evolution ‣ Data Nuggets

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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12.2.16

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.

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 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 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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11.1.16

Finding Mr. Right

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 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

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’s lab’s website, for more information on chickadee cognition!
A YouTube video of one of Carrie’s experimental trials showing a female in the two-choice testing chamber. Students can observe the female chickadee as she decides between the males on her left or the one on her right.
The paper published using these data and testing alternative hypotheses:
- Branch, C.L., Kozlovsky, D.Y., and V.V. Pravosudoc. 2015. Elevation-related differences in female mate preferences in mountain chickadees: are smart chickadees choosier? Animal Behavior 99: 89-94.

About 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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11.1.16

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).

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.

11.1.16

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

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

The activities are as follows:

In nature, animals can be found in a dazzling display of different colors and patterns. Color patterns serve as signals to members of the animal’s own species, or to other species. They can be used to attract mates, camouflage with the environment, or warn predators to stay away. When looking at the diversity of colors found in nature, you may wonder, why do animals have the color patterns they do? One way to study this question is to look at a single species that has individuals of different colors. This variation can be used to uncover the mechanisms that determine color.

The bluefin killifish is a freshwater species that is found mostly in Florida. They are found in two main habitats, springs and swamps. An intriguing aspect of this species is that male bluefin killifish are brightly colored with many different color patterns. The brightest part of the fish is the anal fin, which is found on the bottom of the fish by the tail. Some males have red anal fins, some have yellow anal fins, and others have blue anal fins. This variation in color is called a polymorphism, meaning that in a species there are multiple forms of a single trait. In a single spring or swamp you may see all three colors!

Becky in the field, with her colleague Katy, collecting fish in 26 Mile Bend Swamp.

Becky is a biologist studying bluefin killifish. One day, while out snorkeling for her research, she noticed an interesting pattern. She observed that there were differences in the polymorphism depending on whether she was in a spring or swamp. Springs have crystal clear water that can appear blue-tinted. Becky noticed that most of the males in springs had either red or yellow anal fins. Swamps have brown water, the color of iced tea, due to the dissolved plant materials in the water. Becky noticed that most of the males in swamps had blue anal fins. After noticing this pattern she wanted to find out why this variation in color existed. Becky came up with two possible explanations. She thought males in swamps might be more likely to be blue (1) because of the genes they inherit from their parents, or (2) because individual color is responding to environmental conditions. This second case, where the expression of a trait is directly influenced by the environment that an individual experiences, is known as phenotypic plasticity.

Becky had to design an experiment that could tease apart whether genes, plasticity, or both were responsible for male anal fin color. She did this by collecting male and female fish from the two habitat types, breeding them, and raising their offspring in clear or brown water. If a father’s genes are responsible for anal fin color in their sons, then fathers from swamps would be more likely to leave behind blue sons. If environmental conditions determine the color of sons, then sons raised in brown water will be blue, regardless of the population origin of their father.

Becky’s family helping her out in the field!

Becky and her colleagues collected fish from two populations in the wild – Wakulla Spring, and 26 Mile Bend Swamp – and brought them into the lab. These two populations represent the genetic stocks for the experiment. Fish from Wakulla are more closely related to each other than they are to fish from 26 Mile Bend. In the lab, they mated female fish with male fish from the same population: females from Wakulla mated with males from Wakulla, and females from 26 MB mated with males from 26 MB. The female fish then laid eggs, and after the offspring hatched from their eggs, half were put into tanks with clear water (which mimics spring conditions) and half in tanks with brown water (which mimics swamp conditions). For the brown water treatment, Becky colored the water using ‘Instant, De-caffeinated, No-Sugar, No-Lemon’ tea. They raised the fish to adulthood (3-6 months) so they could determine their sex and the color of the son’s anal fins. Becky then counted the total number of male offspring, and the number of male offspring that had blue anal fins. She used these numbers to calculate the proportion of sons that had blue anal fins in each treatment.

Featured scientist: Becky Fuller from The University of Illinois

Flesch–Kincaid Reading Grade Level = 9.4

To introduce students to bluefin killifish, there is a video showing the blue and red color morphs. Video can be shown on mute (background music is a little corny)!

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10.13.16

Winter is coming! Can you handle the freeze?

Doug, and two members of his team, setting up the reciprocal transplant experiment in Scandinavia.

Doug with the reciprocal transplant experiment in Scandinavia.

The activities are as follows:

Doug is a biologist who studies plants from around the world. He often jokes that he chose to work with plants because he likes to take it easy. While animals rarely stay in the same place and are hard to catch, plants stay put and are always growing exactly where you planted them! Using plants allows Doug to do some pretty cool and challenging experiments. Doug and his research team carry out experiments with the plant species Mouse-ear Cress, or Arabidopsis thaliana. They like this species because it is easy to grow in both the lab and field. Arabidopsis is very small and lives for just one year. It grows across most of the globe across a wide range of latitudes and climates. Arabidopsis is also able to pollinate itself and produce many seeds, making it possible for researchers to grow many individuals to use in their experiments.

Doug, and two members of his team, setting up the reciprocal transplant experiment in Scandinavia.

Part I: Doug wanted to study how Arabidopsis is able to survive in such a range of climates. Depending on where they live, each population faces its own challenges. For example, there are some populations of this species growing in very cold habitats, and some populations growing in very warm habitats. He thought that each of these populations would adapt to their local environments. An Arabidopsis population growing in cold temperatures for many generations may evolve traits that increase survival and reproduction in cold temperatures. However, a population that lives in warm temperatures would not normally be exposed to cold temperatures, so the plants from that population would not be able to adapt to cold temperatures. The idea that populations of the same species have evolved as a result of certain aspects of their environment is called local adaptation.

To test whether Arabidopsis is locally adapted to its environment, Doug established a reciprocal transplant experiment. In this type of experiment, scientists collect seeds from plants in two different locations and then plant them back into the same location (home) and the other location (away). For example, seeds from population A would be planted back into location A (home), but also planted into location B (away). Seeds from population B would be planted back into location B (home), but also planted at location A (away). If populations A and B are locally adapted, this means that A will survive better than B in location A, and B will survive better than A in location B. Because each population would be adapted to the conditions from their original location, they would outperform the plants from away when they are at home (“home team advantage”).

In this experiment, Doug collected many seeds from warm Mediterranean locations at low latitudes, and cold Scandinavian locations at high latitudes. He used these seeds to grow thousands of seedlings. Once these young plants were big enough, they were planted into a reciprocal transplant experiment. Seedlings from the Mediterranean location were planted alongside Scandinavian seedlings in a field plot in Scandinavia. Similarly, seedlings from the Scandinavian locations were planted alongside Mediterranean seedlings in a field plot in the Mediterranean. By planting both Mediterranean and Scandinavian seedlings in each field plot, Doug can compare the relative survival of each population in each location. Doug made two local adaptation predictions:

Scandinavian seedlings would survive better than Mediterranean seedlings at the Scandinavian field plot.
Mediterranean seedlings would survive better than Scandinavian seedlings planted at the Mediterranean field plot.

Doug’s team in the Mediterranean prepped and ready to set up the experiment.

Part II: The data from Doug’s reciprocal transplant experiment show that the Arabidopsis populations are locally adapted to their home locations. Now that Doug confirmed that populations were locally adapted, he wanted to know how it happened. What is different about the two habitats? What traits of Arabidopsis are different between these two populations? Doug now wanted to figure out the mechanism causing the patterns he observed.

Doug originally chose Arabidopsis populations in Scandinavia and the Mediterranean for his research on local adaptation because those two locations have very different climates. The populations may have adapted to have the highest survival and reproduction based on the climate of their home location. To deal with sudden freezes and cold winters in Scandinavia, plants may have adaptations to help them cope. Some plants are able to protect themselves from freezing temperatures by producing chemicals that act like antifreeze. These chemicals accumulate in their tissues to keep the water from turning into ice and forming crystals. Doug thought that the Scandinavian population might have evolved traits that would allow the plants to survive the colder conditions. However, the plants from the Mediterranean aren’t normally exposed to cold temperatures, so they wouldn’t have necessarily evolved freeze tolerance traits.

To see whether freeze tolerance was driving local adaptation, he set up an experiment to identify which plants survived after freezing. Doug again collected seeds from several different populations across Scandinavia and across the Mediterranean. He chose locations that had different latitudes because latitude affects how cold an area gets over the year. High latitudes (closer to the poles) are generally colder and low latitudes (closer to the equator) are generally warmer. Doug grew more seedlings for this experiment, and then, when they were a few days old, he put them in a freezer. Doug counted how many seedlings froze to death, and how many survived, and he used these numbers to calculate the percent survival for each population. To gain confidence in his results, he did this experiment with three replicate genotypes per population.

Doug predicted that if freeze tolerance was a trait driving local adaptation, the seedlings originally from colder latitudes (Scandinavia) would have increased survival after the freeze. Seedlings originally from lower latitudes would have decreased survival after the freeze because the populations would not have evolved tolerance to such cold temperatures.

Featured scientist: Doug Schemske from Michigan State University (MSU). Written by Christopher Oakley from MSU and Purdue University, and Marty Buehler (RET) from Hastings High School.

Flesch–Kincaid Reading Grade Level = 12.0

There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below.

Agren, J. and D.W. Schemske (2012). Reciprocal transplants demonstrate strong adaptive differentiation of the model organism Arabidopsis thaliana in its native range. New Phytologist 194:1112–1122.

8.20.16

Beetle battles

Erin has always loved beetles! Here she is with a dung beetle in Tanzania, during a graduate school class trip.

The activities are as follows:

Male animals spend a lot of time and energy trying to attract females. In some species, males directly fight with other males to become socially dominant. They also fight to take over and control important territories. This process is known as male-male competition. The large antlers of male elk are an example of a trait that has been favored by male-male competition. In other species, males try to court females directly. This process is known as female choice. The flashy tails of male peacocks are a good example of a trait that has been favored by female choice. Lastly, in some species, both male-male competition AND female choice determine which males get to mate. In order to be successful, males have to be good at both fighting other males and making themselves attractive to females. Erin is a biologist interested in these different types of mating systems. She wondered if she could discover a single trait that was favored by both male-male competition and female choice.

Two dung beetle males fighting for ownership of the artificial tunnel. Why is the photo pink? Because beetles mate and fight in dark, underground tunnels, Erin carried out all of her experiments in a dark room under dim red-filtered light. Beetles can’t see the color red, so working under red-filtered light didn’t affect the beetles’ behavior, and allowed Erin to see what the beetles were doing.

In horned dung beetles, male-male competition and female choice are both important in determining which males get to mate. Females dig tunnels underneath fresh piles of dung where they mate and lay their eggs. Beetles only mate inside these underground tunnels, so males fight with other males to become the owner of a tunnel. Males that control the tunnels have a better chance to mate with the female that dug it. However, there is often more than one male inside a breeding tunnel. Small males will sneak inside a main tunnel by digging a connecting side tunnel. Additionally, the constant fights between large males means that the ownership of tunnels is constantly changing. As a result, females meet many different males inside their tunnels. It is up to them to choose the male they find the most attractive, and with whom they’ll mate. In this species of dung beetle, males try to persuade females to mate by quickly tapping on the females’ back with their forelegs and antennae. Previous research has found that females are more likely to mate with males that perform this courtship tapping at a fast rate. Because both fighting and courtship tapping take a lot of strength, Erin wondered if the trait of strength was what she was looking for. Would stronger male dung beetles be favored by both male-male competition and female choice?

To keep beetles alive in the lab, Erin set up a bucket with sand, and placed one pile of dung in the center. Female beetles dug tunnels below the dung.

To test her hypothesis, Erin conducted a series of experiments to measure the mating success, fighting success, and strength of male dung beetles. First, Erin measured the mating success of male beetles by placing one male and one female in an artificial tunnel (a piece of clear plastic tubing). She watched the pair for one hour, and measured how quickly the males courted, and whether or not the pair mated. Second, Erin measured the fighting success of males by staging fights between two males over ownership of an artificial tunnel. Beetle battles consist of a head-to-head pushing match that results in one male getting pushed out of the tunnel, and the other male remaining inside. To analyze the outcome of these fights, Erin randomly selected one male in each pair as the focal male, and scored the interaction as a “win” if the focal male remained inside the tunnel, and as a “loss” if the focal male got pushed out of the tunnel. In some cases, there was not a clear winner and loser because either both males left the tunnel, or both males remained inside. These interactions were scored as a “tie”. Finally, Erin determined each beetles’ strength. She measured strength as the amount of force it took to pull a male out of an artificial tunnel. To do this, she super-glued a piece of string to the back of the beetle, had it crawl into an artificial tunnel, attached the string to a spring scale, and then pulled on the scale until the beetle was pulled out of the tunnel.

Featured scientist: Erin McCullough from the University of Western Australia

Flesch–Kincaid Reading Grade Level = 8.8

Additional resources related to this Data Nugget:

There is one scientific paper associated with the data in this Data Nugget. McCullough, E.L. and L.W. Simmons (2016) Selection on male physical performance during male–male competition and female choice. Behavioral Ecology
Alignment of this activity to NGSS Standards can be found on the NSTA website here.

About Erin: I am fascinated by morphological diversity, and my research aims to understand the selective pressures that drive (and constrain) the evolution of animal form. Competition for mates is a particularly strong evolutionary force, and my research focuses on how sexual selection has contributed to the elaborate and diverse morphologies found throughout the animal kingdom. Using horned beetles as a model system, I am interested in how male-male competition has driven the evolution of diverse weapon morphologies, and how sexual selection has shaped the evolution of physical performance capabilities. I am first and foremost a behavioral ecologist, but my research integrates many disciplines, including functional morphology, physiology, biomechanics, ecology, and evolution.

8.17.16

Feral chickens fly the coop

Red Junglefowl are the same species as chickens (Gallus gallus). On Kauai island, they have mated with feral chickens to produce hybrids (photo by Tontantours).

The activities are as follows:

When domesticated animals that humans keep in captivity escape into the wild, we call them feral. You may have seen feral animals, such as pigeons, cats, or dogs, right in your own backyard. But did you know that there are dozens of other feral species all over the world, including goats, parrots, donkeys, wallabies, and chameleons?

Sometimes feral species interbreed with closely related wild relatives to produce hybrid offspring. Feral dogs, for example, occasionally mate with wolves to produce hybrid pups which resemble both their wolf and dog parents. Over many generations, a population made up of these wolf-dog hybrids can evolve to become more wolf-like or more dog-like. Which direction they take will depend on whether dog or wolf traits help the individual survive and reproduce in the wild. In other words, hybrids should evolve traits that are favored by natural selection.

Photograph of a feral hen on Kauai, with her recently hatched chicks (photo by Pamela Willis).

You might be surprised to learn that, like dogs, chickens also have close relatives living in the wild. These birds, called Red Junglefowl, inhabit the jungles of Asia and also many Pacific islands. Eben is a biologist who studies how the island populations of these birds are evolving over time. He has discovered that Red Junglefowl on Kauai Island, which is part of Hawaii, have recently started interbreeding with feral chickens. This interbreeding has produced a hybrid population of birds that are somewhere in between red junglefowl and domestic chickens.

One of the biggest differences between chickens and Red Junglefowl is their breeding behaviors. Red Junglefowl females lay only a handful of eggs each year and only in the spring. Domestic chickens can lay eggs during any season and sometimes up to 300 or more eggs in one year! Eben wanted to know more about the breeding behaviors of Kauai’s feral populations. In many cases, natural selection favors individuals who produce more offspring during their lifetimes. Because domesticated chickens can lay eggs year-round, Eben thought that the feral population would be evolving to be more like domesticated chickens. He predicted that feral hens would breed in all seasons.

To test his hypothesis, Eben’s research group collected hundreds of photographs and videos of Kauai’s hybrid chickens. Tourists delight in photographing Kauai’s wild chickens and uploading their media to the internet. Fortunately for Eben, their cameras and cell phones often record the dates that images are taken. Eben looked at media posted on websites like Flickr and YouTube to find documentation of feral chickens throughout the year. This allowed him to see whether chicks are present during each of the four seasons. He knew that any hen observed with chicks had recently mated and hatched eggs because the chicks only stay with their mothers for only a few weeks.

Featured scientist: Eben Gering from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.6

To learn more about feral chickens and Eben’s research, check out the popular science articles below:

New York Times Article, “In Hawaii, Chickens Gone Wild”
Nature Article, “When Chickens Go Wild”
MSU Today, “How Did the Chicken Cross the Sea?“
BEACON, “Feral chickens are a-changing: updates on the rapid evolution of Kauai’s hybrid Gallus gallus”

Mini documentary you can watch in class. The video gives a brief history of chickens on the island of Kauai, and shows mother hens with their chicks:

Cock a Doodle Doo from John Goheen on Vimeo.

Students can watch the same videos that Eben used to collect his experimental data. They can find these videos by searching YouTube for “feral chickens Kauai” and many examples will come up, like this video:

About Eben: One of the most exciting things I learned as a college student was that natural populations sometimes evolve very quickly. Biologists used to think evolution was too slow to be studied “in action”, so their research focused on evolutionary changes that occurred over thousands (or even millions) of years. I study feral animal populations to learn how rapid evolutionary changes help them survive and reproduce, without direct help from us.

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5.16.16

How the cricket lost its song, Part II

In Part I you determined that the Kauai flatwing mutation led to a decrease in parasitism rates for male crickets. Today, most of the male crickets on Kauai have evolved flat wings and can no longer produce songs that were previously used to attract female crickets. Without their songs, how do males attract females?

Robin collecting data on satellite behavior in normal and flatwing mutation males.

The activities are as follows:

Without their song, how are flatwing crickets able to attract females? In some other animal species, like birds, males use an alternative to singing, called satellite behavior. Satellite males hang out near a singing male and attempt to mate with females who have been attracted by the song. This helps satellite males in two ways: they don’t use energy to make a song, and they avoid attracting enemies like the fly. Perhaps the satellite behavior gives flatwing males the opportunity to mate with females who were attracted to the few singing males left on Kauai.

Collecting crickets at the speaker.

To test this idea, Robin set up a speaker playing cricket songs in the fields where the crickets live on Kauai, Oahu, and the Island of Hawaii. The speaker tricks male and female crickets into thinking there is a male cricket in the area making songs. Before the start of the experiment, Robin removed all the males found within a 2-meter circle around the speaker. She then broadcast cricket songs from the speaker for 20 minutes. She returned and counted the number of males in the 2-meter circle, measured the distance from male to the speaker, and noted whether each male was normal or flatwing. Robin expected that flatwing males would be more likely to use satellite behavior and, therefore, would be on average closer to the speaker than normal males.

Featured scientist: Robin Tinghitella from the University of Denver

Flesch–Kincaid Reading Grade Level = 10.0

Additional teacher resources related to this Data Nugget include:

A video introducing the study system and describing how, in fewer than 20 generations, crickets on the island of Kuai went from singing to silent!
Listen to cricket songs!
Several papers have been published on this data and study system:
- Zuk, M., Rotenberry, J.T. & Tinghitella, R.M. 2006. Silent Night: Adaptive disappearance of a sexual signal in a parasitized population of field crickets. Biology Letters 2:521-524.
- Tinghitella, R.M. & Zuk, M. 2009. Asymmetric mating preferences accommodated the rapid evolutionary loss of a sexual signal. Evolution 63:2087-2098.
Some popular science writings on this research:
- UC Berkeley’s Understanding Evolution Website: Quick evolution leads to quiet crickets.
- Science News: Crickets on Mute: Hush falls as killer fly stalks singers. Volume 170 (13).
- A blog post by Robin on her research.

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