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.

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 many ways to defend 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 capture more difficult. Anyone who has been stung by a bumblebee understands how stinging could be a great way to keep predators away! However, there is little research that shows 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 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 painful, venomous stings would prevent predator attacks, and that the painless species would be attacked and eaten more often.

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. Once 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 scorpion species that has a painful sting. The other cup contained the 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 three 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 Michigan State University

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

Flesch–Kincaid Reading Grade Level = 7.1

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Shooting the Poop

The activities are as follows:butterfly

Imagine walking through a deciduous forest in the middle of summer. You can hear birds chirping, a slight breeze rustling the leaves, and a faint pinging noise like rain. However, what you hear is not rain – it is the sound of millions of forest insects defecating!

Forest insects, like caterpillars, are a great source of food for many species. As such, caterpillars have many defense strategies to protect themselves and evade predators, including camouflage to avoid detection, nasty defensive chemicals and bright colors to warn predators to stay away, or even building shelters out of plant leaves to hide in. The smell of frass (insect poop) alerts predators that a tasty insect is in the area, so usually insects keep moving and leave their frass behind. But what if the insect relies on a shelter for protection and cannot keep moving away from its home?

The forest insect, Epargyreus clarus (the silver-spotted skipper) has a variety of defense strategies against enemies, including building leaf shelters for protection. While raising E. clarus caterpillars in the lab, a scientist noticed that E. clarus made a pinging noise in their containers. Upon further observation, it was discovered that they “shoot their poop”, sometimes launching their frass over 1.5m! The scientist wanted to determine why these caterpillars might engage in this very strange behavior. Perhaps flinging their poop is a defensive strategy to avoid predator detection.

To evaluate whether the smell of frass alerts predators to the presence of a caterpillar, the scientist Weiss conducted an experiment with the predatory wasp Polistes fuscatus. She allowed two E. clarus larvae to build shelters on a leaf and then carefully removed the larvae. She then inserted 6 frass pellets into one of the shelters, and 6 beads designed to look like frass but with no smell (control treatment) into the other. She placed the leaf in a cage containing an actively foraging wasp colony (n = 10 wasps), and recorded how many times the wasps visited each shelter (control or frass), and how much time the wasps spent exploring each shelter.

Featured scientist: Martha Weiss from Georgetown University. Nugget written by Kylee Grenis.

Flesch–Kincaid Reading Grade Level = 10.2

Additional teacher resources related to this Data Nugget include:

Dangerous Aquatic Prey: Can Predators Adapt to Toxic Algae?

Figure 1: Scientist Finiguerra collecting copepods at the New Jersey experimental site.

Figure 1: Scientist Finiguerra collecting copepods at the New Jersey experimental site.

The activities are as follows:

Phytoplankton are microscopic algae that form the base of all aquatic food chains. While organisms can safely eat most phytoplankton, some produce toxins. When these toxic algae reach high population levels it is known as a toxic algal bloom. These blooms are occurring more and more often across the globe – a worrisome trend! Toxic algae poison animals that eat them, and in turn, humans that eat these animals. For example, clams and other shellfish filter out large quantities of the toxic algae, and the toxic cells accumulate in their tissues. If humans then eat these contaminated shellfish they can become very sick, and even die.

One reason the algae produce toxins is to reduce predation. However, if predators feed on toxic prey for many generations, the predator population may evolve resistance, by natural selection, to the toxic prey. In other words, the predators may adapt and would be able to eat lots of toxic prey without being poisoned. Copepods, small crustaceans and the most abundant animals in the world, are main consumers of toxic algae. Along the northeast coast of the US, there is a toxic phytoplankton species, Alexandrium fundyense, which produces very toxic blooms. Blooms of Alexandrium occur often in Maine, but are never found in New Jersey. Scientists wondered if populations of copepods that live Maine were better at coping with this toxic prey compared to copepods from New Jersey.

Figure 2: A photograph of a copepod (left) and the toxic alga Alexandrium sp. (right).

Figure 2: A photograph of a copepod (left) and the toxic alga Alexandrium sp. (right).

Scientists tested whether copepod populations that have a long history of exposure to toxic Alexandrium are adapted to this toxic prey. To do this, they raised copepods from Maine (long history of exposure to toxic Alexandrium) and New Jersey (no exposure to toxic Alexandrium) in the laboratory. They raised all the copepods under the same conditions. The copepods reproduced and several generations were born in the lab (a copepod generation is only about a month). This experimental design eliminated differences in environmental influences (temperature, salinity, etc.) from where the populations were originally from.

The scientists then measured how fast the copepods were able to produce eggs, also called their egg production rate. Egg production rate is an estimate of growth and indicates how well the copepods can perform in their environment. The copepods were given either a diet of toxic Alexandrium or another diet that was non-toxic. If the copepods from Maine produced more eggs while eating Alexandrium, this would be evidence that copepods have adapted to eating the toxic algae. The non-toxic diet was a control to make sure the copepods from Maine and New Jersey produced similar amounts of eggs while eating a good food source. For example, if the copepods from New Jersey always lay fewer eggs, regardless of good or bad food, then the control would show that. Without the control, it would be impossible to tell if a difference in egg production between copepod populations was due to the toxic food or something else.

Featured scientists: Michael Finiguerra and Hans Dam from University of Connecticut-Avery Point, and David Avery from the Maine Maritime Academy

Flesch–Kincaid Reading Grade Level = 10.6

There are three scientific papers associated with the data in this Data Nugget. The citations and PDFs of the papers are below. 

Colin, SP and HG Dam (2002) Latitudinal differentiation in the effects of the toxic dinoflagellate Alexandrium spp. on the feeding and reproduction of populations of the copepod Acartia hudsonicaHarmful Algae 1:113-125

Colin, SP and HG Dam (2004) Testing for resistance of pelagic marine copepods to a toxic dinoflagellate. Evolutionary Ecology 18:355-377

Colin, SP and HG Dam (2007) Comparison of the functional and numerical responses of resistant versus non-resistant populations of the copepod Acartia hudsonica fed the toxic dinoflagellate Alexandrium tamarense. Harmful Algae 6:875-882

Dangerously bold

An aquarium filled with young bluegill sunfish. Bluegills are a common type of fish that live in freshwater lakes in the eastern United States.

An aquarium filled with young bluegill sunfish. Bluegills are a common type of fish that live in freshwater lakes in the eastern United States.

The activities are as follows:

1

Just as each person has their own personality, animals in the same species can behave very different from one another! For example, pets like dogs have different personalities. Some have lots of energy, some are cuddly, and some like to be alone. Boldness is a behavior that describes whether or not an individual takes risks. Bold individuals take risks, while shy do not. The risks animals take have a big impact on their survival and the habitats they choose to search for food.

Bluegill sunfish are a type of fish that live in freshwater lakes and ponds across the world. Open water and cover are two habitats where young bluegill are found. The open water habitat in the center of the pond is the best place for bluegill to eat lots of food. However, the open water is risky and has very few plants or other places to hide. Predators can easily find and eat bluegill in the open water. The cover habitat at the edge of the pond has many plants and places to hide from predators, but it has less food that is best for bluegill to grow fast. Both habitats have costs and benefits – called a tradeoff.

To determine their personality, Melissa observed bluegill sunfish in the aquarium lab.

To determine their personality, Melissa observed bluegill sunfish in the aquarium lab.

Melissa is a scientist who is interested in whether differences in young bluegill behavior changes the habitats they choose to search for food. First, she looked at whether young bluegill have different personalities by bringing them into an aquarium lab and watching their behavior. She saw that just like in humans and dogs, bluegill sunfish had different personalities. Some bluegill took more risks and were bolder than others. Melissa wanted to know if these differences in behavior changed how the fish behaved back in the pond. She thought that bold fish would take more risks and use the open water habitat more than shy fish. Bold fish would then have more food and grow faster and larger. She thought that shy fish would play it safe and not take risks, so they would use the cover habitat. Shy fish would then eat less food and not be able to grow as large. Because the bold fish would be in the open water habitat, they might get eaten by predators more because shy fish would avoid predators. These differences in the habitats that the fish use would create a tradeoff based on personality.

Melissa designed a study to test the growth and survival of bold and shy fish. When she was watching the fish’s behavior in the lab, she determined if a fish was bold or shy. If a fish took the risk of leaving the safety of the vegetation in a tank so that it could eat food while there was a predator behind a mesh screen, they were called bold. If it did not eat, it was called shy. She marked each fish by clipping the right fin if it was bold or the left fin if it was shy. She placed 100 bold and 100 shy bluegill into an experimental pond with two largemouth bass (predators). The shy and bold fish started the experiment at similar lengths and weights. After two months, she drained the pond and found every bluegill that survived. She recorded survival and size (length and weight) for each fish and noted if it was bold or shy.

Featured scientist: Melissa Kjelvik from Michigan State University

Flesch–Kincaid Reading Grade Level = 7.3

Photo Jul 23, 5 41 38 PM

A view of the aquarium tank used to determine fish personality. A largemouth bass is placed to the left of the barrier, while 3 bluegill sunfish are placed to the right. If a sunfish swims out of the vegetation and eats a bloodworm dropped near the predator, it is considered bold.

A view of the aquarium tank used to determine fish personality. A largemouth bass is placed to the left of the barrier, while 3 bluegill sunfish are placed to the right. If a sunfish swims out of the vegetation and eats a bloodworm dropped near the predator, it is considered bold.

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