Transcriptomics along a sponge life cycle

Abstract

Sponges are morphologically plastic animals that do not possess tissues, and thus lack gonads or reproductive tracts. Gametes are usually found, during the reproductive season, throughout the sponge body (Simpson 1984), although larvae can be found in brood chambers (e.g., Whalan et al. 2005) and, in some cases, oocytes form clusters (Riesgo et al. 2007b). Several sexuality and reproductive modes have been reported in sponges (gonochorism and hermaphroditism; oviparism and viviparism) (e.g., Riesgo et al. 2014b) as well as different types of larvae (amphiblastula and calciblastula for calcareous sponges, parenchymella, coeloblastula and dispherula for demosponges, cinctoblastula for homoscleromorphs, and trichimella for hexactinellids) (Leys & Ereskovsky 2006). Many studies have focused on sponge reproduction (as reviewed by Boury-Esnault & Jamieson 1999; Fell 1974; Reiswig 1983; Simpson 1984) but, because of sponge phenotypic plasticity and genotypic differences, new features are continuously discovered as more species are investigated (e.g., Riesgo & Maldonado 2009b). The G4 order Poecilosclerida is one of the most diverse in the class Demospongiae, both in the number of genera and species (Ereskovsky 2010). Previous studies indicate that most families in Poecilosclerida are viviparous, simultaneous hermaphrodites show a yearly reproductive cycle (De Vos et al. 1991; Ereskovsky 2000; Ilan 1995; Ilan et al. 2004; Leys & Ereskovsky 2006; Reiswig 1973; Riesgo & Maldonado 2009b) and release parenchymella larvae (Ereskovsky 2010; Mariani et al. 2005). Other specific reproductive traits can be anticipated when studying new poecilosclerid species, particularly when the species belong to families that have not been previously studied (see summary in Riesgo et al. 2014b). Reproduction in the family Crellidae (Poecilosclerida) remains poorly known although it includes genera with widespread representatives in several oceans (Hooper & Van Soest 2002). The study of the life cycle of the Mediterranean encrusting crellid, Crella elegans, revealed an annual reproductive cycle from the beginning of April to the end of October. Reproduction starts with seawater temperature increases in spring, lasts during the summer warmer months, and ends with larval release, at the beginning of temperature dropping in the fall. Crella elegans larvae are type II parenchymella (Perez-Porro et al. 2012) with reproductive features similar to those found in other poecilosclerids (Mariani et al. 2005). We are still far from answering questions about reproduction and development of sponges and the effects of climate change in the reproductive mechanisms from a genetic perspective. This is because information on gene expression during gametogenesis and larval development in sponges is scarce (Perovic-Ottstadt et al. 2004), as is the information on their natural expression levels. The main objective of this thesis was to study the biology, ecology and gene expression of the Mediterranean sponge Crella elegans along its life cycle. This served a variety of purposes: 1) to provide additional knowledge on sponge reproduction with emphasis on the order Poecilosclerida, 2) to describe the life cycle of Crella elegans and its reproductive elements, 3) to optimize NGS techniques in poriferans, 4) to generate and characterize the first encrusting sponge transcriptome and 5) to provide the first overview of some physiologic processes along the life cycle of a sponge. ?????