ALBERT

Description: Sponges (Porifera) are one of the most ancient animals present on the planet. They are aquatic, filter-feeding sessile metazoans that rely on asexual and sexual reproduction. These animals have a long history on Earth and had plenty of time to develop different reproductive strategies. Here, we review different aspects of the physiology of reproduction in Porifera. This chapter is divided into six sections. In the first section, we present general features of sponge reproduction, such as factors that trigger the onset of their reproduction, as well as the periodicity of their reproductive cycles. The molecular basis of the hormonal control of gametogenesis is presented although sponges have no endocrine system. The second section deals with gametogenesis, 2including how sex and the germline are determined and maintained in this group, how oocytes and spermatozoa are formed and nourished, and how they behave once released. The third section reviews different topics about the reproductive mode. Here, we discuss the dichotomy in reproductive mode: oviparity vs. viviparity, the spatial distribution of the reproductive elements in the sponge tissue, the effect of symbiosis in reproduction (and vice-versa), and energetic trade-offs during reproduction. The fourth section describes fertilization, and we cover the factors controlling the spawning events and how the sperm are attracted and recognized by the egg. The diversity of developmental modes, the molecular control of sponge embryonic development, and the maternal-embryo relationship are discussed in the fifth section. Finally, in the sixth section, the types of asexual reproduction, factors influencing budding, gemmulation, hibernation, and gemmule development are described. Knowledge about the physiology of reproduction of sponges is still fragmentary and based on studies in very few species. Consequently, there are many generalizations that need further investigation. However, evidence-based on morphological, experimental, and molecular data demonstrates that their physiology is not very different from that of other metazoans