Courtship display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement, vocalizations, mechanical sound production, or displays of beauty, strength, or agonistic ability.
Male display
In some species, males will perform ritualized movements to attract females. The male six-plumed bird-of-paradise exemplifies male courtship display with its ritualized "ballerina dance" and unique occipital and breast feathers that serve to stimulate the female visual system. In Drosophila subobscura, male courtship display is seen through the male's intricate wing scissoring patterns and rapid sidestepping. These stimulations, along with many other factors, result in subsequent copulation or rejection.In other species, males may exhibit courtship displays that serve as both visual and auditory stimulation. For example, the male Anna's hummingbird and calliope hummingbird perform two types of courtship displays involving a combination of visual and vocal display—a stationary shuttle display and dive display. When engaging in the stationary shuttle display, the male displays a flared gorget and hovers in front of the female, moving from side to side while rotating his body and tail. The rhythmic movements of the male's wings produce a distinctive buzzing sound. When conducting a dive display, the male typically ascends approximately in the air then abruptly turns and descends in a dive-like fashion. As the male flies over the female, he rotates his body and spreads his tail feathers, which flutter and collide to produce a short, buzzing sound.
In addition, some animals attempt to attract females through the construction and decoration of unique structures. This technique can be seen in the satin bowerbird of Australia, males of which build and decorate nest-like structures called "bowers". Bowers are decorated with bright and colourful objects to attract and stimulate visiting females. Typically, males who acquire the largest number of decorations tend to have greater success in mating.
In some species, males initiate courtship rituals only after mounting the female. Courtship may even continue after copulation has been completed. In this system, the ability of the female to choose her mate is limited. This process, known as copulatory courtship, is prevalent in many insect species.
In most species, the male sex initiates courtship displays in precopulatory sexual selection. Performing a display allows the male to present his traits or abilities to a female. Mate choice, in this context, is driven by females; direct or indirect benefits to the female often determine which males reproduce and which do not.
Direct benefits may accrue to the female during male courtship displays. Females can raise their own fitness if they respond to courtship behavior that signals benefits to the female rather than the fitness of the male. For example, choosing to mate with males that produce local signals would require less energy for a female as she searches for a mate. Males may compete by imposing lower mating costs on the female or even providing material or offspring contributions to the female.
Indirect benefits are benefits that may not directly affect the parents' fitness but instead increase the fitness of the offspring. Since the offspring of a female will inherit half of the genetic information from the male counterpart, those traits she saw as attractive will be passed on, producing fit offspring. In this case, males may compete during courtship by displaying desirable traits to pass on to offspring.
Female display
Female courtship display is less common in nature as a female would have to invest a lot of energy into both exaggerated traits and in their energetically expensive gametes. However, situations in which males are the sexually selective sex in a species do occur in nature. Male choice in reproduction can arise if males are the sex in a species that are in short supply, for example, if there is a female bias in the operational sex ratio. This could arise in mating systems where reproducing comes at an energy cost to males. Such energy costs can include the effort associated in obtaining nuptial gifts for the female or performing long courtship or copulatory behaviors. An added cost from these time and energy investments may come in the form of increased male mortality rates, putting further strain on males attempting to reproduce.In pipefish, females use a temporary ornament, a striped pattern, to both attract males and intimidate rival females. In this case, the female of a species developed a sexually selected signal which serves a dual function of being both attractive to mates and deterring rivals.
Multi-modal signal processing
Many species of animals engage in some type of courtship display to attract a mate, such as dancing, the creation of sounds, and physical displays. However, many species are not limited to only one of these behaviors. The males of a species across many taxa create complex multi-component signals that have an effect on more than one sensory modality, also known as multi-modal signals. There are two leading hypotheses about the adaptive significance of multi-modal signal processing. The multiple message hypothesis states that each signal that a male exhibits will contribute to a possible mate's perception of the male. The redundant signal hypothesis states that the male exhibits multiple signals that portray the same "message" to the female, with each extra signal acting as a fall-back plan for the male should there be a signaling error. The choosy sex may only evaluate one, or a couple, of traits at a given time when interpreting complex signals from the opposite sex. Alternatively, the choosy sex may attempt to process all of the signals at once to facilitate evaluation of the opposite sex.The process of multi-modal signaling is believed to help facilitate the courtship process in many species. One such species in which multi-modal signaling is seen to improve mating success is the green tree frog. Many anuran amphibians, such as the green tree frog, may use visual cues as well as auditory signals to increase their chances of impressing a mate. When the calls of the tree frogs were held equal, it was determined that females tended to overlook an auditory-only stimulus in favor of males who combined auditory/visual multi-modal signals. It was seen that female green tree frogs preferred when males coupled the visual display with the auditory communication, concluding that male green tree frogs that are visually accessible can increase their probability of mating success.
Peacock spiders are exceptionally sexually dimorphic in appearance and signaling behavior. During courtship, male peacock spiders compete using both visual displays and vibratory signals for intersexual communication. Because of the intense sexual selection on male peacock spiders, the reproductive success of an individual relies heavily on a male spider's ability to combine visual and vibratory displays during courtship. The combination of these displays in courtship offers support both to the redundant signal and multiple messages hypotheses for the evolution of multi-modal signaling in species.
Multi-modal signaling is not limited to males. Females in certain species have more than one trait or characteristic that they use in a courtship display to attract mates. In dance flies, females have two ornaments — inflatable abdominal sacs and pinnate tibial scales — that they use as courtship displays in mating swarms. Intermediate variations of such female-specific ornaments are sexually selected for by male dance flies in wild populations. These ornaments may also be a signal of high fecundity in females.
Mutual display
Often, males and females will perform synchronized or responsive courtship displays in a mutual fashion. With many socially monogamous species such as birds, their duet facilitates pre-copulatory reassurance of pair bonding and strengthens post-copulatory dedication to the development of offspring. For example, male and female crested auklets, Aethia cristatella, will cackle at one another as a vocal form of mutual display that serves to strengthen a bond between the two. In some cases, males may pair up to perform mutual, cooperative displays in order to increase courtship success and attract females. This phenomenon can be seen with long-tailed manakins, Chiroxiphia linearis.Wild turkeys '' also engage in co-operative displays in which small groups of males work together to attract females and deter other competitive males. In many cases, only one male within the group will mate, typically the dominant male. To explain this behaviour, Hamilton's theory of kin selection suggests that subordinate males receive indirect benefits by helping related males copulate successfully.
Sexual ornaments
Sexual ornaments can serve to increase attractiveness and indicate good genes and higher levels of fitness. When exposed to exaggerated male traits, some females may respond by increasing maternal investments. For example, female canaries have been shown to produce larger and denser eggs in response to male supranormal song production.Sexual conflict
is the phenomenon in which the interests of males and females in reproduction are not the same: they are often quite different:- Males: their interest is to mate with a large number of completely faithful females, thus spreading their genes widely throughout a population.
- Females: their interest is to mate with a large number of fit males, thus producing a large quantity of fit and varied offspring.
After mating has taken place, males perform various actions to prevent females from mating again. What action is performed depends on the animal. In some species, the male produces a mating plug after insemination. In some hymenoptera, the male provides a huge quantity of sperm, enough to last the female's entire life. In some birds and mammals, the male may participate in agonistic behaviors with other candidate males.