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

Are you my species?

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

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

The activities are as follows:

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

Michael snorkeling, looking for darters.

Michael snorkeling, looking for darters.

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

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

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

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

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

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

Flesch–Kincaid Reading Grade Level = 10.9

Videos showing darter behavior:

Darter species used in the experiment:

darters

SaveSave

SaveSave

SaveSave

SaveSave

SaveSave

SaveSave

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 he chose to work with the Hawaiian swordtail cricket, Laupala cerasina. He 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 his 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. He wanted to know whether the “micro” nuptial gifts help females lay more eggs and/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. He 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 & Dresden University of Technology

Flesch–Kincaid Reading Grade Level = 8.9

Additional teacher resources related to this Data Nugget include:

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

Videos of a experimental trial – two stalk eyed flies battling in the fighting arena. The video was filmed during the experiment by the researchers listed in this Data Nugget!

Video showing how the long eyestalks of males form!

SaveSave

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

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

McCullough, E.L. and L.W. Simmons (2016) Selection on male physical performance during male–male competition and female choice. Behavioral Ecology


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.

Won’t you be my urchin?

The vegetarian sea urchin Diadema antillarum.

The vegetarian sea urchin Diadema antillarum.

The activities are as follows:

Imagine you are snorkeling on a coral reef where you can see many species living together. Some animals, like sharks, are predators that eat other animals. Other species, like anemones and the fish that live in them, are mutualists and protect each other from predators. There are also herbivores, like urchins, that eat plants and algae on the reef. All of these species, and many more, need the coral reef to survive.

Experimental setup with tiles in bins. Some bins have sea urchins and some do not.

Experimental setup with tiles in bins. Some bins have sea urchins and some do not.

Corals are the animals that build coral reefs. They are very sensitive and can be hurt by human activity, like boating and pollution. Corals reef ecosystems are also in danger from warming waters due to climate change. Sadly, today many coral reefs around the world are dying because the places they grow are changing. Sarah is a marine biologist who is determined to figure out ways to save coral reefs. Sarah wants to understand how to help the dying corals so they can keep building the important and diverse coral reef habitats.

Corals compete with large types of algae, like seaweed, for space to grow on the reef. Corals are picky and only like to live in certain places. If there is too much algae, corals will have no place to attach and grow. Sea urchins are important herbivores and one of the species that like to eat algae. Sarah thought that when urchins are present on the reef, corals will have less competition from algae for space, and thus more room to grow. Maybe adding urchins to a coral reef is a way to help corals!

To test her idea Sarah set up an experiment. She set 8 bins out on the reef. Into half of the bins, Sarah added urchins. Into the other half she left without urchins as a control. Sarah put tiles into all of the bins. Tiles gave an empty space for coral and algae to compete and grow. After a few months, Sarah looked at the tiles. She counted how many corals were growing on each tile. Sarah predicted that more corals would grow on the tiles in bins with sea urchins compared to the control bins with no sea urchins.

B. Photograph of Agaricia juvenile on experimental substratum. C. Photograph of Porites juvenile on experimental substratum

B. Photograph of coral species Agaricia juvenile on experimental tile. C. Photograph of coral species Porites juvenile on experimental tile.

Featured scientist: Sarah W. Davies from University of Texas at Austin

Flesch–Kincaid Reading Grade Level = 6.5

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

Davies SW, MV Matz, PD Vize (2013) Ecological Complexity of Coral Recruitment Processes: Effects of Invertebrate Herbivores on Coral Recruitment and Growth Depends Upon Substratum Properties and Coral Species. PLOS ONE 8(9):e72830

After students have completed the Data Nugget, you can have them discuss the management implications of this research. Watch the news story below and have students consider how urchins can be used as a management tool to help restore coral reefs!

SaveSave

SaveSave

SaveSave

SaveSave

SaveSave

SaveSave