Symbiosis. Making light work of adaptation

Notaulax yamasui sp. n. (Annelida, Sabellidae) from Okinawa and Ogasawara, Japan, with notes on its ecology

The polychaete Notaulaxyamasuisp. n. (Sabellidae) is described from Okinawa and Ogasawara, south Japan, where it was found living embedded in a dead skeleton of the coral Porites sp. The new species is characterized by the presence of a pigmented sub-distal swelling on the tips of the crown radioles, a unique feature among species of the genus. Besides, its collar chaetae have an L-shape orientation, and the dorsal basal flanges of the branchial lobes are long and have a dorsal joint.

Breaking up and getting together: evolution of symbiosis and cloning by fission in sea anemones (Genus Anthopleura)

Clonal growth and symbiosis with photosynthetic zooxanthellae typify many genera of marine organisms, suggesting that these traits are usually conserved. However, some, such as Anthopleura, a genus of sea anemones, contain members lacking one or both of these traits. The evolutionary origins of these traits in 13 species of Anthopleura were inferred from a molecular phylogeny derived from 395 bp of the mitochondrial 16S rRNA gene and 410 bp of the mitochondrial cytochrome oxidase subunit III gene. Sequences from these genes were combined and analyzed by maximum-parsimony, maximum-likelihood, and neighbor-joining methods. Best trees from each method indicated a minimum of four changes in growth mode and that symbiosis with zooxanthellae has arisen independently in eastern and western Pacific species. Alternative trees in which species sharing growth modes or the symbiotic condition were constrained to be monophyletic were significantly worse than best trees. Although clade composition was mostly consistent with geographic sympatry, A. artemisia from California was included in the western Pacific clade. Likewise, A. midori from Japan was not placed in a clade containing only other Asian congeners. The history of Anthopleura includes repeated shifts between clonality and solitariness, repeated attainment of symbiosis with zooxanthellae, and intercontinental dispersal.

The adaptive bleaching hypothesis: experimental tests of critical assumptions

Coral bleaching, the loss of color due to loss of symbiotic zooxanthellae or their pigment, appears to be increasing in intensity and geographic extent, perhaps related to increasing sea surface temperatures. The adaptive bleaching hypothesis (ABH) posits that when environmental circumstances change, the loss of one or more kinds of zooxanthellae is rapidly, sometimes unnoticeably, followed by formation of a new symbiotic consortium with different zooxanthellae that are more suited to the new conditions in the host's habitat. Fundamental assumptions of the ABH include (1) different types of zooxanthellae respond differently to environmental conditions, specifically temperature, and (2) bleached adults can secondarily acquire zooxanthellae from the environment. We present simple tests of these assumptions and show that (1) genetically different strains of zooxanthellae exhibit different responses to elevated temperature, (2) bleached adult hosts can acquire algal symbionts with an apparently dose-dependent relationship between the concentration of zooxanthellae and the rate of establishment of the symbiosis, (3) and finally, bleached adult hosts can acquire symbionts from the water column.