The End of the Cold Loneliness: 3D Comparison between <i>Doto antarctica</i> and a New Sympatric Species of <i>Doto</i> (Heterobranchia: Nudibranchia)

<div><p>Although several studies are devoted to determining the diversity of Antarctic heterobranch sea slugs, new species are still being discovered. Among nudibranchs, <i>Doto antarctica</i> Eliot, 1907 is the single species of this genus described from Antarctica hitherto, the type locality being the Ross Sea. <i>Doto antarctica</i> was described mainly using external features. During our Antarctic research on marine benthic invertebrates, we found <i>D</i>. <i>antarctica</i> in the Weddell Sea and Bouvet Island, suggesting a circumpolar distribution. Species affiliation is herein supported by molecular analyses using cytochrome <i>c</i> oxidase subunit I, 16S rRNA, and histone H3 markers. We redescribe <i>D</i>. <i>antarctica</i> using histology, micro-computed tomography (micro-CT), and 3D-reconstruction of the internal organs. Moreover, we describe a new, sympatric species, namely <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp., and provide an anatomical comparison between the two Antarctic <i>Doto</i> species. Egg masses in both species are also described here for the first time. We demonstrate that micro-CT is a useful tool for non-destructive anatomical description of valuable specimens. Furthermore, our high resolution micro-CT data reveal that the central nervous system of both <i>Doto</i> species possesses numerous accessory giant cells, suggested to be neurons herein. In addition, the phylogenetic tree of all <i>Doto</i> species sequenced to date suggests a scenario for the evolution of the reproductive system in this genus: bursa copulatrix seems to have been reduced and the acquisition of a distal connection of the oviduct to the nidamental glands is a synapomorphy of the Antarctic <i>Doto</i> species. Overall, the combination of thorough morphological and anatomical description and molecular analyses provides a comprehensive means to characterize and delineate species, thus suggesting evolutionary scenarios.</p></div

Photographs of <i>D</i>. <i>antarctica</i> (left column: A,C,E,G) and <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. (right column: B,D,F,H); specimens subjected to micro-CT reconstruction.

<p><b>A</b> Live animal, where most of the cerata were lost; close up of the cerata. <b>B</b> Live picture right after collection, showing the <i>D</i>. <i>carinova</i> n. sp. spawning on top of the gorgonian <i>Primnoisis antarctica</i> (Isididae). <b>C</b>–<b>D</b> Lateral and dorsal view of the preserved animals. <b>E</b>–<b>F</b> Ventral view of the preserved animals. <b>G</b>–<b>H</b> Lateral view of the preserved egg masses.</p

Phylogenetic tree of <i>Doto</i> species based on the combined COI, 16S, and H3 genes using Bayesian inference (BI) and maximum-likelihood (ML).

<p>Numbers on nodes indicate posterior probability values (BI) and bootstrap support values (ML). Specimens sequenced are in bold; <i>Doto antarctica</i> specimens are coloured in red. Schematic drawings of the reproductive system of <i>Doto</i> species are depicted (A–D), as well as the unsequenced <i>D</i>. <i>uva</i> Marcus, 1955 (E). <i>bc</i> bursa copulatrix; <i>gd</i> gonoduct; <i>nigl</i> nidamental glands; <i>pen</i> penis; <i>rs</i> receptaculum seminis; <i>vd</i> vas deferens.</p

Histological slide of outer surface of the egg mass in <i>Doto carinova</i> Moles, Avila & Wägele n. sp.

<p>Histological slide of outer surface of the egg mass in <i>Doto carinova</i> Moles, Avila & Wägele n. sp.</p

Sampling stations where <i>D</i>. <i>antarctica</i> and <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. were collected.

<p>Kapp Norvegia is situated in the eastern Weddell Sea.</p

Scanning electron micrographs (SEM) of the radular teeth of <i>D</i>. <i>antarctica</i>.

<p>Scanning electron micrographs (SEM) of the radular teeth of <i>D</i>. <i>antarctica</i>.</p

Histological slides of the glandular structures in <i>D</i>. <i>antarctica</i>.

<p><b>A</b> Epidermis of the rhinophoral sheath. <b>B</b> Detail of one cerata tubercle showing defensive glandular cells (white punctuation in live animals). <b>C</b> Oral glands. <b>D</b> Giant neurones chain attached to the cerebropleural ganglion; a thin cortex, large nucleus, and nucleolus of each cell can be seen. <b>E</b> Detail of the prostate glandular cells. <b>F</b> Detail of the capsule glandular cells. <b>G</b> Detail of the membrane glandular cells. <b>H</b> Detail of the glandular mucus cells. <i>gc</i> giant cells; <i>lum</i> lumen; <i>muc</i> glandular mucus cell; <i>n</i> nucleus; <i>nu</i> nucleolus; <i>ogl</i> oral glands; <i>pha</i> pharynx; <i>rhn</i> rhinophoral nerve; <i>sin</i> sinus vessel; <i>sgl</i> salivary gland; <i>smc</i> specialised multivacuolised cell; <i>wgc</i> white glandular cells.</p

Left antero-lateral view of the micro-CT reconstruction of the nervous system of <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. <i>cpg</i> cerebropleural ganglion; <i>gc</i> giant cells; <i>peg</i> pedal ganglion; <i>rhg</i> rhinophoral ganglion; <i>sin</i> sinus.

<p>Left antero-lateral view of the micro-CT reconstruction of the nervous system of <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. <i>cpg</i> cerebropleural ganglion; <i>gc</i> giant cells; <i>peg</i> pedal ganglion; <i>rhg</i> rhinophoral ganglion; <i>sin</i> sinus.</p

Micro-CT reconstructions of the internal organs of <i>D</i>. <i>antarctica</i> (left column) and <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. (right column).

<p><b>A</b>–<b>B</b> Right antero-lateral view of all reconstructed organs. <b>C</b>–<b>D</b> Left antero-lateral view of the circulatory, digestive, excretory, and nervous systems. <b>E</b>–<b>F</b> Right lateral view of the male reproductive system. <b>G</b>–<b>H</b> Left lateral view of the reproductive system (mucus gland is not depicted here since it covers the whole view). <i>am</i> ampulla; <i>adiv</i> ampulla diverticulum; <i>au</i> auricle; <i>bc</i> bursa copulatrix; <i>cis</i> circulatory sinuses; <i>cgl</i> capsule gland; <i>cpg</i> cerebropleural ganglion; <i>dg</i> distal gonoduct; <i>dgdiv</i> digestive gland diverticula; <i>dgl</i> digestive gland (only depicted in <i>D</i>. <i>carinova</i> n. sp.); <i>gc</i> giant cells; <i>gon</i> gonad; <i>ht</i> heart; <i>int</i> intestine; <i>kid</i> kidney; <i>megl</i> membrane gland; <i>mugl</i> mucus gland; <i>oes</i> oesophagus; <i>od</i> odontophore; <i>ot</i> oral tube; <i>ov</i> oviduct; <i>peg</i> pedal ganglion; <i>pen</i> penis; <i>per</i> pericardium; <i>pg</i> proximal gonoduct; <i>pha</i> pharynx; <i>pro</i> prostate; <i>rad</i> radula; <i>rhg</i> rhinophoral ganglion; <i>rhi</i> rhinophore; <i>rhs</i> rhinophoral sheath; <i>sgl</i> salivary gland; <i>sin</i> sinus; <i>sp</i> sphincter; <i>sto</i> stomach; <i>vag</i> vagina; <i>vd</i> vas deferens; <i>ven</i> ventricle.</p

Quorum sensing network in clinical strains of A. baumannii : AidA is a new quorum quenching enzyme

Acinetobacter baumannii is an important pathogen that causes nosocomial infections generally associated with high mortality and morbidity in Intensive Care Units (ICUs). Currently, little is known about the Quorum Sensing (QS)/Quorum Quenching (QQ) systems of this pathogen. We analyzed these mechanisms in seven clinical isolates of A. baumannii. Microarray analysis of one of these clinical isolates, Ab1 (A. baumannii ST-2-clon-2010), previously cultured in the presence of 3-oxo-C12-HSL (a QS signalling molecule) revealed a putative QQ enzyme (α/β hydrolase gene, AidA). This QQ enzyme was present in all nonmotile clinical isolates (67% of which were isolated from the respiratory tract) cultured in nutrient depleted LB medium. Interestingly, this gene was not located in the genome of the only motile clinical strain growing in this medium (A. baumannii strain Ab421-GEIH-2010 [Ab7], isolated from a blood sample). The AidA protein expressed in E. coli showed QQ activity. Finally, we observed downregulation of the AidA protein (QQ system attenuation) in the presence of HO (ROS stress). In conclusion, most of the A. baumannii clinical strains were not surface motile (84%) and were of respiratory origin (67%). Only the pilT gene was involved in surface motility and related to the QS system. Finally, a new QQ enzyme (α/β hydrolase gene, AidA protein) was detected in these strains