College of Science

Dr. Eric Crandall, SNS Assistant Professor, recently published a scientific paper in Global Ecology and Biogeography titled "The molecular biogeography of the Indo‐Pacific: Testing hypotheses with multispecies genetic patterns".

Stretching across 2/3 of the Earth’s circumference, from East Africa to Easter Island (Rapa Nui), the Indo-Pacific is the largest biogeographic region in the world. Like a bullseye in the middle of the Indo-Pacific, right in the Indo-Malay-Philippines Archipelago, sits the Coral Triangle: the site of highest marine biodiversity in the world. Biodiversity declines in all directions as you move away from the Coral Triangle, creating a spectacular gradient of species diversity that characterizes the whole Indo-Pacific. The processes underlying this gradient are a persistent source of inquiry for biodiversity scientists around the world.

For example, how do new species evolve in the Indo-Pacific? Because most marine species have a tiny larval stage that can potentially drift on ocean currents for thousands of kilometers, it is unclear where there might be barriers to these larvae that would cause populations on either side of the barrier to become different species.

Because it is so large, biogeographers have subdivided the Indo-Pacific into smaller regions based on a variety of criteria, such as fish endemism or the range limits of coral species (these can be called regionalization hypotheses). For this paper, Dr. Eric Crandall led an international team of researchers (21 co-authors from 7 countries, plus >30 additional consortium co-authors), who assembled about two decades worth of genetic data (>36,000 genetic sequences) from 56 coral reef species sampled across the Indo-Pacific. They then empirically tested how well data from each species fit each hypothesis. They found that the data supported hypotheses which subdivide the Indo-Pacific into relatively few regions. Overall, these results can be taken to mean that there are only about 3 substantial barriers to larval dispersal in the entire Indo-Pacific: one on the western side of Sumatra, one between the continental islands of the West Pacific and the hot spot archipelagos of the Central Pacific, and one between Hawaii and the rest of the Indo-Pacific. How did so many species get created across so few barriers? The mystery of the Coral Triangle continues.

The paper arises from a collaborative network called the Diversity of the Indo-Pacific Network (DIPnet), which is co-founded and led by Dr. Crandall. The goal of the network is to foster international collaboration for research on ecology and evolution in the Indo-Pacific.