Spineless and overlooked: DNA metabarcoding of autonomous reef monitoring structures reveals intra- and interspecific genetic diversity in Mediterranean invertebrates.

The ability to gather genetic information using DNA metabarcoding of bulk samples obtained directly from the environment is crucial to determine biodiversity baselines and understand population dynamics in the marine realm. While DNA metabarcoding is effective in evaluating biodiversity at community level, genetic patterns within species are often concealed in metabarcoding studies and overlooked for marine invertebrates. In the present study, we implement recently developed bioinformatics tools to investigate intraspecific genetic variability for invertebrate taxa in the Mediterranean Sea. Using metabarcoding samples from Autonomous Reef Monitoring Structures (ARMS) deployed in three locations, we present haplotypes and diversity estimates for 145 unique species. While overall genetic diversity was low, we identified several species with high diversity records and potential cryptic lineages. Further, we emphasize the spatial scale of genetic variability, which was observed from locations to individual sampling units (ARMS). We carried out a population genetic analysis of several important yet understudied species, which highlights the current knowledge gap concerning intraspecific genetic patterns for the target taxa in the Mediterranean basin. Our approach considerably enhances biodiversity monitoring of charismatic and understudied Mediterranean species, which can be incorporated into ARMS surveys.

Staining and Tracking Methods for Studying Sponge Cell Dynamics.

To better understand the origin of animal cell types, body plans, and other morphological features, further biological knowledge and understanding are needed from non-bilaterian phyla, namely, Placozoa, Ctenophora, and Porifera. This chapter describes recent cell staining approaches that have been developed in three phylogenetically distinct sponge species-the homoscleromorph Oscarella lobularis, and the demosponges Amphimedon queenslandica and Lycopodina hypogea-to enable analyses of cell death, proliferation, and migration. These methods allow for a more detailed understanding of cellular behaviors and fates, and morphogenetic processes in poriferans, building on current knowledge of sponge cell biology that relies chiefly on classical (static) histological observations.

In Situ Hybridization Techniques in the Homoscleromorph Sponge Oscarella lobularis.

The Porifera are one of the best candidates as the sister group to all other metazoans. Studies on this phylum are therefore expected to shed light on the origin and early evolution of key animal features. Transcriptomic or genomic data acquired during the last 10 years have highlighted the conservation of most of the main genes and pathways involved in the development of the other metazoans. The next step is to determine how similar genetic tool boxes can result in widely dissimilar body plan organization, dynamics, and life histories. To answer these questions, three main axes of research are necessary: (1) conducting more gene expression studies; (2) developing knockdown protocols; and (3) reinterpreting sponge cell biology using modern tools. In this chapter we focus on the in situ hybridization (ISH) technique, needed to establish the spatiotemporal expression of genes, both on whole mount individuals and paraffin sections, and at different stages of development (adults, embryos, larvae, buds) of the homoscleromorph sponge Oscarella lobularis.