11.1.16

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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10.21.16

Bon Appétit! Why do male crickets feed females during courtship?

Mating pair of Hawaiian swordtail cricket with macrospermatophore on the male (left). The male and female (right) are marked with paint pens for individual identification.

Mating pair of Hawaiian swordtail cricket with macrospermatophore on the male (left). The male and female (right) are marked with paint pens for individual identification.

The activities are as follows:

In many species of insects and spiders, males provide females with gifts of food during courtship and mating. This is called nuptial feeding. These offerings are eaten by the female and can take many forms, including prey items the male captured, substances produced by the male, or parts from the male’s body. In extreme cases the female eats the male’s entire body after mating! Clearly these gifts can cost the male a lot, including time and energy, and sometimes even their lives.

So why do males give these gifts? There are two main hypotheses explaining why nuptial feeding has evolved in so many different species. First, giving a gift may attract a female and improve a male’s chance of getting to mate with her, or of fathering her young. This is known as the mating effort hypothesis. Second, giving a gift may provide the female with the energy and nutrients she needs to produce young. The gift helps the female have more, or healthier, offspring. This is known as the paternal investment hypothesis. These two hypotheses are not mutually exclusive – meaning, for any given species, both mechanisms could be operating, or just one, or neither.

Biz is a scientist who studies nuptial gifts, and they work with the Hawaiian swordtail cricket. They chose this species because it uses a particularly interesting example of nuptial feeding. In most other cricket species, the male provides the female with a single package of sperm, called a spermatophore. After sperm transfer, the female removes the spermatophore from her genitalia and eats it. However, in the Hawaiian swordtail cricket, males produce not just one but a whole bunch of spermatophores over the course of a single mating. Most of these are smaller, and contain no sperm – these are called “micros”. Only the last and largest spermatophore to be transferred, called the “macro” actually contains sperm. The number of micros that a male gives changes from mating to mating.

From some of their previous research, and from reading papers written by other scientists, Biz learned that micros increase the chance that a male’s sperm will fertilize some of the female’s eggs. Also, the more micros the male gives, the more of the female’s offspring he will father. This research supports the mating effort hypothesis for the Hawaiian swordtail cricket. Knowing this, Biz wanted to test the paternal investment hypothesis as well. They wanted to know whether the “micro” nuptial gifts help females lay more eggs, or help more of those eggs hatch into offspring.

Biz used two experiments to test the paternal investment hypothesis. In the first experiment, 20 females and 20 males were kept in a large cage outside in the Hawaiian rainforest. The crickets were allowed to mate as many times as they wanted for six weeks. In the second experiment, 4 females and 4 males were kept in cages inside in a lab. Females were allowed to mate with up to 3 different males, and were then moved to a new cage to prevent them from mating with the same male more than once. In both experiments Biz observed all matings. They recorded the number of microspermatophores transferred during each mating and the number of eggs laid. If females that received a greater number of total micros over the course of all matings produced more eggs, or if their eggs had a higher rate of hatching, then the paternal investment hypothesis would be supported.

Featured scientist: Biz Turnell from Cornell University and Technische Universität Dresden

Flesch–Kincaid Reading Grade Level = 8.9

Additional teacher resources related to this Data Nugget include:

10.5.16

Raising Nemo: Parental care in the clown anemonefish

Clown anemonefish caring for their eggs.

Clown anemonefish caring for their eggs.

The activities are as follows:

When animals are born, some offspring are able to survive on their own, while others rely on parental care. Parental care can take many forms. One or both parents might help raise the young, or in some species other members of the group help them out. The more time and energy the parents invest, the more likely it is that their offspring will survive. However, parental care is costly for the parents. When a parent invests time, energy, and resources in their young, they are unable to invest as much in other activities, like finding food for themselves. This results in a tradeoff, or a situation where there are costs and benefits to the decisions that must be made. Parents must balance their time between caring for their offspring and other activities.

The severity of the tradeoff between parental care and other activities may depend on environmental conditions. For example, if there is a lot of food available, parents may spend more time tending to their young because finding food for themselves takes less time and energy. Scientists wonder if parents are able to adjust their parental care strategies in response to environmental changes.

Photo of Tina (left) with other members of her lab. The glowing blue tanks around them all contain anemonefish!

Photo of Tina (left) with other members of her lab. The glowing blue tanks around them all contain anemonefish!

Tina is a scientist studying the clown anemonefish. She is interested in how parental care in this species changes in response to the environment. She chose to study anemonefish because they use an interesting system to take care of their young, and because the environment is always changing in the coral reefs where they live.

Anemonefish form monogamous pairs and live in groups of up to six individuals. The largest female is in charge of the group. Only the largest male and female get to mate and take care of the young. Both parents care for eggs by tending them, mouthing the eggs to clean the nest and remove dead eggs, and fanning eggs with their fins to oxygenate them. A single pair may breed together tens or even hundreds of times over their lifetimes. But here is the cool part – anemonefish can change their sex! If the largest female dies, the largest male changes to female, and the next largest fish in line becomes the new breeding male. That means that a single parent may have the opportunity to be a mother and a father during its lifetime.

Parents will fan the eggs to increase oxygen by the nest, or mouth them to remove dead eggs and clean the nest.

Parents will fan the eggs to increase oxygen by the nest, or mouth them to remove dead eggs and clean the nest.

On the reef, anemonefish groups also experience shifts in how much food is available. In years with lots of food, the breeding pair has lots of young, and in years with little food they do not breed as often. Tina presumed that food availability determines how much time and energy the parents invest in parental care behaviors. She collected data from 20 breeding pairs of fish, 10 of which she gave half rations of food, and 10 of which she gave full rations. The experiment ran for six lunar months. Every time a pair laid a clutch of eggs, Tina waited 7 days and then took a 15-minute video of the parents and their nest. She watched the videos and measured three parental care behaviors: mouthing, fanning, and total time spent tending for both males and females. Some pairs laid eggs more than once, so she averaged these behaviors across the six months of the experiment. Tina predicted that parents fed a full ration would perform more parental care behaviors, and for a longer amount of time, than parents fed a half ration.

Watch video of the experimental trials, demonstrating the mouthing and fanning behaviors:

Featured scientist: Tina Barbasch from Boston University

Flesch–Kincaid Reading Grade Level = 9.4

barbasch_photoAbout Tina: I first became interested in science catching frogs and snakes in my backyard in Ithaca, NY. This inspired me to major in Biology at Cornell University, located in my hometown. As an undergraduate, I studied male competition and sperm allocation in the local spotted salamander, Ambystoma maculatum. After graduating, I joined the Peace Corps and spent 2 years in Morocco teaching environmental education and 6 months in Liberia teaching high school chemistry. As a PhD student in the Buston Lab, I study how parents negotiate over parental care in my study system the clownfish, Amphiprion percula, otherwise known as Nemo. More here!

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8.29.16

How do brain chemicals influence who wins a fight?

fighting-fly-360wThe activities are as follows:

In nature, animals compete for resources. These resources include space, food, and mates. Animals use aggression as a way to capture or defend these resources, which can improve their chances of survival and mating. Aggression is a forceful behavior meant to overpower opponents that are competing for the same resource. The outcome (victory or defeat) depends on several factors. In insects, the bigger individuals often win. However, if two opponents are the same size, other factors can influence outcomes. For example, an individual with more experience may defeat an individual with less experience. Also individuals that are fighting to gain something necessary for their survival have a strong drive, or motivation, to defeat other individuals.

Researchers Andrew, Ken, and John study what role an animal’s brain plays in regulating behavior when motivation is present. They wanted to know if specific chemicals in the brain influenced the outcome of a physically aggressive competition. Andrew, Ken, and John read a lot papers written by other scientists and learned that there is a brain chemical that plays an important role in regulating aggressive behavior. This chemical is called serotonin and is found in the brains of all animals, including humans. Even a small amount of this chemical can make a big impact on aggressive behavior, and perhaps the outcome of competition.

The researchers decided to do an experiment to test what happens to aggression during competition as serotonin levels in the brain increase. They used stalk-eyed flies in their experiment. Stalk-eyed flies have eyes on the ends of stalks that stick out from the sides of their heads (Pictures 1 & 2). They reasoned that brain serotonin levels in stalk-eyed flies influence their aggressive behaviors in battle and therefore impact the outcome of competition. If their hypothesis is true, they predicted that increasing the brain serotonin in a stalk-eyed fly would make it more likely to use aggressive behaviors, and flies that used more aggressive behaviors would be more likely to win. Battling flies use high-intensity aggressive attacks like jumping on or striking an opponent. They also use less aggressive behaviors like flexing their front legs or rearing up on their hind legs.

Two stalk-eyed flies rearing/extending forearms in battle. Photo credit: Sam Cotton.

Two stalk-eyed flies rearing/extending forearms in battle. Photo credit: Sam Cotton.

To test their hypothesis, the researchers set up a fair test. A fair test is a way to control an experiment by only changing one piece of the experiment at a time. By changing only one variable, scientists can determine if that change caused the differences they see. Since larger flies tend to win fights, the flies were all matched up with another fly that was the same size. This acted as an experimental control for size, and made it possible to look at only the impact of serotonin levels on aggression. The scientists also controlled for the age of the flies and made sure they had a similar environment since the time they were born. The experiment had 20 trials with a different pair of flies in each. In each trial, one fly received corn mixed with a dose of serotonin, while another fly received plain corn as a control. That way, both flies received corn to eat, but only one received serotonin.

Each pair of flies was placed in a fighting arena and starved for 12 hours to increase their motivation to fight over food. Next, food was placed in the center of the arena, but only enough for one fly! The researchers observed the flies, recording three types of behaviors for each opponent. High intensity behaviors were when the fighting flies touched one another. Low-intensity behaviors were when the flies did not touch each other, for example jump attacks, swipes, and lunges. The last behavior type was retreating from the fight. Flies that retreated fewer times than their opponent were declared the winners. After the battles, the researchers collected the brains of the flies and measured the concentration of serotonin in each fly’s brain.

Featured scientists: Andrew Bubak and John Swallow from the University of Colorado at Denver, and Kenneth Renner from the University of South Dakota

Flesch–Kincaid Reading Grade Level = 9.2

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

Bubak, A.N., K.J. Renner, and J.G. Swallow. 2014. Heightened serotonin influences contest outcome and enhances expression of high-intensity aggressive behaviors. Behavioral Brain Research 259: 137-142.

An article written about the research in this Data Nugget: John Swallow: Co-authors study on insect aggression and neurochemistry

Video showing two stalk eyed flies battling in the fighting arena.

Video showing how the long eyestalks of males form!

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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.

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.

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 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:

erinAbout 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).

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).

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:

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:

2013-02-25 18.11.57

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.

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.

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:

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11.5.15

Data Nugget Workshop at NABT 2015: A Tail of Two Scorpions

You can get the slides from our NABT talk here: A Tail of Two Scorpions

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10.7.15

How to Escape a Predator

A stalk-eyed fly and spider interacting in the arena.

A stalk-eyed fly and spider interacting in the arena.

The activities are as follows:

Stalk-eyed flies are insects that have their eyes on the ends of eyestalks, or long projections from the sides of their head. Eyestalks are a sexual signal that males use to attract females. The longer the eyestalks, the more attractive a male is to females and the more mates he gets. For these flies, sexual selection leads to an elaborate trait, just like a peacock’s tail. Males with longer eyestalks have more babies and pass their traits on. Over generations, sexual selection leads to longer and longer eyestalks in males.

However, these eyestalks may come with a cost. Males with longer eyestalks may not be able to move easily and quickly. If they can’t move as fast, males with long eyestalks are potentially worse at escaping predators. Natural selection may select against long eyestalks if males with more elaborate traits are killed and eaten more often by predators. If predators eat males with longer eyestalks before the flies reproduce, they will not get to pass on their traits, regardless of how attractive they are to females.

Variation between stalk-eyed fly species in eyestalk length.

Variation between stalk-eyed fly species in eyestalk length.

In addition to eyestalk length, other traits could affect survival in male stalk-eyed flies. Perhaps the fly’s behavior is more important than its eyestalk length when faced with a predator. When biologists Amy and John first started researching how eyestalk length affected survival, they noticed something intriguing! The flies showed many different behaviors when face to face with a spider predator. Some examples of behaviors included grooming, walking or flying towards the predator, quickly walking or flying away from the predator, displaying forelegs, and bobbing their abdomens. When prey use these antipredator behaviors, predators must put in more work to catch prey, and they will sometimes give up. Therefore, antipredator behaviors may influence the predator’s choice of prey, and certain behaviors that make prey harder to catch could lead to increased survival.

To test whether differences in eye stalk length and/or antipredator behavior were important for survival, male stalk-eyed flies were put in cages with predators. Amy and John filmed the fly behaviors and analyzed the footage. They calculated the frequency and proportion of time that flies were displaying antipredator behaviors. If males with longer eyestalks have lower survival than males with shorter eyestalks, it suggests that longer eyestalks make it harder to avoid predators. However, if eyestalk length has no effect on survival, it suggests that male flies with long eyestalks are able to compensate for their lack of speed through behavior.

Featured scientists: Amy Worthington and John Swallow from Washington State University and University of Colorado, Denver. Written by: Brooke Ravanelli from Denver Public Schools and John Swallow.

Flesch–Kincaid Reading Grade Level = 10.7

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

Video showing how the long eyestalks of males form!

Videos of a stalk eyed fly and spider predator together in cages. First video shows male fly displaying, grooming, and approaching spider.

8.13.15

A tail of two scorpions

Ashlee & Matt Rowe

Ashlee and Matt Rowe at the Santa Rita Experimental Range in Arizona

The activities are as follows:

Animals have evolved many ways to defend themselves against predators. Many species use camouflage to avoid being seen. Others rely on speed to escape. Some species avoid capture by hiding in a safe place. Other animals use painful and venomous bites or stings to try to prevent attacks or to make being captured more difficult. Anyone who has been stung by a bee or wasp understands how stinging could be a great way to keep predators away! However, there is little research that documents if painful stings or bites deter predators.

The grasshopper mouse lives at the base of the Santa Rita Mountains in Arizona. Scientists Ashlee and Matt have been studying populations of this mouse for many years and wanted to know what the mouse ate. In the mountains, there are two scorpions that make a great food source for the mice. One of the scorpion species has a painful sting. The other species is slightly larger, but its sting is not painful. Ashlee and Matt thought that the use of a painful, venomous sting helped the smaller species avoid most predator attacks.

The Santa Rita foothills - habitat for the grasshopper mouse and scorpions

The Santa Rita foothills – habitat for the grasshopper mouse and scorpions

The scientists collected six grasshopper mice from the wild. Back in the lab, they trained the mice to expect a food reward when they tipped over a small cup containing live prey. Once trained, the mice were used in an experiment. The mice were presented with two cups to choose from. One contained the small scorpion species that has a painful sting. The other cup contained the larger scorpion species that has a painless sting. Ashlee and Matt collected data on which cup the mice chose to approach, inspect, or pursue (by tipping over the cup). They also recorded if the mice attacked or consumed the painless or painful species of scorpion. Each trial ended when the mouse finished consuming one of the scorpions. If painful stings prevent a predator from attacking, they predicted the mice would choose to eat the scorpion species with the painless sting more often.

Watch a video of one of the experimental trials:

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Mouse Trial
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Watch five additional videos on the grasshopper mouse and scorpions:

Images of the southern grasshopper mouse (Onychomys torridus) capturing and eating the painful species of scorpion (Centruroides sculpturatus).

Ot vs Cs 4

Ot vs Cs 1

Ot vs Cs 2

Size differences of the two scorpions used in the experiments (painful Arizona bark scorpion, Centruroides sculpturatus is on the left; painless stripe-tailed scorpion, Hoffmannius spinigerus on the right)size comparison 1 (1 of 1)

Featured scientists: Ashlee and Matt Rowe from University of Oklahoma

Undergraduate researchers involved with the project: Travis Tate and Crystal Niermann from Sam Houston State University; Rolando Barajas, Hope White, and Amber Suto from Michigan State University

Flesch–Kincaid Reading Grade Level = 7.1

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