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

Abstract

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.

Population substructure and signals of divergent adaptive selection despite admixture in the sponge Dendrilla antarctica from shallow waters surrounding the Antarctic Peninsula

“…One of them corresponded to an uncharacterized protein, and another one matched a bacterial aminotransferase (Table ). This low ratio of only one RAD‐tag matching a bacterial gene out of the 140 under positive selection (0.7%) is in agreement with previous knowledge on the microbiome of D. antarctica , a sponge that is considered to have low microbial abundance (Koutsouveli et al, ). For the 14 remaining annotated loci, gene characterization and david functional annotation analysis assigned them to six cellular functions (Figure ): (a) cytoskeleton reorganization, cell morphology and motility; (b) ubiquitination; (c) apoptosis; (d) response to environmental stressors; (e) biological detoxification and (f) RNA post‐transcriptional modifications.…”

“…Our results revealed high admixture and lack of population differentiation, supported by the low global F ST of 0.011 and the nonsignificant pairwise F ST values (Table ), suggesting high connectivity and dispersal capability of D. antarctica throughout the sampling area, which covered most of the species distribution. We propose that this could be due to the relatively long planktonic life of D. antarctica larvae as a result of the great amount of proteinaceous yolk that they contain (Koutsouveli et al, ) in comparison with sponge larvae from congeneric species from lower latitudes (e.g., Ereskovsky & Tokina, ). Furthermore, the strong oceanic currents in the study area (Moffat, Beardsley, Owens, & Van Lipzig, ; Zhou, Niiler, & Hu, ; see Figure b) may increase the dispersal ability of D. antarctica larvae.…”

“…Its distribution spans along the Antarctic Peninsula and its associated islands, to the South Orkney Archipelago as the northernmost point of its range (data from World Porifera Database: http://www.marinespecies.org/porifera/porifera.php?p=taxdetails%26xml:id=164875). D. antarctica is a brooding sponge, with yolky lecithotrophic larvae that are released during the Antarctic summer (Koutsouveli et al, ). In the present study, we aim to assess the genetic diversity, demographic history, and genetic connectivity of D. antarctica at a regional scale in the WAP and South Shetland Islands using double digest (dd)RADseq‐derived SNPs.…”

Behavior and development of larvae in the sponge Haliclona amboinensis

“…During metamorphosis, the sponge larval cells undergo rapid and dramatic reorganization of the body plan, with the posterior ring being reabsorbed to form the aquiferous system of the juvenile sponge (Amano & Hori, 1994, 1996; Degnan, Leys, & Larroux, 2005; Kaye & Reiswig, 1991; Leys & Degnan, 2002; Nakanishi, Sogabe, & Degnan, 2014). High energy reserves in sponge larvae promote this rapid organization of the larval body plan (Koutsouveli et al., 2018; Maldonado & Young, 1999; Riesgo et al., 2015). Metamorphosis is considered completed once the osculum develops (Leys & Degnan, 2002).…”

­Reproductive strategies of two common sympatric Mediterranean sponges:Dysidea avara(Dictyoceratida) andPhorbas tenacior(Poecilosclerida)

“…Furthermore, sponges are at the base of the animal tree of life ( Feuda et al, 2017 ) and are therefore a key group for understanding the evolution of reproductive traits in Metazoa. However, although studies on sponge reproduction proliferated steadily in the last decades (reviewed in Ereskovsky, 2010 ; Lanna et al, 2018a ), only a tiny fraction of the sponge species has been studied so far, and new species-specific reproductive traits, which are driving factors of the species’ distribution and abundance, are being revealed (e.g., Abdo, Fromont & McDonald, 2008 ; Piscitelli et al, 2011 ; Pérez-Porro, González & Uriz, 2012 ; Koutsouveli et al, 2017 ). The current gaps in the knowledge of reproductive parameters of sponges prevent generalizations about reproductive strategies across taxonomic groups, growth forms, or habitat characteristics.…”