strobili in comparison to polleniferous strobili. The sex ratio study (Chapter three) showed a predominantly male bias for most of the populations examined. This result was mainly attributed to differences in reproductive costs. Specialized and obligate antagonistic interactions are typical of cycads around the world, such as those of Eumaeus minyas Hübner (Lepidoptera: Lycaenidae) (Chapter four) and those registered for Z. boliviana. Periodic observations of cycad populations and the conduct of experiments in the natural environment revealed insect visitors (seasonal visitors and opportunistically unreliable visitors), their behavior and the efficiency as vectors of pollination (Chapter five). The results demonstrated that wind is not necessary for pollination of this cycad. On the other hand, we revealed the existence of obligate and specialized mutualism between a species of beetle and this cycad, which is a mechanism also known in other Zamia spp. The host cycad is pollinated by a new species of Pharaxonotha (Coleoptera: Erotylidae) as described in this dissertation. Pharaxonotha cerradensis Skelley and Segalla maintains its life cycle in association with the reproductive structures of Z. boliviana and the bioclimatic seasonality of the Cerrado. It is likely that the combination of physical, chemical and biological factors (e.g., bioclimatic, morphological, adaptive, defensive and interactions) allowed the survival of this and other Zamia spp. to other understory plants. Our research corroborates previous studies on the biology and ecology of Zamia spp. and points to the need for research with dioecious species and their interactions in South America. This knowledge is essential to understand and conserve biological systems co-dependent on endemic, rare and long-lived species, such as the relic and ecologically restricted populations of Zamia spp.
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Palavras-chave
Conservação de cicadáceas, Interações ecológicas, Sistema reprodutivo, Tempo reprodutivo, Custo de reprodução, Cycad conservation, Ecological interactions, Reproductive system, Reproductive timing, Reproductive cost, Ciclo de vida de besouros, Herbívoros obrigatórios, Plantas hospedeiras, Viés sexual, Vida útil de estróbilos, Beetle life cycle, Host plants, Obligate-herbivores, Lifespan strobili, Sex bias