Primates indispensable for regeneration of tropical forests

Moustached tamarins (Saguinus mystax) contribute crucially to the seed dispersal of the neotropical tree Parkia panurensis. Credit: Julia Diegmann

Primatologist and plant geneticists have studied the dispersal of tree seeds by New World primates.

Primates can influence seed dispersal and spatial genetic kinship structure of plants that serve as their food source. This is the result of a cooperation project of behavioral ecologist Eckhard W. Heymann from the German Primate Center (DPZ) with plant geneticists Birgit Ziegenhagen and Ronald Bialozyt from the Philipps-University Marburg. This study was funded by the German Research Foundation.

At the DPZ-field station Estación Biológica Quebrada Blanco in the Peruvian Amazonian lowlands, scientists studied how feeding, sleeping, and ranging habits of two species of New World monkeys affect the dispersal of the neotropical legume tree Parkia panurensis. For this, the researchers observed a group of Brown-mantled tamarins (Saguinus nigrifrons) and Moustached tamarins (Saguinus mystax), who jointly moved through home ranges in search of edible plants which included Parkia trees.

Fruits from these trees are pods that contain 16 to 23 seeds, each of which is surrounded by edible gum. The monkeys feed on the gum content of the pods and at the same time swallow the Parkia seeds which are later defecated intact in a different area.

During behavioral observations, researchers recorded the food intake of tamarins as well as the location of the Parkia trees that they visited. In addition, they collected faecal samples of the tamarins that contained seeds. "With the help of genetic analyses of the DNA found in the seed coat, which is of maternal origin, we could make an exact assignment of the corresponding "mother tree" for the seeds," says Eckhard W. Heymann from the DPZ. "This allowed us to determine how far Parkia seeds were dispersed by the monkeys."

In order to analyze the effect of seed dispersal by monkeys on a spatial genetic level, the scientists examined three different developmental stages of the trees. In addition to the seeds that contain the plant embryo, they collected leaves from young and mature Parkia trees in the home range of tamarins. "With the help of analysis from microsatellites, short repeated DNA sequences, we were able to identify genetic similarities of individual trees," says Heymann.

The analysis of the spatial genetic structure of the Parkia population revealed a significant genetic relationship of the plant embryos and young trees within a radius of 300 meters, which coincides with the distance within which most seeds are dispersed by the tamarins. For mature trees, the relationship was reduced to a radius of only up to 100 meters.

"In tropical rain forests, the seeds of 80 to 90 percent of trees and lianas are dispersed by animals. In addition to primates, birds and bats are the major animal groups that are responsible for seed dispersal," says behavioral ecologist Heymann. "For the plants, transport of their seeds is extremely important. As sedentary organisms, this is the only way that their offspring -- the embryos contained in the seeds -- can reach appropriate sites for germination and growth. Furthermore, this reduces the density-dependent mortality which occurs when the seeds fall under the mother plants," says Eckhard W. Heymann. Fruit-eating primates such as tamarins are therefore invaluable to the natural regeneration and diversity of ecosystems in which they live.

Source: German Primate Center

No 'bird brains'? Crows exhibit advanced relational thinking, study suggests

Study finds crows spontaneously solve higher-order relational-matching tasks. Credit: Photo courtesy of Lomonosov Moscow University.

Crows have long been heralded for their high intelligence -- they can remember faces, use tools and communicate in sophisticated ways.

But a newly published study finds crows also have the brain power to solve higher-order, relational-matching tasks, and they can do so spontaneously. That means crows join humans, apes and monkeys in exhibiting advanced relational thinking, according to the research.

Russian researcher Anna Smirnova studies a crow making the correct selection during a relational matching trial.

"What the crows have done is a phenomenal feat," says Ed Wasserman, a psychology professor at the University of Iowa and corresponding author of the study. "That's the marvel of the results. It's been done before with apes and monkeys, but now we're dealing with a bird; but not just any bird, a bird with a brain as special to birds as the brain of an apes is special to mammals."

"Crows Spontaneously Exhibit Analogical Reasoning," which was published December 18 in Current Biology, was written by Wasserman and Anna Smirnova, Zoya Zorina and Tanya Obozova, researchers with the Department of Biology at Lomonosov Moscow State University in Moscow, Russia, where the study was conducted.

Wasserman said the Russian researchers have studied bird species for decades and that a main theme of their work is cognition. He credits his counterparts with a thoughtful and well-planned study.

"This was a very artful experiment," Wasserman says. "I was just bowled over by how innovative it was."

The study involved two hooded crows that were at least 2 years old. First, the birds were trained and tested to identify items by color, shape and number of single samples.

Here is how it worked: the birds were placed into a wire mesh cage into which a plastic tray containing three small cups was occasionally inserted. The sample cup in the middle was covered with a small card on which was pictured a color, shape or number of items. The other two cups were also covered with cards -- one that matched the sample and one that did not. During this initial training period, the cup with the matching card contained two mealworms; the crows were rewarded with these food items when they chose the matching card, but they received no food when they chose the other card.

Once the crows has been trained on identity matching-to-sample, the researchers moved to the second phase of the experiment. This time, the birds were assessed with relational matching pairs of items.

These relational matching trials were arranged in such a way that neither test pairs precisely matched the sample pair, thereby eliminating control by physical identity. For example, the crows might have to choose two same-sized circles rather than two different-sized circles when the sample card displayed two same-sized squares.

What surprised the researchers was not only that the crows could correctly perform the relational matches, but that they did so spontaneously--without explicit training.

"That is the crux of the discovery," Wasserman says. "Honestly, if it was only by brute force that the crows showed this learning, then it would have been an impressive result. But this feat was spontaneous."

Still the researchers acknowledge that the crows' relational matching behavior did not come without some background knowledge.

"Indeed, we believe that their earlier IMTS (identity matching-to-sample) training is likely to have enabled them to grasp a broadly applicable concept of sameness that could apply to novel two-item samples and test stimuli involving only relational sameness," the researchers wrote. "Just how that remarkable transfer is accomplished represents an intriguing matter for future study."

Anthony Wright, neurobiology and anatomy professor at the University of Texas-Houston Medical School, says the discovery ranks on par with demonstrations of tool use by some birds, including crows.

"Analogical reasoning, matching relations to relations, has been considered to be among the more so-called 'higher order' abstract reasoning processes," he says. "For decades such reasoning has been thought to be limited to humans and some great apes. The apparent spontaneity of this finding makes it all the more remarkable."

Joel Fagot, director of research at the University of Aix-Marseille in France, agrees the results shatter the notion that "sophisticated forms of cognition can only be found in our 'smart' human species. Accumulated evidence suggests that animals can do more than expected."

Wasserman concedes there will be skeptics and hopes the experiment will be repeated with more crows as well as other species. He suspects researchers will have more such surprises in store for science.

"We have always sold animals short," he says. "That human arrogance still permeates contemporary cognitive science."

Source: University of Iowa