Collective behavior could help animals survive a changing environment

Princeton researchers found that collective intelligence is vital to certain animals’ ability to evaluate and respond to their environment. Conducted on golden shiners, the research demonstrated that social animals such as schooling fish rely heavily on grouping to effectively navigate their environment. (Image by Sean Fogarty)

Princeton researchers found that collective intelligence is vital to certain animals’ ability to evaluate and respond to their environment. Conducted on golden shiners, the research demonstrated that social animals such as schooling fish rely heavily on grouping to effectively navigate their environment. (Image by Sean Fogarty)

For social animals such as schooling fish, the loss of their numbers to human activity could eventually threaten entire populations, according to a finding that such animals rely heavily on grouping to effectively navigate their environment.

Princeton researchers have found that collective intelligence is vital to certain animals’ ability to evaluate and respond to their environment. Conducted on fish, the research demonstrated that small groups and individuals become disoriented in complex, changing environments. However, as group size is increased, the fish suddenly became highly responsive to their surroundings.

These results should prompt a close examination of how endangered group or herd animals are preserved and managed, said Iain Couzin, a professor of ecology and evolutionary biology. If wild animals depend on collective intelligence for migration, breeding and locating essential resources, they could be imperiled by any activity that diminishes or divides the group, such as overhunting and habitat loss, he explained.

“Processes that increase group fragmentation or reduce population density may initially appear to have little influence, yet a further reduction in group size may suddenly and dramatically impact the capacity of a species to respond effectively to their environment,” Couzin said. “If the mechanism we observed is found to be widespread, then we need to be aware of tipping points that could result in the sudden collapse of migratory species.”

The work is among the first to experimentally explain the extent to which collective intelligence improves awareness of complex environments, the researchers write. As it’s understood, a group of individuals gain an advantage by pooling imperfect estimates with those around them, which more or less “averages” single experiences into surprisingly accurate common knowledge.

With their work, Couzin and his co-authors uncovered an additional layer to understanding collective intelligence. The conventional view assumes that individual group members have some level of knowledge albeit incomplete. Yet the Princeton researchers found that in some cases individuals have no ability to estimate how a problem needs to be solved, while the group as a whole can find a solution through their social interactions. Moreover, they found that the more numerous the neighbors, the richer the individual — and thus group — knowledge is.

These findings correlate with recent research showing that collective intelligence — even in humans — can rely less on the intelligence of each group member than on the effectiveness of their communal interaction, Couzin said. In humans, research suggests that such cooperation would take the form of open and equal communication among individuals regardless of their respective smarts, he said.

The researchers placed fish known as golden shiners in experimental tanks in groups as low as one and as high as 256. The tanks featured a moving light field that was bright on the outer edges and tapered into a dark center. To reflect the changing nature of natural environments, they also incorporated small patches of darkness that moved around randomly. Prolific schoolers and enthusiasts of darkness, the golden shiners would pursue the shaded areas as the researchers recorded their movement using computer vision software. Although the fish sought the shade regardless of group size, their capability to do so increased dramatically once groups spanned a large enough area.

The researchers then tracked the motion of individual fish to gauge the role of social influence on their movement. They found that individuals adjusted their speed according to local light level by moving faster in more brightly lit areas, but without social influence the fish did not necessarily turn toward the darker regions. Groups, however, readily swam to dark areas and were able to track those preferred regions as they moved.

This collective sensing emerged due to the coherent nature of social interactions, the authors report. As one side of the group slowed and turned toward the shaded area, the other members did as well. Also, slowing down increased density and resulted in darker regions becoming more attractive to these social animals.

Couzin worked with lead authors Andrew Berdahl, a Princeton graduate student, and postdoctoral fellow Colin Torney, both in Couzin’s lab, as well as with former lab members Christos Ioannou and Jolyon Faria, who are now at the University of Bristol and the University of Oxford, respectively. The work was published in the Jan. 31, 2013, issue of Science, and was supported in part by grants from the National Science Foundation, the U.S. Office of Naval Research, the U.S. Army Research Office and the Natural Sciences and Engineering Research Council of Canada.

–By Morgan Kelly

Far from random, evolution follows a predictable pattern

Large milkweed bugs

Large milkweed bugs (above) feed on plants that produce a class of steroid-like cardiotoxins called cardenolides as a natural defense. The ability to eat these plants has evolved separately but in a predictable manner in several different orders of insects, including butterflies and moths (Lepidoptera); beetles and weevils (Coleoptera); and aphids, bed bugs, milkweed bugs and other sucking insects (Hemiptera). (Photo courtesy of Peter Andolfatto)

Evolution, often perceived as a series of random changes, might in fact be driven by a simple and repeated genetic solution to an environmental pressure, according to new research.

“Is evolution predictable? To a surprising extent the answer is yes,” according to Peter Andolfatto, an assistant professor in Princeton’s Department of Ecology and Evolutionary Biology and the Lewis-Sigler Institute for Integrative Genomics.

Andolfatto’s team has found that knowing how external conditions affect the proteins encoded by a species’ genes could allow researchers to determine a predictable evolutionary pattern driven by outside factors. Scientists could then pinpoint how the diversity of adaptations seen in the natural world developed even in distantly related animals.

The researchers carried out a survey of DNA sequences from 29 distantly related insect species, the largest sample of organisms yet examined for a single evolutionary trait. Fourteen of these species have evolved a nearly identical characteristic due to one external influence — they feed on plants that produce cardenolides, a class of steroid-like cardiotoxins that are a natural defense for plants such as milkweed and dogbane.

Though separated by 300 million years of evolution, these diverse insects — which include beetles, butterflies and aphids — experienced changes to a key protein called sodium-potassium adenosine triphosphatase, or the sodium-potassium pump, which regulates a cell’s crucial sodium-to-potassium ratio.

The protein in these insects eventually evolved a resistance to cardenolides, which usually cripple the protein’s ability to “pump” potassium into cells and excess sodium out.

To make this discovery, Andolfatto and his co-authors first sequenced and assembled all the expressed genes in the studied species. They used these sequences to predict how the sodium-potassium pump would be encoded in each of the species’ genes based on cardenolide exposure.

The researchers found that the genes of cardenolide-resistant insects incorporated various mutations that allowed them to resist the toxin. During the evolutionary timeframe examined, the sodium-potassium pump of insects feeding on dogbane and milkweed underwent 33 mutations at sites known to affect sensitivity to cardenolides. These mutations often involved similar or identical amino-acid changes that reduced susceptibility to the toxin. On the other hand, the sodium-potassium pump mutated just once in insects that do not feed on these plants.

Jianzhi Zhang, a University of Michigan professor of ecology and evolutionary biology, said that the Princeton-based study shows that certain traits have a limited number of molecular mechanisms, and that numerous, distinct species can share the few mechanisms there are. “The finding of parallel evolution in not two, but numerous herbivorous insects increases the significance of the study because such frequent parallelism is extremely unlikely to have happened simply by chance,” said Zhang, who is familiar with the study but had no role in it.

Andolfatto worked with lead author and Postdoctoral Research Associate Ying Zhen, and graduate students Matthew Aardema and Molly Schumer, all from Princeton’s ecology and evolutionary biology department, as well as Edgar Medina, a biological sciences graduate student at the University of the Andes in Colombia. The research was supported by grants from the Centre for Genetic Engineering and Biotechnology, the National Science Foundation and the National Institutes of Health and was published in the Sept. 28, 2012, issue of Science.
–By Morgan Kelly

Wildlife and Cows can be partners, not enemies, in search for food

Cows

Image courtesy of Dan Rubenstein

Princeton researchers are leading an effort to put to pasture the long-held convention of cattle ranching that wild animals compete with cows for food. Two studies offer the first experimental evidence that allowing cattle to graze on the same land as wild animals can result in healthier, meatier bovines by enhancing the cows’ diet. The findings suggest a new approach to raising cattle that could help spare wildlife from encroaching ranches, and produce more market-ready cows in less time.

The reports stem from large-scale studies conducted in Kenya wherein cows shared grazing land with donkeys in one study and, for the other, grazed with a variety of wild herbivorous animals, including zebras, buffalo and elephants. The lead author on both papers was Wilfred Odadi, a postdoctoral research associate in the lab of Daniel Rubenstein, the Class of 1877 Professor of Zoology and chair of Princeton’s Department of Ecology and Evolutionary Biology.

Researchers

Wilfred Odadi (rear, in white hat), a postdoctoral research associate in Dan Rubenstein’s lab based at Kenya’s Mpala Research Center, was lead author on both Princeton papers. The project stemmed from the senior thesis of Meha Jain (front left), who earned her bachelor’s degree from Princeton in 2007.

Rubenstein and Odadi reported in the journal Evolutionary Ecology Research in August 2011 that cattle paired with donkeys gained 60 percent more weight than those left to graze only with other cows. The researchers proposed that the donkeys — which were chosen as tamer stand-ins for zebras and other wild horses — ate the rough upper-portion of grass that cows have difficulty digesting, leaving behind the lush lower vegetation on which cattle thrive.

In a second study, Odadi and his co-authors reported in the journal Science in September 2011 that other grazers, especially zebras, did remove the dead-stem grass layer and that cattle indeed seemed to benefit from sharing land with wild animals. Cows in mixed grazing pastures took in a more nutritious diet and experienced greater daily weight gain — but this effect was limited to the wet season. Cattle competed with wild species for food in the dry months.

Nonetheless, the studies help counter an enduring perception that wildlife is an inherent threat to the food supply of livestock, Rubenstein explained. These results could prove crucial to preserving animals that are increasingly threatened as the human demand for food drives the expansion of land used to raise cattle. Zebras and wild horses are especially vulnerable to the spread of pastures because of their abundance.

“These experiments suggest that in certain cases cattle can actually experience considerable advantages in terms of growth when allowed to graze with other species,” Rubenstein said. Odadi has presented his findings to local farmers, but understands the difficulty of overturning long-held views about the livestock/wildlife competition. “The farmers we have presented these findings to are generally surprised that zebras and other wildlife can facilitate cattle,” Odadi said.

Rubenstein conducted the experiment reported in Evolutionary Ecology Research with Odadi, who is based at Kenya’s Mpala Research Center — with which Princeton is a partner — and co-author Meha Jain, who earned her bachelor’s degree from Princeton in 2007 and whose senior thesis was the basis of the project. The work was supported by grants from the National Science Foundation (NSF), the Keller Family Trust and Wageningen University in the Netherlands.

For the second study, Odadi worked with ecology professor Truman Young of the University of California-Davis; Moses Karachi of Egerton University in Kenya; and Shaukat Abdulrazak, chief executive officer of the National Council for Science and Technology in Kenya. The study was supported by grants from the NSF, the National Geographic Society, the U.S. Fish and Wildlife Service, and the International Foundation for Science.