Insights into the reproduction of some Antarctic dendroceratid, poecilosclerid, and haplosclerid demosponges

Sponges are a dominant element of the Antarctic benthic communities, posing both high species richness and large population densities. Despite their importance in Antarctic ecosystems, very little is known about their reproductive patterns and strategies. In our study, we surveyed the tissue of six different species for reproductive elements, namely, Dendrilla antarctica Topsent, 1905 (order Dendroceratida), Phorbas areolatus (Thiele, 1905), Kirkpatrickia variolosa (Kirkpatrick, 1907), and Isodictya kerguelenensis (Ridley & Dendy, 1886) (order Poecilosclerida), and Hemigellius pilosus (Kirkpatrick, 1907) and Haliclona penicillata (Topsent, 1908) (Haplosclerida). Samples of these six species containing various reproductive elements were collected in Deception Island and were processed for both light and transmission electron microscopy (TEM). Even though we were not able to monitor the entire reproductive cycle, due to time and meteorological conditions, we report important aspects of the reproduction of these species. This includes oocyte and embryo morphology and cell ultrastructure, follicular structures and nurse cell activity, as well as vitellogenesis. All species were brooding their embryos within their mesohyl. Both oocytes and embryos were registered in the majority of the studied species, and a single sperm cell being carried to an egg for fertilization was observed in H. penicillata. While the reproductive periods of all species coincided temporally, some of them seemed to rely on a single spawning event, this being suggested by the synchronic oogenesis and embryogenesis occurrence of D. antarctica, P. areolatus and I. kerguelenensis. In contrast, K. variolosa had an asynchronous embryo development, which suggests several larval release events. Our results suggest that differences in the reproductive strategies and morphological traits might succeed in the coexistence of these species at the same habitat avoiding the direct competition between them.COPYRIGHT: © 2018 Koutsouveli et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. FUNDING: This work was carried out within two research grants from the Spanish Ministry of Economy and Competitivity, http://www.idi.mineco.gob.es/ (ACTIQUIM-II CGL2010-17415/ANT, and DISTANTCOM CTM2013-42667/ANT) to CA, a grant from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 679849 ('SponGES') to AR and JC, and a DIF grant of the Natural History Museum of London, www.nhm.ac.uk (SDF14032) to AR. ACKNOWLEDGMENTS: We are thankful to Gonzalo Giribet, Carlos Leiva, Patricia Álvarez-Campos, Maria Bas, Carlos Angulo-Preckler, Laura Núñez-Pons, and Blanca Figuerola for their help during field sampling, and the crew of the Spanish Antarctic Base Gabriel de Castilla and the R/V Hespérides for their logistic support. Gonzalo Giribet contributed the image of K. variolosa live embryos shown in Fig 1C. Thanks are also due to the staff at the CCIT-UB for technical support. This work is part of the AntEco (State of the Antarctic Ecosystem) Scientific Research Programme