Developmental modularity in the colonial ascidian Symplegma: individual intercommunication, colony hematopoiesis, and environmental factors involved in coloniality

• Autor(a) principal: Gutierrez, Arianna Stefania Osorio
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/41/41133/tde-24092019-095624/
• topic: Colonialidade; Coloniality; Cooperação; Cooperation; Heterochronia; Heterochrony; Modularidade; Modularity; Symplegma-tunicate; Symplegma-tunicate

Colonial animals are biological systems composed of discrete units (zooids) that are physiologically interconnected and require coordinated development for the colony to function properly. The origins of modular developmental mechanisms that facilitated the evolution of coloniality remain unclear. Genus Symplegma is a clade from the tunicate family Styelidae, in which coloniality evolved repeatedly from a solitary ancestor. My main objective is understand the process involved in evolution of colonial life history, studying the colonial strategy in Symplegma clade. Symplegma zooids are embedded in a common tunic and present a vascular system which interconnect zooids. Inside the blood vessels systems are in constant circulation. I classified S. brakenhielmi S.rubra blood cells by morphology using cytohistological assays and transmission electron microscopy. Eleven types of hemocytes were founded: (a) macrophage-like cells (MLCs) involved in phagocytosis and programmed cell death (PCD); (b) undifferentiated cells (UCs) involved in budding and regeneration; (c) morula cells (MC) involved in immune reactions; (d) nephrocytes or pigment cells involved in storage and excretion. Precursors cells changed their proportions during regeneration, suggesting continuous hematopoiesis, and hemocyte differentiation processes in the blood of the colonies. In vivo and histological observations suggest that the lifespan of zooids is controlled by endogenous mechanisms of the colony. As well that aging zooids are phagocyted and recycled for the colony. Colonial answer to external perturbations was tested by systemic bud or zooid removals. The vascular tissues of the colonies self-organize and rearrangement to regenerate zooids. As well the development of the buds accelerated when buds are absence after a systematical remotion of the buds. The results show that the zooids in Symplegma colonies are replacement components, which life span and development time are controlled by endogenous mechanisms related to colony necessities. Symplegma colonies are acting like a self-regulated system that can rearrange its components in case of particular perturbations. Therefore Symplegma colonies evolved communication between modules in the form of specialized migrating cells that transmit matter and information across the colony, coordinating the biological process of the zooids. The evolution of coloniality in this clade is mediated by novelties in the communication and cooperation between modules such as the PCD of old zooids and their resorption by the migration of MLC to recycle its tissues and use for the next generations of zooids