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Project 11

Ecological and evolutionary role of horizontal transmission in vestimentiferan tubeworms

PhD position. Supervisor: Monika Bright (UniVienna) and Nicole Dubilier (MPIMM) (with input from Sabine Gollner, UniVienna). Host: UniVienna. Secondment internship: to MPIMM.

Rationale

The gutless giant tubeworm Riftia pachyptila co-occurrs with two smaller vestimentiferan relatives Tevnia jerichonana and Oasisia alvinae in high densities at deep-sea hydrothermal vents of the East Pacific Rise. Upon major disturbances after volcanic eruptions, tubeworm colonization of new vents is rapid, but successional replacement can also occur quickly in this short-lived, extreme environment. Based on 16S rRNA sequences, the three host species share the same endosymbiont, which thrives in a specialised organ, the trophosome. Recently, the genome of this symbiont, Candidatus Endoriftia persephone from Riftia was published. Horizontal transmission occurs anew each host generation after settlement of the larvae and a free-living population, also detected in the surrounding environment, serves as inoculum.

Objectives

To better understand the ecological and evolutionary role horizontal transmission plays in the vestimentiferan symbiosis. The objectives of the proposed PhD thesis are (i) to obtain a detailed understanding of colonization and successional patterns of the three vent tubeworm species in relation to the distribution of the free-living microbial partner, including an understanding of how metabolic activity of the symbionts influences transmission and succession (ii) the connectivity between symbiotic and free-living population, and (iii) to test existing and further develop biomathematical models on symbiont transmission.

Key methods

(i) Long-term in situ deployments and recoveries of artificial tubeworm settlement cubes (TASCs) for molecular identification and quantification of tubeworm hosts and free-living counterpart of symbiont prior eruption in 2006 (2001-2005) and post eruption (2006-2010). (ii) Experimental testing for symbiont release into the environment using high pressure vessels during the MESCAL cruise in May 2010 as well as molecular and morphological techniques (electron microscopy, FISH, Raman and NanoSIMS). (iii) Computational part of thesis using a set of key parameters identified in an extensive review on transmission, for analyses, testing and simulations of biomathematical models on symbiont transmission.