ECR feature: Patricia Wepfer on the evolution and population dynamics of reef-building corals

Patricia H. Wepfer is a postdoc at the Institute of Spatial and Landscape Development, ETH Zurich. She is broadly interested in biogeographic processes shaping species distribution patterns. Here, Patricia shares her recent work on the evolution and population dynamics of reef-building corals from the North-Western Pacific.

Patricia Wepfer collecting coral polyps at site Oku, Okinawa Island

Institute. Institute of Spatial and Landscape Development, ETH Zurich.

Academic life stage. Postdoc.

Major research themes. Geographically driven evolution; population connectivity; urban design and architecture

Current study system. Reef-building corals are fascinating in that they are animals but are plant-like in many aspects. They live on photosynthesis products provided by their symbiotic dinoflagellates, which helped them to become the successful reef-builders they are today. Their dispersal resembles wind-dispersed plants, as their larvae travel passively with ocean currents. With the ability to model ocean currents, it is extremely interesting to study dispersal-related questions in pelagic dispersers. Corals belong to the Metazoa and are ancient creatures with unclear species boundaries in the current taxonomy. However, Galaxea is a large-polyped coral that is fluorescently green and is therefore easy to identify, which makes it a good target to study the history of a self-contained evolutionary group.

Ogasawaran lineage of Galaxea fascicularis from around Chichi Island

Recent JBI paper. Wepfer, P. H., Nakajima, Y., Fujimura, A., Mikheyev, A. S., Economo, E. P., & Mitarai, S. (2022). The oceanographic isolation of the Ogasawara Islands and genetic divergence in a reef-building coral. Journal of Biogeography 49 (11), 1978–1990.

Motivation behind this paper. The Ogasawara Islands are an interesting island system because of their exceptional degree of isolation. They are oceanic volcanos, hundreds of kilometres away from the next continental land masses or island groups. Due to the lack of major ocean currents passing them, they are oceanographically even more isolated than the Galapagos islands. That our coral taxon was the most common and dominant reef-builder in the coral community on this archipelago, unlike in all Asia and Australia, additionally made this site a must-visit on our sampling list for our connectivity study.

Cliffs at the Southern coast of Chichi Island

Key methodologies. We combined high-throughput sequencing (RAD-seq) with a novel inverse particle tracking approach in our study. The loci obtained from RAD-seq enabled the investigation of an evolutionary time scale by looking at the demographic history, while the biophysical dispersal model was able to identify contemporary oceanographic dispersal patterns. By linking the two we found that the coral around the Ogasawara Islands have been isolated like today for a very long time. It implies that even for well-dispersed marine animals, geographic isolation can be linked to high degrees of differentiation and diversification of a taxon.

Unexpected challenges. As usual with corals, it was challenging to collect them. Due to their vulnerability, it is important to collect minimal amounts while gathering enough to ensure a good sample size. It was challenging also to go through the administrative procedure to travel to such a remote place, involving multiple days of travel on a rolling ship.

Major results. It was unexpected that we would find such a highly differentiated lineage on Ogasawara. We thought that the Ogasawaran coral must be somewhat connected to the Mariana Islands, since the alternative dispersal route was over temperate climate zones. However, it turned out that this archipelago hardly receives any migrants from the South, and only rarely from the North. Whether other marine animals follow similar patterns is still unclear, yet our results allow us place the hypothesis that the endemicity under water could be as high as on land, for which the Ogasawara islands are already famous for.

Next steps for this research. The next step will be to further investigate the oceanographic patterns in this region. The dispersal modelling will be refined including more potential stepping-stones along this island chain and isolated solitary islands to the West. From the genetic side, it will be important to sample more in Guam to verify the genetic composition there, as well as specimens from the Northern Mariana Islands for a more detailed analysis of the connectivity between the archipelagos.

If you could study any organism on Earth, what would it be? There isn’t a particular organism on my mind, but I would probably continue studying more different coral species and their distribution around Western Pacific Islands. Although it was challenging to study their evolution because species boundaries are so vague and much less understood than for example in plants. Sampling procedures are also hard because of their CITES status. For these reasons, I would also consider switching back to plants. However, I now switched to an entirely new field: urban planning and architecture – maybe this could be considered studying the microecology of the human species.

Anything else to add? The visit to the Ogasawara Islands was definitely a highlight of my PhD. I visited many islands but the Ogasawara Islands felt especially wild and natural, thanks to their comprehensive environmental protection. It is a place where turtles are unimpressed by human presence and dolphins curiously swim up to one.

Sea turtle resting on the coral reef between Anijima and Chichijima

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