Encyclopedia of Life Blog

  By Joshua Drew, EOL/Field Museum PostDoc

Recently I received a message from a collaborator, Dr. Gerry Allen of the Western Australian Museum.  Gerry had written me because he thought he had discovered a new species of coral reef fish and wanted me to do a genetic analysis to help determine if this species was really distinct from other fish. If it was, we also wanted to determine how it fit into the larger tree of life.  Part of my research here at EOL and the Field Museum is not only to describe new species, but also to figure out why and how one species becomes multiple species. This fish looked like a great opportunity to do just that. 

 The particular fish that Gerry had sent me was called Chrysiptera rex and came from the Philippines, which is in the mega-diverse region of the world called the Coral Triangle. I was particularly anxious to look at this case because, while we know that the Coral Triangle is the richest area of marine biodiversity, we do not understand why. I hoped this case might shed some light onto the subject.

 In order to do a proper description we needed to compare our new species with the original.  To do this, we obtained additional samples from Japan, where the species was originally described. These original specimens are called the type locality. Additionally, we knew that this species had significant variation in its color patterns, so with the help of another collaborator, Dr. Mark Erdmann of Conservation International, we collected samples of a different color variety, found in Indonesia.

 When the genetic analysis was done we noticed that the samples grouped into three distinct clusters, one from Taiwan, one from the Philippines and one from Indonesia.  This genetic data, combined with the differences in coloration led us to believe that this fish, which was previously thought to be a single widespread species, was actually a complex mosaic of genetically distinct groups, several of which may be new species.

 Now back to the question of why the Coral Triangle is so diverse – to understand why it is important to understand a little of the geology of the area.  During the ice age, the sea level in this part of the world was up to 200 meters lower.  While today the Coral Triangle is an area of scattered islands and numerous coral reefs, during periods of low sea levels much more land was exposed and those islands were actually mountaintops. 

For marine species during this time there was much less habitat. Essentially, what is currently a contiguous seaway was a series of isolated marine lakes and shallow seas 10,000 years ago. What is really interesting about the study we did was that each genetically distinct color morph was found only in one particular area. In fact, each color morph is mainly restricted to the area covered by those shallow seas.

 What we think happened was that approximately 25,000 years ago, a single species of fish was forced to migrate into several shallow seas as the water level dropped.  Once isolated in these shallow seas, the process of evolution sped up; colors changed and different genes became fixed.  By the time waters rose and the fish were able to move around freely, they had been sequestered for so long that they had become different species.  This process, called vicarance, has been hypothesized as one of the major reasons the Coral Triangle is so diverse. While this is certainly not the only method by which species are created, our example is a clear demonstration of how Earth history and biological history intertwine to create new biodiversity.

 Despite the fact that this project was initially focused on describing new species, throughout our research we were able to take a look into some of the processes that have helped make the Earth such a rich and vibrant place to explore.

This entry was posted on Thursday, February 4th, 2010 at 3:02 pm and is filed under Biodiversity Synthesis Group. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.