Seawater carbonate chemistry, fertilization and early development of the coral eating crown-of-thorns starfish, Acanthaster planci in a laboratory experiment

Outbreaks of crown-of-thorns starfish (COTS), Acanthaster planci, contribute to major declines of coral reef ecosystems throughout the Indo-Pacific. As the oceans warm and decrease in pH due to increased anthropogenic CO2 production, coral reefs are also susceptible to bleaching, disease and reduced calcification. The impacts of ocean acidification and warming may be exacerbated by COTS predation, but it is not known how this major predator will fare in a changing ocean. Because larval success is a key driver of population outbreaks, we investigated the sensitivities of larval A. planci to increased temperature (2-4 °C above ambient) and acidification (0.3-0.5 pH units below ambient) in flow-through cross-factorial experiments (3 temperature × 3 pH/pCO2 levels). There was no effect of increased temperature or acidification on fertilization or very early development. Larvae reared in the optimal temperature (28 °C) were the largest across all pH treatments. Development to advanced larva was negatively affected by the high temperature treatment (30 °C) and by both experimental pH levels (pH 7.6, 7.8). Thus, planktonic life stages of A. planci may be negatively impacted by near-future global change. Increased temperature and reduced pH had an additive negative effect on reducing larval size. The 30 °C treatment exceeded larval tolerance regardless of pH. As 30 °C sea surface temperatures may become the norm in low latitude tropical regions, poleward migration of A. planci may be expected as they follow optimal isotherms. In the absence of acclimation or adaptation, declines in low latitude populations may occur. Poleward migration will be facilitated by strong western boundary currents, with possible negative flow-on effects on high latitude coral reefs. The contrasting responses of the larvae of A. planci and those of its coral prey to ocean acidification and warming are considered in context with potential future change in tropical reef ecosystems.

Comparative study of breakwater crown wall – calculation methods

An investigation was undertaken consisting of a state-of-the-art and comparative analysis of currently available methods for calculating the structural stability of wave walls in sloping breakwaters. A total of six design schemes are addressed. The conditions under which the formulations and ranges of validity are explicitly indicated by their authors, are given. The lack of definition in parameters to be used and aspects not taken into account in their investigations are discussed and the results of this analysis are given in a final table.

Discussion: Comparative study of breakwater crown wall - calculation methods

This paper presents an extensive and useful comparison of existing formulas to estimate wave forces on crown walls. The paper also provides valuable insights into crown wall behaviour, suggesting the use of formulas for prior sizing and recommending, in any case, tests on a physical model in order to confirm the final design. The authors helpfully advise to use more than one method to obtain results closer to reality, always taking into account the test conditions under which each formula was developed

Agrobacterium VirD2 protein interacts with plant host cyclophilins

Agrobacterium tumefaciens induces crown gall tumors on plants by transferring a nucleoprotein complex, the T-complex, from the bacterium to the plant cell. The T-complex consists of T-DNA, a single-stranded DNA segment of the tumor-inducing plasmid, VirD2, an endonuclease covalently bound to the 5′ end of the T-DNA, and perhaps VirE2, a single-stranded DNA binding protein. The yeast two-hybrid system was used to screen for proteins interacting with VirD2 and VirE2 to identify components in Arabidopsis thaliana that interact with the T-complex. Three VirD2- and two VirE2-interacting proteins were identified. Here we characterize the interactions of VirD2 with two isoforms of Arabidopsis cyclophilins identified by using this analysis. The VirD2 domain interacting with the cyclophilins is distinct from the endonuclease, omega, and the nuclear localization signal domains. The VirD2–cyclophilin interaction is disrupted in vitro by cyclosporin A, which also inhibits Agrobacterium-mediated transformation of Arabidopsis and tobacco. These data strongly suggest that host cyclophilins play a role in T-DNA transfer.

Phylogenetic relationships between the Acantharea and the Polycystinea: A molecular perspective on Haeckel’s Radiolaria

Polycystine radiolaria are among few protistan groups that possess a comprehensive fossil record available for study by micropaleontologists. The Polycystinea and the Acantharea, whose skeletons do not become fossilized, were once members of the class “Radiolaria” (“Radiolaria” sensu lato: Polycystinea, Phaeodarea, and Acantharea) originally proposed by Haeckel but are now included in the superclass Actinopoda. Phylogenetic relationships within this superclass remain largely enigmatic. We investigated the evolutionary relationship of the Acantharea and the Polycystinea to other protists using phylogenetic analyses of 16S-like ribosomal RNA (rRNA) coding regions. We circumvented the need to culture these organisms by collecting and maintaining reproductive stages that contain many copies of their genomic DNA. This strategy facilitated extraction of genomic DNA and its purification from symbiont and prey DNA. Phylogenetic trees inferred from comparisons of 16S-like coding regions do not support a shared history between the Acantharea and the Polycystinea. However, the monophyly of the Acantharea and the separate monophyly of the Polycystinea (Spumellarida) are well supported by our molecular-based trees. The acantharian lineage branches among crown organisms whereas the polycystine lineage diverges before the radiation of the crown groups. We conclude that the Actinopoda does not represent a monophyletic evolutionary assemblage and recommend that this taxonomic designation be discarded.

Origin and evolution of the slime molds (Mycetozoa)

The Mycetozoa include the cellular (dictyostelid), acellular (myxogastrid), and protostelid slime molds. However, available molecular data are in disagreement on both the monophyly and phylogenetic position of the group. Ribosomal RNA trees show the myxogastrid and dictyostelid slime molds as unrelated early branching lineages, but actin and β-tubulin trees place them together as a single coherent (monophyletic) group, closely related to the animal–fungal clade. We have sequenced the elongation factor-1α genes from one member of each division of the Mycetozoa, including Dictyostelium discoideum, for which cDNA sequences were previously available. Phylogenetic analyses of these sequences strongly support a monophyletic Mycetozoa, with the myxogastrid and dictyostelid slime molds most closely related to each other. All phylogenetic methods used also place this coherent Mycetozoan assemblage as emerging among the multicellular eukaryotes, tentatively supported as more closely related to animals + fungi than are green plants. With our data there are now three proteins that consistently support a monophyletic Mycetozoa and at least four that place these taxa within the “crown” of the eukaryote tree. We suggest that ribosomal RNA data should be more closely examined with regard to these questions, and we emphasize the importance of developing multiple sequence data sets.