Fast weeds in farmer’s fields

Native and weedy radish plants.

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 adaptationscould allow them to grow better and pass on more of their genes to the next generation.

Weedy radishis 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

Hold on for your life! Part II

In Part I the data showed that, after the hurricanes, anole lizards had on average larger 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:

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

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:

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.

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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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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Why are butterfly wings colorful?

The red postman butterfly, Heliconius erato.

The activities are as follows:

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.

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There are two publications related to this Data Nugget:

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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Sticky situations: big and small animals with sticky feet

Travis in the lab measuring the stickiness of a gecko’s toe.

Travis in the lab measuring the stickiness of a gecko’s toe.

The activities are as follows:

Species are able to do so many amazing things, from birds soaring in the air, lizards hanging upside-down from ceilings, and trees growing hundreds of feet tall. The study of biomechanics looks at living things from an engineering point of view to study these amazing abilities and discover why species come in such a huge variety of shapes and sizes. Biomechanics can improve our understanding of how plants and animals have adapted to their environments. We can also take what we learn from biology and apply it to our own inventions in a process called biomimicry. Using this approach, scientists have built robotic jellyfish to survey the oceans, walking robots to help transport goods, and fabrics that repel stains like water rolling off a lotus leaf.

Travis studies biomechanics and is interested in the ability of some species to climb and stick to walls. Sticky, or adhesive, toe pads have evolved in many different kinds of animals, including insects, arachnids, reptiles, amphibians, and mammals. Some animals, like frogs, bats, and bugs use suction cups to hold up their weight. Others, like geckos, beetles, and spiders have toe pads covered in tiny, branched hairs. These hairs actually adhere to the wall! Electrons in the molecules that make up the hairs interact with electrons in the molecules of the surface they’re climbing on, creating a weak and temporary attraction between the hairs and the surface. These weak attractions are called van der Waals forces.

Travis catching lizards in the Dominican Republic.

Travis catching lizards in the Dominican Republic.

The heavier the animal, the more adhesion they will need to stick and support their mass. With a larger toe surface area, more hairs can come in contact with the climbing surface, or the bigger the suction cup can be. For tiny species like mites and flies, tiny toes can do the job. Each fly toe only has to be able to support a small amount of weight. But when looking at larger animals like geckos, their increased weight means they need much larger toe pads to support them.

When comparing large and small objects, the mass of large objects grows much faster then their surface area does. As a result, larger species have to support more mass per amount of toe area and likely need to have non-proportionally larger toes than those needed by lighter species. This results in geckos having some crazy looking feet! This relationship between mass and surface area led Travis to hypothesize that larger species have evolved non-proportionally larger toe pads, which would allow them to support their weight and stick to surfaces.

To investigate this idea, Travis looked at the data published in a paper by David Labonte and fellow scientists. In their paper they measured toe pad surface area and mass of individual animals from 17 orders (225 species) including insects, arachnids, reptiles, amphibians, and mammals. From their data, Travis calculated the average toe pad area and mass for each order.

Travis then plotted each order’s mass and toe pad area on logarithmic axes so it is easier to compare very small and very large values. Unlike a standard axis where the amount represented between tick marks is always the same, on logarithmic axes each tick mark increases by 10 times the previous value. For example, if the first tick represents 1.0, the second tick will be 10, and the next 100. As an example, look at the graphs below.

gecko-graph

The left plot shows hypothetical gecko species of different sizes, but with proportional toes. Their mass per toe pad area ratio (g/mm2) varies, with larger species having larger g/mm2 ratios. In this case, larger species have to support more mass per toe pad area. In the right plot, larger gecko species have disproportionally larger toes. These differences change each species’ mass per toe pad area ratios, so that all species, regardless of their size, have the same mass per toe pad area ratio.

Featured scientists: David Labonte, Christofer J. Clemente, Alex Dittrich, Chi-Yun Kuo, Alfred J. Crosby, Duncan J. Irschick, and Walter Federle. Written by: Travis Hagey

Data Nugget Flesch–Kincaid Reading Grade Level = 10.3

Scaling Up – Math Activity Flesch–Kincaid Reading Grade Level = 9.5

There is a scientific paper associated with the data in this Data Nugget. The data was used with permission from D. Labonte.

Labonte, D., Clemente, C.J., Dittrich, A., Kuo, C.Y., Crosby, A.J., Irschick, D.J. and Federle, W., 2016. Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing. Proceedings of the National Academy of Sciences, p.201519459.

To learn more about Travis and his research on geckos, read this blog post, “An evolving sticky situation” and check out the video below!

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For a video and article on using “gecko power” to scale a building, check out this article – Climbing a Glass Building? Try a Gecko’s Sticky Pads


dr-fowleriAbout Travis: Ever since Travis was a kid, he was interested in animals and wanted to be a paleontologist. He even had many dinosaur names memorized to back it up! In college he discovered evolutionary biology, which drove him to apply for graduate school and become a scientist. There, he fell in love with comparative biomechanics, which combines evolutionary biology and mechanical engineering. Today Travis studies geckos and their sticky toes that allow them to scale surfaces like glass windows and tree branches.

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Are you my species?

Michael holding a male darter. The bright color patterns differ for each of the over 200 species. Photo by Tamra Mendelson.

Michael holding a male darter. The bright color patterns differ for each of the over 200 species. Photo by Tamra Mendelson.

The activities are as follows:

What is a species? The biological species concept says species are groups of organisms that can mate with each other but do not reproduce with members of other similar groups. How then do animals know who to choose as a mate and who is a member of their own species? Communication plays an important role. Animals collect information about each other and the rest of the world using multiple senses, including sight, sound, sonar, and smell. These signals may be used to figure out who would make a good mate and who is a member of the same species.

Michael snorkeling, looking for darters.

Michael snorkeling, looking for darters.

Michael is a scientist interested in studying how individuals communicate within and across the boundaries of species. He studies darters, a group of over 200 small fish species that live on the bottom of streams, rivers, and lakes. Michael first chose to study darters because he was fascinated by the bright color patterns the males have on their bellies during the breeding season. Female darters get to select which males to mate with and the males fight with each other for access to the females during the mating season. Species identification is very important during this time. Females want to make sure they choose a member of their own species to mate with. Males want to make sure they only spend energy fighting off males of their own species who are competing for the same females. What information do females and males use to guide their behavior and how do they know which individuals are from their own species?

Across all darter species, there is a huge diversity of color patterns. Because only males are brightly colored and there is such a diversity of colors and patterns, Michael wondered if males use the color patterns to communicate species identity during mating. Some darter species have color patterns that are very similar to those of other darter species. Perhaps, Michael thought, the boundaries of species are not as clear as described by the biological species concept. Some darter species may be able to hybridize, or mate with members of a different species if their color patterns are very close. Thus, before collecting any data, Michael predicted that the more similar the color patterns between two males, the more likely they would be to hybridize and act aggressively towards each other. If this is the case, it would serve as evidence that color pattern may indeed serve as a signal to communicate darter species identity.

Michael (right) in the field, collecting darters. Photo by Tamra Mendelson.

Michael (right) in the field, collecting darters. Photo by Tamra Mendelson.

Michael collected eight pairs of darter species (16 species in all) from Alabama, Mississippi, Tennessee, Kentucky, South Carolina, and North Carolina and brought them all back to the lab. In some species pairs the color patterns were very similar, and in some they were very different. For each species pair, he put five males of both species and five females of both species in the same fish tank and observed their behavior for five hours. He did this eight times, once for each species pair (for a total of 1,280 fish!). During the five-hour observation period, he recorded (1) how many times females mated with males of their own species or of a different species and (2) how many times males were aggressive towards males of their own species or of a different species. He used these data to calculate an index of bias for each behavior, to show whether individuals had stronger reactions towards members of their own species.

Featured scientist: Michael Martin from the University of Maryland, Baltimore County

Flesch–Kincaid Reading Grade Level = 10.9

Videos showing darter behavior:

Darter species used in the experiment:

darters

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Finding Mr. Right

Mountain chickadee, photo by Vladimir Pravosudov

Mountain chickadee, photo by Vladimir Pravosudov

The activities are as follows:

Depending on where they live, animals can face a variety of challenges from the environment. For example, animal species that live in cold environments may have adaptive traits that help them survive and reproduce under those conditions, such as thick fur or a layer of blubber. Animals may also have adaptive behaviors that help them deal with the environment, such as storing food for periods when it is scarce or hibernating during times of the year when living conditions are most unfavorable. These adaptations are usually consistently seen in all individuals within a species. However, sometimes populations of the same species may be exposed to different conditions depending on where they live. The idea that populations of the same species have evolved as a result of certain aspects of their environment is called local adaptation.

Mountain chickadees are small birds that live in the mountains of western North America. These birds do not migrate to warmer locations like many other bird species; they remain in the same location all year long. To deal with living in a harsh environment during the winter, mountain chickadees store large amounts of food throughout the forest during the summer and fall. They eat this food in the winter when very little fresh food is available. There are some populations of the species that live near the tops of mountains, and some that live at lower elevations. Birds at higher elevations experience harsher winter conditions (lower temperature, more snow) compared to birds living at lower elevations. This means that birds higher in the mountains depend more on their stored food to survive winter.

Carrie conducting field research in winter, photo by Vladimir Pravosudov

Carrie conducting field research in winter, photo by Vladimir Pravosudov

Carrie studies mountain chickadees in California. Based on previous research that was done in the lab she works in, she learned these birds have excellent spatial memory, or the ability to recall locations or navigate back to a particular place. This type of memory makes it easier for the mountain chickadees to find the food they stored. Carrie’s lab colleagues previously found that populations of birds from high elevations have much better spatial memory compared to low-elevation birds. Mountain chickadees also display aggressive behaviors and fight to defend resources including territories, food, or mates. Previous work that Carrie and her lab mate conducted found that male birds from low elevations are socially dominant over male birds from high elevations, meaning they are more likely to win in a fight over resources. Taken together, these studies suggest that birds from high elevations would likely do poorly at low elevations due to their lower dominance status, but low-elevation birds would likely do poorly at high elevations with harsher winter conditions due to their inferior memory for finding stored food items. These populations of birds are likely locally adapted – individuals from either population would likely be more successful in their own environments compared to the other.

In this species, females choose which males they will mate with. Males from the same elevation as the females may be best adapted to the location where the female lives. This means that when the female lays her eggs, her offspring will likely inherit traits that are well suited for that environment. If she mates with males that match her environment, she is setting up her offspring to be more successful and have higher survival where they will live. Carrie wondered if female mountain chickadees prefer to mate with males that are from the same elevation and therefor contribute to local adaptation by passing the adaptive behaviors on to the offspring. This process could contribute to the populations becoming more and more distinct. Offspring born in the high mountains will continue to inherit genes for good spatial memory, and those born at low elevations will inherit genes that allow them to be socially dominant.

Mountain chickadee, photo by Vladimir Pravosudov

Mountain chickadee, photo by Vladimir Pravosudov

To test whether female mountain chickadees contribute to local adaptation by choosing and mating with males from their own elevation, Carrie brought high- and low-elevation males and females into the lab. Carrie made sure that the conditions in the lab were similar to the light conditions in the spring when the birds mate (14 hours of light, 10 hours of dark). Once a female was ready, she was given time to spend with both males in a cage that is called a two-choice testing chamber. On one side of the testing chamber was a male from a low-elevation population, and on the other side was a male from a high-elevation population. Each female could fly between the two sides of the testing chamber, allowing her to “choose” which male she preferred to spend time close to (measured in seconds [s]). There was a cardboard divider in the middle of the cage with a small hole cut into it. This allowed the female to sit on the middle of the cardboard, which was not counted as preference for either male. Females from both high- and low-elevation populations were tested in the same way. The female bird’s preference was determined by comparing the amount of time the female spent on either side of the cage. The more time a female spent on the side of the cage near one male, the stronger her preference for that male.

Watch a video of one of the experimental trials:

Featured scientist: Carrie Branch from University of Nevada Reno

Flesch–Kincaid Reading Grade Level = 11.5

Additional teacher resources related to this Data Nugget include:


carrie-branchAbout Carrie: I have been interested in animal behavior and behavioral ecology since my second year in college at the University of Tennessee. I am primarily interested in how variation in ecology and environment affect communication and signaling in birds. I have also studied various types of memory and am interested in how animals learn and use information depending on how their environment varies over space and time. I am currently working on my PhD in Ecology, Evolution, and Conservation Biology at the University of Nevada Reno and once I finish I hope to become a professor at a university so that I can continue to conduct research and teach students about animal behavior. In my spare time I love hiking with my friends and dogs, and watching comedies!

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Why so blue? The determinants of color pattern in killifish, Part II

In Part 1, you examined the effects of genetics and environment on anal fin color in male bluefin killifish. The data from Becky’s experiment showed that both genetics and environment work together to determine whether male offspring had blue, yellow, or red anal fins. You will now examine how the father’s genetics, specifically their fin color pattern, affects anal fin color in their sons. When we factor in the genetics of the father, and not just the population he came from, does this influence our interpretation of the data?

The color polymorphism in bluefin killifish – males display anal fins in blue, red, or yellow.

The activities are as follows:

For her experiment, Becky collected male and female fish from both a swamp (26 Mile Bend) and a spring (Wakulla) population. Most of the males in the swamp have blue anal fins, but some have red or yellow. Most of the males from the spring have red or yellow anal fins, but some have blue. Becky decided to add data about the father’s fin color pattern into her existing analysis from Part 1 to see how it affected her interpretation of the results.

In Part 1, Becky was looking at the genetics from the population level. Looking at the data this way, we saw parents from the 26 Mile Bend swamp population were more likely to have sons with blue anal fins than parents from the Wakulla spring. Parents from the 26 Mile Bend were also much more likely to have sons with higher levels of plasticity, meaning they responded more to the environment they were raised in. This means there was a big difference between the proportion sons with blue anal fins in the clear and brown water treatments.

Bringing in the color pattern of the fathers now allows Becky to look at the genetics from both the population and the individual level. From both the swamp and spring population, Becky collected males of all colors. Becky measured the color pattern of the fathers and recorded the color of their anal fins and the rear part of their dorsal fins. She used males that were red on the rear portion of the dorsal fin with a blue anal fin (rb), males that were red on both fins (rr), males that were yellow on both fins (yy), and males that were yellow on the rear portion of the dorsal fin with blue a blue anal fin (yb).

colormorph

She randomly assigned each father’s sons into one of the water treatments, either clear or brown water. Once the sons developed their fin colors, she recorded the anal fin color. This experimental design allowed her to test whether sons responded differently to the treatment depending on the genetics of their father. She thought that the anal fin color of the sons would be inherited genetically from the father, but would also respond plastically to the environment they were raised in. She predicted fathers with blue anal fins would be more likely to have sons with blue anal fins, especially if they were raised in the brown water treatment. She also predicted that fathers with red and yellow anal fins could have sons with blue anal fins if they were raised in the brown water treatment, but not as many as the blue fathers.

Featured scientist: Becky Fuller from The University of Illinois

Flesch–Kincaid Reading Grade Level = 10.9


About Becky: I consider myself to be an evolutionary biologist who studies fishes. I grew up in a small town riding horses in 4-H and working in a veterinary clinic. As an undergraduate at the University of Nebraska at Lincoln, I was interested in biology and considering either medical or veterinary school. Two things led to me research in ecology and evolution. In the summer of 1991, I was taking courses at Cedar Point Biological Field Station which was run by the University of Nebraska. I met Dr. Anthony Joern (Tony) who was studying grasshopper community ecology. Tony hired me onto his field crew that summer after the courses were finished. I went on to do an undergraduate thesis under Tony’s mentorship where I studied predation on grasshoppers. I caught the “science bug” and never looked back. Following my undergraduate work, I went to Uppsala University in Sweden on a Fulbright Scholarship. Here, I developed my love for fish and aquatics. I worked with Dr. Anders Berglund on pipefish in a fjord on the west coast of Sweden. Since then, I have had many wonderful advisers, instructors, mentors, and collaborators who have helped me develop skills along the numerous fronts required for a successful career in science. I consider myself very fortunate to have a job where I can do science and teach young, enthusiastic undergraduates.