Unpicking the mysterious symbiosis of Mycoplasma in salmonids

Lacking a peptidoglycan cell wall, mycoplasmas are the smallest self-replicating life forms. Members of this bacterial genus are known to parasitise a wide array of metazoans including vertebrates. Whilst much research has been significant targeted at parasitic mammalian mycoplasmas, very little is known about their role in other vertebrates. In the current study, we aim to explore the biology and evolution of Mycoplasma in salmonids, including cellular niche, genome size structure and gene content. Using Fluorescence in-situ hybridisation (FISH), mycoplasmas were identified in epithelial tissues across the digestive tract (stomach, pyloric caecum and midgut) during the developmental stages (eggs, parr, subadult) of farmed Atlantic salmon (Salmo salar), showing a high abundance in acidic compartments. With high throughput sequencing from subadults farmed Atlantic salmon, we assembled a nearly complete genome (~0.57 MB) via shotgun-metagenomics. The phylogenetic inference from the recovered genome revealed successful taxonomic proximity to Mycoplasma penetrans (~1.36 Mb) from the recovered genome. Although, no significant correlation between genome size and its phylogeny was observed, we recovered functional signatures, especially, riboflavin encoding genes pathway and sugars transporters, suggesting a symbiotic relationship between Mycoplasma and the host. Though 247 strains of Mycoplasma are available in public databases, to the best of our knowledge, this is the first study to demonstrate ecological and functional association between Mycoplasma and Salmo salar which delineates symbiotic reductive evolution and genome erosion primarily and also serves as a proxy for salmonid health in aquaculture processes (cell lines, in vitro gut models).

Reproductive biology of the starfishPharia pyramidatus(Echinodermata: Asteroidea) from the Mexican tropical Pacific

The starfishPharia pyramidatusis a tropical species of high ecological importance, mainly because of its role as generalist predator. Nevertheless, there are no studies about its reproduction. This study analysed the reproductive biology ofP. pyramidatusbased on monthly time-series samples from April 2008 to March 2009 at Isla Montosa in the Mexican tropical Pacific. The gonad index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads.Pharia pyramidatusis a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Gametogenesis showed high synchrony among males and females and five stages were recognized for both sexes. Spawning occurred from July to September. Maximum oocyte size was ~150μm and mean fecundity was 7.3 ± 1.2 millions of oocytes per female. GI and PCI showed seasonal variations and an inverse relationship from May to August. Sea-bottom temperature and photoperiod showed a direct relationship with GI, and apparently constitute the proximate causes of the seasonal reproductive pattern observed inP. pyramidatus, while the highly seasonal rainfall and strong upwelling probably act as ultimate causes.

Contrasting relationships between pyloric caecum and gonad growth in the starfish Asterias rubens: combined field and experimental approaches

The common starfish, Asterias rubens, occurs in fluctuating environments in the North Atlantic. To better understand energy allocation dynamics, we recorded gonad, body wall, and pyloric caeca (storage organ) indices between 2000 and 2004 from three different habitats. We applied a Fourier transform to the data to evaluate and compare the seasonal variation in these indices. Specific effects of emersion and salinity variation were examined in two laboratory studies. Differences in energy allocation were found between sites and temporally within sites. Food availability appeared to be the most important factor controlling allocation dynamics while fluctuating salinity and/or emersion had a significant but smaller impact. Only severe food shortage reduced reproductive investment indicating a preferential energy allocation to gonads. This study is the first to encompass a broad range of populations over several reproduction cycles and emphasizes the ability of A. rubens to adapt to a fluctuating environment.

Reproduction, recruitment and juvenile ecology of the starfish,Asterias rubensandMarthasterias glacialis

Reproductive cycles are described for subtidal and intertidal populations of the, starfishAsterias rubensL. and for a subtidal population of the starfishMarthasterias glacialisL. on the south-west coast of Britain. IntertidalA. rubenshad a clearly defined reproductive cycle with spring-early summer spawning. Pyloric caecum indices were inversely related to gonad indices. SubtidalA. rubenshad lower gonad indices and less seasonal variation in the pyloric caecum indices. Gonad indices ofM. glacialissuggest few animals in the population studied were breeding, but it is likely that this species also spawns in summer.Plankton samples and larval rearing studies suggest a planktotrophic pelagic life of approximately 90 days forA. rubens. Field observations and laboratory experiments show larvae settle on a wide range of substrata. Recruitment to an intertidal population ofA. rubensat Hollicombe Reef occurred in July 1980 and September 1981. Growth of juvenile starfish was followed for 17 months. Juvenile starfish feed carnivorously at the completion of metamorphosis. Early growth is rapid; however, there is a reduction in the growth rate during winter months. Feeding and growth of juvenileA. rubensis compared with published data on juvenile starfish of other species.