All organisms are affected by their environment. In previous units, we have discussed some ways that organisms are changed by their environment including phenotypic expression and speciation. However, individual organisms are also able to receive signals from the environment and respond to them behaviorally and physiologically. These responses can help an individual survive and have reproductive success. There are several different ways that organisms receive cues from their environment. Some examples are: 

  • Chemoreception is the identification of chemical substances and their concentrations. This sensory mechanism is found in even the most primitive life forms. The familiar senses of taste and smell are both forms of chemoreception. Many animals release pheromones to cause a specific response by the receiving organism. Pheromone release and reception constitutes one of the most primitive forms of communication and is widely used in nature for a variety of purposes.  

  • Thermoreception, the detection of temperature changes, is present in most animals. For instance, many insects have temperature-sensitive nerve endings, either on their legs to detect ground temperature or on their antennae to detect air temperature. This allows them to change their behavior as necessary in response to these environmental changes. 

  • Mechanoreception is found in many organisms and is the response to physical vibrations. Many arthropods have vibration sensitive hairs in their limb joints. Tactile sensations can be propagated via hairs or by the deformation of skin neurons. Such neurons are called mechanoreceptors. These receptors are also involved in hearing. Sound waves are propagated by vibrations of air or water molecules. Small changes in pressure that result from these vibrations are detected by mechanoreceptors and are sensitive to sound vibrations. 

Communication 

Communication between organisms contributes to the success of a population. It allows individuals to receive information and pass it on to others in the population. This improves the overall fitness of individuals and populations as a whole. Communication can be in a variety of forms: visual, audible, tactile, electrical, or chemical. Animals specifically use communication to indicate dominance, find food, establish territory, and seek reproductive success. 

Chemical Communication 

All forms of life must selectively detect and take in chemicals, and so chemical signaling occurs at many levels in all cells. Hormones operate within an organism, pheromones are signals between conspecifics, and allomones are intended for interspecies communication. In this section, we will focus on pheromones. 

Two different systems of reception are employed for chemical communication. Airborne and waterborne chemicals received at a distance from their source are detected by olfactory reception, or smell. Other chemicals require contact reception, which is the direct contact of the receiver with the source of the pheromone. Pheromones are usually produced by glands located on the skin, or by tissues within the body that have ducts leading to the body's exterior; the second variety of glands are known as exocrine glands. Mammals produce pheromones in the sudoriferous (fluid-producing) gland and the sebaceous (waxy-substance producing) gland. Some mammals have other specialized glands. Insects produce a large variety of pheromones, most notably from their mandibular glands, thoracic glands, and stingers. 

A good example of a multipurpose pheromone is the Queen substance employed by some eusocial bees. This pheromone motivates and attracts workers, releases swarming, and is a sex pheromone. The absence of queen substance indicates the colony has grown too large (the queen is too far away to smell her) and so workers will build queen cells to rear new queens. An abrupt absence of Queen substance results in emergency queen rearing, since that absence is probably an indication of the queen's death. 

Ants and snakes employ trail pheromones to mark the path to a food source. These chemicals are laid out along a trail, and the next ant will follow the trail by means of contact reception. Many animals, from moths to cats, use pheromones to attract mates. 

Visual Communication 

Visual signals are limited because they require a direct line of sight and they only last as long as the sender is signaling. Humans and primates are much more dependent on this type of communication than non-primate animals. The sender can send a signal by performing a display or by assuming a specific body posture. The receiver perceives the signal through the eyes, which the brain translates into a visual image. Visual images are received in real-time, and so are generally dynamic signals. 

Acoustic Communication 

Acoustic signals are energetically costly, but can travel great distances, degrading with increasing distance. Many animals produce sounds to impart information, however only humans have a well-developed language. Many species use sound to send out alarm calls, attract mates, and communicate other information. There are also several other species, such as dolphins and whales, that are known to have sophisticated acoustic communication. 

Tactile Communication 

Physical contact is limited in its ability to communicate because it is extremely short-range. Many invertebrates use antennae as the first line of contact with objects and organisms. The honeybee waggle dance used to explain the location of a food source is often performed in a dark hive, and so the foragers receive their information by interpreting the dance with their antennae.  

Electrical Communication 

Sharks and some fish have electroreceptors that are used to detect objects and to socially communicate. Electrolocation is a form of autocommunication; signalers send and receive their own signals. The difference between the emitted and received signals yield information about the environment through which the signal has passed. Species that use electrical signals for social communication are nocturnal or inhabit murky waters where visual communication is limited. Electrical signals are useful because they are extremely precise; they are limited to use in aquatic environments, though, because air is ineffective as an electrical insulator or conductor. 

Animal Behavior 

Animal behavior is the way that animals interact with other organisms and the physical environment. This includes how they change their activity in response to external or internal stimuli. Natural selection favors behaviors that increase survival and reproductive fitness, and often these behaviors are passed on from parent to offspring. There are two main categories of behavior – innate and learned. Innate behaviors are coded for in the organisms’ genetics and are inherited from an organism’s parents. Learned behaviors are developed during an organism’s lifetime through experience and communication with other individuals. While behavior can be considered through these two lenses, most behaviors have both innate and learned components. 

Most behaviors do not occur in isolation but rather are the result of interactions between members of a species or between members of different species. Communication is one example of this, as each form requires both a sending and a receiving organism. Cooperative behavior is another example, involving interactions between individuals that are mutually beneficial. These behaviors tend to increase the fitness of the individual and the survival of the population. For instance, wolves live in packs that allow them to hunt together, share food, and share the responsibility of caring for offspring. 

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