Alien life on Mars – caught in crystals?

Magnesium sulfate crystals trapping liquid water.

The activities are as follows:

Is there life on other planets besides Earth? This question is not just for science fiction. Scientists are actively exploring the possibility of life beyond Earth. The field of astrobiology seeks to understand how life in the universe began and evolved, and whether life exists elsewhere. Our own solar system contains a variety of planets and moons. In recent years scientists have also discovered thousands of planets around stars other than our Sun. So far, none of these places are exactly like Earth. Many planets have environments that would be very difficult for life as we know it to survive. However, there are life forms that exist in extreme environments that we can learn from. On Earth there are extremely hot or acidic environments like volcanic hot springs. Organisms also live in extremely cold places like Antarctic glacier ice. Environments with extremely high pressure, like hydrothermal vents on the ocean floor, also support life. If life can inhabit these extreme environments here on Earth, might extreme life forms exist elsewhere in the universe as well?

A view of the astrobiology lab.

Charles is an astrobiologist from Great Britain who is interested in finding life on other planets. The list of places that we might look for life grows longer every day. Charles thinks that a good place to start is right next door, on our neighboring planet, Mars. We know that Mars currently is cold, dry, and has a very thin atmosphere. Charles is curious to know whether there might still be places on Mars where life could exist, despite its extreme conditions.While there is no liquid water on the surface of Mars anymore, Mars once had a saltwater ocean covering much of its surface. The conditions on Mars used to be much more like Earth. Liquid water is essential for life as we know it. If there are places on Mars that still hold water, these could be great places to look for evidence of life. Charles thought that perhaps salt crystals, formed when these Martian oceans were evaporating, could trap pockets of liquid water.

Charles and his fellow researcher Nikki knew that there are a number of kinds of salts found in Martian soils, including chlorides, sulfates, perchlorates and others. They wanted to test their idea that water could get trapped when saltwater with these salts evaporate. They decided to compare the rate of evaporation for solutions with magnesium sulfate (MgSO4) with another commonsalt solution: sodium chloride, or table salt (NaCl). They chose to investigate these two salts because they are less toxic to life as we know it than many of the other chloride, perchlorate, or sulfate salts. Also, from reading the work of other scientists, Charles knows the Martian surface is particularly rich in magnesium sulfate.

Charles and Nikki measured precise quantities of saturated solutions of magnesium sulfate and sodium chloride and placed them into small containers. Plain water was used as a control. There were three replicate containers for each treatment – nine containers in total. They left the containers open to evaporate and recorded their mass daily. They kept collecting data until the mass stopped changing. At this point all of the liquid had evaporated or a salt crust had formed that was impermeable to evaporation. They then compared the final mass of the control containers to the other solutions. They also checked the resulting crusts for the presence or absence of permanent water-containing pockets. Charles and Nikki used these data to determine if either saltmakes crystals that can trap water in pockets when it evaporates.

Featured scientists: Charles Cockell, UK Centre for Astrobiology, University of Edinburgh, & Nikki Chambers, Astrobiology Teacher, West High School, Torrance, CA

Flesch–Kincaid Reading Grade Level = 8.7

Additional teacher resource related to this Data Nugget:

Clique wars: social conflict in daffodil cichlids

A male and female daffodil cichlid

The activities are as follows:

Have you ever thought about what it would be like to live completely alone, without contact with other people? Nowadays, humans are constantly connected by phones, texting, and social media. Our social interactions affect us in many unexpected ways. Strong social relationships can increase human lifespan, and lower the risk of cancer, cardiovascular disease, and depression. Social relationships are so important that they are actually a stronger predictor of premature death than smoking, obesity, or physical inactivity! Like humans, social interactions are important for other animals as well.

Jennifer is a behavioral ecologist who is interested in daffodil cichlids, a social species of fish from Lake Tanganyika, a Great Lake in Africa. Daffodil cichlids live in social groups of several small fish and one breeding pair. Each group defends its own rock cluster in the lake. The breeding male and female are the largest fist in the group, and the smaller fish help defend territory against predators and help care for newly hatched baby fish. About 200 social groups together make up a colony.

Social groups of daffodil cichlids in Lake Tanganyika

Behavior within a social group may be influenced by the presence of other groups in the colony. For example, neighboring groups can be a threat because they may try to take away territory or resources. After reading about previous research on social interactions in species that live in groups, Jennifer noticed there were very few studies that looked at how neighboring groups affected behavior within the group. Jennifer thought that the presence of neighboring groups may force the breeding pair to be less aggressive towards each other and work together to protect their group’s resources against the outside threat.

To test her idea, Jennifer formed breeding pairs of daffodil cichlids in an aquarium laboratory. She first observed the breeding pairs for any aggressive behaviors when they were isolated and could not see other groups. She observed each group for 30 minutes a day for 10 days. Next, Jennifer set up a clear barrier between the breeding pair and a neighboring group. The fish could see each other but not physically interact. Jennifer again watched the breeding pair and documented any aggressive behaviors to see how the presence of a neighboring group affected conflict within the pair. She again observed each group with neighbors for 30 minutes a day for 10 days.

During these behavioral tests, Jennifer counted the total number of behaviors done by the breeding pair. She measured several behaviors. Physical attacks were counted every time contact between the fish was made (biting or ramming each other). Aggressive displays were counted when fish give signals of aggression without making physical contact (raising their fins or swimming rapidly at another fish). Submissive behaviors, or actions used to prevent aggression between the breeding pair, were also counted. Finally, behaviors used to encourage social bonding were counted and are called affiliative behaviors. Jennifer predicted that the breeding pair would perform fewer physical attacks and aggressive displays when a neighboring group was present compared to when the breeding pair was alone. She also thought the breeding pair would perform more submissive and affiliative behaviors when the neighboring group was present. In this way, the presence of an outside group would impact the behaviors within a group.

Featured scientist: Jennifer Hellmann from The Ohio State University

Flesch–Kincaid Reading Grade Level = 11.3

Tree-killing beetles

A Colorado forest impacted by a mountain pine beetle outbreak. Notice the dead trees mixed with live trees. Forests like this with dead trees from mountain pine beetle outbreaks cover millions of acres across western North America.

The activities are as follows:

A beetle the size of a grain of rice seems insignificant compared to a vast forest. However, during outbreaks the number of mountain pine beetles can skyrocket, leading to the death of many trees. The beetles bore their way through tree bark and introduce blue stain fungi. The blue stain fungi kills the tree by blocking water movement. Recent outbreaks of mountain pine beetles killed millions of acres of lodgepole pine trees across western North America. Widespread tree death caused by mountain pine beetles can impact human safety, wildfires, nearby streamflow, and habitat for wildlife.

Mountain pine beetles are native to western North America and outbreak cycles are a natural process in these forests. However, the climate and forest conditions have been more favorable for mountain pine beetles during recent outbreaks than in the past. These conditions caused more severe outbreaks than those seen before.

Logs from mountain pine beetle killed lodgepole pine trees. The blue stain fungi is visible around the edge of each log. Mountain pine beetles introduce this fungus to the tree.

When Tony moved to Colorado, he drove through the mountains eager to see beautiful forests. The forest he saw was not the green forest he expected. Many of the trees were dead! Upon closer examination he realized that some forests had fewer dead trees than others. This caused him to wonder why certain areas were greatly impacted by the mountain pine beetles while others had fewer dead trees. Tony later got a job as a field technician for Colorado State University. During this job he measured trees in mountain forests. He carefully observed the forest and looked for patterns of where trees seemed to be dead and where they were alive.

Tony thought that the size of the trees in the forest might be related to whether they were attacked and killed by beetles. A larger tree might be easier for a beetle to find and might be a better source of food.To test this idea, Tony and a team of scientists visited many forests in northern Colorado. At each site they recorded the diameter of each tree’s trunk, which is a measure of the size of the tree. They also recorded the tree species and whether it was alive or dead. They then used these values to calculate the average tree size and the percent of trees killed for each site.

Featured scientist: Tony Vorster from Colorado State University

Flesch–Kincaid Reading Grade Level = 8.3

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

Are forests helping in the fight against climate change?

Bill setting up a large metal tower in Harvard Forest in 1989, used to measure long-term CO2 exchange.

The activities are as follows:

As humans drive cars and use electricity, we release carbon in the form of carbon dioxide (CO2) into the air. Because COhelps to trap heat near the surface of the earth, it is known as a greenhouse gas and contributes to climate change. However, carbon is also an important piece of natural ecosystems, because all living organisms contain carbon. For example, when plants photosynthesize, they take COfrom the air and turn it into other forms of carbon: sugars for food and structural compounds to build their stems, roots, and leaves. When the carbon in a living tree’s trunk, roots, leaves, and branches stays there for a long time, the carbon is kept out of the air. This carbon storage helps reduce the amount of COin the atmosphere. However, not all of the COthat trees take from the air during photosynthesis remains as part of the tree. Some of that carbon returns to the air during a process called respiration.

Another important part of the forest carbon cycle happens when trees drop their leaves and branches or die. The carbon that the tree has stored breaks down in a process called decomposition. Some of the stored carbon returns to the air as CO2, but the rest of the carbon in those dead leaves and branches builds up on the forest floor, slowly becoming soil. Once carbon is stored in soil, it stays there for a long time. We can think of forests as a balancing act between carbon building up in trees and soil, and carbon released to the air by decomposition and respiration. When a forest is building up more carbon than it is releasing, we call that area a carbon sink, because overall more COis “sinking” into the forest and staying there. On the other hand, when more carbon is being released by the forest through decomposition and respiration, that area is a carbon source, because the forest is adding more carbon back into the atmosphere than it is taking in through photosynthesis.

In the 1990s, scientists began to wonder what role forests were having in this exchange of carbon in and out of the atmosphere. Were forests overall storing carbon (carbon sink), or releasing it (carbon source)? Bill is one of the scientists who decided to explore this question. Bill works at the Harvard Forest in central Massachusetts, a Long-Term Ecological Research site that specializes in setting up big experiments to learn how the environment works. Bill and his team of scientists realized they could measure the COcoming into and out of an entire forest. They built large metal towers that stand taller than the forest trees around them and use sensors to measure the speed, direction, and COconcentration of each puff of air that passes by. Bill compares the COin the air coming from the forest to the ones moving down into the forest from the atmosphere. With the COdata from both directions, Bill calculates the Net Ecosystem Exchange (or NEE for short). When more carbon is moving into the forest than out, NEE is a negative number because COis being taken out of the air. This often happens during the summer when trees are getting a lot of light and are therefore photosynthesizing. When more COis leaving the forest, it means that decomposition and respiration are greater than photosynthesis and the NEE is a positive number. This typically happens at night and in the winter, when trees aren’t photosynthesizing but respiration and decomposition still occur. By adding up the NEE of each hour over a whole year, Bill finds the total amount of COthe forest is adding or removing from the atmosphere that year.

Bill and his team were very interested in understanding NEE because of how important it is to the global carbon cycle, and therefore to climate change. They wanted to know which factors might cause the NEE of a forest to vary. Bill and other scientists collected data on carbon entering and leaving Harvard Forest for many years to see if they could find any patterns in NEE over time. By looking at how the NEE changes over time, predictions can be made about the future: are forests taking up more COthan they release? Will they continue to do so under future climate change?

Featured scientist: Bill Munger from Harvard University

Written by: Fiona Jevon

Flesch–Kincaid Reading Grade Level = 10.5

Additional teacher resource related to this Data Nugget:

  • There are several publications based on the data from the Harvard Forest LTER. PDFs for all papers can be found online here. Citations below:
    • Wofsy, S.C., Goulden, M.L., Munger, J.W., Fan, S.M., Bakwin, P.S., Daube, B.C., Bassow, S.L. and Bazzaz, F.A., 1993. Net exchange of CO2 in a mid-latitude forest. Science260(5112), pp.1314-1317.
    • Goulden, M.L., Munger, J.W., Fan, S.M., Daube, B.C. and Wofsy, S.C., 1996. Exchange of carbon dioxide by a deciduous forest: response to interannual climate variability. Science271(5255), pp.1576-1578.
    • Barford, C.C., Wofsy, S.C., Goulden, M.L., Munger, J.W., Pyle, E.H., Urbanski, S.P., Hutyra, L., Saleska, S.R., Fitzjarrald, D. and Moore, K., 2001. Factors controlling long-and short-term sequestration of atmospheric CO2 in a mid-latitude forest. Science294(5547), pp.1688-1691.
    • Urbanski, S., Barford, C., Wofsy, S., Kucharik, C., Pyle, E., Budney, J., McKain, K., Fitzjarrald, D., Czikowsky, M. and Munger, J.W., 2007. Factors controlling CO2 exchange on timescales from hourly to decadal at Harvard Forest. Journal of Geophysical Research: Biogeosciences112(G2).
    • Wehr, R., Munger, J.W., McManus, J.B., Nelson, D.D., Zahniser, M.S., Davidson, E.A., Wofsy, S.C. and Saleska, S.R., 2016. Seasonality of temperate forest photosynthesis and daytime respiration. Nature534(7609), p.680.
  • Our Changing Forests Schoolyard Ecology project – Do your students want to get involved with research monitoring carbon cycles in forests? Check out this hands-on field investigation, led by a team of Ecologists at Harvard Forest. Students can contribute to this study by monitoring a 20 meter by 20 meter plot in a wooded area near their schools.
  • Additional images from Harvard Forest, diagrams of NEE, and a vocabulary list can be found in this PowerPoint.

Bringing back the Trumpeter Swan

Joe with a Trumpeter Swan.

The activities are as follows:

The Kellogg Bird Sanctuary was created in 1927 to provide safe nesting areas for waterfowl such as ducks, geese, and swans. During that time many waterfowl species were in trouble due to overhunting and the loss of wetland habitats. One species whose populations had declined a lot was the Trumpeter Swan. Trumpeter swans are the biggest native waterfowl species in North America. At one time they were found across North America, but by 1935 there were only 69 known individuals in the continental U.S.! The swans were no longer found in Michigan.

The reintroduction, or release of a species into an area where they no longer occur, is an important tool in helping them recover. In the 1980s, many biologists came together to create a Trumpeter Swan reintroduction plan. Trumpeter Swans in North America can be broken up into three populations – Pacific Coast, Rocky Mountain, and Interior. The Interior is further broken down into Mississippi/Atlantic and High Plains subpopulations. Joe, the Kellogg Bird Sanctuary manager and chief biologist, wrote and carried out a reintroduction plan for Michigan. Michigan is part of the Mississippi/Atlantic subpopulation. Joe and a team of biologists flew to Alaska in 1989 to collect swan eggs to be reared at the sanctuary. After two years the swans were released throughout Michigan.

The North American Trumpeter Swan survey has been conducted approximately every 5 years since 1968 as a way to estimate the number of swans throughout their breeding range. The survey is conducted in late summer when young swans can’t yet fly but are large enough to count. Although the surveys are conducted across North America, the data provided focuses on just the Interior Population, which includes swans in the High Plains and Mississippi/Atlantic Flyways.

Featured scientist: Wilbur C. “Joe” Johnson from the W.K. Kellogg Bird SanctuaryWritten by: Lisa Vormwald and Susan Magnoli from Michigan State University.

Flesch–Kincaid Reading Grade Level = 11.5

Additional teacher resource related to this Data Nugget:

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The case of the collapsing soil

An area in the Florida Everglades where strange soil collapse has been observed.

The activities are as follows:

As winds blow through the large expanses of grass in the Florida Everglades, it looks like flowing water. This “river of grass” is home to a wide diversity of plants and animals, including both the American Alligator and the American Crocodile. The Everglades ecosystem is the largest sub-tropical wetland in North America. One third of Floridians rely on the Everglades for water. Unfortunately, this iconic wetland is threatened by rising sea levels caused by climate change. Sea level rise is caused by higher global temperatures leading to thermal expansion of water, land-ice melt, and changes in ocean currents.

With rising seas, one important feature of the Florida Everglades may change. There are currently large amounts of carbon stored in the wetland’s muddy soils. By holding carbon in the mud, coastal wetlands are able to help in the fight against climate change. However, under stressful conditions like being submersed in sea water, soil microbes increase respiration. During respiration, carbon stored in the soil is released as carbon dioxide (CO2), a greenhouse gas. As sea level rises, soil microbes are predicted to release stored carbon and contribute to the greenhouse effect, making climate change worse.

Shelby collecting soil samples from areas where the soil has collapsed in the Everglades.

Shelby and John are ecologists who work in southern Florida. John became fascinated with the Everglades during his first visit 10 years ago and has been studying this unique ecosystem ever since. Shelby is interested in learning how climate change will affect the environment, and the Everglades is a great place to start! They are both very concerned with protecting the Everglades and other wetlands. Recently when John, Shelby, and their fellow scientists were out working in the Everglades they noticed something very strange. It looked like areas of the wetland were collapsing! What could be the cause of this strange event?

John and Shelby thought it might have something to do loss of carbon due to sea level rise. They wanted to test whether the collapsing soils were the result of increased microbial respiration, leading to loss of carbon from the soil, due to stressful conditions from sea level rise. They set out to test two particular aspects of sea water that might be stressful to microbes – salt and phosphorus.

Phosphorus is found in sea water and is a nutrient essential for life. However, too much phosphorus can lead to over enriched soils and change the way that microbes use carbon. Sea water also contains salt, which can stress soil microbes and kill plants when there is too much. Previous research has shown that both salt and phosphorus exposure on their own increase respiration rates of soil microbes.

A photo of the experimental setup. Each container has a different level of salt and phosphorus concentration.

To test their hypotheses, a team of ecologists in John’s lab developed an experiment using soils from the Everglades. They collected soil from areas where the soil had collapsed and brought it into the lab. These soils had the microbes from the Everglades in them. Once in the lab, they put their soil and microbes into small vials and exposed them to 5 different concentrations of salt, and 5 different concentrations of phosphorus. The experiment crossed each level of the two treatments. This means they had soil in every possible combination of treatments – some with high salt and low phosphorus, some in low salt and high phosphorus, and so on. Their experiment ran for 5 weeks. At the end of the 5 weeks they measured the amount of COreleased from the soils.

Featured scientists: John Kominoski and Shelby Servais from Florida International University. Written by Shelby, John, and Teresa Casal.

Flesch–Kincaid Reading Grade Level = 9.2

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What big teeth you have! Sexual selection in rhesus macaques

Cayo Santiago rhesus macaques. Photo by Raisa Hernández Pacheco.

The activities are as follows:

It is easy to identify a deer as male when you see his huge antlers, or a peacock as male by his stunning set of colorful tail feathers. But you may wonder, how do these traits come about, and why don’t both males and females have them? These extravagant traits are thought to be the result of sexual selection. This process happens when females mate with males that they think have the sexiest traits. These traits get passed on to future male offspring, leading to a change in the selected traits over time. Because females are only choosing these traits in males, sexual selection often leads to sexual dimorphism between males and females. This means that the sexes do not look the same. Often males will be larger and have more elaborate traits than females.

Craniums of an adult male (left) and an adult female (right) rhesus macaque. Photo by Raisa Hernández Pacheco and Damián A. Concepción Pérez.

One species that shows strong sexual dimorphism is rhesus macaques. In this species of monkey, males are much larger than females. Cayo Santiago is a small island off the shore of Puerto Rico. On this island lives one of the oldest free-ranging rhesus macaque colonies in the world. This population has no predators and food is plentiful. Scientists at Cayo Santiago have gathered data on these monkeys and their habitat for over 70 years. Every year when new monkeys are born they are captured, marked with a unique tattoo ID, and released. This program allows scientists to monitor individual monkeys over their entire lives and record the sex, date of birth, and date of death. Once a monkey dies and its body is recovered in the field, skeletal specimens are stored in a museum for further research.

Damián measuring canine length in a rhesus macaque skeletal specimen. Photo by Raisa Hernández Pacheco.

These skeletal specimens can be used by scientists today to ask new and exciting questions. Raisa and Damián are both interested in studying sexual dimorphism in rhesus macaques. They want to find out what causes the differences between the sexes. They chose to focus on the length of the very large canine teeth in male and female macaques. They expected that canine teeth may be under sexual selection in males for two reasons. First, rhesus macaques are mostly vegetarians, so they don’t need long canines for the same purpose as other meat-eating species that use them to catch prey. Second, male rhesus macaques often bare their teeth at other males when they are competing for mates. Females could see the long canines as a sign of good genes and may prefer to mate with that trait. Excited by these ideas, Raisa and Damián set out to investigate the museum’s skeletal specimens to check whether there is sexual dimorphism in canine length. This is the first step in collecting evidence to see whether male canines are under sexual selection by females.

They measured canine length of four male and four female rhesus skeletal specimens dating back to the 1970s. Measurements were only taken from individuals that died as adults to make sure canines were fully developed and that differences in length could not be attributed to age. Raisa and Damián predicted that males would have significantly longer canines compared to those of females. If so, this would be the first step to determine whether sexual selection was operating in the population.

Featured scientists: Raisa Hernández-Pacheco from University of Richmond and Damián A. Concepción Pérez from Wilder Middle School. Research conducted at the Laboratory of Primate Morphology at the University of Puerto Rico Medical Sciences Campus. Skeletal specimens came from the population of rhesus macaques on Cayo Santiago.

Flesch–Kincaid Reading Grade Level = 9.8

Damián and Raisa created a teaching module, called Unknown Bones. It is an inquiry-based educational activity for high school students in which they apply data analysis and statistics to understand sexual selection and illustrate sexual dimorphism in Cayo Santiago rhesus macaques.


About Raisa: I am interested in understanding the drivers shaping population dynamics, and have dedicated my studies to modeling the effects of biotic and abiotic factors on populations of invertebrates and vertebrates. In 2013, I obtained my PhD from the University of Puerto Rico after assessing the effects of mass bleaching on Caribbean coral populations. Right after, I joined the Caribbean Primate Research Center and the Max-Planck Odense Center to study the long-term dynamics of the Cayo Santiago rhesus macaque population. At the Grayson lab, I am studying the population of red-backed salamanders in Richmond; its density, spatial arrangement, and space use.


About Damián: I am a middle and high school Science and Math teacher. I have always been searching for innovative ways to get my students engaged in the science classroom and to connect their new knowledge with the real-world. In thinking of ways to help my students learn, I engaged my self with the scientific community collaborating in scientific projects and creating hands-on, interactive, and inspiring teaching lessons. It is my main interest to develop ideas that could positively contribute to any student’s STEM education.

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Which would a woodlouse prefer?

Woodlice are small crustaceans that live on land. They look like bugs, but are actually more closely related to crabs and lobsters! Photo credit Liz Henwood.

The activities are as follows:

Woodlice are small crustaceans that live on land. They look like bugs, but are actually more closely related to crabs and lobsters. To escape predators they hide in dark places. They spend most of their time underground and have very poor eyesight.

One day, when digging around in the dark dirt of her compost pile, Nora noticed that there were many, many woodlice hiding together. This made her wonder how woodlice decide where to live. Because woodlice have very simple eyesight, Nora thought that maybe they use dark and light colors to decide where to go. They might choose to move towards darker colors and away from lighter colors to prevent ending up above ground where predators can easily find them.

Nora collecting woodlice from the compost pile.

Nora, along with classmates in her ecology class at Michigan State University, decided to run an experiment to study woodlice behavior. She collected 10 woodlice from her compost pile and placed them in a jar. She brought the jar into the lab. Then she chose a set of trays to work with from what she had in the lab – white, with tall sides. The sides of the tray were tall and smooth so the woodlice were not able to climb out. On one end of the tray Nora put some dark soil, and on the other side she put lighter leaves. If her hypothesis was correct, Nora predicted that woodlice would more often choose to move towards the dark soil habitat, compared to the lighter leaves habitat.

For each trial, Nora gently picked up a single woodlouse with forceps. She then placed it in the center of the tray. All the woodlice were positioned so they started facing the top of the tray, not at either habitat type. The woodlice then chose to move towards one end of the tray or the other. When they reached one of the piles the students recorded which habitat they chose. It was then picked up with forceps. Nora and her classmates recorded its length and placed it in a new jar so it could be released back into the compost pile once the experiment was done.

The tray where the preference trials were conducted. To the right of the tray is the soil pile, and to the left is the leaf pile. The center was purposefully left empty and wiped down before each run.

After running this experiment and looking at the data, Nora realized it did not work. The small sample size of only 10 individuals was not enough to see a pattern. Also, she realized that after one woodlouse went a certain way, all the others would follow it, maybe because they were following a scent trail. She decided she had to do the experiment again, this time with more woodlice and in a way that would prevent them following each other’s scent trails.

For her second try, Nora collected 51 woodlice from a different compost pile. Just like the first experiment, Nora placed lighter leaves on one end of a white tray and dark soil on the other. All the methods were the same, except for a few important changes. To get rid of scent trails, this time Nora wiped down the middle of the tray with a clean wet paper towel between trials. She also added equal amounts of water to both habitats to control for humidity. This ensured that if woodlice did show a preference for either habitat it would be due to habitat color, not humidity. This time Nora used a stopwatch and recorded how long it took for an individual to choose one of the two habitats.

Featured scientist: Nora Straquadine from Michigan State University

 Flesch–Kincaid Reading Grade Level = 7.7

Additional teacher resource related to this Data Nugget:

  • PowerPoint slideshow of images of woodlice and Nora’s experiment.
  • A great video to show before the Data Nugget to engage students with the activity – gives background on woodlice and describes the role that water plays for these crustaceans that live on land:

  • A video of woodlice on a fallen tree. This video has no audio, but can be useful for students to observe woodlice behavior:


About Nora: Nora is currently an undergraduate getting her B.S. in Zoology with a concentration in Zoo and Aquarium as well as a minor in Marine Ecosystem Management from Michigan State University. Although aquatic life is her main interest, she think it’s important to appreciate other animal groups and take a break to play and explore the nature around you. That curiosity was how she was able to volunteer in labs on campus from entomology to genetics, and how she came to spend a summer at the Kellogg Biological Station in Michigan.

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Is it better to be bigger?

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

The activities are as follows:

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

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

Aaron with a baby anole lizard.

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

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

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

Flesch–Kincaid Reading Grade Level = 11.7

Additional teacher resource related to this Data Nugget:

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

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

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Is it dangerous to be a showoff?

A male anole lizard showing his bright dewlap.

The activities are as follows:

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

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

Aaron with a baby anole lizard.

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

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

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

Flesch–Kincaid Reading Grade Level = 10.3

Additional teacher resource related to this Data Nugget:

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

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