No abstract

The diversification of life-histories is mediated by cooperation, innovations of biological information, modularity, and heterochrony in developmental processes. These processes are defined, contextualized, and exemplified, studying the evolution of coloniality (i.e. life-history involving modularization of the multicellular individual) in the family of benthic tunicates Styelidae. This study proposes that in these colonial tunicates there is an inter-generational division of labor, where one generation is feeding, a second is developing by morphogenetic processes, and a third is aging by programmed cell death and phagocytosis. The communication system developed in these colonies is mediated, by changes in proportion, location, and gene expression of specialized blood cells. Colonial life-history in animals is related to the reduction of individual size; development of extra-corporeal tissues to interconnect zooids; the inter-generational division of labor; and the reduction of zooid’s individuality. Processes analogous with the widely accepted major evolutionary transitions (METs), suggesting that coloniality could be studied as a MET. The understanding of colonial life-histories could provide information about key mechanisms for life diversification.

Biological complexity is defined as the number of modules that compose an organism or a biological system, the type of interactions between these modules, and new hierarchies that describe these interactions. These patterns in biological complexity are changing during the evolution of life-histories, such as the evolution of coloniality in animals. In relation to coloniality, it is possible to observe an increment in all the aspects defined in the concept of biological complexity. First, in colonial animals, there is an increment in the modules that compound the system (i.e. zooids) compared with a solitary organism in which the multicellular individual a unity. Consequently, this transformation of the multicellular individual, in a component of the modular architecture in colonies, involves an increase in the regulatory processes of colonial system. This is precisely the case of the colonial life history evolution from solitary ancestors in the Styelids tunicates. Therefore, the main question of this study is How is the regulation of the asexual developmental processes that occurred simultaneously in the modules of the colonies? This question was studied, by the research of colonial strategy in the styelid Symplegma. Using in vivo observations of the budding process, description and classification of the extra-corporeal blood vessels system and the blood cells, by cytohistological assays. The conclusion is that the regulation of the simultaneous developmental processes that occurred in Symplegma colonies is mediated by the system of extra-corporeal blood vessels, which maintain physically the cohesion of the individuals, the plasma, and migratory blood cells transport signals between the individuals of the colonies.

Marine invertebrates are model organisms in several areas of biological sciences, being a source of massive biological information. Although, the scientific relevance of marine invertebrates, the research with them can be limited for their tissue characteristics and troubles for the replication of physical and chemical properties of seawater. Thence, the main goal of this laboratory workflow is to provide a useful methodological approach to reduce the experimental limitations during the study of marine invertebrates. The present study describes experimental methodologies for the collection, transport, and maintenance of sessile tunicates. Also, an approach to observe and characterize, a diverse population of blood cells in marine invertebrates, by several cytological stains and electron microscopy. Lastly, suggestions and protocols to extract quality RNA from samples with high concentrations of salts, pigments, secondary metabolites, and polysaccharides. This methodological approach can be easily adapted to other marine invertebrates, moreover uses low-cost reagents and widely available laboratory equipment. Making possible the study of different types of marine animals in diverse locations.