Introduction: Agonistic Behavior in Betta splendens

Introduction:
Agonistic Behavior in Betta splendens
Ethology is a branch of zoology focused on the study of animal behavior in natural
situations. While the ethologist usually spends a great deal of time studying wild animals in the
field, such studies of animal behavior are often complemented by laboratory and/or field
experiments. The goal of the ethologist is to understand natural behaviors in relation to the
species’ evolution, adaptive strategies, reproduction, and place in its ecosystem.
While it may sound strange to the student new to the study of animal behavior, one of the
primary tools of the ethologist’s trade is simple observation of animals in the wild without
manipulating anything in the environment. Any artificial changes might affect the study
animal’s natural behavior, calling into question the study’s validity.
For example, if one wished to study the natural mating behavior of a particular bird, the
investigator should not alter anything about the bird or its environment. Rather, careful
observations should be made, with the animal unaware of the investigator’s presence, if
possible. Only once the bird’s natural behavior is established via field studies might the
investigator might perform lab experiments in which various stimuli are manipulated. The
bird’s natural reaction could then be observed, quantified for analysis, and compared to the
natural field observations.
In this half of the semester, you will begin to learn how to study animal behavior. Our
model organism will be the Siamese Fighting Fish, Betta splendens.* Although you will not be
observing these animals in a wild, natural situation (the aquarium version of this species has
been quite domesticated), you will be able to observe these fish and their behavioral
responses to manipulated environmental stimuli. You will rely on the primary literature to
discover the natural behaviors of Betta splendens. As before, you and your team will then
come up with an interesting, relevant question regarding Betta splendens behavior, devise an
overall hypothesis, and then design an experiment to test that hypothesis.
I. Behavior and Evolution
Behavior is defined as the way an organism responds to stimuli in its environment. A
stimulus can be any change in an organism’s internal or external environment that influences
its activity. Behaviors can range from the very simple—a bacterial cell behaving by moving
toward an area with a higher sugar concentration—to the complex—(think about all the ways
you responded to your environment the last time you drove a vehicle). Behaviors can also be
classified into differing categories, based on what environmental conditions elicit the behavior
and what other organisms are involved. Some basic categories of behavior include behaviors
associated with locating and consuming food, avoiding predators, parental care of offspring,
aggression towards competitors, and reproduction, among others.
The behaviors an organism exhibits may be learned, meaning that the organism alters its
behavior as a result of previous experiences, but often behaviors are instinctual, meaning the
behavior is encoded by the organism’s genes. Often, behaviors may exist as some mix of the
two. Learned behaviors require experience to allow an organism to form associations between
stimuli in the environment and the behavior in question. Instinctual behaviors, on the other
hand, occur without any prior experience to a particular stimulus. Many instinctual behaviors
are highly stereotyped, which means that they occur in the same way in different individuals
of a species. In the case of instinctual behaviors, a releaser (some specific
*Note that the genus name is pronounced “beh’-tuh” (hear the pronunciation at http://www.thefreedictionary.com/betta),
not “bay’-tuh” (compare with the pronunciation of the Greek letter β here: http://www.thefreedictionary.com/beta)
Introduction: Betta Behavior-1
environmental stimulus) will trigger a fixed action pattern, an innate, stereotyped behavior.
For example, the mere sight of an egg outside its nest will trigger innate egg retrieval behavior
on the part of a nesting sea gull, whether or not that egg is its own.
Because instinctual behaviors have a genetic basis, they are heritable traits. Even the
capacity to learn a particular behavior may be encoded by an organism’s genes. Because
many behaviors are genetic traits, they are subject to the process of evolution—just like any
other heritable trait.
When ethologists study animal behaviors, they attempt to address both how a behavior
works mechanistically, and why a behavior exists in an evolutionary sense. “How” questions
are known as proximate questions, and seek to find answers regarding what the physical
basis of a trait is or how that trait developed. In this lab, we will be asking “why” questions, or
ultimate questions. Ultimate questions seek to discover either the adaptive value of a
behavior (how it contributes to an organism’s survival or reproduction) or the phylogeny of a
behavior (its evolutionary history).
Let’s consider a behavior with which you are likely familiar—birdsong. As you walk across
campus today, you are likely to hear some small bird singing from a nearby tree. A proximate
question about this behavior might be, “How do birds sing?” The answer might include how
the length of day (which changes during the year) affects hormone levels, which are
responsible for stimulating birdsong. Or, you might consider the development of birdsong, and
investigate how birds develop their song from the time that they are very young to when they
are adults. An ultimate questions might be, “Why do birds sing? What is the adaptive value of
birdsong?” Research into this line of thinking would include investigating how singing improves
a bird’s fitness. In the temperate zone, males sing to defend their breeding territories against
other males, and to attract females—both of which will improve their chances for producing
offspring and passing on their genes. When developing ultimate questions, consider what
environmental pressures an organism faces and how this trait may have changed as it was
passed down from ancestors.
II. Study System: Betta splendens, Siamese Fighting Fish
Wild Betta splendens are colorful, sexually dimorphic (i.e., males and females look different
from one another) fish, with males being more brightly colored than females (Figure 1).
Because of their attractive colors and interesting behaviors, this species has been subject to
many years of artificial selection (particularly the males) for mutant color morphs and very long
fins and tails. Despite the domestic variety's showier appearance (Figure 2), its basic
courtship and other intraspecific (i.e., between members of the same species) displays have
remained relatively similar to those of its ancestors.
A. Natural History
Betta splendens (Actinopterygii, Perciformes, Osphronemidae) commonly known as the
"Siamese Fighting Fish" is native to tropical Southeast Asia including the northern Malay
Peninsula, central and eastern Thailand, Cambodia, and southern Vietnam. They live and
breed in rice paddies, shallow ponds, and slow-moving streams, and are known for their ability
to survive in rather fetid, oxygen-poor water by gulping air from the surface, when necessary.
Interestingly, newly hatched Betta splendens rely on their gills for oxygen exchange. The
species ability to surface-breathe develops later.
Adult males reach a total length of about 7cm, and females are slightly smaller. Cultivated
Bettas have been artificially selected for many decades so that the "domesticated" males are
characterized by colorful pigmentation and long, showy fins. Females are slightly smaller, less
brightly colored, and have shorter fins than males.
Bettas are popular as aquarium fish because of their spectacular colors, and because they
are relatively easy to keep and breed. They appear to thrive comfortably (long term) in a
Introduction: Betta Behavior-2
volume as small as 3 gallons of water, and when living in an appropriate, stress-free
environment, will breed. Males build a nest of mucus-coated bubbles on the surface of the
water, and as the eggs laid by the female hatch, he will carry each hatchling to the nest in his
mouth and spit it into the nest. Hatchlings grow in relative safety in their bubble environment,
guarded by the male.
Figure 1. Wild type Betta splendens male (left) and female (right). The male is fanning
his fins and tail in the beginnings of an agonistic (aggressive) display.
Figure 2. Artificially selected Betta splendens males showing various mutant color
morphs and fin morphologies. The fish in the upper lefthand corner and lower
righthand corner are not displaying. All other fish shown are engaging in agonistic
displays of varying intensity.
Every experienced aquarium hobbyist knows that only one male Betta can occupy an
aquarium at a time. The males are extremely aggressive towards males of their own species.
When fighting, males will nip at each others fins until one of them is too tired to continue,
though this usually takes long enough so that the fins of both combatants resemble rags by the
time one of the fish concedes defeat by retreating.
Introduction: Betta Behavior-3
B. Betta splendens External Anatomy
In order to accurately describe and record data on behavior, you'll need to know the proper
names of the body parts your fish use to communicate with their conspecifics (i.e., members of
the same species). Refer to Figure 3 for an overview of the general external anatomy of Betta
splendens (which is pretty much the same as that of any other bony fish, with superficial
modifications).
Note that male and female Bettas use all their fins in their displays, as well as their
opercula and the fleshy, colorful extensions beneath the opercula. Your team will need to
decide in advance (1) what anatomical features you will monitor during the fish display
behaviors, (2) how you will quantify their use, and (3) what statistical test is most appropriate
for analysis of your data set, once your experiment is complete.
Figure 3. External anatomy of Betta splendens.
C. Agonistic Behavior in Betta splendens
Agonistic (from the Greek agonistes, meaning "champion") behavior in animals is defined
as that exhibited during a contest, combat, escape, attack, or appeasement episode between
two animals. The term is often used to describe the display behaviors exhibited by male
animals when they compete for mating opportunities with females.
Male Bettas may fight to claim territory, or to protect their eggs or offspring from rival males.
But physical combat is invariably preceded by a display sometimes called "flaring." When
stimulated by the sight of a rival male (the releaser), a male Betta will exhibit several types of
genetically determined aggressive movements (fixed action patterns). The fish will spread his
fins, shudder his body, extend his gill opercula and membranes, and generally appear much
larger than his resting size. Bettas do not recognize themselves in a mirror, and will display to
their reflections as aggressively as they might to another male.
VI. Assignment: Literature Search
You should already know that an essential part of undertaking a research
project is to find out what is already known about your area of interest, and
why it is important and relevant. Previous research might give you ideas
about what questions still need to be addressed in this area.
For example, you might be interested in finding out if a particular type of
stimulus elicits a particular behavior in a male Betta splendens. However, it’s
Introduction: Betta Behavior-4
quite possible that research in this area has already been done. Don’t reinvent the wheel. Conduct a literature search and review before embarking
on your experimental project.
A literature search is an organized search for published material on a
selected topic. For our purpose, you will be required to use databases that
retrieve academic sources of high quality and reliability. Literature databases
allow you to search a wide array of journals and other sources, and enable
you to collect scholarly references. Some of these may be in the form of an
abstract, whereas others might be the full text of a journal article. You can
usually save these to your own computer for future reference.
An effective literature search takes an organized approach:
1. Decide on a search topic
With your team, formulate a question to narrow and define the topic. For
example, if you wish to determine the effect of an opponent’s size on a male
Betta’s display, you might ask, “Does agonistic behavior in male Betta
splendens change in response to a change in an opponent’s size?”
2. Use appropriate keywords to use in your search
Identify important keywords. In the example above, you might include “Betta
splendens, agonistic, size, aggression,” or any number of terms related to this
area. Also consider:
• When to use broad terms, and when to use narrower terms to refine your
search
• Use synonyms for your keywords to find every possible variant of the
vocabulary used in the research on this topic.
• Use dictionaries to check spelling and find keyword synonyms
• Using online encyclopedias (e.g., Wikipedia) to find initial background
information that might help you refine your search or choose an area for your
research topic.
3. Choose a Database
GoogleScholar is an excellent place to start, but there are other databases
available through the UM library system that you may wish to use.
4. Perform your Search
• Use Boolean operators (always use them un upper case) to combine
search keywords.
• Truncate (shorten) your keywords to make your search broader.
• If you are not sure how to spell a keyword, use wildcards.
• To narrow your search, use phrases enclosed on quotation marks. For
example, “opponent size effect on agonistic display”.
• Use the database to search for keywords in different places, such as
“title” or “abstract”.
• If you find a useful article by a particular author, search that author’s
name to find papers on the same topic.
• If you find a useful article, search its Literature Cited section to find
additional, related sources.
• Make sure the literature you are citing is recent and current.
• Make sure the literature you use is from a peer-reviewed, scientific
journal.
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•
Make sure to identify whether your source is a journal article, a book, a
thesis, etc.
5. Determine the availability of the material you wish to reference.
If the paper you wish to read is not available online, you may be able to
get a copy by contacting the people at the Richter Library Help Desk. If our
library does not have the paper you need, they may be able to get it via
interlibrary loan. Since this requires turnaround time, this is one very good
reason to start this assignment immediately, and not find yourself hamstrung
by time constraints.
Each student will be assigned the task of finding at least one relevant
paper from a refereed scientific journal on the topic of reproductive behavior
in Betta splendens (or a more general paper related to this area in some
relevant way), and preferably narrowed to an area discussed in advance by
your team. Once you find a paper of interest, read it completely and
analytically. Your assignment is to turn in (1) the journal paper and (2) a onepage summary and review of the paper to your instructor. At the end of your
summary, include at least three questions that the research paper inspires.
One or more of these could lead your team to an interesting and unique
research project of your own design.
Your laboratory instructor will give you additional details about this
assignment.
Your literature search paper and summary are due at your laboratory session
next week. Your Laboratory Instructor will give you the information you need
to turn this in on time.
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