Molecular and morphological analysis of the developing nemertean brain indicates convergent evolution of complex brains in Spiralia

Background The brain anatomy in the clade Spiralia can vary from simple, commissural brains (e.g., gastrotrichs, rotifers) to rather complex, partitioned structures (e.g., in cephalopods and annelids). How often and in which lineages complex brains evolved still remains unclear. Nemerteans are a clade of worm-like spiralians, which possess a complex central nervous system (CNS) with a prominent brain, and elaborated chemosensory and neuroglandular cerebral organs, which have been previously suggested as homologs to the annelid mushroom bodies. To understand the developmental and evolutionary origins of the complex brain in nemerteans and spiralians in general, we investigated details of the neuroanatomy and gene expression in the brain and cerebral organs of the juveniles of nemertean Lineus ruber. Results In the juveniles, the CNS is already composed of all major elements present in the adults, including the brain, paired longitudinal lateral nerve cords, and an unpaired dorsal nerve cord, which suggests that further neural development is mostly related with increase in the size but not in complexity. The ultrastructure of the juvenile cerebral organ revealed that it is composed of several distinct cell types present also in the adults. The 12 transcription factors commonly used as brain cell type markers in bilaterians show region-specific expression in the nemertean brain and divide the entire organ into several molecularly distinct areas, partially overlapping with the morphological compartments. Additionally, several of the mushroom body-specific genes are expressed in the developing cerebral organs. Conclusions The dissimilar expression of molecular brain markers between L. ruber and the annelid Platynereis dumerilii indicates that the complex brains present in those two species evolved convergently by independent expansions of non-homologous regions of a simpler brain present in their last common ancestor. Although the same genes are expressed in mushroom bodies and cerebral organs, their spatial expression within organs shows apparent differences between annelids and nemerteans, indicating convergent recruitment of the same genes into patterning of non-homologous organs or hint toward a more complicated evolutionary process, in which conserved and novel cell types contribute to the non-homologous structures.publishedVersio

Molecular and morphological analysis of the developing nemertean brain indicates convergent evolution of complex brains in Spiralia

Background The brain anatomy in the clade Spiralia can vary from simple, commissural brains (e.g., gastrotrichs, rotifers) to rather complex, partitioned structures (e.g., in cephalopods and annelids). How often and in which lineages complex brains evolved still remains unclear. Nemerteans are a clade of worm-like spiralians, which possess a complex central nervous system (CNS) with a prominent brain, and elaborated chemosensory and neuroglandular cerebral organs, which have been previously suggested as homologs to the annelid mushroom bodies. To understand the developmental and evolutionary origins of the complex brain in nemerteans and spiralians in general, we investigated details of the neuroanatomy and gene expression in the brain and cerebral organs of the juveniles of nemertean Lineus ruber. Results In the juveniles, the CNS is already composed of all major elements present in the adults, including the brain, paired longitudinal lateral nerve cords, and an unpaired dorsal nerve cord, which suggests that further neural development is mostly related with increase in the size but not in complexity. The ultrastructure of the juvenile cerebral organ revealed that it is composed of several distinct cell types present also in the adults. The 12 transcription factors commonly used as brain cell type markers in bilaterians show region-specific expression in the nemertean brain and divide the entire organ into several molecularly distinct areas, partially overlapping with the morphological compartments. Additionally, several of the mushroom body-specific genes are expressed in the developing cerebral organs. Conclusions The dissimilar expression of molecular brain markers between L. ruber and the annelid Platynereis dumerilii indicates that the complex brains present in those two species evolved convergently by independent expansions of non-homologous regions of a simpler brain present in their last common ancestor. Although the same genes are expressed in mushroom bodies and cerebral organs, their spatial expression within organs shows apparent differences between annelids and nemerteans, indicating convergent recruitment of the same genes into patterning of non-homologous organs or hint toward a more complicated evolutionary process, in which conserved and novel cell types contribute to the non-homologous structures

Case 3849 – Emplectonematidae Bürger, 1904 and Emplectonema Stimpson, 1857 (Nemertea, Monostilifera): proposed conservation of current usage by reversal of precedence of the family name with respect to Eunemertidae Joubin, 1894 and designation of a new type species for the genus

The purpose of this application, under Articles 23.9.3, 41, 65.2, and 70.2 of theCode, is to conserve the current usage and year of priority of the name Emplectonematidae Bürger, 1904 for a family of ribbon worms by reversing its precedence with respect toa senior synonym, E unemertidae Joubin, 1894, and to conserve the current concept andusage of its type genus, Emplectonema Stimpson, 1857, by designating Emplectonemaviride Stimpson, 1857 as the type species. In preparation for these rulings, a common typespecies, Nemertes gracilis Johnston, 1837, is designated herein for the nominal generaNemertes Johnston, 1837 (a largely neglected junior homonym of Nemertes Cuvier, 1816)and Eunemertes Joubin, 1894, thereby rendering the latter an objective junior synonym ofthe former and of its valid substitute name. The type species of Nemertes Cuvier, 1816was excluded from N emertidae sensu McIntosh, 1874 and sensu Hubrecht, 1879, which,having been recognized as a valid grouping by later authors, required a new name. Ofthe two available candidates, Eunemertidae Joubin, 1894 has been almost unused sincethe 1900s, whereas Emplectonematidae Bürger, 1904 has been in universal use sinceits proposal. The latter name has an uncertain date of priority; 1874, 1894 or 1904,depending on whether and how Art. 40.2 applies to it. Emplectonema viride Stimpson,1857, or its senior synonym Emplectonema gracile (Johnston, 1837), has universally beenregarded as the type species of Emplectonema since the 1950s; however, two overlookedfixations in 1892 and 1893 of Borlasia camillea Quatrefages, 1846 as the type speciesof this genus now threaten the stability of nemertean genus- and family-level taxonomy.Fil: Kajihara, Hiroshi. Hokkaido University; JapónFil: Grygier, Mark J.. National Taiwan Ocean University; ChinaFil: Andrade, Sónia C. S.. Universidade de Sao Paulo; BrasilFil: Bartolomaeus, Thomas. Universitat Bonn; AlemaniaFil: Cherneva, Irina A.. Lomonosov Moscow State University; RusiaFil: Chernyshev, Alexei V.. Russian Academy Of Science; RusiaFil: von Döhren, Jörn. Universitat Bonn; AlemaniaFil: Ellison, Christina I.. University of Oregon; Estados UnidosFil: Gibson, Ray. Liverpool John Moores University (liverpool John M. University);Fil: Giribet, Gonzalo. Harvard University; Estados UnidosFil: Hiebert, Terra. University of Oregon; Estados UnidosFil: Hookabe, Natsumi. University of Tokyo; JapónFil: Junoy, Juan. Universidad de Alcalá. Facultad de Ciencias; EspañaFil: Kvist, Sebastian. Royal Ontario Museum; CanadáFil: Maslakova, Svetlana A.. University of Oregon; Estados UnidosFil: Mendes, Cecili B.. Universidade de Sao Paulo; BrasilFil: Norenburg, Jon L.. National Museum Of Natural History. Departamento de Zoología. Area de Invertebrados; Estados UnidosFil: Polyakova, Neonila E.. Russian Academy Of Science; RusiaFil: Sagorny, Christina. Universitat Bonn; AlemaniaFil: Schwartz, Megan L.. University of Washington; Estados UnidosFil: Strand, Malin. Swedish University of Agricultural Sciences; SueciaFil: Sun, Shichun. Ocean University Of Chin; ChinaFil: Turbeville, James M.. Virginia Commonwealth University; Estados UnidosFil: Zattara, Eduardo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin