Evolutionary patterns of host switching, lifestyle mode, and the diversification history in symbiotic zoantharians.

Symbioses play important roles in forming the structural and distributional patterns of marine diversity. Understanding how interspecies interactions through symbioses contribute to biodiversity is an essential topic. Host switching has been considered as one of the main drivers of diversification in symbiotic systems. However, its process and patterns remain poorly investigated in the marine realm. Hexacoral species of the order Zoantharia (=zoantharians) are often epizoic on other marine invertebrates and generally use specific taxa as hosts. The present study investigates the patterns of host switching and the diversification history of zoantharians based on the most comprehensive molecular phylogenetic analyses to date, using sequences from three mitochondrial and three nuclear markers from representatives of 27 of 29 genera. Our results indicate that symbiotic zoantharians, in particular those within suborder Macrocnemina, diversified through repeated host switching. In addition, colonization of new host taxa appears to have driven morphological and ecological specialization in zoantharians. These findings have important implications for understanding the role of symbioses in the morphological and ecological evolution of marine invertebrates.

Disappearance and Return of an Outbreak of the Coral-killing Cyanobacteriosponge Terpios hoshinota in Southern Japan.

Masashi Yomogida, Masaru Mizuyama, Toshiki Kubomura, and James Davis Reimer (2017) Terpios hoshinota is cyanobacteriosponge that can cause serious damage to coral reef ecosystems by undergoing rapid breakouts in which it smothers and encrusts hard substrates, killing living sessile benthic organisms and reducing biodiversity of the a ected area. The reasons for these outbreaks are still unclear, as are long-term prognoses of affected reefs. Some reports have suggested outbreaks may not be permanent, but very little long-term monitoring information exists. In this study, we report on a T. hoshinota outbreak (~24% coverage) at Yakomo, Okinoerabu-jima Island, Kagoshima, Japan between 2010 to 2014. In this period, the existing outbreak was seen to almost completely disappear (~0%) after unusually severe Typhoon Songda passed by in early June 2011. After this, macroalgae and a cyanobacterial bloom became the dominant benthos, but by September 2014, T. hoshinota coverage had recovered to approximately half of its pre-typhoon coverage, suggesting the conditions that had caused the outbreak still persisted at Yakomo. While the conditions promoting T. hoshinota growth at this site remain uncertain, it appears that subtropical typhoons could play an important role in the dynamics of T. hoshinota outbreaks and disappearances.