Christmas Island is alive with crabs. The 52-square-mile island, located roughly 270 miles from the Indonesian island of Java, is home to the Christmas Island red crab. Every year, millions upon millions of these land crabs click-clack across the jungle floor on a journey to spawn near the ocean. The scarlet spectacle is the stuff of breathtaking wildlife documentaries, but it’s just a taste of the island’s biodiversity.
“A lot of people call it the Galapagos of the Indian Ocean, just because it’s so biologically interesting,” said Victoria Morgan, a Population Biology Ph.D. student. “You’ll go into the forest and it’ll just be scuttling with crabs, especially after the rains. It’s just so alive and rich and vibrant and lush and wild in a way that I hadn’t experienced before.”
In summer 2017, Morgan traveled to Christmas Island on a fieldwork expedition. She was fascinated by the breadth of the island’s land crab species.
“There are more than 24 species of land crabs that live on this really tiny island and a lot of the species are endemic, so they’re found on Christmas Island and nowhere else in the world,” said Morgan. “Some only come out of the water for short bursts of time and some live full-time on land,rarely see the sea, and only subsist on dew drops and puddles.”
Morgan thought that maybe the crabs’ genetics held clues to their ability to adapt to land, a biological trait known as terrestriality. For one month in 2017, she spent her days traversing the island’s jungles and collecting crabs from three different species: the Christmas Island red crab (Gecarcoidea natalis), the Christmas Island blue crab (Discoplax celeste) and its sister species, the orange-legged crab (Discoplax magna).
She then exposed the crabs to different environmental conditions and collected tissue samples, which she shipped back to the lab of Prof. Richard Grosberg, Distinguished Professor of Evolution and Ecology.
“Vicky’s work centers on understanding at the deepest mechanistic levels the evolution of the critical genetic, physiological and morphological innovations that allowed marine arthropods to colonize terrestrial environments, and eventually diversify into the millions of species of insects and other arthropods that now inhabit the earth,” said Grosberg.
In the Grosberg Lab, Morgan could investigate the crabs’ transcriptomes, which she called “a library of all the genes that an animal is expressing at any one time.”
“If you think back to the beginning of life on Earth, all life started in the oceans but now most of our macroscopic species actually live on land, meaning that at some point their ancestors had to leave the ocean and come up onto land,” said Morgan. “It’s a really important transition not only just for crabs but for our history as well. How did our fishy ancestor leave the ocean to come up onto land?”
Biology to take your breath away
For Morgan, the ocean was always a constant. Raised in Miami, Fla. with her siblings by a single mother, Morgan and her family moved around a lot during her childhood. In her application to the National Science Foundation’s Graduate Research Fellowship Program, Morgan recounted attending five different elementary schools and wrote that in her life “stability was the stuff of fairy tales.” But she could always count on trips to the beach and the local aquarium.
“[My mom] did whatever she could to just get us out in nature and she often took us to the library to learn about the world around us,” said Morgan. “I feel like her putting us in those circumstances really made me fall in love with nature.”
Morgan knew she wanted to be a marine biologist. She enrolled in Cornell University, trading warm Miami beaches for the cold Ithaca, N.Y. Finger Lakes valley. Despite the paradoxical terrain shift, she found opportunities to indulge her marine fascination. She spent the summer following her freshman year in Woods Hole, Mass. interning at the Marine Biological Laboratory’s Ecosystems Center, where she learned biological and physical oceanography from leading experts.
But Morgan’s most formative undergraduate experience happened in Indonesia. Working with UCLA, the Smithsonian National Museum of Natural History, and the Indonesian Biodiversity Research Center, she participated in an effort to map and catalogue the biodiversity of the Coral Triangle, an area in the Pacific Ocean teeming with marine life.
In order to help, Morgan learned how to scuba dive during the trip. Her first dive was on a reef that had swallowed up an old shipwreck off the coast of Tulamben in Bali.
It was “this wooden structure that just erupted with life and beauty, with corals and sponges and clams and everything just coming out of every crevice,” she said. “I think I ran out of air in my tank really fast because I was just so excited.”
Reflecting on the experience today, Morgan can still conjure that sense of awe she felt beneath the waves. “It just blows my mind.”
Crawling with curiosity
The coast called again for Morgan after she graduated from Cornell. She moved to San Diego and worked for the Scripps Institution of Oceanography as a laboratory manager for Assistant Professor Jennifer Taylor. It was in Taylor’s lab that Morgan was introduced to land crabs as a model organism.
“Jennifer Taylor was really interested in how the land crab body changes to deal with the stresses of it being on land,” said Morgan. “Biomechanically, how do they bear the weight of their body without the water buoying them up?”
Morgan’s intrigue grew. She learned some crabs have organs in their legs that sense vibrations in the ground.
“We were just exploring all these cool things about land crabs using biomechanics,” she said. “That experience sort of led to the development of my project on the genomics of land crabs.”
Morgan heard about the UC Davis Population Biology Graduate Group and applied to the program. She found a conducive research environment in Grosberg’s lab, where her colleagues work with different marine animals like anemones, sea slugs, and sea urchins to understand the genetics of adaptation.
“It just seemed like a really good fit for me because we’re all asking the same sorts of questions using similar tools but in different systems,” she said.
A crabby look at our origin story on land
Today, Morgan is still analyzing the tissue samples she collected on Christmas Island in 2017. She’s extracting RNA from the samples and analyzing their transcriptomes, which can vary from sample to sample.
“If an animal is in a resting state and it’s not stressed, it has a certain transcriptome, but when it gets stressed out, let’s say it gets dehydrated or it’s really hot, there are some genes that get turned on or off to help them deal with that new challenge,” said Morgan. “By looking at how these genes are regulated— turned on and off—as they’re dealing with stressors, you can get some idea about which genes are helpful for them dealing with certain challenges that are unique to a life on land.”
Morgan’s threes crab species of interest showcase different degrees of terrestriality, with Gecarcoidea natalis being the most terrestrial of the three crab species, and D. magna coming in a close second. “My idea is to compare the transcriptomes of these species to look for genes that seem to be important to helping them adapt to land,” she said.
“Although I’ve worked with Vicky for just over three years, it is absolutely clear that she is one of those all-too-rare students with the intelligence, talent, focus and energy to revolutionize an emerging discipline that examines the genetic changes underlying one of the most important shifts in the history of life on this planet,” said Grosberg.
While her focus is crabs, Morgan’s research could provide clues that reveal broader trends of terrestriality across all species.
According to Morgan, crabs are advantageous because they’ve made this jump from water to land multiple times over the course of their evolution. “It’s about the crabs,” she said. “But it’s also about the beginnings of terrestrial life on Earth.”