Banner image: A colony of fluted bryozoans (Hippodiplosia insculpta) off the coast of California. (Credit: by Ed Bierman via )
Human societies have long depended on the division of labor to thrive鈥攚alk into any town, and you can probably find bakers baking bread, truck drivers driving that bread to market and grocers selling it.
A new fossil study from paleobiologists at the 抖阴旅行射听Museum of Natural History offers insight on how some colony-forming animals, like ants or bees, may have evolved their own system for divvying up work millions of years ago. The team鈥檚 findings suggest that when colonies share resources like food efficiently, it can free up some individuals to evolve never-before-seen traits.
A fossil bryozoan colony smaller than a grain of rice seen under the听microscope. (Credit: Sarah Leventhal)
The research taps into a universal drive for both tiny animals and human beings, said Sarah Leventhal, lead author of the in the journal PNAS Nexus.
鈥淚f we look around us, this division of labor exists almost everywhere,鈥� said Leventhal, who earned her PhD in geological sciences from 抖阴旅行射 Boulder this year. 鈥淏ut before this study, it hadn鈥檛 really been investigated using the fossil record.鈥�
Floating time capsules
The study casts a spotlight on a little-known group of aquatic animals called bryozoans. They tend to be small and sometimes look like globs of mucus floating in the water. They also grow in thin sheets over surfaces like corals and piers. They鈥檙e not really individuals: Bryozoans are made up of dozens to thousands of microscopic 鈥渮ooids鈥� that live together in a single, cohesive colony.
In the new research, the team assembled fossils from a short but critical period in the evolution of bryozoans belonging to the genus Wilbertopora鈥攔oughly from 103 to 96 million years ago, or during the reign of dinosaurs.听
The researchers discovered that during that window, some zooids in bryozoan colonies began to lose the ability to feed themselves. But they didn鈥檛 die off. Instead, other members of the colony likely shared resources to keep those evolutionary oddballs alive. In the process, these new zooids were able to evolve a wide range of never-before-seen abilities.听
鈥淒espite this loss in feeding, those non-feeding members could still be supported by the colony without costing it much,鈥� Leventhal said. 鈥淭his gave them the freedom to explore all those different functions.鈥�
Fossil听bryozoan colony as seen under the microscope. Each of the oval shapes was once an individual zooid. (Credit: Sarah Leventhal)
Specialized workers
Leventhal noted that, among modern bryozoans, most zooids in a colony, which are genetically identical, tend to look the same鈥攖hey鈥檙e shaped like tiny shoe boxes with a round hole at the top. But a few strange zooids, known as 鈥渁vicularia,鈥� don鈥檛 fit the mold.听
In some species, for example, avicularia have evolved appendages that look a bit like the head of a flamingo. They use them to poke at animals that get too close to their colonies.
鈥淵ou can find some Caribbean colonies that, to avoid getting buried by sand, use their avicularia to crawl over the sea floor,鈥� Leventhal said.
An 1899 illustration of some of the forms of modern bryozoans. (Credit: )
To date, however, scientists have struggled to explain how such a division of labor could emerge in natural populations. One popular explanation borrows from human economics. In early human societies, the thinking goes, every individual did a little bit of everything: They cooked. They cleaned. They hunted and gathered, and on and on. But over time, some individuals became specialists in one job (say, hunting), while others did something else (say, cooking). In the same way, ancient animals may have evolved distinct jobs by becoming specialists at tasks their ancestors were already doing.
In their new research, Leventhal and her听colleagues decided to put that idea to the test.
The group assembled roughly 120 fossils of bryozoan colonies from the Smithsonian Institution鈥檚 National Museum of Natural History. The Smithsonian鈥檚 Stewart Edie was also a co-author of the new study.
Sharing is caring
Leventhal explained that bryozoans began to evolve avicularia roughly 103 million years ago. But in the blink of an eye鈥攅volutionarily speaking鈥攖he holes at the top of those zooids began to take on shapes and sizes unlike anything seen in their ancestors. (Some, for example, became spatula-shaped, not round). Many of these new zooids also lost the ability to feed.
Put differently, these organisms weren鈥檛 just specializing like the conventional wisdom might suggest. They were becoming something entirely new.听
鈥淚t鈥檚 like, all of a sudden, they discovered these new possibilities, and they just ran with them,鈥� said study co-author Carl Simpson, curator of invertebrate paleontology at the 抖阴旅行射 Museum of Natural History and assistant professor in the Department of Geological Sciences.
To find out how they managed to survive, study co-author Rebecca Morrison, assistant professor of computer science at 抖阴旅行射 Boulder, developed a series of mathematical simulations. They mimicked how nutrients and other resources may have cycled through these ancient bryozoan colonies. The group discovered that normal zooids could easily have collected enough nutrients to sustain their entire colonies, including the non-feeding avicularia. Those avicularia, in turn, may have played a critical role in keeping food moving through the colony鈥檚 digestive system.
The researchers can鈥檛 be sure whether other colony-forming animals, such as ants and bees, underwent similar evolutionary pathways. Simpson, for his part, recently teamed up with a group of archaeologists to study how the division of labor may have emerged in a completely different group of animals: humans.
鈥淲e get together and say, 鈥榃e can鈥檛 believe we鈥檙e studying the same problem,鈥欌�� Simpson said.
