Noa Simon-Blecher

Striving for normality: whole body regeneration through a series of abnormal generations

Embryogenesis and asexual reproduction are commonly considered to be coordinated developmental processes, which depend on accurate progression through a defined sequence of developmental stages. Here we report a peculiar developmental scenario in a simple chordate, Botryllus schlossenri, wherein a normal colony of individuals (zooids and buds) is regenerated from the vasculature (vascular budding) through a sequence of morphologically abnormal developmental stages. Vascular budding was induced by surgically removing buds and zooids from B. schlossenri colonies, leaving only the vasculature and the tunic that connects them. In vivo imaging and histological sections showed that the timing and morphology of developing structures during vascular budding deviated significantly from other asexual reproduction modes (the regular asexual reproduction mode in this organism and vascular budding in other botryllid species). Subsequent asexual reproduction cycles exhibited gradual regaining of normal developmental patterns, eventually leading to regeneration of a normal colony. The conversion into a normal body form suggests the activation of an alternative pathway of asexual reproduction, which involves gradual regaining of normal positional information. It presents a powerful model for studying the specification of the same body plan by different developmental programs.—Voskoboynik A., Simon‐Blecher, N., Soen, Y., Rinkevich, B., De Tomaso A. W., Ishizuka, K. J., Weissman I. L., Striving for normality: whole body regeneration through a series of abnormal generations. FASEB J. 21, 1335–1344 (2007)

The distribution and molecular diversity of the Eastern Atlantic and Mediterranean chthamalids (Crustacea, Cirripedia)

The three chthamalids Chthamalus stellatus, C. montagui and Euraphia depressa are common inhabitants of the intertidal zone in the Eastern Atlantic, Mediterranean Sea and Black Sea. In this study, we investigated the occurrence of these barnacles in a wide range of their distribution. Population divergences of these two species have been inferred using three molecular markers — internal transcribed spacer (ITS), elongation factor 1α (EF‐1α) and cytochrome oxidase subunit I (COI). ITS sequences of C. stellatus were identical throughout the species range, whereas ITS sequences of C. montagui indicated that the Black Sea and Mediterranean populations are isolated from the Atlantic population. The COI and EF‐1α sequences were the most variable and informative. They indicated a high genetic divergence between Atlantic, Mediterranean and Black Sea populations for C. montagui. In addition significant genetic structure was found among the populations of C. stellatus based on EF‐1α but not COI. Interestingly, our molecular dating analysis correlated the pattern of diversification in C. montagui to major geological changes that occurred in the Mediterranean during the end of the Messinian and Pleiocene periods. We suggest that palaeohistory shaped the divergences between Chthamalus populations that have probably been maintained by current hydrographic conditions. Finally, COI phylogenetic analysis placed the genus Euraphia within the Chthamalus clade, suggesting the need for a taxonomic revision of Euraphia. This study represents the most detailed phylogeographical analysis of intertidal Mediterranean species to date, and shows that geological events have strongly shaped the current diversity pattern of this fauna.

Molecular phylogeny, systematics and morphological evolution of the acorn barnacles (Thoracica: Sessilia: Balanomorpha).

The Balanomorpha are the largest group of barnacles and rank among the most diverse, commonly encountered and ecologically important marine crustaceans in the world. Paradoxically, despite their relevance and extensive study for over 150years, their evolutionary relationships are still unresolved. Classical morphological systematics was often based on non-cladistic approaches, while modern phylogenetic studies suffer from severe undersampling of taxa and characters (both molecular and morphological). Here we present a phylogenetic analysis of the familial relationships within the Balanomorpha. We estimate divergence times and examine morphological diversity based on five genes, 156 specimens, 10 fossil calibrations, and six key morphological characters. Two balanomorphan superfamilies, eight families and twelve genera were identified as polyphyletic. Chthamaloids, chionelasmatoid and pachylasmatoids split first from the pedunculated ancestors followed by a clade of tetraclitoids and coronuloids, and most of the balanoids. The Balanomorpha split from the Verrucidae (outgroup) in the Lower Cretaceous (139.6 Mya) with all the main lineages, except Pachylasmatoidea, having emerged by the Paleocene (60.9 Mya). Various degrees of convergence were observed in all the assessed morphological characters except the maxillipeds, which suggests that classical interpretations of balanomorphan morphological evolution need to be revised and reinterpreted.

Phylogenetic position and evolutionary history of the turtle and whale barnacles (Cirripedia: Balanomorpha: Coronuloidea).

Barnacles of the superfamily Coronuloidea are obligate epibionts of various marine mammals, marine reptiles and large crustaceans. We used five molecular markers: 12S rDNA, 16S rDNA, 18S rDNA, 28S rDNA and Histone 3 to infer phylogenetic relationships among sixteen coronuloids, representing most of the recent genera of barnacles of this superfamily. Our analyses confirm the monophyly of Coronuloidea and that this superfamily and Tetraclitoidea are sister groups. The six-plated Austrobalanus clusters with these two superfamilies. Based on BEAST and ML trees, Austrobalanus is basal and sister to the Coronuloidea, but the NJ tree places Austrobalanus within the Tetraclitoidae, and in the MP tree it is sister to both Coronuloidea and Tetraclitoidae. Hence the position of Austrobalanus remains unresolved. Within the Coronuloidea we identified four clades. Chelonibia occupies a basal position within the Coronuloidea which is in agreement with previous studies. The grouping of the other clades does not conform to previous studies. Divergence time analyses show that some of the time estimates are congruent with the fossil record while some others are older, suggesting the possibility of gaps in the fossil record.

Darwin's Pyrgoma (Cirripedia) Revisited: Revision of the Savignium Group, Molecular Analysis and Description of New Species

Abstract Darwin recognized the coral inhabiting barnacles as congeneric belonging to Pyrgoma. Ross and Newman (1973) assigned those with fused shell and elongated scuta to the genus Savignium. Later those with tooth like articular projection on tergum were assigned to Trevathana dentata. We sequenced and analyzed the divergence of three mithochondrial genes (12S rDNA, 16S rDNA, COI) of Savignium crenatum from two host coral, of Neotrevathana elongata from Echinopra and of T. dentata from five host corals genera, Leptastrea, Platygyra, Favia, Favites, and Cyphastrea. Based on the molecular analysis of these genes we show that members of populations of the nominal species T. dentata occupying different host corals display clear genetic differences, suggesting that the barnacles from these five different coral genera represent five distinct biological species. These species display host specificity at the generic level. Barnacles colleted from the same host genus but different geographical regions, clustered in the same clades. We described morphological characters of the shell, opercular valves, and limb characteristics, trophi and cirri, of barnacles from these host coral. We concluded that the material extracted from Leptastrea conform with Darwins type and the specific epithet of Trevathana from Leptastrea should continue to be dentata, specimens from the four other host corals are four new species of Trevathana; namely T. mizrachae n. sp. from Platygyra, T. margaretae n. sp. from Favia, T. jensi n. sp. from Favites, and T. sarae n. sp. from Cyphastrea. The morphological data confirm the results of the molecular analysis that species of coral inhabiting barnacles are highly genus-level host-specific.

Profiling molecular and behavioral circadian rhythms in the non-symbiotic sea anemone Nematostella vectensis

Endogenous circadian clocks are poorly understood within early-diverging animal lineages. We have characterized circadian behavioral patterns and identified potential components of the circadian clock in the starlet sea anemone, Nematostella vectensis: a model cnidarian which lacks algal symbionts. Using automatic video tracking we showed that Nematostella exhibits rhythmic circadian locomotor activity, which is persistent in constant dark, shifted or disrupted by external dark/light cues and maintained the same rate at two different temperatures. This activity was inhibited by a casein kinase 1δ/ε inhibitor, suggesting a role for CK1 homologue(s) in Nematostella clock. Using high-throughput sequencing we profiled Nematostella transcriptomes over 48 hours under a light-dark cycle. We identified 180 Nematostella diurnally-oscillated transcripts and compared them with previously established databases of adult and larvae of the symbiotic coral Acropora millepora, revealing both shared homologues and unique rhythmic genes. Taken together, this study further establishes Nematostella as a non-symbiotic model organism to study circadian rhythms and increases our understanding about the fundamental elements of circadian regulation and their evolution within the Metazoa

Tidal and diel orchestration of behaviour and gene expression in an intertidal mollusc

Intertidal inhabitants are exposed to the 24-hour solar day, and the 12.4 hour rising and falling of the tides. One or both of these cycles govern intertidal organisms’ behaviour and physiology, yet little is known about the molecular clockworks of tidal rhythmicity. Here, we show that the limpet Cellana rota exhibits robust tidally rhythmic behaviour and gene expression. We assembled a de-novo transcriptome, identifying novel tidal, along with known circadian clock genes. Surprisingly, most of the putative circadian clock genes, lack a typical rhythmicity. We identified numerous tidally rhythmic genes and pathways commonly associated with the circadian clock. We show that not only is the behaviour of an intertidal organism in tune with the tides, but so too are many of its genes and pathways. These findings highlight the plasticity of biological timekeeping in nature, strengthening the growing notion that the role of ‘canonical’ circadian clock genes may be more fluid than previously thought, as exhibited in an organism which has evolved in an environment where tidal oscillations are the dominant driving force.

On the genus Spirobranchus (Annelida, Serpulidae) from the northern Red Sea, and a description of a new species

Abstract. Species of the genus Spirobranchus, commonly known as Christmas tree worms, are abundant throughout tropical Indo-Pacific and Atlantic Oceans. Information on the species inhabiting the Red Sea in general and the Gulf of Eilat (Gulf of Aqaba) in particular, has so far been very limited. Here we present a multigene phylogenetic analysis, examining both mitochondrial (Cyt-b) and nuclear (ITS2 and 18S) markers, to support the presence of four distinct Spirobranchus species in the Gulf of Eilat: S. corniculatus (including three taxa previously regarded as full species: S. gaymardi, S. cruciger, and S. corniculatus), S. cf. tetraceros, S. gardineri and a new species Spirobranchus aloni, likely endemic to the Red Sea (including two morphotypes with slightly different opercular morphology). The results presented here emphasise that the combination of molecular and in-depth morphological evaluation holds great prospects for a better understanding of species divergence and relationships.

Population genetics and reproductive strategies of two Notostraca (Crustacea) species from winter ponds in Israel

Fluorescent-amplified fragment length polymorphism (FAFLP) fingerprinting assay was used to compare the genetic diversity within and between tadpole shrimps (Notostraca) populations of Lepidurus apus (n=7) and Triops cancriformis (n=2) from rain pools in Israel. Each ephemeral water body has revealed a unique fingerprint pattern with an entailed genetic drift between nearby ponds. High similarity of genotypic diversity within each geographic area led to three clusters of water bodies, north, south and center of Israel. FAFLP assays on several newly hatched individuals of T. cancriformis revealed high identity amongst kin, as compared to L. apus where newly hatched from the same maternal source showed high diversity. Results indicate that T. cancriformis populations from Israel are probably parthenogenetic as indicated by clonal structures. The higher genetic variability in the L. apus populations and in laboratory-hatched specimens indicates the existence of sexual reproduction.

The rise and fall of Pyrgopsella youngi – rediscovery of a lost species

The coral-inhabiting barnacle Pyrgopsella annandalei was collected in 1888 off the reefs of the Andaman Islands in the Indian Ocean, diagnosed in 1906, and described in full in 1907. Since then, this barnacle has not been recorded. In 2006, several specimens of Pyrgopsella were found embedded in the hermatypic coral Symphyllia radians. Based on morphological differences between this material and the drawings and written description of P. annandalei, the specimens from Symphyllia were assigned to a new species, P. youngi. The discovery of a single individual of Pyrgopsella in the collection of the Natural History Museum, London, labeled “cotype,” and its comparison to the recent material from Symphyllia, revealed that the differences between P. annandalei and P. youngi represent no more than intraspecific morphological variation. This conclusion is supported by a comparison of the DNA sequences of the CO1 and 12S rRNA genes from specimens representing both morphological varieties. It is concluded that P. youngi is a junior synonym of P. annandalei, and the latter name should be used in its place.