Sociality, cognition and brain complexity in Neotropical cichlids
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Data
2020-02-28
Autores
Brandão, Manuela Lombardi
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Universidade Estadual Paulista (Unesp)
Resumo
A organização cerebral em animais sociais pode ser explicada pelas relações filogenéticas – i.e., o cérebro evolui de acordo com uma linha de parentesco entre as espécies – e, também, pela seleção de estruturas direcionadas pela complexidade do ambiente social. O objetivo desta tese foi comparar a possível associação entre complexidade social, cerebral e cognitiva em espécies de peixes próximas filogeneticamente dentro da família Cichlidae que apresentam interações sociais consideradas mais complexas (cuidado biparental da prole em espécies monogâmicas) ou menos complexas (cuidado materno da prole em espécies poligínicas). As mesmas tiveram seus cérebros dissecados em macroáreas (telencéfalo, diencéfalo, teto óptico e cerebelo), posteriormente dissociadas através da técnica do fracionador isotrópico, permitindo a quantificação do número de neurônios e células não-neuronais que compõem essas macroáreas. Assim, em um primeiro estudo, comparamos os valores obtidos de neurônios e células não-neuronais com medidas cerebrais e morfométricas de cada espécie. Constatamos que, diferentemente do que é observado em estudos com mamíferos, espécies de peixes próximas filogeneticamente apresentam diferentes formas de organização cerebral, sugerindo que peixes são mais sujeitos às influências do ambiente comportamental. Após obtermos os dados sobre como os cérebros das espécies escolhidas são organizados, comparamos, em um segundo estudo, as espécies em seus tipos de cuidado parental e sistema de acasalamento. Peixes monogâmicos apresentaram mais neurônios apenas no teto óptico e cerebelo quando comparadas com espécies poligínicas. Indivíduos que cuidam da prole na boca apresentaram mais neurônios apenas no cerebelo. O ciclídeo anão, A. agassizii, foi a espécie que apresentou as maiores densidades de células cerebrais, destoando dos demais ciclídeos analisados, e revelando que as diferenças encontradas para esse peixe podem estar mais relacionadas à miniaturização sofrida por essa espécie do que a padrões sociais ligados à reprodução. Por fim, investigamos como o número de células cerebrais poderia estar associado à flexibilidade cognitiva e à socialidade apresentada pelos ciclídeos. Para isso, utilizamos o peixe monogâmico G. brasiliensis, espécie na qual ambos os pais cuidam da prole no substrato. Ao contrário do que esperávamos, o telencéfalo foi a única estrutura cerebral que não apresentou nenhuma associação entre os testes comportamentais aplicados e os valores de células cerebrais analisados. Já o diencéfalo, cerebelo e teto óptico mostraram correlações que parecem estar associadas a uma melhor avaliação do ambiente social por parte do animal. De forma geral, um maior número de células nessas regiões mostrou-se positivamente relacionado a indivíduos menos agressivos, que passam mais tempo próximos a coespecíficos e que são menos persistentes em tarefas irrelevantes, revelando animais mais cautelosos e avaliadores. Esse trabalho é inovador já que pouco se conhece sobre os mecanismos evolutivos e fisiológicos envolvidos com o controle do comportamento social em peixes neotropicais.
The cerebral organization in social animals can be explained by both, phylogenetic relationships (i.e., the brain evolves by a line of interrelationship between species) and by the selection of structures driven by the complexity of the social environment. The aim of this thesis was to compare the possible association between social behavior, brain complexity and cognitive ability in phylogenetically close fish species within the Cichlidae family, which present social interactions considered more complex (biparental brood care in monogamous species) or less complex (maternal brood care in polygynous species). Individuals had their brains dissected into macroareas (telencephalon, diencephalon, optic tectum and cerebellum), and subsequently dissociated using the isotropic fractionator technique, which allows the quantification of the number of neurons and nonneuronal cells that compose these macroareas. Therefore, in a first study, we compared the values obtained from neurons and nonneuronal cells with brain and morphometric measures of each species. We found that, differently from what is observed for mammals, phylogenetically close fish species have different brain organizations, suggesting that fish are more liable to the influences of the behavioral environment. After obtaining the data on how the brains of the chosen species are organized, in a second study we compared the species in their types of parental care and mating system. Monogamous fish presented more neurons only in the optic tectum and in the cerebellum when compared to polygynous species. Mouthbrooder individuals had more neurons in the cerebellum alone. The dwarf cichlid, A. agassizii, was the species that presented the highest brain cells densities, different from the other cichlids, revealing that the differences found for this fish may be more related to the miniaturization suffered by this species than to social patterns linked to reproduction. Finally, we investigated how the number of brain cells could be associated with cognitive flexibility and sociality presented by cichlid fish. For this, we used the monogamous fish G. brasiliensis, a species in which both parents take care of the brood in the substrate. Contrary to what we expected, the telencephalon was the only brain structure that showed no association between the applied behavioral tests and the brain cell values. The diencephalon, cerebellum and optic tectum showed correlations that seem to be associated with a better individual evaluation of the social environment. In general, a larger number of cells in these regions was positively related to individuals that were less aggressive, spent more time near conspecifics, and were less persistent in irrelevant tasks, revealing more cautious and evaluative animals. This work is innovative as little is known about the evolutionary and physiological mechanisms involved in social behavior control in Neotropical fish.
The cerebral organization in social animals can be explained by both, phylogenetic relationships (i.e., the brain evolves by a line of interrelationship between species) and by the selection of structures driven by the complexity of the social environment. The aim of this thesis was to compare the possible association between social behavior, brain complexity and cognitive ability in phylogenetically close fish species within the Cichlidae family, which present social interactions considered more complex (biparental brood care in monogamous species) or less complex (maternal brood care in polygynous species). Individuals had their brains dissected into macroareas (telencephalon, diencephalon, optic tectum and cerebellum), and subsequently dissociated using the isotropic fractionator technique, which allows the quantification of the number of neurons and nonneuronal cells that compose these macroareas. Therefore, in a first study, we compared the values obtained from neurons and nonneuronal cells with brain and morphometric measures of each species. We found that, differently from what is observed for mammals, phylogenetically close fish species have different brain organizations, suggesting that fish are more liable to the influences of the behavioral environment. After obtaining the data on how the brains of the chosen species are organized, in a second study we compared the species in their types of parental care and mating system. Monogamous fish presented more neurons only in the optic tectum and in the cerebellum when compared to polygynous species. Mouthbrooder individuals had more neurons in the cerebellum alone. The dwarf cichlid, A. agassizii, was the species that presented the highest brain cells densities, different from the other cichlids, revealing that the differences found for this fish may be more related to the miniaturization suffered by this species than to social patterns linked to reproduction. Finally, we investigated how the number of brain cells could be associated with cognitive flexibility and sociality presented by cichlid fish. For this, we used the monogamous fish G. brasiliensis, a species in which both parents take care of the brood in the substrate. Contrary to what we expected, the telencephalon was the only brain structure that showed no association between the applied behavioral tests and the brain cell values. The diencephalon, cerebellum and optic tectum showed correlations that seem to be associated with a better individual evaluation of the social environment. In general, a larger number of cells in these regions was positively related to individuals that were less aggressive, spent more time near conspecifics, and were less persistent in irrelevant tasks, revealing more cautious and evaluative animals. This work is innovative as little is known about the evolutionary and physiological mechanisms involved in social behavior control in Neotropical fish.
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Palavras-chave
Neurônios, Células não-neuronais, Geophagus brasiliensis, Geophagus sveni, Satanoperca pappaterra, Apistogramma agassizii, Fracionador isotrópico, Neurons, Nonneuronal cells, Isotropic fractionator