Organism Behavior and Fitness

Is it a bird? A plane? Or a human? All jokes aside, if it's a human, then it couldn't fly, so that would be easy to eliminate through observation.

A plane and a bird are vastly different; one is a living thing with feathers, while the other is an artificial machine. The only commonality is that both can fly. One flies thanks to jet fuel and the other thanks to evolution by natural selection.But what about being able to tell apart two different types of birds? Such as woodpeckers and owls. Well, in this case, we could look at their individual traits, characteristics, and behaviors.

Woodpeckers produce loud vibrations from pecking at trees to find food. In contrast, owls are known to be able to turn their heads 270 degrees, hoot, and are nocturnal. All Animals have certain traits, characteristics, and behaviors that allow us to identify them, making observations of organism behavior necessary.

So, without further ado, let's dive into organism behavior and fitness!

• First, we will look at the definition of organism behavior.
• Then, we will talk about the behavior of Microorganisms.
• After, we will look at the definition of fitness.
• Lastly, we will explore the evolutionary history of an organism's behavior.

Organism Behavior Definition

In biology, an organism is an individual living being made up of Cells. Organisms are categorized into taxonomies that include multicellular organisms such as Plants, Animals, Fungi, and unicellular Microorganisms, which we will elaborate on in the next section.

This means that organism behavior can be thought of as a change in an organism's action or activity in response to internal or external stimuli. An animal is a type of multicellular organism or an organism with multiple Cells.

Generally, when we mention organism behavior, we refer to animals because Plants do not have brains and aren't motile or moving. This means that plant behavior is usually innate and deals with moving toward sunlight (phototropism) and placing their roots where they can most efficiently absorb nutrients and water.

Behaviors can be innate or learned.

• Innate behaviors occur due to an animal's Genes or heredity.

• Learned behaviors are behaviors that aren't hardwired and instead come with experience.

Innate behaviors are often highly predictable because they occur automatically in response to certain stimuli, and most of the same species will exhibit the same behaviors. For example, all birds migrate, as shown in Figure 1.

But how do they know when to migrate? The answer is that they use Innate Behavior to understand how, when, and where to migrate.

Figure 1: Bird Migration. Wikimedia, USFWS (Public Domain).

Animal behaviors refer to how animals interact with themselves, other living beings, and their surroundings. This signifies that animal behaviors can involve biotic (living) and abiotic (non-living) factors.

Some examples of innate behaviors include Reflexes in humans. For example, the famous knee-jerk reflex in humans is innate, as we have no control over it. The knee-jerk reflex refers to our kicking motion when the tendons below our knees are tapped or kicked. Other innate behaviors include spiders making webs and birds building nests.

Examples of learned behaviors include waking up to the sound of an alarm clock for humans.

Microorganism Behavior

Microorganisms are types of organisms that are microscopic or too small to be seen with just our eyes.

Examples of microorganisms include Bacteria, Archaea, Fungi, and protists. This section will mainly focus on bacteria, the most abundant life forms.

Bacteria are unicellular microorganisms that have cell walls but not membrane-bound organelles. Unicellular organisms are organisms made of single cells. At the same time, organelles are specialized structures within a cell that perform specific jobs.

Basic bacterial behavior consists of growth and proliferation. They are one of the fastest-growing organisms worldwide as, depending on the species, they can double every 4 to 20 minutes. This means that if you start with one fast-growing bacteria species, in the next 4 to 20 minutes, you'd have two of the same species, then four, and so on, as bacteria grow exponentially.

Other common behaviors displayed by most bacteria include:

• Motility or the ability to move and swim through the usage of a flagellum. A flagellum is a hair-like appendage that protrudes from bacteria and allows them to move.

• They can aggregate together to create biofilms or a film of bacteria that sticks to the surface. The advantage of biofilms for bacteria is that living in a community of bacteria can ensure a reliable nutrient source, protection, antibiotic resistance, and even metabolic exchanges!

• An example of a biofilm of Staphylococcus aureus on a catheter is shown in Figure 2. A catheter is a tube inserted into the patient's bladder in hospitals, and bacteria such as S. aureus grow biofilms, causing severe infections.

• Conjugation, or transferring Genetic Information between bacterial cells by pili. Pili are hair-like appendages found in many archaea and bacteria that conduct conjugation. The Genes transferred are usually beneficial and lead to greater tolerance and antibiotic resistance.

• Bacterial Populations can use quorum sensing or control the expression of genes based on their population density. Through quorum sensing, bacteria can regulate virulence and biofilm formation.

Figure 2: Biofilm formation on a catheter. Wikimedia, CDC (Public Domain).

Organism Fitness Definition

Behavior can also be affected by natural selection.

Natural selection is the theory coined by Charles Darwin that deals with organisms' differential survival and reproduction rates due to phenotypic variations. In other words, natural selection states that the organisms that are better "fit" or adapted to an environment have a higher chance of surviving and therefore reproducing.

While we might think that fitness refers to exercise, strength, and maybe even speed, that's not the case in biology. In biology, an organism's fitness refers only to its reproductive success.

This mean's that the higher the fitness of an organism, the higher the number of offspring it has. When we refer to fitness, we usually want to know how good an organism's specific genotype is at leaving behind offspring compared to other genotypes.

For instance, if brown birds were to leave consistently more offspring when compared to yellow ones, then we'd say that brown birds had a higher fitness. This is because we only refer to reproductive success when discussing evolution.

The behavior of organisms can either increase or decrease their fitness. Usually, the behavior of organisms increases their fitness as organisms will inherently try to increase their chances of reproductive success.

Examples of behaviors that increase fitness are packs of wolves forming social groups to increase their survival rates and reproduction, mutualistic relationships between different organisms, etc.

Reduced Organism Fitness

When an organism has reduced fitness, it has less chance to reproduce and therefore is not as well adapted to its current environment.

An organism's fitness depends on where the organism lives. For instance, during the industrial revolution, moths turned black because of the contamination of soot and smoke from factories that blackened the environment. Moths went from white to black to camouflage better. As humans cleaned up the environment, the moths returned to being white as the habitat was restored.

The concept of fitness combines everything from survival to finding mates to reproduction. This is because if animals do not survive to reproductive age, they will not be able to find mates and reproduce to pass down offspring to the next generation. This means that environmental factors such as natural disasters, human impact, or changes in the number of predators could affect an organism's chances of surviving till reproduction, affecting its fitness.

In rare circumstances, the behavior of organisms can also decrease their fitness. For example, one ground squirrel can warn the other squirrels about incoming predators by alerting them with a call. This sound will attract the predators to the squirrel, making the sound while saving the others. This type of behavior in animals is called altruism.

Altruism reduces the fitness of the squirrel making the call but helps the rest. Overall, it is helpful for the species of ground squirrels as a whole but damaging to one squirrel's fitness. This concept is still being researched by scientists and shows that behavior and fitness aren't always 100% straightforward.

Evolutionary History of an Organism's Behavior

Some behaviors can have a genetic basis. Generally, these behaviors are called innate behaviors.

Innate behaviors, as mentioned before, are highly predictable and always happen the same way as genes control them. Scientists believe that these instinctual fixed behavior patterns were shaped by evolution for many successive generations as they were advantageous to the organism's survival and overall fitness.

In general, if a behavior, character, or trait increases the fitness of an organism, then it's likely to become more and more common as time passes through generations of organisms. Another way to think about innate and learned behaviors is to think about the nature-nurture debate.

Innate behaviors can also be referred to as natural behaviors, while learned behaviors can also be considered nurtured. In the real world, most behaviors are affected by both nature and nurture.

An example of a nurtured behavior acquired through communication is howls. Wolves that are designated as alpha have lower-pitched howls than the other wolves. Pups also learn to howl by imitating adult wolves. Other dominant behaviors are also learned but ultimately can and have become innate because having them increases fitness.

Overall, organism behavior and fitness aren't as cut and dry as they seem! For more regarding organism behavior and fitness, head over to our flashcards!