Element/Ca, C and O isotope ratios in modern brachiopods: Species-specific signals of biomineralization

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Fossil brachiopods are of major importance for the reconstruction of palaeoenvironmental conditions, particularly of the Paleozoic. In order to better understand signals of ancient shell materials, modern analogue studies have to be conducted. Here we present C and O isotope data in conjunction with Mg/Ca, Sr/Ca, Mn/Ca and Fe/Ca data for nine modern rhynchonellid and terebratulid brachiopod species from tropical to intermediate latitudes and shallow to very deep marine settings. C and O isotope signals of most species suggest formation of secondary shell layers near or in isotopic equilibrium with ambient seawater. Some species – especially in the suborder Terebratellidina – show partly distinct disequilibrium signals, suggesting some degree of phylogenetic control on the expression of vital effects. Mn/Ca and Fe/Ca ratios measured in the modern species form a baseline to assess fossil preservation, but also yield environmental information. Mg/Ca and Sr/Ca ratios follow previously observed patterns, with all studied brachiopod species comprising low-Mg calcite. Strong covariation of Sr/Ca ratios with Mg/Ca ratios is only observed in rhynchonellids and possibly one terebratulid species, potentially linking the incorporation behaviour of alkaline earth metals to phylogeny. Sr/Ca show a strong negative correlation with δ13C values in terebratellidinid species which exhibit major isotopic disequilibrium and also combined data from three localities for which two species were studied indicate such a negative relation. The observed covariation of Sr/Ca ratios with δ13C values may therefore become a useful tool to detect δ13C disequilibrium and to robustly estimate δ13C values of ambient DIC in deep time.The authors acknowledge comments from two anonymous reviewers and Alberto Pérez-Huerta as well as the editor Michael E. Boettcher which helped to improve the quality and clarity of the manuscript. The authors thank the Museum für Naturkunde Berlin for providing brachiopod specimens of the species F. sanguinolenta (ZMB Bra 1934), M. venosa (ZMB Bra 2028), N. nigricans (ZMB Bra 2441), S. crosnieri (ZMB Bra 2442), C. inconspicua (ZMB Bra 2443), C. racovitzae (ZMB Bra 2444) and L. neozelanica (ZMB Bra 2445) and Andy Gale for providing specimens of T. transversa and Terebratulina sp. The authors are indebted to the crews of RV SONNE during the cruises SO 168 ZEALANDIA and SO 233 WALVIS 2 and their respective shipboard scientific parties. Financial support by the German Ministry of Education and Research (BMBF) within the project SO 168 ZEALANDIA (FKZ: 03G0168) and SO 233 WALVIS 2 (FKZ: 03G0233A) to CL is gratefully acknowledged. CVU acknowledges funding from the Leopoldina – German National Academy of Sciences (grant no. LPDS 2014-08)

The complete mitochondrial genome of Flustra foliacea (Ectoprocta, Cheilostomata) - compositional bias affects phylogenetic analyses of lophotrochozoan relationships

<p>Abstract</p> <p>Background</p> <p>The phylogenetic relationships of the lophophorate lineages, ectoprocts, brachiopods and phoronids, within Lophotrochozoa are still controversial. We sequenced an additional mitochondrial genome of the most species-rich lophophorate lineage, the ectoprocts. Although it is known that there are large differences in the nucleotide composition of mitochondrial sequences of different lineages as well as in the amino acid composition of the encoded proteins, this bias is often not considered in phylogenetic analyses. We applied several approaches for reducing compositional bias and saturation in the phylogenetic analyses of the mitochondrial sequences.</p> <p>Results</p> <p>The complete mitochondrial genome (16,089 bp) of <it>Flustra foliacea </it>(Ectoprocta, Gymnolaemata, Cheilostomata) was sequenced. All protein-encoding, rRNA and tRNA genes are transcribed from the same strand. <it>Flustra </it>shares long intergenic sequences with the cheilostomate ectoproct <it>Bugula</it>, which might be a synapomorphy of these taxa. Further synapomorphies might be the loss of the DHU arm of the tRNA L(UUR), the loss of the DHU arm of the tRNA S(UCN) and the unique anticodon sequence GAG of the tRNA L(CUN). The gene order of the mitochondrial genome of <it>Flustra </it>differs strongly from that of the other known ectoprocts. Phylogenetic analyses of mitochondrial nucleotide and amino acid data sets show that the lophophorate lineages are more closely related to trochozoan phyla than to deuterostomes or ecdysozoans confirming the Lophotrochozoa hypothesis. Furthermore, they support the monophyly of Cheilostomata and Ectoprocta. However, the relationships of the lophophorate lineages within Lophotrochozoa differ strongly depending on the data set and the used method. Different approaches for reducing heterogeneity in nucleotide and amino acid data sets and saturation did not result in a more robust resolution of lophotrochozoan relationships.</p> <p>Conclusion</p> <p>The contradictory and usually weakly supported phylogenetic reconstructions of the relationships among lophotrochozoan phyla based on mitochondrial sequences indicate that these alone do not contain enough information for a robust resolution of the relations of the lophotrochozoan phyla. The mitochondrial gene order is also not useful for inferring their phylogenetic relationships, because it is highly variable in ectoprocts, brachiopods and some other lophotrochozoan phyla. However, our study revealed several rare genomic changes like the evolution of long intergenic sequences and changes in the structure of tRNAs, which may be helpful for reconstructing ectoproct phylogeny.</p

Clustered brachiopod Hox genes are not expressed collinearly and are associated with lophotrochozoan novelties

Temporal collinearity is often considered the main force preserving Hox gene clusters in animal genomes. Studies that combine genomic and gene expression data are scarce, however, particularly in invertebrates like the Lophotrochozoa. As a result, the temporal collinearity hypothesis is currently built on poorly supported foundations. Here we characterize the complement, cluster, and expression of Hox genes in two brachiopod species, Terebratalia transversa and Novocrania anomala. T. transversa has a split cluster with 10 genes (lab, pb, Hox3, Dfd, Scr, Lox5, Antp, Lox4, Post2, and Post1), whereas N. anomala has 9 genes (apparently missing Post1). Our in situ hybridization, real-time quantitative PCR, and stage-specific transcriptomic analyses show that brachiopod Hox genes are neither strictly temporally nor spatially collinear; only pb (in T. transversa), Hox3 (in both brachiopods), and Dfd (in both brachiopods) show staggered mesodermal expression. Thus, our findings support the idea that temporal collinearity might contribute to keeping Hox genes clustered. Remarkably, expression of the Hox genes in both brachiopod species demonstrates cooption of Hox genes in the chaetae and shell fields, two major lophotrochozoan morphological novelties. The shared and specific expression of Hox genes, together with Arx, Zic, and Notch pathway components in chaetae and shell fields in brachiopods, mollusks, and annelids provide molecular evidence supporting the conservation of the molecular basis for these lophotrochozoan hallmarks

Run and hide: visual performance in a brittle star

Spatial vision was recently reported in a brittle star, Ophiomastix wendtii, which lacks discrete eyes, but little is known about its visual ecology. Our aim was to better characterize the vision and visual ecology of this unusual visual system. We tested animals’ orientation relative to vertical bar stimuli at a range of angular widths and contrast, to identify limits of angular and contrast detection. We also presented dynamic shadow stimuli, either looming towards or passing overhead the animal, to test for potential defensive responses. Finally, we presented animals lacking a single arm with a vertical bar stimulus known to elicit a response in intact animals. We found that O. wendtii orients to large (≥50°), high-contrast vertical bar stimuli, consistent with a shelter-seeking role and with photoreceptor acceptance angles estimated from morphology. We calculate poor optical sensitivity for individual photoreceptors, and predict dramatic oversampling for photoreceptor arrays. We also report responses to dark stimuli moving against a bright background - this is the first report of responses to moving stimuli in brittle stars and suggests additional defensive uses for vision in echinoderms. Finally, we found that animals missing a single arm orient worse to static stimuli, which requires further investigation

New insights into the larval development of Macandrevia cranium (Müller, 1776) (Brachiopoda:Rhynchonelliformea)

The terebratulid Macandrevia cranium (Müller, 1776) is a representative of articulate brachiopods. However, little is known about its embryology and larval development. In order to obtain reproducible results we used a strict protocol of artificial fertilization under controlled temperature conditions as a basis for our morphological study. Sampling of embryos or developing larvae at frequent intervals led to the most comprehensive collection of preserved developmental stages, ranging from early zygotes to late three-lobed stage larvae. SEM studies of all these stages showed that the development of M. cranium is similar to that of other terebratulid brachiopods. This includes the presence of four bundles of larval setae in three-lobed stage larvae. Our results contradict earlier observations on the development of M. cranium and show that this species exhibits more typical features of articulate brachiopod development than previously thought