They don’t know it, but changed the world. These closely related species — native to the Galapagos Islands — each sport a uniquely shaped beak that matches their preferred diet. Studying these birds helped Charles Darwin develop the theory of evolution by natural selection.

A group of bats has a similar — and more expansive — evolutionary story to tell. There are more than 200 species of noctilionoid bats, mostly in the American tropics. And despite being close relatives, their jaws evolved in wildly divergent shapes and sizes to exploit different food sources. A published Aug. 22 in Nature Communications shows those adaptations include dramatic, but also consistent, modifications to tooth number, size, shape and position. For example, bats with short snouts lack certain teeth, presumably due to a lack of space. Species with longer jaws have room for more teeth — and, like humans, their total tooth complement is closer to what the ancestor of placental mammals had.

According to the research team behind this study, comparing noctilionoid species can reveal a lot about how mammalian faces evolved and developed, particularly jaws and teeth. And as a bonus, they can also answer some outstanding questions about how our own pearly whites form and grow.

“Bats have all four types of teeth — incisors, canines, premolars and molars — just like we do,” said co-author , a 91̽�� professor of biology and curator of mammals at the . “And noctilionoid bats evolved a huge diversity of diets in as little as 25 million years, which is a very short amount of time for these adaptations to occur.”

“There are noctilionoid species that have short faces like bulldogs with powerful jaws that can bite the tough exterior of the fruits that they eat. Other species have long snouts to help them drink nectar from flowers. How did this diversity evolve so quickly? What had to change in their jaws and teeth to make this possible?” said lead author , an incoming faculty member at the Institute of Evolutionary Science of Montpellier in France, who began this project as a postdoctoral researcher at the University California, Los Angeles.

Scientists don’t know what triggered this frenzy of dietary adaptation in noctilionoid bats. But today different noctilionoid species feast on insects, fruit, nectar, fish and even blood — since this group also includes the infamous vampire bats.

The team used CT scans and other methods to analyze the shapes and sizes of jaws, premolars and molars in more than 100 noctilionoid species. The bats included both museum specimens and a limited number of wild bats captured for study purposes. The researchers compared the relative sizes of teeth and other cranial features among species with different types of diets, and used mathematical modeling to determine how those differences are generated during development.

The team found that, in noctilionoid bats, certain “developmental rules” caused them to generate the right assortment of teeth to fit in their diet-formed grins. For example, bats with long jaws — like nectar-feeders — or intermediate jaws, like many insect-eaters, tended to have the usual complement of three premolars and three molars on each side of the jaw. But bats with short jaws, including most fruit-eating bats, tended to ditch the middle premolar or the back molar, if not both.

“When you have more space, you can have more teeth,” said Sadier. “But for bats with a shorter space, even though they have a more powerful bite, you simply run out of room for all these teeth.”

Having a shorter jaw may also explain why many short-faced bats also tended to have wider front molars.

“The first teeth to appear tend to grow bigger since there is not enough space for the next ones to emerge,” said Sadier.

“This project is giving us the opportunity to actually test some of the assumptions that have been made about how tooth growth, shape and size are regulated in mammals,” said Santana. “We know surprisingly little about how these very important structures develop!”

Many studies about mammalian tooth development were done in mice, which have only molars and heavily modified incisors. Scientists are not entirely sure if the genes and developmental patterns that control tooth development in mice also operate in mammals with more “ancestral” sets of chompers — like bats and humans.

Sadier, Santana and their colleagues believe their project, which is ongoing, can start to answer these questions in bats — along with many other outstanding questions about how evolution shapes mammalian features. They’re expanding this study to include noctilionoid incisors and canines, and hope to uncover more of the genetic and developmental mechanisms that control tooth development in this diverse group of bats.

“We see such strong selective pressures in these bats: Shapes have to closely match their function,” said Santana. “I think there are many more evolutionary secrets hidden in these species.”

Co-authors are Neal Anthwal, a research associate at King’s College London; Andrew Krause, an assistant professor at the Durham University in the U.K.; Renaud Dessalles, a mathematician with Green Shield Technology; Robert Haase, a researcher at the Dresden University of Technology in Germany; UCLA research scientists Michael Lake, Laurent Bentolila and Natalie Nieves; and Karen Sears, a professor at UCLA. The research is funded by the National Science Foundation.

For more information, contact Santana at ssantana@uw.edu and Sadier at alexa.sadier@gmail.com.

These nocturnal flying mammals live in cities and rural areas and in most climates around the world – and maybe even in your own backyard.

, a 91̽�� professor of biology and curator of mammals at the , explains that there are over 1,400 species of bats spanning an incredible diversity. Only three of the species are vampire bats which feed on the blood of birds or mammals. Most bats feed on insects, but diets vary from lizards, birds or mice to fruit and nectar. Bats play a vital role in ecosystems by controlling insect populations, pollinating plants as they move from bloom to bloom, and spreading seeds as they fly and poop.

One focus of Santana’s research is how bats have evolved to have different abilities and specializations. Bats are the only mammals that fly by flapping their wings (compared to gliding). Their handlike, membraned wing structures are incredibly maneuverable in tight spaces. Flying has enabled bats to access a lot of different food sources, she explains, which has probably shaped their diversity over time. 

Bat skulls, for example, have different shapes. Fruit-eating bats tend to have a shorter skull, optimized for a stronger bite, whereas a nectar bat’s long snout houses a long tongue. But they’re not limited to foraging with their mouths. Many bats will scoop up insects with a membrane that stretches between their hind legs like a sail while flying. 

Even vampire bats, who sidle up to their animal prey to make a small incision with sharp teeth and lick the resulting blood, have evolved to hop and scoot using their legs and folded wings to get away quickly from their victims. After a big meal, it turns out, they can be too heavy to fly.

Santana hopes people will get past bats’ scary reputation. 

“It would make sense that because we can’t quite discern what these animals are at night, we might be a little scared of them. But if you see the faces of bats – some flying foxes look like little puppies – you realize they can be super cute.”

For more information, contact Sharlene Santana / ssantana@uw.edu

A published Aug. 11 in the Proceedings of the Royal Society B by researchers at the 91̽�� and Stony Brook University reports on how bats and pepper plants in Central America have coevolved to help each other survive.

The team — led by , a 91̽��professor of biology and curator of mammals at the Burke Museum of Natural History and Culture — focused on the complex mixture of volatile organic compounds, or VOCs, produced by fruits on pepper plants in the genus Piper at prime ripeness. The study showed how these VOCs may have evolved to attract scent-oriented, short-tailed fruit bats from the genus Carollia, who then eat the fruits and excrete the seeds into the landscape.

Plant–animal interactions have captured the attention of biologists for centuries, and are key to maintaining the biodiversity of tropical ecosystems. The dispersal syndrome hypothesis — an explanation of how mutually beneficial relationships between plants and fruit-eating animals may lead to coevolution — proposes that, when animals are effective seed dispersers, they may select for fruit traits, including size, color and odor, that match their sensory abilities, such as vision and olfaction. But few studies have tested this hypothesis for complex traits like fruit scents. This research provides one of the first tests of bat-driven, fruit scent evolution.

The study is based on data collected during fieldwork at La Selva Biological Station in Costa Rica. There, Piper is highly diverse, with more than 50 recognized species. It is also a location where three Carollia species — C. castanea, C. sowellii and C. perspicillata — are some of the most abundant bats year-round and coexist with approximately 62 other bat species.

The team spent hundreds of hours searching and collecting ripe fruits from Piper to extract and quantify the VOCs that make up their fragrant scent. They also collected fecal samples from live bats and then released them back into the wild to determine which Piper species the bats were eating and how much. In addition, the researchers conducted behavioral experiments with wild bats where they offered options of unripe fruits enhanced with the most common VOCs found in local Piper plants. Video cameras and microphones recorded the bats’ feeding behaviors and echolocation calls.

The team found Piper fruit scent bouquets were complex and diverse. The authors identified and quantified 249 VOCs in ripe fruit scents across 22 Piper species. Some compounds were found in the fruit scent of most species — like alpha-caryophyllene, which has a spicy scent like cinnamon or cloves. Others, like 2-heptanol, were only found in a few Piper species. The diet experiments showed that, while the three Carollia fruit bat species varied in their reliance on Piper as a food source, all consumed a lot of a few Piper species, and a little of many others. Surprisingly, this was not related to how abundant the Piper species are at La Selva, so the bats must choose Piper fruits based on other characteristics and not just how well represented they are across the landscape. The team’s behavioral experiments provided some clues to what might be happening: Bats preferred samples spiked with 2-heptanol, a VOC found in the fruit scents of the Piper species they eat the most.

“These findings suggest bats use specific chemicals in the fruit scent bouquet not only to select ripe fruits, but to find the specific Piper species that make up the bulk of their diet,” said Santana, who is co-lead author on the study. “By helping them communicate with the bats, these chemical signals are likely a component of a dispersal syndrome in these plants.”

Through statistical and evolutionary analyses of the data on fruit scent chemistry and bat diet, the team further demonstrated that the evolutionary patterns of chemical diversity and the presence of specific compounds in Piper fruit scents is associated with greater bat consumption and scent preferences. This highlights the potential effect of bat fruit consumption on the evolution of fruit chemistry, a relationship that contributes to the extreme diversity of tropical fruiting plants worldwide.

“Flying in the dark means bats cannot find ripe fruit by sight, but rely on olfaction instead,” said co-author , a professor at Stony Brook University. “Olfaction is the bridge between the plant signal and bat fruit consumption, and finding the specific VOCs bats respond to opens the door to matching olfactory receptor genes to important VOCs, which has been impossible until now.”

Understanding the relationship between bats and pepper plants not only contributes to knowledge about coevolution of these species, but also has benefits for rainforest habitat conservation. Piper are some of the first plants to grow in forest gaps and edges, and Carollia ― as key dispersers of Piper seeds ― can help restore plant life in logged areas.

“Our current and future work is identifying the odorant receptors that allow the bats to detect the fruit scents. This will allow us to link the ecology and evolution of these relationships with the physiological mechanisms,” said co-author , a 91̽��professor of biology.

Co-lead author on the paper is former 91̽��postdoctoral researcher Zofia Kaliszewska. Other co-authors are 91̽��doctoral alum Leith Leiser-Miller, M. Elise Lauterbur at the University of Arizona and Jessica Arbour at Middle Tennessee State University. The research was funded by the National Science Foundation.

For high-resolution images, video and interviews, contact burkepr@uw.edu.

Humans may be forgiven for overlooking bats. After all, many bat species are out and about when we’re turning in. And generations of Dracula lore may have made us a little wary.

But bats are a diverse bunch. They make up one of the largest groups of mammals, with more than 1,300 species worldwide. Up close, bat species look quite different from one another. Some have large ears. Others sport elaborate noses or long jaws. With so much morphological variety, bats represent an opportunity to learn what types of evolutionary forces shape the shapes of animals.

A team of biologists at the 91̽�� has been using bats to do just that. Postdoctoral researchers and and , 91̽��associate professor of biology and curator of mammals at the UW’s , focused on the diversity among bat skulls. The researchers performed high-resolution scans of the skulls of more than 200 bat species. They used the scans, as well as information on the evolutionary relationships among bat species, to analyze the types of physical changes that evolved in bat skulls over tens of millions of years and correlate them with specific events in bat evolution, such as when a lineage switched diets or adapted to a new ecological niche. In published May 2 in , they report that two major forces have shaped bat skulls over their evolutionary history: echolocation and diet. They were even able to determine when in bat history these forces were dominant.

“Our study sought to address a major question about the evolution of diversity in the bat skull: What explains the large number of differences that we see in skull shape?” said Santana. “We found that echolocation is a major — and ancient — contributor to skull shape. Diet is also important, but generally more recent.”

Santana used microCT to study the evolution and mechanics of bite force in , a large and diverse taxonomic family of bats from the Americas. In the current study, her group investigated a wider swathe of bat diversity. They performed microCT scans of skulls from 203 species across all 20 taxonomic families of bats. The skulls came from collections at the Burke Museum, the American Museum of Natural History, the Field Museum, the Smithsonian Institution and the Natural History Museum of Los Angeles County.

“Museum collections of bat specimens played a critical role in allowing us to sample so broadly across bats families and really dig into the evolution of such a diverse group,” said Arbour.

The scans gathered detailed data on the 3D shape of the lower jaw for 191 species, and the cranium — the upper portion of the skull that includes the upper jaw and braincase — for 202 species. The researchers then used computational modeling to combine the microCT scan data on the skulls with data on the evolutionary relationships among the bat species, as well as ecological characteristics such as diet. Their analysis allowed them not just to compare skull differences among and within bat lineages, but also to focus on specific parts of the skull, like the lower jaw.

“It’s important to independently analyze different parts of the skull because some parts of the skull have many different jobs, which may constrain the changes they can undergo,” said Santana. “For example, the cranium has many functions, such as feeding, respiration and protecting the brain. The lower jaw is largely just involved in feeding, which could give it more freedom to evolve in response to dietary changes.”

The team’s analyses indicated that early in bat evolution — from about 58 million to 34 million years ago — echolocation was a primary driver of skull shape across bat families. Most bats to hunt, forage and navigate in light-poor settings. Bats echolocate by emitting specific types of high-pitched sounds with the larynx and then hearing the echoes as those sound waves bounce off of objects in their path. The fossil record indicates that in bats early, at least 52 million years ago. Since then, different bat families have evolved unique mechanisms for echolocation — such as projecting sounds through the nostrils instead of the mouth. One group, the , even lost the ability to echolocate laryngeally.

The team found that starting about 26 million years ago, diet became the more dominant driving force behind skull shape evolution, but not in all bats. While some bat families are fairly uniform in diet, with all species eating insects, for example, the include species that eat vastly different types of food, ranging from insects to fruit to small vertebrates — even blood. The team found that the evolution of different diets within the leaf-nosed bats was actually the major driver of changes in skull shape across this group.

“The leaf-nosed bats stand out for their extraordinary diversity in skull shape and diet,” said Santana. “Over a relatively short period of time, they evolved a suite of skull adaptations as they radiated into different dietary niches.”

Diet and echolocation also did not affect skull evolution uniformly. Instead, the researchers saw a “decoupling” of skull parts in terms of how the two forces shaped them. Diet was the stronger driver on the lower jaw, while echolocation had a greater effect on the cranium.

Santana’s team is continuing this work as part of a larger effort funded by the National Science Foundation to compare the evolutionary forces that shape skull diversity among different groups of mammals, including bats, primates and carnivores. These studies could determine whether the patterns seen in bats — such as decoupling of skull parts or diversification of shapes as species adapt to new ecological niches — apply to other lineages, including our own.

The research was funded by the National Science Foundation, the American Museum of Natural History and the Natural Sciences and Engineering Research Council of Canada.

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For more information, contact Santana and 206-221-6488 or ssantana@uw.edu.

Grant number: 1557125

A $2.5 million National Science Foundation grant will daylight thousands of specimens from their museum shelves by CT scanning 20,000 vertebrates and making these data-rich, 3-D images available online to researchers, educators, students and the public.

The project oVert, short for openVertebrate, complements other NSF-sponsored museum digitization efforts, such as , by adding a crucial component that has been difficult to capture — the internal anatomy of specimens.

With virtual access to specimens, researchers could peel away the skin of a passenger pigeon to glimpse its circulatory system, a class of third graders could determine a copperhead’s last meal, undergraduate students could 3-D print and compare skulls across a range of frog species and a veterinarian could plan a surgery on a giraffe in a zoo.

“In a time when museums and schools are losing natural history collections and giving up due to costs, we are recognizing the information held in these specimens is only getting more valuable,” said project co-principal investigator , assistant professor of aquatic and fishery sciences at the 91̽�� and curator of fishes at the Burke Museum of Natural History and Culture.

“I think this project is going to help create a renaissance of the importance of natural history collections,” he said.

The 91̽��joins 15 other institutions in this new project, led by the Florida Museum of Natural History at the University of Florida. The grant will enable researchers over four years to transport specimens from museum collections to scanners, scan and upload images, and organize them on the public database for easy access.

More than one quarter of the world’s vertebrate species will be scanned and digitized through this project, and researchers will aim to include specimens from more than 80 percent of existing vertebrate genera. A selection of these will also be scanned with contrast-enhancing stains to characterize soft tissues. There are almost 70,000 vertebrate species described today, and more than half of those are fishes.

The 91̽��has already made a dent in many of the fish species included in this project through the effort, led by , a 91̽��professor of aquatic and fishery sciences and of biology. For the past two years, Summers and colleagues have used a small CT scanner at to produce scores of fish scans from specimens gathered around the world.

CT scanning is a non-destructive technology that bombards a specimen with X-rays from every angle, creating thousands of snapshots that a computer stitches together into a detailed 3-D visual replica that can be virtually dissected, layer by layer, to expose cross-sections and internal structures.

The scans allow scientists to view a specimen inside and out — its skeleton, muscles, internal organs, parasites, even its stomach contents — without touching a scalpel.

“Our goal is to provide data that offer a foothold into vertebrate anatomy across the Tree of Life,” said , oVert’s lead principal investigator and associate curator of amphibians and reptiles at the Florida Museum of Natural History. “This is a unique opportunity for museums to have a pretty big reach in terms of the audience that interacts with their collections. We believe oVert will be a transformative project for research and education related to vertebrate biology.”

In addition to the 91̽��and University of Florida, scanning will occur at the University of Michigan, Harvard University, Texas A&M University and the Field Museum at the University of Chicago. The team’s largest scanner can image specimens as large as a garbage can, so for large mammals, scientists will focus on scanning their skulls or other key anatomical features, Tornabene said.

In contrast, micro-CT scanners like the one at Friday Harbor Labs can pick up incredible detail of small vertebrates that are difficult to study at life size, he explained. 91̽��scientists have scanned some of the smallest fish in the world and can zoom in to the digital file to examine anatomy not visible with the naked eye. They can also 3-D print specimens larger than life.

“We are going to be exploring the capabilities of understanding vertebrate anatomy at the finest scales,” Tornabene said.

The UW’s three CT scanners will focus mainly on digitizing key species in the Burke Museum’s collection of 12 million fish specimens, as well as the museum’s large bat collection. In addition to Tornabene and Summers, Katherine Maslenikov, Burke Museum fish collections manager, and , curator of mammals at the museum and assistant professor of biology, will lead the effort at the UW.

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For more information, contact Tornabene at ltorna1@uw.edu or 206-685-4254 and Blackburn at dblackburn@flmnh.ufl.edu or 352-273-1943.

This release was adapted from a Florida Museum of Natural History .

But over the 52-million-year history of these flying mammals, a few have evolved a taste for their fellow vertebrates. Now biologists at the 91̽�� and the are shedding light on how these so-called “” adapted to the daunting task of chowing down their backboned prey.

“Vertebrate prey are a unique challenge for carnivorous bats,” said lead author , a 91̽��assistant professor of biology and curator of mammals at the Burke Museum. “They eat flesh, bones and everything else within their prey, and we wanted to understand the evolutionary changes that help them accomplish this.”

Santana and co-author Elena Cheung, a 91̽��undergraduate, wanted to understand how these adaptations influenced changes in skull shape and size. When talking about diet, this is no small question.

“The skull and mandible provide attachment points for the jaw muscles, and variation in these attachment sites results in differences in bite force, and how wide of a gape the jaws are capable of,” said Santana.

Their findings, May 11 in the , reveal surprising patterns of change that helped carnivorous bats catch and eat vertebrates. Though there are currently more than 1,300 species of bats, only a few dozen eat vertebrates, from fish to land animals — including a few species that eat other bats. This evolutionary transition — from insects to vertebrates – has occurred at least six times over bat history.

Santana and Cheung took high-resolution images of skulls from 140 bats across 35 species, representing all six lineages of carnivorous bats as well as bats that eat insects, or a combination of vertebrates and insects. The skulls were from the Burke Museum and the Los Angeles County Museum.

They used these images in a complex computer-based comparison of landmarks on the skulls, which takes into account the position, scale and orientation of those features to determine differences in shape among species.

“The unique features found in the skulls of carnivorous bats may reflect the adaptations that would have enabled them to adopt a diet of vertebrate prey instead of insects,” said Santana.

Through this process, Santana and Cheung also discovered that larger animal-munching bats — whether they ate insects or vertebrates — tended to have longer snouts, which may allow them to consume relatively larger prey. Carnivorous bats tended to be larger and had skulls that emphasized a strong bite force when the jaws are opened wide.

Surprisingly, the main exception to this trend were carnivorous bats that ate a particular subset of vertebrates — fish. The skulls of fish-eating bats were optimized for a strong bite force at a relatively narrow jaw gape.

“Many fish have flatter bodies compared to land vertebrates, which may explain the distinctive jaws and bite force of fish-eating bats,” said Santana. “In addition, fish-eating bats must spend a lot of time chewing the carcass thoroughly, breaking up those sharp and tiny bones into chunks that are easier to swallow and digest.”

Santana and Cheung also collected data from the skulls of other carnivorous vertebrates, including a polar bear, puma, lion and several species of hyenas and wolves. This wider comparison helped them understand if the skulls of carnivorous bats showed adaptations shared by other mammalian carnivores.

“This is important to understand because, unlike other mammalian carnivores, carnivorous bats don’t have the strong, blade-like teeth that can tear flesh — these bats chew and consume the whole body of their prey, bones and all,” said Santana.

She and Cheung found that the skulls of carnivorous bats emphasized a strong bite force at the expense of gape width when compared to other mammalian carnivores, perhaps indicating that some of the key trade-offs in feeding and chewing strategies enabled these bats to subsist on a vertebrate-rich diet.

Santana hopes their conclusions will inform ecological studies of carnivorous bats, which by and large reside in tropical and sub-tropical environments around the globe. In addition, Santana says this study demonstrates how ecological factors like diet can so heavily depend on the adaptive changes that evolution provides.

Their research was funded by the 91̽��.

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For more information, contact Santana at 206-221-6488 or ssantana@uw.edu.

The students will attend the Jan. 2016 of the in Portland, Oregon. Known commonly by its acronym, SICB, this broad scientific research society of 3,500 members promotes research and collaboration on diverse topics within biology such as evolution, developmental biology, anatomy, ecology and biodiversity.

91̽��biology professor says she hopes this grant — which includes $15,000 for meeting fees, lodging and travel expenses for the six students — will help recruit Native American students into science careers where they are sharply underrepresented. Santana and her colleague, anatomy and vertebrate paleontology professor of Oklahoma State University , decided to recruit Native American students after noticing a dearth of Native American colleagues within SICB.

“Less than half a percent of our society’s members are Native American,” said Santana, who is also curator of mammals at the . “Our goal was to specifically target this demographic and increase their participation.”

Native Americans are one of the most underrepresented minorities in the natural sciences. , in 2010 nearly 20,000 doctoral degrees were awarded to U.S. citizens or permanent residents for research in mathematics, science and engineering. Just 76 of them were Native Americans.

“The grant will enable us to bring greater exposure to to an underrepresented population,” said Gignac. “By meeting with experts and exploring the differing careers options that are available, these students will learn more about STEM and hopefully continue their education in one of these fields.”

Santana hopes that attending the SICB meeting will help the six undergraduates envision future careers in science as they witness a tradition of scientific discovery — meeting with colleagues and sharing new research findings. She and Gignac will pair each undergraduate with one graduate student at the meeting.

“These graduate students will be mentors who will guide them throughout the meeting,” said Santana. “They can help the students navigate through all the different events, talks, symposia and social gatherings. They will help them choose which talks to go to, talk to them about career options and introduce them to colleagues.”

Santana believes that a professional scientific meeting will immerse the six students in the collaborations and connections that form the basis of a research career.

“We intend for them to learn about our research community and expose them to different stages of this career,” she said. “The graduate student mentors will be a good ‘stepping stone’ on this career path who they can relate to. But they will also meet faculty members, postdoctoral researchers, technicians and other undergraduates. They can do a lot of networking and see many different opportunities and career paths.”

The selected students will also attend a at the SICB meeting that Gignac and Santana are organizing on ecomorphology, which explores the interactions between an animal’s anatomy and the resources it uses. The SICB meeting is an opportunity to bring together dozens of their colleagues to address this emerging field within biology.

Santana and Gignac have not yet chosen the six undergraduates, who will come from colleges and universities around the country. They may select some students through an application process and others through the , which Gignac is affiliated with at Oklahoma State University Center for Health Sciences. Santana says they would like to select students with a variety of interests in biology, and hopes that this unique meeting experience will inspire more of them to pursue careers in research.

“There’s so much transformative value to this experience,” said Santana. “There might be someone thinking about going to medical school, but here they can realize all these other options for careers and research.”

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For more information, contact Santana at 206-221-6488 or ssantana@uw.edu.