Morphological and ecological adaptation of Basterotia bivalves (Galeommatoidea: Sportellidae) to symbiotic association with burrowing echiuran worms.

The burrows created by benthos in tidal flats provide various habitats to other organisms. Echiuran burrows are unique among these in being persistently disturbed by the host's undulating activity, but little is known on how symbionts adapt to such a unique habitat. We report here the morphological and ecological adaptation by two bivalve species of Basterotia (Sportellidae), including one new species, which are commensals with burrowing echiuran worms. The burrows of Ikedosoma gogoshimense were inhabited by Basterotia gouldi at intertidal gravelly mud flats in the central Seto Inland Sea, whereas those of Ochetostoma erythrogrammon were inhabited by Basterotia carinata n. sp. at an intertidal gravelly coral-sand flat at Amami-Ohshima Island. Both bivalve species were found embedded in the burrow wall with their posterior inhalant and exhalant apertures gaping to the burrow lumen, suggesting that they utilize the water currents created by host echiurans. The posteriorly robust, laterally inflated shell with developed carina is considered an adaptation to symbiotic life, as it is exposed to pressure caused by the host's persistent undulating activity. Females of Basterotia bivalves were larger than males, suggesting size-dependent sex change, and possessed brooded veligers in the ctenidium. Our findings suggest that species-specific intimate association with echiurans may be widespread among the Sportellidae bivalves, whose biology remains poorly understood

Molecular phylogeny of the bivalve superfamily Galeommatoidea (Heterodonta, Veneroida) reveals dynamic evolution of symbiotic lifestyle and interphylum host switching

Abstract Background Galeommatoidea is a superfamily of bivalves that exhibits remarkably diverse lifestyles. Many members of this group live attached to the body surface or inside the burrows of other marine invertebrates, including crustaceans, holothurians, echinoids, cnidarians, sipunculans and echiurans. These symbiotic species exhibit high host specificity, commensal interactions with hosts, and extreme morphological and behavioral adaptations to symbiotic life. Host specialization to various animal groups has likely played an important role in the evolution and diversification of this bivalve group. However, the evolutionary pathway that led to their ecological diversity is not well understood, in part because of their reduced and/or highly modified morphologies that have confounded traditional taxonomy. This study elucidates the taxonomy of the Galeommatoidea and their evolutionary history of symbiotic lifestyle based on a molecular phylogenic analysis of 33 galeommatoidean and five putative galeommatoidean species belonging to 27 genera and three families using two nuclear ribosomal genes (18S and 28S ribosomal DNA) and a nuclear (histone H3) and mitochondrial (cytochrome oxidase subunit I) protein-coding genes. Results Molecular phylogeny recovered six well-supported major clades within Galeommatoidea. Symbiotic species were found in all major clades, whereas free-living species were grouped into two major clades. Species symbiotic with crustaceans, holothurians, sipunculans, and echiurans were each found in multiple major clades, suggesting that host specialization to these animal groups occurred repeatedly in Galeommatoidea. Conclusions Our results suggest that the evolutionary history of host association in Galeommatoidea has been remarkably dynamic, involving frequent host switches between different animal phyla. Such an unusual pattern of dynamic host switching is considered to have resulted from their commensalistic lifestyle, in which they maintain filter-feeding habits even in symbiotic habitats. The results of the molecular phylogenetic analysis did not correspond with the current taxonomic circumscription. Galeommatidae and Lasaeidae were polyphyletic, and Basterotia, which is traditionally assigned to Cyamioidea, formed a monophyletic clade within Galeommatoidea.</p

Molecular Phylogeny of Echiuran Worms (Phylum: Annelida) Reveals Evolutionary Pattern of Feeding Mode and Sexual Dimorphism

<div><p>The Echiura, or spoon worms, are a group of marine worms, most of which live in burrows in soft sediments. This annelid-like animal group was once considered as a separate phylum because of the absence of segmentation, although recent molecular analyses have placed it within the annelids. In this study, we elucidate the interfamily relationships of echiuran worms and their evolutionary pattern of feeding mode and sexual dimorphism, by performing molecular phylogenetic analyses using four genes (18S, 28S, H3, and COI) of representatives of all extant echiuran families. Our results suggest that Echiura is monophyletic and comprises two unexpected groups: [Echiuridae+Urechidae+Thalassematidae] and [Bonelliidae+Ikedidae]. This grouping agrees with the presence/absence of marked sexual dimorphism involving dwarf males and the paired/non-paired configuration of the gonoducts (genital sacs). Furthermore, the data supports the sister group relationship of Echiuridae and Urechidae. These two families share the character of having anal chaetae rings around the posterior trunk as a synapomorphy. The analyses also suggest that deposit feeding is a basal feeding mode in echiurans and that filter feeding originated once in the common ancestor of Urechidae. Overall, our results contradict the currently accepted order-level classification, especially in that Echiuroinea is polyphyletic, and provide novel insights into the evolution of echiuran worms.</p> </div

Maximum-likelihood tree of echiuran worms based on the combined dataset of 18S, 28S, H3 and COI genes.

<p>Numbers above branches indicate maximum-likelihood bootstrap support values followed by Bayesian posterior probabilities. The colors of the boxes to the right of the family names indicate whether the family is sexually dimorphic (black) or monomorphic (white). The capital letters in the boxes indicate the feeding mode of the family, i.e., deposit feeding (D) or filter feeding (F). The colors shading the family names indicate the order to which the family belongs, as defined by Ruppert <i>et al</i>. (2004) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056809#pone.0056809-Ruppert1" target="_blank">[3]</a>.</p

Sampling information for the specimens used in this study.

<p>Taxonomic classification follows Ruppert <i>et al</i>. (2004) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056809#pone.0056809-Ruppert1" target="_blank">[3]</a>.</p

Various echiuran worms that utilized for the analyses.

<p>A. <i>Echiurus echiurus</i>, B. <i>Ikedosoma gogoshimense</i>, C. <i>Thalassema owstoni</i>, D. <i>Listriolobus sorbillans</i>, E. <i>Ochetostoma erythrogrammon</i>, F. <i>Ochetostoma</i> sp. 1, G. <i>Ochetostoma</i> sp. 2, H. <i>Ochetostoma</i> sp. 3, I. <i>Urechis unicinctus</i>, J. <i>Bonellia viridis</i>, K. <i>Ikeda taenioides</i>, L. <i>Ikeda</i> sp. 1. Scale bar = 2 cm.</p

Edoxaban Exerts Antioxidant Effects Through FXa Inhibition and Direct Radical-Scavenging Activity

The interplay between oxidative stress, inflammation, and tissue fibrosis leads to the progression of chronic kidney disease (CKD). Edoxaban, an activated blood coagulation factor Xa (FXa) inhibitor, ameliorates kidney disease by suppressing inflammation and tissue fibrosis in animal models. Interestingly, rivaroxaban, another FXa inhibitor, suppresses oxidative stress induced by FXa. Thus, FXa inhibitors could be multitargeted drugs for the three aforementioned risk factors for the progression of CKD. However, the exact mechanism responsible for eliciting the antioxidant effect of FXa inhibitors remains unclear. In this study, the antioxidant effect of edoxaban was evaluated. First, the intracellular antioxidant properties of edoxaban were evaluated using human proximal tubular cells (HK-2 cells). Next, direct radical scavenging activity was measured using the electron spin resonance and fluorescence analysis methods. Results show that edoxaban exhibited antioxidant effects on oxidative stress induced by FXa, indoxyl sulfate, and angiotensin II in HK-2 cells, as well as the FXa inhibitory activity, was involved in part of the antioxidant mechanism. Moreover, edoxaban exerted its antioxidative effect through its structure-specific direct radical scavenging activity. Edoxaban exerts antioxidant effects by inhibiting FXa and through direct radical-scavenging activity, and thus, may serve as multitargeted drugs for the three primary risk factors associated with progression of CKD