Stephen Pratt

Pest control lessons from wasps

dianeb — Wed, 27 Jan 2010 09:09:23 -0700

by Margaret Coulombe

Parasitic wasps kill pest insects, but their existence has been largely overlooked by the public – until now. Four researchers from Arizona State University are among a consortium of 157 scientists (the Nasonia Genome Working Group) led by John Werren, a professor of biology at the University of Rochester, and Stephen Richards at the Genome Sequencing Center at the Baylor College of Medicine, who have sequenced the genomes of three parasitoid wasp species. The genomes reveal many features that could be useful in pest control, medicine and the understanding of genetics and evolution. The study appears in the Jan. 15 issue of Science.

Plaguing pests
Parasitoid wasps females are like “smart bombs” – they seek out specific insect, tick or mite hosts and inject venom and lay their eggs, with the wasp young emerging to devour the host insect. These are traits that make them valuable assets as agents for biological control.

"Parasitic wasps attack and kill pest insects, but many of them are smaller than the head of a pin, so people don't notice them or know of their important role in keeping pest numbers down," Werren said. “There are more than 600,000 species of these amazing critters, and we owe them a lot. If it weren't for parasitoids and other natural enemies, we would be knee-deep in pest insects."

The three genomes sequenced are in the wasp genus Nasonia, which is considered to be the “lab rat” of parasitoid insects. The study’s architects suggest that the genomes could enhance pest control by providing information about which insects a parasitoid will attack, the dietary needs of parasitoids (to assist in economical, large-scale rearing of parasitoids) and identification of parasitoid venoms. Because parasitoid venoms manipulate cell physiology in diverse ways, they may also provide an unexpected source for new drug development.

Genetic toolkit
In ASU’s School of Life Sciences, Nasonia species have been utilized to conduct studies in genetics, epigenetics, male courtship behavior, evolution of speciation and social insect societies by consortium members Juergen Gadau, associate professor and associate dean for graduate studies; Stephen Pratt, assistant professor; Florian Wolschin, assistant research professor; and Joshua Gibson, doctoral student, who also are members of the Social Insect Research Group in ASU’s College of Liberal Arts and Sciences. Gadau was one of eight researchers, including Werren and Richards, who developed the original Nasonia Whitepaper sent to the National Institutes of Health to encourage funding for the sequencing project in 2004.

Like the fruit fly Drosophila, a standard model for genetic studies for decades, Nasonia are small, can be easily grown in a laboratory, and reproduce quickly. However, Nasonia wasps offer an additional feature of interest, as the males have only one set of chromosomes, instead of two sets such as fruit flies and people.

“A single set of chromosomes, which is more commonly found in lower single-celled organisms such as yeast, is a handy genetic tool, particularly for studying how genes interact with each other,” Werren said.

Unlike fruit flies, these wasps also modify their DNA in ways similar to humans and other vertebrates – a process called “methylation,” which plays an important role in regulating how genes are turned on and off during development.

“In human genetics we are trying to understand the genetic basis for quantitative differences between people such as height, drug interactions and susceptibility to disease,” Richards said. “These genome sequences combined with haploid-diploid genetics of Nasonia allow us to cheaply and easily answer these important questions in an insect system, and then follow up any insights in humans.”

The wasps have an additional advantage in that closely related species of Nasonia can be cross-bred, facilitating the identification of genes involved in species’ differences.

"Nasonia is currently the best genomic model system for understanding the genetic architecture of early speciation and complex phenotypes such as behavior,” Gadau said.

Mitochondrial messaging
“Because we have sequenced the genomes of three closely related species, we are able to study what changes have occurred during the divergence of these species from one another,” Werren said. “One of the interesting findings is that DNA of mitochondria, a small organelle that ‘powers’ the cell in organisms as diverse as yeast and people, evolves very fast in Nasonia. Because of this, the genes of the cell’s nucleus that encode proteins for the mitochondria must also evolve quickly to keep up.”

It is these co-adapting gene sets that appear to cause problems in hybrids when the species mate with each other. Gadau’s ASU team is among the research groups delving into these mitochondrial-nuclear gene interactions. Since mitochondria are involved in a number of human diseases, as well as fertility and aging, the rapidly evolving mitochondria of Nasonia and coadapting nuclear genes could be useful research tools to investigate these processes.

“Mitochondrial diseases in humans which have their origin in the malfunction of this interaction are the most frequent genetic disorders in humans,” Gadau said. “What we learn in Nasonia might help us to understand how these diseases work and may lead to cures.”

Another startling discovery is that Nasonia has been picking up and using genes from bacteria and Pox viruses (relatives of the human smallpox virus).

“We don’t yet know what these genes are doing in Nasonia,” Werren said. “But the acquisition of genes from bacteria and viruses could be an important mechanism for evolutionary innovation in animals, and this is a striking potential example.”

Study springboard
A series of companion papers are set to be released, in addition to the Science study. One, published today in Public Library of Science (PLoS) Genetics, reports the first identification of the DNA responsible for a quantitative trait gene in Nasonia, and heralds Nasonia joining the ranks of model genetic systems. Eight more publications, authored by the ASU investigators and their colleagues, will soon follow, to be published in Heredity, Insect Molecular Biology and PLoS.

“Emerging from these genome studies are a lot of opportunities for exploiting Nasonia in topics ranging from pest control to medicine, genetics and evolution,” Werren said.

Ants more rational than humans

dianeb — Thu, 13 Aug 2009 12:26:51 -0600

by Margaret Coulombe

In a study released online on July 22 in the journal Proceedings of the Royal Society: Biological Sciences, researchers at Arizona State University and Princeton University show that ants can accomplish a task more rationally than our multimodal, egg-headed, tool-using, bipedal, opposing-thumbed selves.

This is not the case of humans being “stupider” than ants. Humans and animals simply often make irrational choices when faced with very challenging decisions, note the study’s architects Stephen Pratt and Susan Edwards.

“This paradoxical outcome is based on apparent constraint: most individual ants know of only a single option, and the colony’s collective choice self-organizes from interactions among many poorly-informed ants,” says Pratt, an assistant professor in the School of Life Sciences in ASU’s College of Liberal Arts and Sciences.

The authors’ insights arose from an examination of the process of nest selection in the ant, Temnothorax curvispinosus. These ant colonies live in small cavities, as small as an acorn, and are skillful in finding new places to roost. The challenge before the colony was to “choose” a nest, when offered two options with very similar advantages.

What the authors found is that in collective decision making in ants, the lack of individual options translated into more accurate outcomes by minimizing the chances for individuals to make mistakes. A “wisdom of crowds” approach emerges, Pratt believes.

“Rationality in this case should be thought of as meaning that a decision maker, who is trying to maximize something, should simply be consistent in its preferences.” Pratt says. “For animals trying to maximize their fitness, for example, they should always rank options, whether these are food sources, mates, or nest sites, according to their fitness contribution.”

“Which means that it would be irrational to prefer choice ‘A’ to ‘B’ on Tuesday and then to prefer ‘B’ to ‘A’ on Wednesday, if the fitness returns of the two options have not changed.”

“Typically we think having many individual options, strategies and approaches are beneficial,” Pratt adds, “but irrational errors are more likely to arise when individuals make direct comparisons among options.”

Studies of how or why irrationality arises can give insight into cognitive mechanisms and constraints, as well as how collective decision making occurs. Insights such as Pratt’s and Edward’s could also translate into new approaches in the development of artificial intelligence.

“A key idea in collective robotics is that the individual robots can be relatively simple and unsophisticated, but you can still get a complex, intelligent result out of the whole group,” says Pratt. “The ability to function without complex central control is really desirable in an artificial system and the idea that limitations at the individual level can actually help at the group level is potentially very useful.” Pratt is a member of Heterogeneous Unmanned Networked Team (HUNT), a project funded by the Office of Naval Research (ONR) to enable to development of bio-inspired solutions to engineering problems.

What do these findings potentially say about understanding human social systems?

“It is hard to say. But it’s at least worth entertaining the possibility that some strategic limitation on individual knowledge could improve the performance of a large and complex group that is trying to accomplish something collectively,” Pratt says.

This study was supported in part by a grant from the Pew Charitable Trusts. For media inquiries, contact Margaret Coulombe, School of Life Sciences, margaret.coulombe@asu.edu, 480.727.8934.

‘HUNTing’ skills lead to bio-inspired solutions

dianeb — Wed, 06 May 2009 12:50:17 -0600

by Margaret Coulombe

Hungry lions on the savanna or porpoises in the sea work as teams to catch prey. Schooling fish dart in unison to escape a predator. Even “Meerkat Manor” depicts complex groups with clearly defined duties. What do these complex activities all have in common? For Stephen Pratt, assistant professor in Arizona State University’s School of Life Sciences, they represent different aspects of the hunt, but in ways that most people could barely begin to imagine.

ASU and Pratt hosted engineers, computer scientists, biologists and social scientists at a recent workshop—Heterogeneous Unmanned Networked Teams (HUNT)—that focused on developing bio-inspired solutions to engineering problems.

The workshop is part of a five-year project of the same name funded by the Office of Naval Research (ONR). The effort is led by 10 engineers and computer scientists from the University of Pennsylvania, University of California, Berkeley, and the Georgia Institute of Technology, in addition to ASU’s Pratt, who is the sole biologist in the group.

Why would naval research and other engineering research institutions look to nature for bio-inspired solutions? “Robustness, scalability, and the ability to function without complex central control are things that are really desirable in an artificial system,” Pratt points out. “All kinds of natural systems have them; from the movement of fish in schools and birds in flocks to social insects building specific, complex nest structures.”

“One of ONR’s long-term grand challenges is how to deal with the interaction of large numbers of fairly sophisticated autonomous vehicles—flying drones, vehicles underwater or on land,” Pratt explains. “All kinds of increasingly diverse and complex artificial systems will have to interact with each other and with humans.”

Military applications present particular challenges because of the large numbers of people, machines and unpredictable situations.

Photo by Karl Hedrick/Center for the Collaborative Control of Unmanned Vehicles

However, the engineering product is more likely to be a focus towards the end of the project, Pratt says. In the meantime, the workshop was all about thinking outside the box and creating an atmosphere for a rapid exchange of ideas.

Some of the more than 20 consultants attached to the project, spanning the fields of engineering, social sciences and biology, joined the project leaders at the workshop held March 9-10 at ASU. The goal was to pair up particular complimentary problems from biology and engineering.

For example, James Rehg and Tucker Balch of Georgia Tech are using their expertise to design automated computer vision systems to track films of animals in nature—namely, lion teams hunting—and be able to recognize and classify the behavior of each individual. This will enable African savanna ecologist Craig Parker of the University of Minnesota to get large quantities of data efficiently and empower him to ask questions about the coordination of group behavior over long time periods. Previously, this could only be done by painstakingly analyzing months of footage.

“Rehg, Balch and their research groups are really interested in doing this kind of thing—partly because it helps them study their own artificial collective systems by testing the ability of their system to analyze complex biological data,” Pratt says with a knowing smile. “Also, they like the idea of a really challenging computer vision problem; they get to do something new and different with our data.”

Another pair of researchers, Lori Marino of Emory University, an expert on porpoise teamwork, and Magnus Egerstedt of Georgia Tech, a robotics engineer, are delving into what porpoises do when they encircle prey. Porpoises are of particular interest because they are very good at switching team strategies quickly to meet changing circumstances. Egerstedt hopes to develop control algorithms for artificial systems that can effect the same sorts of rapid functional changes. Eventually these algorithms could be used to control groups of underwater or fleets of flying vehicles.

Pratt’s first taste of this “HUNTsian” type of collaborative endeavor came when he was asked to be a part of SWARMS (Scalable sWarms of Autonomous Robots and Mobile Sensors) an invitation based on his innovative research on collective decision making in acorn ants. Pratt clarifies, “SWARMS was directed at what could be learned from natural systems with many animals; where all the individuals are simple—maybe even a little bit stupid. Imagine a swarm of army ants.”

The naval research project steps up the complexity in problem-solving, focusing on smaller groups of organisms, each with a unique position and attribute. “The HUNT project leaders originally thought exclusively about vertebrates,” Pratt says. “But, I convinced them that ants carry out tasks which are much more sophisticated than they had initially thought.”

Picture this, Pratt says: “A single ant finds a tasty fig piece (left by a scientist) in an open desert patch. Alone, she cannot rescue the piece from a larger competitor; but wait, five sisters arrive, each picks up a side and together they negotiate this morsel—many times larger than themselves—over a tough terrain and back to the nest. Dinner is served. In order to accomplish this task, the ants must work as a team, each one with a unique job: guiding, spinning or doing the heavy lifting.”

Pratt teams up with Vijay Kumar, with the University of Pennsylvania, to address this issue of collective retrieval: a big problem in collective robotics. “I’m getting the biological data; they’re devising tools that I would never be able to make. For example, force sensors that we try to get the ants to carry with them,” says Pratt.

“What I take away is a much more detailed description and measurement of what these insects are actually doing. What they get is inspiration for programming their robots to do the parallel task,” he says.

In some ways, the HUNT teams are analogous to their project, with each member playing a unique and essential role. Alone, each individual might be slow or lack efficiency in carrying the proverbial fig, but by combining their distinctive expertise, together they make one extraordinary, bio-inspired problem-solving team.

Media Contact:
Margaret Coulombe
(480) 727-8934
margaret.coulombe@asu.edu