Research
My research asks how animals are built, how they evolved, and how they live in partnership with microorganisms. My main model group is the siboglinids (Siboglinidae) — remarkable marine worms that have no mouth or gut and instead feed through symbiotic bacteria living inside their bodies. Using them, I explore fundamental questions in anatomy, development, and evolution. More recently I have turned to the physiology of this partnership — how host and symbionts actually interact — and have extended my work to other symbiotic animals, such as acoel flatworms that host photosynthetic algae.
Structure, and growth shaped by the environment
My early work mapped the anatomy of siboglinid tubeworms in fine detail. Combining thin serial sections, electron microscopy, and three-dimensional reconstruction, I described every organ system — from the muscles and blood-vascular system to the tentacles and the excretory (protonephridial) system — of the giant hydrothermal-vent worm Riftia pachyptila, and placed these features in a comparative framework across the whole family. This work showed that every organ system I examined is shaped by the unusual chemistry of the animals’ deep-sea habitat. [22, 24, 26, 27, 28, 29, 31, 32, 35, 36]
Evolution and flexibility of the nervous system
By comparing the nervous systems of siboglinids (Riftia, Osedax, Siboglinum) with those of early-branching relatives (the oweniid worms Galathowenia and Owenia), I found that both groups lack the repeated nerve clusters — segmental ganglia — usually strung along an annelid’s nerve cords, and that both share a sessile, stay-in-one-place lifestyle. This tells us that the annelid nervous system is far more flexible than a single fixed blueprint: similar features, such as a diffuse cordlike organisation and cross-connected nerve cords, evolved independently more than once, with the nervous layout following the body’s segmentation and elongation rather than a rigid ground plan. [19, 28, 33, 34]
Development and the origin of the siboglinid body
Because the adult siboglinid body is so specialised, I became interested in how it is assembled during development, and in how the larva is already adapted to its future life. By tracing the formation of the nervous system and musculature in the larvae of Siboglinum fiordicum, I showed how the worm’s unusual segmentation is set up step by step, and how the different body regions are gradually specified as the animal becomes a sessile, symbiont-dependent worm. [10, 16]
The trophosome — a key innovation
The trophosome is the special internal organ that houses the worms’ chemosynthetic bacteria [39], and it is the central evolutionary invention that made the siboglinid way of life possible. It is the focus of my current work. I am studying how it is built and how it develops in two early-branching siboglinid lineages — Sclerolinum and the frenulates — using electron microscopy, molecular labelling of the bacteria in place (FISH), gene-expression analysis, and spatial transcriptomics (which maps which genes are switched on, and where, within a tissue). I have established a laboratory culture of Sclerolinum that reproduces on its own, and we are working to raise young Siboglinum so that we can watch the trophosome form directly. I am now widening this into a comparative study that includes several related worms, in order to pin down the genetic signature that defines the trophosome and to reconstruct how this organ first arose.
How nutrition depends on symbionts
The chemical “fingerprints” left by carbon and nitrogen — their stable isotopes — reveal what an animal actually eats. Comparing Arctic methane-seep communities with nearby non-seep ones, I showed that ordinary seep animals opportunistically tap into carbon produced by chemosynthetic bacteria, while the fully symbiotic worm Oligobrachia sits in a completely separate nutritional world — drawing essentially all of its carbon and nitrogen from its sulphur-oxidising symbionts rather than from the surrounding food web. These results put a number on just how completely a host can depend on its microbial partners, and they set up the mechanistic questions I ask now. [4]
Toward the physiology of symbiosis
My work has moved steadily from the structure and evolution of the hosts toward the workings of the partnership itself. How does a host acquire exactly the right chemosynthetic bacteria or photosynthetic algae? What drives the dramatic bodily transformation that accompanies the start of symbiosis? And how does the immune system learn to tell friend from foe? [2, 5, 22]
I now want to go a step further — beyond structure, to how symbiosis is established and maintained at the physiological level: the host’s immune status, the exchange of nutrients and metabolites, and how those nutrients are shared between symbiont and host. At heart these are physiological questions: how an animal, as it develops, builds its defences yet still lets its symbionts in; and how nutrients are transported, sensed, and distributed inside a body that depends on internal microbial partners. My goal is to move from describing symbiotic animals to understanding how symbiosis works at the physiological level.