The universe is a tapestry of galaxy congregations and vast voids. In a new study being reported in The Astrophysical Journal, Brent Tully’s team applies the same tools from an earlier study to map the size and shape of an extensive empty region they called the Local Void that borders the Milky Way galaxy. Using the observations of galaxy motions, they infer the distribution of mass responsible for that motion, and construct three-dimensional maps of our local Universe.

Galaxies not only move with the overall expansion of the universe, they also respond to the gravitational tug of their neighbors and regions with a lot of mass. As a consequence, relative to the overall expansion they are moving towards the densest areas and away from regions with little mass — the voids.

Although we live in a cosmic metropolis, back in 1987 Tully and Richard Fisher noted that our Milky Way galaxy is also at the edge of an extensive empty region that they called the Local Void. The existence of the Local Void has been widely accepted, but it remained poorly studied because it lies behind the center of our galaxy and is therefore heavily obscured from our view.

Now, Tully and his team have measured the motions of 18,000 galaxies in the Cosmicflows-3 compendium of galaxy distances, constructing a cosmographic map that highlights the boundary between the collection of matter and the absence of matter that defines the edge of the Local Void. They used the same technique in 2014 to identify the full extent of our home supercluster of over one hundred thousand galaxies, giving it the name Laniakea, meaning “immense heaven” in Hawaiian.

For 30 years, astronomers have been trying to identify why the motions of the Milky Way, our nearest large galaxy neighbor Andromeda, and their smaller neighbors deviate from the overall expansion of the Universe by over 600 km/s (1.3 million mph). The new study shows that roughly half of this motion is generated “locally” from the combination of a pull from the massive nearby Virgo Cluster and our participation in the expansion of the Local Void as it becomes ever emptier.

An 11-minute video demonstrating the shape and extend of these cosmic structures is available online at:

https://vimeo.com/326346346

Interactive visualizations that allow the user to rotate, pan, and zoom maps of the mass distribution can be found at:

https://sketchfab.com/models/f0a44df256aa4faf93391887d66010e2

https://sketchfab.com/models/78885b3d303d4b6e99cfe099b43929fb

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The idea came to lead author Kasim Rafiq after hours with his Land Rover grill-deep in an abandoned warthog burrow. Rafiq, then a Ph.D. candidate at Liverpool John Moores University, had been following the tracks of a one-eared leopard named Pavarotti that he’d been searching for for months.

“Eventually I got out of the hole and spoke with the safari guides who I met on the road nearby, and who were laughing,” says Rafiq, who is about to begin a Fulbright Fellowship to expand the project further at UC Santa Cruz. “They told me that they’d seen Pavarotti earlier that morning. At that point, I really began to appreciate the volume of information that the guides and tourists were collecting and how it was being lost.”

Traditionally, animal population surveys in Africa are done using one of three methods: camera traps, track surveys, and call-in stations. Each has advantages and disadvantages. Camera traps, for example, are particularly useful to understand the variety and densities of species in an area, but they also have an immense up-front cost with no guaranteed lifespan. “For one of my other projects, I had an elephant knock down one of the camera traps, and then lion cubs ran away with the camera. When I collected it, it just had holes in it,” Rafiq says.

To test whether tourist photographs could be used for wildlife surveying, the researchers provided participating tourists with small GPS trackers, originally designed for tracking pet cats. These allowed researchers to later tag the wildlife photographs with location data. The photographs were then filtered not only by the species identified, but also by the individual animal, for the top predators, and then analyzed using computer modeling to estimate densities.

Rafiq and his team manually identified animals by their coloration patterns or, in the case of lions, by their whisker spots. The tourist photograph method was carried out alongside camera trap, track, and call-in station surveys to compare the wildlife density estimates obtained from each and the costs to get this information.

“The results suggest that for certain species and within areas with wildlife tourism, tourist-contributed data can accomplish a similar goal as traditional surveying approaches but at a much lower cost, relative to some of these other methods,” says Rafiq.

For example, the tourist-photograph method was the only approach to identify cheetahs in the study area and provided density estimates for many of the other carnivore species that were largely comparable to those from the other methods. Most of the costs of the tourist photograph method were down to the manual processing of images. These are tasks that in the future could be outsourced to artificial intelligence to reduce survey costs further.

“If we could combine advances in artificial intelligence and automated image classification with a coordinated effort to collect images, perhaps by partnering with tour operators, we would have a real opportunity for continuous, rapid assessment of wildlife populations in high-value tourism areas,” he says.

This method of surveying animal populations is most applicable when studying the charismatic megafauna that tourists are usually interested in, and in areas with established tourism programs.

“There isn’t one silver bullet that will be useful in every situation,” Rafiq says. “Instead, as conservationists and researchers, we have a toolkit of different techniques that we can dip into depending on our project’s requirements and needs. This study adds to the growing body of evidence that citizen science is a powerful tool for conservation. This approach provides the opportunity to not only aid the monitoring of charismatic megafauna highly valued by society, but also has the potential to shape how we can meaningfully participate in conservation efforts.”

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“Horizontal gene transfer, the movement of genetic material from one organism into the genome of another species, is very common in microbes and is a major way that bacteria can acquire antibiotic resistance,” said Claude dePamphilis, professor of biology at Penn State and senior author of the study. “We don’t see many examples of horizontal gene transfer in complex organisms like plants, and when we do see it, the transferred genetic material isn’t generally used. In this study, we present the most dramatic case known of functional horizontal gene transfer ever found in complex organisms.”

Parasitic plants like dodder cannot live on their own by generating energy through photosynthesis. Instead, they use structures called haustoria to tap into a host plant’s supply of water and nutrients. Dodder wraps itself around its host plant, growing into its vascular tissue, and often feeds on multiple plants at one time. It can parasitize many different species, wild plants as well as those of agricultural and horticultural importance.

“Parasitic plants live very intimately in connection with their host, extracting nutrients,” said dePamphilis. “But they also get genetic material in the process, and sometimes they incorporate that material into their genome. Previous studies focused on single transferred genes. Here, we used genome-scale datasets about gene expression to determine whether the large amount of genetic material coming over through horizontal gene transfer is actually being used.”

The research team identified 108 genes that have been added to dodder’s genome by horizontal gene transfer and now seem to be functional in the parasite, contributing to haustoria structure, defense responses, and amino acid metabolism. One stolen gene even produces small segments of RNA known as micro RNAs that are sent back into the host plant, acting as weapons that may play a role in silencing host defense genes.

The team used rigorous criteria to determine whether the stolen genetic material was likely to be functional: The genes had to be full length, they had to contain all the necessary parts of a gene, they had to be transcribed into an RNA sequence that later builds proteins, and they had to be expressed in relevant structures. The team also explored the evolution of these transferred genes as additional support for functionality.

“We compare a gene’s genetic sequence with closely related genes, and look for a special signature in how that sequence evolves to tell if it’s likely to be functional,” said dePamphilis. “Certain kinds of mutations in a gene do not affect the protein that the gene codes for and therefore do not impact the gene’s function. When we see large amounts of these kinds of mutations, as opposed to mutations that might change or disrupt the gene’s function, it is strong evidence that natural selection is acting to keep the proteins intact and useful.”

Eighteen of the 108 genes appear in all dodder species, suggesting that these genes were originally stolen by the ancestral form of dodder and are maintained in modern species.

“This is the first time any study has seen evidence that horizontal gene transfers occurred early in the evolution of a parasitic group,” said dePamphilis. “In this case, 18 of these genes were present in the common ancestor of all the living dodder species, which may have contributed to successful spread of these parasites.”

The team also identified 42 regions in the dodder genome that appear to result from horizontal gene transfer, but do not have any functional genes.

“Because such a huge quantity of genetic material has come over through horizontal gene transfer, we suspect that the parasitic plants cannot filter what is coming in,” said dePamphilis. “But natural selection is helping maintain the useful genes and filter out the less useful segments.”

The researchers are currently investigating how exactly genetic material is being transferred from host to parasite. They would also like to explore whether this transfer is a one-way street, or if the host can obtain genetic material from its parasite.

“We’d love to know how extensive horizontal gene transfer really is,” said dePamphilis. “We looked at just one of species of dodder, which is just one of over 4000 species of parasitic plants. Does horizontal gene transfer of functional genes happen to the same extent in other species? Is it possible in non-parasitic plants? In other complex organisms? This may be the tip of the iceberg.”

In addition to dePamphilis the research team includes first author Zhenzhen Yang, a graduate student in the Plant Biology Graduate Program at Penn State at the time of the research, as well as Penn State researchers Eric Wafula, Saima Shahid, Joel McNeal, Paula Ralph, Prakash Timilsina, Wen-bin Yu, Elizabeth Kelley, Huiting Zhang, Thomas Nate Person, Naomi Altman, and Michal Axtell; and Virginia Tech researchers Gunjune Kim and co-corresponding author James Westwood. This work was funded in part by the National Science Foundation and the United States and Department of Agriculture. Additional support was provided by the National Institute of Food and Agriculture, the Penn State Department of Biology, and the Penn State Huck Institutes of the Life Sciences.