adaptation ‣ Data Nuggets

8.3.23

Size matters – and so does how you carry it!

The activities are as follows:

In the wild, animals compete for limited resources. Things like food, water, shelter, and even reproductive mates can be hard to come by. Animals with traits and behaviors that make them more likely to survive and reproduce are said to have higher evolutionary fitness. Some animals have evolved special traits that advertise their fitness to potential mates. Male deer, elk, and moose have large antlers that they use to compete with other males, which demonstrates their fitness to females. Another interesting example is the stalk-eyed flies, in which the males grow long eye stalks to attract a mate. In these cases, females are more likely to choose males with the biggest traits.

Scientists have long predicted that these traits come with both benefits and costs. Large antlers or eyestalks may help a mate notice you, but also come with some costs. Extra weight takes more energy to move around and could make it more difficult to escape from predators. And yet, many studies have failed to find any measurable costs to males having these seemingly impractical traits.

This scientific mystery puzzled Jerry and John, who study stalk-eyed flies. They had failed to identify and document any costs to having longer eyestalks, measured as the distance between the eyes, or eyespan. Common sense told them that having longer eye stalks should make flying more awkward for these flies. However, their data did not support this hypothesis. “When I started collecting data, I focused a lot on the performance costs and got kind of fixated on that,” John says of the team’s initial research. “It was frustrating when we couldn’t identify any actual decline in performance.”

John in the field when he first started his research – many decades ago!

The team began looking for an alternative explanation. They read about research supporting a new idea in a completely different kind of flying animal – barn swallows. Male barn swallows have long, ornate tails. These tails make male barn swallows less aerodynamic during flight. But males have also evolved to have larger wings relative to their body size. This could help them compensate for the extra burden associated with their long tails.

Jerry and John wondered if a similar thing might be at work in stalk-eyed fly wings. Perhaps the male stalk-eyed flies, like male barn swallows, had evolved to have larger wings relative to their body size to help them compensate for long eye stalks when flying. If this were the case, then they expected to see a positive correlation between wing size and eyespan. Could this be why they were unable to measure any disadvantage associated with having longer, more awkward eye stalks? In other words, male stalk-eyed flies with larger wings would be able to support longer eye stalks.

Eyespan (horizontal arrow) and body size (vertical arrow) of a stalk-eyed fly.

Jerry, John, and their team decided to test their new hypothesis by raising stalk-eyed flies in the lab to maturity, then collecting data about their body length, eyespan, and wing area.

To account for natural variation in body size among stalk-eyed flies, the team needed to use “relative” measurements based on body size. With these kinds of measurements, a value of zero (0) means that wing size or eyespan is exactly what you would predict for a fly of that body size. Negative values mean that wing size or eyespan are smaller than you would predict for that body size, while positive values mean that wing size or eyespan is greater than you would predict for that body size. For example, if a fly has a relative eyespan of -0.010, then the distance between the eyestalks was 0.010 millimeters shorter than expected based on its body size.

Featured scientists: Jerry Husak from the University of St. Thomas and John Swallow from the University of Colorado-Denver. Written by: Sam Holloway

Flesch–Kincaid Reading Grade Level = 8.8

Additional teacher resources related to this Data Nugget include:

You can find lessons to accompany many of John’s studies with insects on the Data Nuggets website! Check out the following Data Nugget activities!

A peer-reviewed journal article: Husak, J. F., Ribak, G., Wilkinson, G. S., & Swallow, J. G. 2011. Compensation for exaggerated eye stalks in stalk‐eyed flies (Diopsidae). Functional Ecology, 25(3), 608-616.

A video of a stalk-eyed fly in flight:

3.16.23

Benthic buddies

Danny and Kaylie sampling benthic animals

The activities are as follows:

Lagoons are areas along the coast where a shallow pocket of sea water is separated from the ocean most of the time. During some events, like high tides, the ocean water meets back up with the lagoon. Coastal lagoons are found all over the world – even in the most northern region of Alaska, called the High Arctic!

These High Arctic lagoons go through many extreme changes each season. In April, ice completely covers the surface. The mud at the bottom of the shorelines is frozen solid. In June, the ice begins to break up and the muddy bottoms of the lagoons begin to thaw. The melting ice adds freshwater to the lagoons and lowers the salt levels. In August, lagoon temperatures continue to rise until there is only open water and soft mushy sediment.

You would think these harsh conditions would make High Arctic lagoons not suitable to live in. However, these lagoons support a surprisingly wide range of marine organisms! Marine worms, snails, and clams live in the muddy sediment of these lagoons. This habitat is also called the bottom, or benthic, environment. Having a rich variety of benthic animals in these habitats supports fish, which migrate along the shoreline and eat these animals once the ice has left. And people who live in the Arctic depend on fishing for their food.

Ken, Danny, and Kaylie are a team of scientists from Texas interested in learning more about how the extreme seasons of the High Arctic affect the marine life that lives there. They want to know whether the total number of benthic species changes with the seasons. Or does the benthic community of worms, snails, and clams stay constant throughout the year regardless of ice, freezing temperatures, and large changes in salt levels? The science team thought that the extreme winter conditions in the Arctic lagoons cause a die-off each year, so there would be fewer species found at that time. Once the ice melts each year, benthic animals likely migrate back into the lagoons from deeper waters and the number of species would increase again.

Ken, Danny, and Kaylie had many discussions about how they could answer their questions. They decided the best approach would be to travel to Alaska to take samples of the benthic animals. To capture the changes in lagoon living conditions, they would need to collect samples during the three distinct seasons.

The science team chose to sample Elson Lagoon because it is in the village of Utqiaġvik, Alaska and much easier to reach than other Arctic lagoons. They visited three times. First, in April, during the ice-covered time, again in June when the ice was breaking up, and a final time in summer when the water was warmer. In April, they used a hollow ice drill to collect a core sample of the frozen sediment beneath the ice. In June and August, they deployed a Ponar instrument into the water, which snaps shut when it reaches the lagoon bottom to grab a sample. Each time they visited the lagoon, they collected two sediment samples.

Back in the lab, they rinsed the samples with seawater to remove the sediment and reveal the benthic animals. The team then sorted and identified the species present. They recorded the total number of different species, or species richness, found in each sample.

Featured scientists: Ken Dunton, Daniel Fraser, and Kaylie Plumb from the University of Texas Marine Science Institute

Written by: Maria McDonel from Flour Bluff and Corpus Christi Schools

Flesch–Kincaid Reading Grade Level = 8.9

Additional teacher resources related to this Data Nugget include:

Two short videos that you can play to introduce students to Arctic lagoons and the research that is done there:
- Scientists drill through coastal sea ice to deploy an array of instruments and employ a variety of sampling techniques.
- Scientists use ROVs from Deep Trekker to explore life beneath the frozen lagoons of the Alaskan Arctic

A National Geographic article about Arctic research.
More information on the Beufort Lagoon Long-term Ecological Research site and who to contact.

11.1.21

Round goby, skinny goby

An invasive round goby from the Kalamazoo River, Michigan.

The activities are as follows:

Animals often have adaptations, or traits that help them live in certain environments. For fish, that can mean having a body shape that allows them to feed on available prey, better hide from predators, or swim more effortlessly. When these traits vary within the same species from one location to another, they are called local adaptations. Such adaptations were once thought to only evolve slowly over hundreds or thousands of generations. However, new evidence shows that evolution can result in meaningful adaptations much more quickly than originally thought, sometimes in just a few generations!

Invasive species are those that have been moved by humans to areas where they do not usually exist and cause disruptions to native ecosystems. Because they have been moved to new places where they did not evolve, invasive species often have traits that aren’t matched to their new habitats. When mismatches occur, species may be able to adapt in just a few generations in their new locations.

Several invasive species have been problematic in the Great Lakes of North America. The round goby is a small invasive fish species that arrived in the Great Lakes around 1990. It is a bottom-dwelling species that is able to quickly reproduce and crowd out native fish species. Both avid anglers, Jared and Bailey observed the increasing numbers of round gobies during their time spent outdoors. They noticed that sometimes round gobies would even outnumber all other native fish in an area.

Originally appearing just in the Great Lakes themselves, the species is increasingly being found in rivers throughout the region. Jared and Bailey were surprised this species did so well in both river and large lake habitats since they are very different environments for fish to live. For example, water is constantly flowing downstream in rivers, whereas lakes can be still or have waves near the shore. Also, these two habitats have different predator and prey species living in them and differ in water chemistry characteristics. With the spread of more and more round gobies into rivers, Jared and Bailey set out to learn how this species is successful in both habitats. They thought that round gobies found in rivers would have adaptations to help navigate fast flowing waters. Fish with narrower body shapes can move more easily in flowing waters, giving narrow-bodied individuals an advantage over those with bulkier bodies. Over time, those individuals with such an advantage would be more likely to survive and reproduce in the rivers, eventually shifting the entire river-dwelling population to a narrow body shape. They predicted that round gobies from rivers would have shorter body depths and narrower caudal peduncles, which is the area between the fish’s body and tail. To test their idea, Jared and Bailey captured and measured hundreds of round gobies from both Great Lakes and inland river habitats.

Michigan State University researcher Bailey Lorencen fishing for gobies in a Michigan river.

Featured scientists: Jared Homola (he/him) and Bailey Lorencen (she/her) from Michigan State University

Flesch–Kincaid Reading Grade Level = 11.2

11.4.20

Corals in a strange place

Marine Biologist, Karina, snorkeling in the mangroves. Photo by John Finnerty.

The activities are as follows:

When you imagine a coral, you likely picture it living on a coral reef, bathed in sunlight, surrounded by crystal clear waters teeming with colorful fishes. But corals can actually live in a range of habitats, even habitats that are sometimes murky and much darker!

As marine biologists, Karina and John often snorkel around the mangroves in Belize, where they do their research. Mangroves are trees that have roots able to grow in saltwater. By capturing mud and sediment, these underwater roots build habitat for marine life. While Karina and John were documenting the different marine life that can grow on underwater roots, they noticed something shocking. The same corals that live on coral reefs were growing in the mangrove forests too! This surprised Karina and John because coral reefs and mangrove forests are very different habitats. Coral reefs have clear water and bright light, while mangrove forests are darker with murky water that has a lot of nutrients. How can corals live in such different places?

Karina and John started to wonder if the corals that live in the mangroves look different than the corals on the reefs. Sometimes animals can look different based on where they live. These differences may be adaptations that help them live in different environments. Karina and John measured differences between two different coral species that were found in both habitat types. The two species they used are the mounding mustard hill coral and the branching thin finger coral.

Featured scientists: Karina Scavo Lord and John Finnerty from Boston University

Flesch–Kincaid Reading Grade Level = 8.9

1.25.19

Fast weeds in farmer’s fields

The activities are as follows:

Weeds in agricultural fields cost farmers $28 billion per year in just the United States alone. When fields are full of weeds the crops do not grow as well. Sometimes weeds even grow better than the crops in the same field. This may make you wonder, how do weeds grow so well compared to other types of plants? Scientists think that weeds may have evolved certain traits that allow them do well in agricultural fields. These adaptations could allow them to grow better and pass on more of their genes to the next generation.

Weedy radish is considered one of the world’s worst agricultural weeds. This plant has spread around the world and can now be found on every continent except Antarctica. Weedy radish commonly invades wheat and oat fields. It grows better than crops and lowers the amount of food produced in these fields. Weedy radish evolved from native radish only after humans started growing crops. Native radish only grows in natural habitats in the Mediterranean region.

Because weedy radish evolved from native radish recently, they are still very closely related. They are so closely related they are actually listed as the same species. However, some traits have evolved rapidly in weedy radish. For example, native radish grow much slower and take a few months to make flowers. However, weedy radish can make flowers only three weeks after sprouting! In a farmer’s field, the crop might be harvested before a native radish would be able to make any seeds, while weedy radish had plenty of time to make seeds.

Ashley collecting data on the traits of weedy and native radish.

The differences between native versus weedy radish interested Ashley, a teacher in Michigan. To learn more she sought out a scientist studying this species. She found Jeff, a plant biologist at the Kellogg Biological Station and she joined his lab for a summer to work with him. That summer, Ashley ran an experiment where she tested whether the rapid flowering and seed production of weedy radish was an adaptation to life in agricultural fields.

Ashley planted four populations of native radish and three populations of weedy radish into fields growing oat crops. Ashley made sure to plant multiple populations of radish to add replication to her experiment. Multiple populations allowed her to see if patterns were the same across populations or if each population grew differently. For each of these populations she measured flowering frequency. This trait is the total number of plants that produced flowers within the limited time between tilling and harvesting. Ashley also measured fitness, by counting the total number of seeds each plant produced over its lifetime. Whichever plant type produced a greater number of seeds had higher fitness. Oats only grow for 12 weeks so if radish plants were going to flower and make seeds they would have to do it fast. Ashley predicted the weedy radish population would produce more flowers and seeds than native radish during the study. Ashley expected few native radish plants would flower before harvest.

Featured scientists: Ashley Carroll from Gull Lake Middle School and Jeff Conner from the Kellogg Biological Station at Michigan State University

Flesch–Kincaid Reading Grade Level = 9.1

1.15.19

Hold on for your life! Part II

In Part I the data showed that, after the hurricanes, anole lizards had on average smaller bodies, shorter legs, and larger toe pads. The patterns were clear and consistent across the two islands, indicating that these traits are adaptations shaped by natural selection from hurricanes. At this point, however, Colin was still not convinced because he was unable to directly observe the lizards during the hurricane.

Still shot of lizard clinging to an experimental perch in hurricane-force winds. Wind speed meter is displaying in miles per hour

The activities are as follows:

Colin was unable to stay on Pine Cay and Water Cay during the hurricanes and directly observe the lizards. To be more confident in his explanation, Colin needed to find out how lizards behave in hurricane-force winds. He thought there were two options for what they might do. First, he thought they might get down from the branch and hide in tree roots and cracks. Alternatively, they might hold onto branches and ride out the storm. If they tried to hold on in high winds, it would make sense that traits like the length of their limbs or the size of their toepads would be important for their survival. However, if they hid in roots or cracks, these traits might not be adaptations after all.

To see how the lizards behaved, Colin needed to design a safe experiment that would simulate hurricane-force winds. He bought the strongest leaf blower he could find, set it up in his hotel room on Pine Cay, and videotaped 40 lizards as they were hit with high winds. Colin first set up this experiment to observe behavior, but he ended up learning not only that, but a lot about how the traits of the lizards interacted with high winds.

To begin the experiment, Colin placed the anoles on a perch. He slowly ramped up the wind speed on the leaf blower until the lizards climbed down or they were blown, unharmed, into a safety net. He recorded videos of each trial and took pictures.

Featured scientist: Colin Donihue from Harvard University

Written with: Bob Kuhn and Elizabeth Schultheis

Flesch–Kincaid Reading Grade Level = 8.4

Additional teacher resources related to this Data Nugget:

This study was published in the journal Nature in 2018. Colin would like to thank his coauthors Anthony Herrel, Anne-Claire Fabre, Anthony Geneva, Ambika Kamath, Jason Kolbe, Tom Schoener, and Jonathan Losos. You can read the paper here.
Colin wrote a blog post about his experience. He shares more about the lead-up to the project and how a chance occurrence changed the entire trajectory of his research.
Colin also put together a story map with more images and animated gifs of this research.
We put together a PowerPoint of images from Colin’s research that you can show in class to accompany the activity.

To engage students in this activity, show the following video in class. This video gives some information on the experiment and Colin’s research.

1.15.19

Hold on for your life! Part I

Anolis scriptus, the Turks and Caicos anole, on Pine Cay.

The activities are as follows:

On the Caribbean islands of Turks and Caicos, there lives a small brown anole lizard named Anolis scriptus. The populations on two small islands, called Pine Cay and Water Cay, have been studied by researchers from Harvard University and the Paris Natural History Museum for many years. In 2017, Colin, one of the scientists, went to these islands to set up a long-term study on the effect of rats on anoles and other lizards on the islands. Unbeknownst to him, though, a storm was brewing to the south of the islands, and it was about to change the entire trajectory of his research.

While he was collecting data, Hurricane Irma was developing into a massive category 5 hurricane. Eventually it became clear that it would travel straight over these small islands. Colin knew that this might be the last time he would see the two small populations of lizards ever again because they could get wiped out in the storm. It dawned on him that this might be a serendipitous moment. After the storm, he could evaluate whether lizards could possibly survive a severe hurricane. He was also interested in whether certain traits could increase survival. Colin and his colleagues measured the lizards and vowed to come back after the hurricane to see if they were still there. They measured both male and female lizards and recorded trait values including their body size, femur length, and the toepad area on their forelimbs and hindlimbs.

Colin was not sure whether the lizards would survive. If they did, Colin formed two alternative hypotheses about what he might see. First, he thought lizards that survived would just be a random subset of the population and simply those that got lucky and survived by chance. Alternatively, he thought that survival might not be random, and some lizards might be better suited to hanging on for their lives in high winds. There might be traits that help lizards survive hurricanes, called adaptations. He made predictions off this second hypothesis and expected that survivors would be those individuals with large adhesive pads on their fingers and toes and extra-long legs – both traits that would help them grab tight to a branch and make it through the storm. This would mean the hurricanes could be agents of natural selection.

Not only did Hurricane Irma ravage the islands that year, but weeks later Hurricane Maria also paid a visit. Upon his return to Pine Cay and Water Cay after the hurricanes, Colin was shocked to see there were still anoles on the islands! He took the measurements a second time. He then compared his two datasets from before and after the hurricanes to see if the average trait values changed.

Featured scientist: Colin Donihue from Harvard University

Written with: Bob Kuhn and Elizabeth Schultheis

Flesch–Kincaid Reading Grade Level = 9.9

Additional teacher resources related to this Data Nugget:

This study was published in the journal Nature in 2018. Colin would like to thank his coauthors Anthony Herrel, Anne-Claire Fabre, Anthony Geneva, Ambika Kamath, Jason Kolbe, Tom Schoener, and Jonathan Losos. You can read the paper here.
Colin wrote a blog post about his experience. He shares more about the lead-up to the project and how a chance occurrence changed the entire trajectory of his research.
Colin also put together a story map with more images and animated gifs of this research.
We put together a PowerPoint of images from Colin’s research that you can show in class to accompany the activity.

To engage students in this activity, show the following video in class. This video gives some information on the experiment and Colin’s research. For Part I stop the video at minute 1:30.

11.27.17

Is it better to be bigger?

An anole lizard on the island, about to be captured by Aaron.

The activities are as follows:

When Charles Darwin talked about the “struggle for existence” he was making the observation that many individuals in the wild don’t survive long enough to reach adulthood. Many die before they have the chance to reproduce and pass on their genes to the next generation. Darwin also noted that in every species there is variation in physical traits such as size, color, and shape. Is it simply that those who survive to reproduce are lucky, or do these traits affect which individuals have a greater or lesser chance of surviving? Evolutionary biologists often work to see how differences in traits, such as body size, relate to differences in survival among individuals. When differences in traits are related to chances of survival, they are said to be under natural selection.

Brown anole lizards are useful for studies of natural selection because they are abundant in Florida and the Caribbean, easy to catch, and have a short life span. Brown anoles are very small when they hatch out of the egg. Because of their small size, these anole hatchlings are eaten by many different animals, including birds, crabs, other species of anole lizards, and even adult brown anoles! Predators could be a significant force of natural selection on brown anole hatchlings. Juvenile anoles that get eaten by predators will not survive to reproduce. Traits that help young brown anoles avoid predation and reproduce will get passed on to future generations.

Aaron with a baby anole lizard.

Aaron and Robert are scientists who study brown anoles on islands in Northeastern Florida. Along with their colleagues, they visit these islands every 6 to 10 weeks during the summer to survey the populations and measure natural selection in action. Aaron and Robert selected a small island that had a large brown anole population because they were able to find and measure all of the individuals on the island. Aaron observed that in the late summer there were thousands of hatchling lizards on the island, but by the middle of the summer the following year, only a few hundred of those lizards remained alive. He also observed that hatchlings varied greatly in body size and wondered if those differences in size affected the chances that an individual would survive to adulthood. He predicted that smaller hatchlings are more likely to die than larger ones because they are not as fast, and therefore not as likely to escape from predators and face a higher risk of being eaten.

To test this, Aaron and Robert captured hatchlings in July, assigned a unique identification number to each anole, measured their body length, and then released them back onto the island. In October of the same year, they returned to the island to capture and measure all surviving lizards. They calculated the average percent survival for each size category. Aaron predicted longer individuals would have higher survival. This would indicate that there was natural selection for larger body size in hatchlings.

Featured scientists: Aaron Reedy and Robert Cox from the University of Virginia. Co-written by undergraduate researcher Matt Kustra.

Flesch–Kincaid Reading Grade Level = 11.7

Additional teacher resource related to this Data Nugget:

For additional images of Robert and Aaron’s research with anoles in Florida, we have created PowerPoint slides that can be shown in class.
Aaron conducted this research as a graduate student in Robert Cox’s lab. To learn more about anole research, visit the lab’s website. To learn more about Aaron, visit his website.

Once your students have completed this Data Nugget, check out this video on anole size and natural selection from hurricanes!

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11.27.17

Is it dangerous to be a showoff?

A male anole lizard showing his bright dewlap.

The activities are as follows:

Natural selection happens when differences in traits within a population give some individuals a better chance of surviving and reproducing than others. Traits that are beneficial are more likely to be passed on to future generations. However, sometimes a trait may be helpful in one context and harmful in another. For example, some animals communicate with other members of their species through visual displays. These signals can be used to defend territories and attract mates, which helps the animal reproduce. However, these same bright and colorful signals can draw the unwanted attention of predators.

Brown anoles are small lizards that are abundant in Florida and the Caribbean. They have an extendable red and yellow flap of skin on their throat, called a dewlap. To communicate with other brown anoles, they extend their dewlap and move their head and body. Males have particularly large dewlaps, which they often display in territorial defense against other males and during courtship with females. Females have much smaller dewlaps and use them less often.

Aaron with a baby anole lizard.

Aaron is a scientist interested in how natural selection might affect dewlap size in male and female brown anoles. He chose to work with anoles because they are ideal organisms for studies of natural selection; they are abundant, easy to catch, and have short life spans. Aaron wanted to know whether natural selection was acting in different ways for males and females to cause the differences in dewlap size. He thought that a male with a larger dewlap may be more effective at attracting females and passing on his genes to the next generation. However, males with larger, showy dewlaps may catch the eye of more predators and have higher chances of being eaten. Aaron was curious about this tradeoff and how it affected natural selection on dewlap size. For female brown anoles, Aaron thought that this tradeoff would be less important for survival because females have smaller dewlaps and use them less frequently as a signal. In other words, there may not be selection on dewlap size in females.

Using a population of brown anoles on a small island in Florida, Aaron set up a study to determine how dewlap size is related to survival and whether there is a difference between the sexes. He worked with his advisor, Robert, and other members of the lab. They designed a study to track every brown anole on the island and see who survived. In May 2015, they caught the adult lizards on the island and recorded their sex, body length, and dewlap size before releasing them with a unique identification number. Then, the lab returned to the island in October and collected all the adults once again to determine who survived and who didn’t. Aaron predicted that male anoles with larger than average dewlap size would be less likely to survive due to an increased risk of predation. He also predicted that dewlap size would not influence female survival.

Featured scientists: Aaron Reedy and Robert Cox from the University of Virginia. Co-written by undergraduate researcher Cara Giordano.

Flesch–Kincaid Reading Grade Level = 10.3

Additional teacher resource related to this Data Nugget:

For additional images of Robert and Aaron’s research with anoles in Florida, we have created PowerPoint slides that can be shown in class.
Aaron conducted this research as a graduate student in Robert Cox’s lab. To learn more about anole research, visit the lab’s website. To learn more about Aaron, visit his website.
To engage students before the Data Nugget and introduce them to brown anoles, check out this video that shows how brown anoles use dewlap signaling to attract mates and send rival males signals during confrontations:

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6.26.17

Why are butterfly wings colorful?

The red postman butterfly, Heliconius erato.

The activities are as follows:

Éste Data Nugget también está disponible en Español:

You’ve probably noticed a bright orange butterfly in your garden. It’s hovering over a plant, and then pausing to lay an egg. It’s landing on a flower, and then sipping the tasty syrup. Big wings allow butterflies to fly everywhere with ease. But you may wonder, why are their wings so brightly colored? One reason why butterflies might have brightly colored wings is that these colors warn birds and other predators that they would not make a tasty meal. Another potential reason for butterflies to have bright colors and dramatic patterns is to attract mates. However, there is little research that shows whether color alone or color pattern together deter predators or attract mates.

Susan holding a different species of butterfly in the field.

The red postman butterfly lives in rainforests in Mexico, Central America, and South America. The color pattern on its wing is usually a mix of red, yellow, and black. These patterns vary a lot depending on their location; for instance one variant has a red bar on the forewings and a yellow bar on its hind wings while another variant has red rays on the hindwings and a yellow bar on the forewings. Scientists Susan, Adriana, and Robert have been studying this species for many years. While hiking in the rainforest, they noticed that not all butterfly species are brightly colored. They started to wonder why the red postman butterfly has bright colors, but other species do not. They thought maybe the red and yellow colors and patterns signaled toxicity to predators, like birds; or these wing features may be used to help find and attract mates. Susan, Adriana and Robert predicted that brightly colored butterflies would be avoided by birds and approached more often by other butterflies of the same species. They also predicted that the local color pattern would get the strongest response from predators and mates, because it would be most recognized in that area.

To test their ideas, the team of butterfly scientists created three kinds of artificial red postman butterfly models using paper and a printer. Each model had a plastic body and paper wings. Model A had the same pattern as the local butterflies at the study site in the La Selva Tropical Biological Station in Sarapiquí, Costa Rica, with brightly colored red and yellow wings. Model B also had the same pattern as the local butterflies, but only had black and white tones. Model C had a different pattern than the locals with bright red and yellow colors.

One of the 400 black and white models in the rainforest during the experiment.

To test for differences in predation attempts based on wing color and patterns, they placed 4 of each model at 100 different sites in the rainforest. This made a total of 1,200 model butterflies with 400 of each type! Models were placed far enough apart that they were not within human visible range from one another (on average separated by 5-10 m), and were positioned approximately 1.5 m above the ground, which is consistent with natural roosting heights. The models were left out in the forest for a total of 96 hours. Each day they were inspected and counted for bird beak marks on their wings and plastic bodies. Only new marks were scored each day, so attacks on individual models were only counted once. To test whether red postman butterflies were more attracted to bright colors, or the local wing pattern, Susan and her student field assistants also caught 51 wild red postman butterflies from the rainforest and brought them to a greenhouse. They then presented the live butterflies with the three models and counted how many times they approached each model type.

Featured scientists: Susan Finkbeiner, Adriana Briscoe, and Robert Reed from University of California, Irvine

Flesch–Kincaid Reading Grade Level = 9.9

Watch two videos of experimental trials from the greenhouse experiment:

The first shows a male butterfly approaching a butterfly paper model with color. The second shows a butterfly as it chooses between a butterfly paper model that is black-and-white and one that has color.

Video Trial 1

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Video Trial 2

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There are two publications related to this Data Nugget:

Finkbeiner SD, Briscoe AD, Reed RD. 2014. Warning signals are seductive: Relative contributions of color and pattern to predator avoidance and mate attraction in Heliconius butterflies. Evolution, 68:3410-20. DOI: 10.1111/evo.12524
Finkbeiner SD, Fishman DA, Osorio D, Briscoe AD. 2017. Ultraviolet and yellow reflectance but not fluorescence is important for visual discrimination of conspecifics by Heliconius erato. Journal of Experimental Biology 220: 1267-1276, doi: 10.1242/jeb.153593

You can follow all three scientists on Twitter where they tweet about the latest scientific discoveries involving butterflies, animals, vision and behavior! Adriana @AdrianaBriscoe, Susan @Fink_about_it, and Robert @FascinatingPupa.

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