University professor helps answer long debated question

Photo credit: Warrenski/Creative Commons

Edwive Seme/Staff Writer

Who came first, the chicken or the egg? This is one of the many mysteries of the world. However, Assistant Professor in the Marine Sciences Program Heather Bracken-Grissom led a research group that has helped answer one of the most debated questions in evolutionary biology about the relationship between Hermit crabs and King crabs after nearly 30 years. Which evolved from which? The group consisted of experts from George Washington University, the Smithsonian National Museum of Natural History and the Australian Museum.

Bracken-Grissom has always been interested in the study of sea organisms, especially arthropod crustaceans; the organisms within the group are each unique and have a high degree of body shape variation no matter how close they are.

“I was really intrigued by the diversity of the group and the variation in body shape,” said Bracken-Grissom.

She was a perfect fit for this group of researchers given her passion for crustaceans and the fact that she has been studying the evolutionary relationships of organisms for many years. Her involvement in the project was partly driven by her curiosity.

“I thought this was a really interesting case because we knew these crabs were relatives, but we just didn’t know how close of relatives they were. We have these two different forms of crabs and I wanted to know more about how they’re related to each other,” said Bracken-Grissom.

Apart from belonging to the same infraorder, the Anomura, the relationship between Hermit crabs and King crabs isn’t too obvious because the two organisms have different physical characteristics, with only minor similarities. This infraorder contains more than 2,500 species who have all evolved differently to adapt to their ecology. Hermit crabs tend to be smaller and have a shell for protection, while King crabs are considered one of the largest crustaceans and instead of having a shell, they use their exoskeleton for protection.

One of the ways they established that the two crabs might be related was by looking at physical characteristics to find clues that might suggest it.

“Both of them are united because they have a reduced sixth leg,” said Bracken-Grissom.  “Even though they look very different, hermit crabs have an asymmetrical abdomen. It’s curved to help them attach to the shell, and there is some evidence of this asymmetrical abdomen in female King crabs.”

Knowing that there might be a link between the two was just the beginning. In order to prove their hypotheses, they needed more than just a couple minor physical similarities. After collecting many species, they had to study their genetic makeup, which wouldn’t have been as easy three decades ago.

“Over the years, scientists have put more time into working on resources for these kind of studies,” said Lensley St. Felix, senior biology major. “It’s important to study other organisms because of their relationships with each other and with us humans, and the more scientists realized that, the more important it became to develop technology to ease these studies.”

Using all the resources available, they were able to continue their research and find what was the exact relationship between the two crabs.

“We came to the conclusion based on DNA sequencing to infer evolutionary relationships. We used molecular data to study relationships, examined morphological characters and did in-depth analysis of their physical character, their larvae and development,” said Bracken-Grissom. “All of that evidence put together allowed us to come to the conclusion.”

Bracken-Grissom and the group were able to show that Hermit crabs evolved into King crabs.

Knowing how organisms are related to each other helps see patterns of diversity in organisms and it can tell you more about the ecology the organism is in and how it affects it.

“It’s important to know about the Hermit and King crabs because they’re economically important,” said Bracken-Grissom.

Hermit crabs are very essential to the aquarium trade, and King crabs are important for human consumption; they are a main seafood dish at many restaurants. According to Bracken-Grissom, studying these organisms gives insight about biodiversity. “[You get to] know something about their ecology and life history.”

The study lasted more than 30 years, and all the years were spent collecting organisms from the two species to study and compare. “The hardest part was the decades it took to collect all these organisms. Many of the specimens were rare and difficult to find,” said Bracken-Grissom. “It takes a really long time to build up the inventory that we need.”

Their research was published under the title, “A comprehensive and integrative reconstruction of evolutionary history for Anomura (Crustacea: Decapoda),” on BMC Evolutionary Biology, a peer reviewed journal consisting mainly of articles about molecular and non-molecular evolution of organisms.

It doesn’t stop there for Bracken-Grissom, however. She wants to continue studying the evolutionary relationships of different organisms and she will most likely focus on invertebrates.

 edwive.seme@fiusm.com