Research
My research primarily concerns the co-evolution of the Proterozoic biosphere (2.5-0.539 billion years ago) and eukaryotic life — a topic I approach by studying modern organisms and environments
The ecology of microbial eukaryotes
The Proterozoic biosphere witnessed the origin of eukaryotic life — perhaps the most significant evolutionary event since the origin of life itself. How the global environment of the Proterozoic, including atmospheric oxygen levels perhaps a hundredth of what they are now, shaped the ecology and evolution of the earliest eukaryotes represents a major thread of historical geobiological research. By studying the effects of deoxygenation on the community structure of microbial eukaryotes in Saanich Inlet — a persistently anoxic fjord on the coast of Vancouver Island, British Columbia, Canada (see map below) — the control of oxygen concentration on microbial eukaryotic ecology can be tracked and quantified. These fundamental relationships can then be used to 1) reconstruct the earliest eukaryotic ecosystems on Earth, and 2) predict the microbial eukaryotic responses to ongoing marine deoxygenation.
Saanich Inlet, the primary field site for this research, is a persistently anoxic fjord on the southeast side of Vancouver Island, British Columbia, Canada, and serves as a model ecosystem for exploring the relationships between marine oxygen availability and microbial community dynamics. This research is part of a 10-year time-series experiment based at the University of British Columbia. Preliminary results were presented at the 2020 Ocean Sciences Meeting in San Diego, California, USA.
The origin of phagocytosis
The distinction between eukaryotic cells from the cells of bacteria and archaea has been called “the greatest single evolutionary discontinuity to be found in the present-day living world” (Stanier et al., 1963). One of the major traits separating eukaryotes from bacteria and archaea is the widespread ability of eukaryotes to phagocytose. The origin of phagocytosis (or ‘cell eating’) has been central to discussions on the origin of eukaryotes for decades, where it is argued as being either a prerequisite for, or consequence of, the acquisition of the ancestral mitochondrion. While phagocytosis likely evolved sometime during the Proterozoic, its timing of appearance within the Proterozoic is only broadly constrained. Determining when phagocytosis — and by extension phagotrophy, the predatory mode in which eukaryotes reliably ingest entire prey cells for nutrition — first appeared in Earth history remains vital to understanding the origin of modern ecosystems.
A timeline compiling molecular clock (MC) estimates for the age of LECA (the last eukaryotic common ancestor), as well as the paleontological and organic geochemical evidence used to argue for the presence and ecological importance of eukaryotic predators. Details, along with a version of this figure, can be found here. A more detailed PDF of this figure can also be found here.
The origins of eukaryotic multicellularity
Multiple eukaryotic lineages have transitioned from microscopic, single-celled morphologies to macroscopic, multicellular ones. The Phanerozoic Eon — literally ‘the age of visible life’ — is defined by its unprecedented abundance of multicellular forms. While animals and red algae (specifically florideophytes) appear to be the oldest groups to display ‘complex’ multicellularity, brown algae (specifically the kelps, or laminarialeans) appear to be the youngest, located much closer in time to the modern day than to the origin of these other groups (see figure below). How (and why) these different eukaryotic lineages obtained multicellularity, and how the global environment may have influenced these transitions, remains largely unknown. By studying the effects of dissolved oxygen concentration and other environmental variables on the physiology and colony-forming behavior of microbial eukaryotes, the potential role of ancient environmental conditions in controlling the multiple origins of eukaryotic multicellularity can be better constrained.
A timeline showing when the six major eukaryotic clades displaying complex multicellularity likely evolved. The horizontal bars represent the highest confidence intervals (95%) for the age of each multicellular clade, as taken from various molecular clock (MC) analyses. The diamonds indicate the mean estimates for the age of each clade. Ma = million years ago. An earlier version of this figure was published here, and a PDF of this version can be downloaded here.
Early animal evolution
The co-evolution of biospheric oxygen availability and early animals is a perennial theme of historical geobiology, going back to the origin of the field itself. Indeed, the abrupt (and relatively late) appearance of animal fossils in the rock record has long puzzled Earth historians. Beginning in the mid-20th century, a number of Earth and life scientists developed the idea that low atmospheric oxygen levels prevented the origin and expansion of animal life until right before the time of the earliest animal fossils, when atmospheric oxygen rose to levels supportive of animals for the first time. While many aspects of this narrative have been refined (and refuted), ideas on how various aspects of early animal evolution were controlled or dictated by changing oxygen levels remain widespread. To test these scenarios, and to constrain how environmental oxygen concentration fundamentally controls animal physiology and metabolism, experiments on modern animals — particularly non-bilaterian taxa like sponges and ctenophores (see below) — are essential.
The marine sponge Tethya wilhelma, an emerging model organism for understanding the earliest evolution of animal life, can survive under 500 nM O2 (and perhaps even lower), which is equivalent to 0.25% of the oxygen content of the modern atmosphere. You can read more about these results here and here.