Evolution of oogenese in Bryozoa

Wider research context: Oogenesis is a key element of sexual reproduction, linking its all major aspects from fertilization to larval type, and directly influencing the developmental trajectory and lifehistory. Shifts in oogenesis occurring multiple times in the history of various animal groups resulted in transitions to new reproductive strategies and larval types that inevitably affected their evolutionary fate. The evolutionary dynamics of the female gametogenesis has been poorly understood, however, and it seems it is much more complex than appreciated. The project is aimed at understanding fundamental questions related to evolution of sexual reproduction in marine invertebrates, using phylum Bryozoa as a model. This ecologically important, but poorly studied group has highly variable ovarian morphology, several oogenetic modes and different larval types often co-existing in the same clades, thus indicating that oogonesis changed many times in the bryozoan history. Hypotheses//objectives: The main objective of the study is to comparatively describe and analyze the diversity and distribution pattern of oogenetic modes and ovarian structure in all major bryozoan lineages (classes and orders) and apply it onto molecular phylogeny. This will allow to recognize (1) the ancestral oogenetic mode, (2) clades in which transitions in oogenetic modes have occurred, and directions of these transitions, and (3) to compare ovarian structure and vitellogenic mechanisms between and within major clades. The main goal of such comparative analysis is to propose hypothetical scenarios explaining evolutionary dynamics of female gametogenesis in Bryozoa. Together with known data on larval types and evolution of embryonic incubation, it will allow to make an integral picture describing evolution of the modern diversity of bryozoan reproductive patterns and strategies, and compare it with evolutionary pathways in sexual reproduction in other invertebrate groups. Methods: Histological technique, light and transmission electron microscopy will be applied to study ovarian microanatomy and ultrastructure and oogenesis in 48 bryozoan species from 30 families. They are representatives of all three bryozoan classes, and all extant orders and major superfamilies. Level of originality: This will be the first comparative study on invertebrate oogenesis aiming to cover all major clades and build an integral picture of evolution of sexual reproduction in the entire animal phylum. Altogether, this will allow us to get closer to understanding the events underlying the emergence of new reproductive patterns and recognition of convergent aspects of evolution of sexual reproduction in animals in general. Primary researchers involved: Dr A. Ostrovsky (University of Vienna).