Genetic analysis confirms the freshwater origin of the endemic Caspian sponges (Demospongiae, Spongillida, Metschnikowiidae)

The Caspian Sea is a unique inland brackish waterbody inhabited by highly endemic fauna. This fauna consists of species of both marine and freshwater origin. Some Caspian invertebrates cannot be confidently referred to as animals of either origin. The endemic monophyletic family of sponges, Metschnikowiidae, is among them. Although these sponges are considered as fresh water in the modern literature, no researcher has seen them alive for many years, and its status is actually unconfirmed. Here, we present the first photos of Metschnikowia tuberculata Grimm, 1877 and report evidence for its freshwater origin based on analysis of ITS1 and ITS2 sequences and partial sequences of CO1 gene. According to the genetic analysis, M. tuberculata belongs to the order Spongillida. We observed specimens of diverse appearance, but their spicule complement proved to be similar, and ITS sequences were identical. Thus, we conclude that they belong to the same species. The obtained results expand our knowledge about the dispersal ability of freshwater sponges.

Freshwater Sponge Tubella variabilis Presents Richer Microbiota Than Marine Sponge Species

Sponges can host diverse and abundant communities of microorganisms, which constitute an interesting source of bioactive compounds. Thus, to broaden our knowledge about the diversity of the microbiota that is found in freshwater sponges, the microbial community of Tubella variabilis was analyzed using culture-independent and culture-dependent approaches. Additionally, sponge-associated bacteria were compared with those living in the surrounding waters. Bacteria were also tested for antimicrobial production. Overall, the microbial composition identified comprises at least 44 phyla belonging mainly to Proteobacteria and low percentages of Bacteroidetes, Acidobacteria, and Verrucomicrobia. Alphaproteobacteria was the dominant class in T. variabilis while Betaproteobacteria was dominant in freshwater. Our data also revealed a high richness of bacteria in comparison to another freshwater sponge and 32 marine sponges. A global comparison of the structure of microbiota of different sponges showed that the main structuring factor may be the sponge environment, with T. variabilis and all freshwater sponges clustering together, and far away from the marine sponges. Bacterial strains from sponges and from freshwater were isolated and 163 morphotypes were phylogenetically identified. These belong to 26 genera, of which 12 were exclusively found in sponge samples and three only in freshwater. Inhibitory activities were also detected among 20–25% of the isolates from sponges and freshwater, respectively. This study presents new information on the composition of the microbial community found in freshwater sponges, which is diverse, abundant and distinct from some marine sponges. Moreover, the antimicrobial activity observed from the bacterial strains might play an important role in shaping microbial communities of the environment.

Minimalist barcodes for sponges: a case study classifying African freshwater Spongillida

African sponges, particularly freshwater sponges, are understudied relative to demosponges in most other geographical regions. Freshwater sponges (Spongillida) likely share a common ancestor; however, their evolutionary history, particularly during their radiation into endemic and allegedly cosmopolitan groups, is unclear. Freshwater sponges of at least 58 species of 17 genera and four families are described from Central and Eastern Africa, but the diversity is underestimated due to limited distinguishable morphological features. The discovery of additional cryptic species is very likely with the use of molecular techniques such as DNA barcoding. The Royal Museum of Central Africa (MRAC, Tervuren, Belgium) hosts one of the largest collections of (Central) African freshwater sponge type material. Type specimens in theory constitute ideal targets for molecular taxonomy; however, the success is frequently hampered by DNA degradation and deamination, which are a consequence of suboptimal preservation techniques. Therefore, we genotyped African demosponge holotype material of the MRAC with specific short primers suitable for degenerated tissue and compare the results with the current, morphology-based classification. Our results demonstrate the utility of minimalistic barcodes for identification of sponges, potentially enabling efficient identification of individuals in taxonomic or metabarcoding studies, and highlight inconsistencies in the current freshwater sponge classification.