lecture 31 - communication and sexual selection Flashcards
What are different types of signal?
Communication also plays a role in animal behavior. The sophistication of animal communication varies enormously, and can be seen by the variety of types of signal. A number of species have evolved forms of communication that convey remarkably complex and specific information. Signals can be: visual, auditory, electrical, chemical, and mechanical.
The simplest definition of communication is the transfer of information between two individuals, the sender and the receiver. The sender supplies a signal that elicits a response from the receiver. It is thought that communication has often evolved through co-opting and modifying behaviors used in another context. This process is called ritualization, and it involves;
increasing the conspicuousness of the behavior;
reducing the amount of variation in the behavior so that it can be immediately recognized;
increasing its separation from the original function.
What is communication?
Transfer of information between two individuals
The individuals are the sender and receiver
The sender has to intend to change the behaviour of the receiver
How do signals evolve?
Co-opting existing behaviours via “ritualization”. Involves a) More conspicuous – so detected b) Less variable so easily recognized c) Different from original function e.g. Scent marking in mammals. Originally just waste elimination Strategically placed Makes intruder turn back
How is strength assessed?
With limited resources, competition is common
Resolving competition can lead to contests
But contests can be costly to both parties
Conflicts often resolved in assessment displays- Red deer stag roaring
How can communication can be dishonest?
Camouflage
heckles of frightened wolves exaggerate their size and intimidate opponents
angler fish lure is bioluminsecent and attracts small fish, suggests false presence of food
How is bird song learnt?
Bird song is one of the best known and richest forms of animal communication. Because of the clear connection between sensory perception and motor output involved in this form of communication, songbirds have served as a model system in the study of learning and communication. These songs are complex sequences of sounds, often repeated over and over. Like cricket and frog calls, bird songs are advertisement displays, behaviors by which individuals draw attention to their status. Bird songs are typically produced in the breeding season and usually only by males, although in some species females also sing and perform “duets” with their mates.
The process of song acquisition has been developed by Peter Marler and his studies of the White-Crowned Sparrow. Song in White-Crowned Sparrows is learned by imprinting: The young male hears adult song during a sensitive period, 10–50 days after hatching. Then, shortly afterward, young male White-Crowned Sparrows produce unstructured twittering sounds, known as a subsong, comparable to the babbling of human babies. If deprived of hearing adult song, for example by isolation during the sensitive period, the bird sings for the rest of his life a song not much different from unstructured twittering, even if he hears his father sing both before and after isolation.
So, White-Crowned Sparrows have a programmed predisposition for when song learning takes place. Even more interestingly, what can be learned is similarly constrained. If a tape of another species’ song is played during the sensitive period, even the song of closely related Swamp Sparrows, the White-Crowned male cannot learn that song; his adult song ends up being not much different from his unstructured twittering. However, if he is provided with a live tutor, such as a live male Swamp Sparrow rather than a tape, his ability to learn the other bird’s songs is greatly improved. Furthermore, if he hears tapes of both the song of his own species and that of closely related species played together, he can pick out the correct elements and sing a perfect White-Crowned Sparrow song. Thus, birds preferentially learn their species-specific song, but they cannot sing without learning it.
How do honeybees communicate?
Honeybees have an elaborate means of communication that is quite different from the sound-based communication of birds. The hive can be considered a kind of giant organism, fixed in one spot but sending out foragers in all directions. As social insect expert and evolutionary biologist E. O. Wilson points out, if honeybee workers were as large as people, they would cover an area the size of Texas in their daily search for food. Given the vastness of this task, it is not surprising that returning workers use a variety of cues to inform outgoing foragers about the location and nature of the food resources they have found.
Returning workers pass samples of the collected food to other workers that gather around the forager when she returns to the hive. The returning foragers then begin a series of movements in specific patterns that encode information about the direction and distance of food sources. This is the dance language of honeybees, originally discovered by Karl von Frisch.
If the food source is within about 50 m of the hive, a simple dance called the round dance—rapid movement in little circles, in both clockwise and counterclockwise directions—is sufficient. Outgoing foragers then know that the source is close and they search at random in the vicinity of the hive until they find the source. If the food source is farther away, the incoming forager does a more complex dance, the waggle dance. The forager moves quickly back and forth (“waggles”) as it moves forward, circles back and repeats the waggle, then circles back the other way, and so on. This dance usually goes on for several minutes and may take much longer.
What is sexual selection?
Sexual selection is selection for traits that increase the probability of mating success
It may run counter to natural selection
Sexual dimorphism results from differences in
investment in offspring by the sexes.
Females tend to invest more in each offspring
So female fitness is limited by quality of resources and mates
Male fitness is limited by the number of mates
What are the two forms of sexual selection?
Sexual Selection can be intra-sexual or inter-sexual
In On the Origin of Species, Darwin recognized two forms of sexual selection.
In one form, members of one sex (usually the males) compete with one another for access to the other sex (usually the females). This form is called intrasexual selection since it focuses on interactions between individuals of one sex. Because competition typically occurs among males, it is in males that we see physical traits such as large size and horns and other elaborate weaponry, as well as behaviors such as fighting. Larger, more powerful males tend to win more fights, hold larger territories, and have access to more females.
Darwin also recognized a second form of sexual selection. Here, males (typically) do not fight with one another, but instead compete for the attention of the female with bright colors or advertisement. This form of selection is called intersexual selection, since it focuses on interactions between females and males.
In general, females have evolved behaviors to ensure the quality of their mate (they tend to be choosy), whereas males have evolved behaviors to maximize the number of matings they have (they tend to be competitive).
