Sexual selection is a mechanism of evolution in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. These two forms of selection mean that some individuals have greater reproductive success than others within a population, for example because they are more attractive or prefer more attractive partners to produce offspring. Successful males benefit from frequent mating and monopolizing access to one or more fertile females. Females can maximise the return on the energy they invest in reproduction by selecting and mating with the best males.
The bowl and doily spider is a species of sheet weaver found in North and Central America. It is a small spider, about 4 mm (0.16 in) long, that weaves a fairly complex and unique sheet web system consisting of an inverted dome shaped web, or "bowl," suspended above a horizontal sheet web, or "doily", hence its common name. The spider hangs from the underside of the "bowl", and bites through the web small flies, gnats and other small insects that fall down into the non-sticky webbing. The webs are commonly seen in weedy fields and in shrubs, and may often contain both a male and a female spider in late summer—like many linyphiids, Frontinella males and females may cohabitate for some time. Males exhibit competition for female mates both by fighting and sperm competition. Uniquely, these spiders exhibit behavioral thermoregulation and have lengthened circadian rhythms.
Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.
External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. It is contrasted with internal fertilization, in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism.
The forest tent caterpillar moth is a moth found throughout North America, especially in the eastern regions. Unlike related tent caterpillar species, the larvae of forest tent caterpillars do not make tents, but rather, weave a silky sheet where they lie together during molting. They also lay down strands of silk as they move over branches and travel as groups along these pheromone-containing silk trails. The caterpillars are social, traveling together to feed and massing as a group at rest. Group behavior diminishes as the caterpillars increase in size, so that by the fifth instar (molt) the caterpillars are feeding and resting independently.
Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.
Extra-pair copulation (EPC) is a mating behaviour in monogamous species. Monogamy is the practice of having only one sexual partner at any one time, forming a long-term bond and combining efforts to raise offspring together; mating outside this pairing is extra-pair copulation. Across the animal kingdom, extra-pair copulation is common in monogamous species, and only a very few pair-bonded species are thought to be exclusively sexually monogamous. EPC in the animal kingdom has mostly been studied in birds and mammals. Possible benefits of EPC can be investigated within non-human species, such as birds.
Sexual cannibalism is when an animal, usually the female, cannibalizes its mate prior to, during, or after copulation. It is a trait observed in many arachnid orders, several insect and crustacean clades, gastropods, and some snake species. Several hypotheses to explain this seemingly paradoxical behavior have been proposed. The adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis are among the proposed hypotheses to explain how sexual cannibalism evolved. This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ. In many species that exhibit sexual cannibalism, the female consumes the male upon detection. Females of cannibalistic species are generally hostile and unwilling to mate; thus many males of these species have developed adaptive behaviors to counteract female aggression.
The sexy son hypothesis in evolutionary biology and sexual selection, proposed by Patrick J. Weatherhead and Raleigh J. Robertson of Queen's University in Kingston, Ontario in 1979, states that a female's ideal mate choice among potential mates is one whose genes will produce males with the best chance of reproductive success. This implies that other benefits the father can offer the mother or offspring are less relevant than they may appear, including his capacity as a parental caregiver, territory and any nuptial gifts. Fisher's principle means that the sex ratio is always near 1:1 between males and females, yet what matters most are her "sexy sons'" future breeding successes, more likely if they have a promiscuous father, in creating large numbers of offspring carrying copies of her genes. This sexual selection hypothesis has been researched in species such as the European pied flycatcher.
The quacking frog, also known as the red-thighed froglet due to its legs tending to be bright red, is a species of frog from the Myobatrachidae family and is in a clad with five other species. The frog is well known for the sound it produces which resembles a quack. It has up to 11 notes and can change the notes in their call. It has larger testes compared to other frogs within the genus and has started to be used in experiments. This frog is found in southwest Australia. It is found in ponds and pools and other moisture filled areas. These frogs engage in polyandry and can result in multiple paternity of its offspring. Additionally, the tadpoles of this species can change the rate they metamorphosize depending on the conditions. The males tend to have larger arm girth and can adopt different mating strategies depending on size. The mating strategy is dependent on male density. The frogs also vary in terms of colour and texture of its skin. The tadpoles are generally golden with transparent tails.
Female sperm storage is a biological process and often a type of sexual selection in which sperm cells transferred to a female during mating are temporarily retained within a specific part of the reproductive tract before the oocyte, or egg, is fertilized. This process takes place in some species of animals. The site of storage is variable among different animal taxa and ranges from structures that appear to function solely for sperm retention, such as insect spermatheca and bird sperm storage tubules, to more general regions of the reproductive tract enriched with receptors to which sperm associate before fertilization, such as the caudal portion of the cow oviduct containing sperm-associating annexins. Female sperm storage is an integral stage in the reproductive process for many animals with internal fertilization. It has several documented biological functions including:
Formally, a nuptial gift is a material presentation to a recipient by a donor during or in relation to sexual intercourse that is not simply gametes in order to improve the reproductive fitness of the donor. Often, such a gift will improve the fitness of the recipient as well. This definition implies neutral gifts, costly gifts and beneficial gifts regarding the fitness of the recipient.
Dryomyza anilis is a common fly from the family Dryomyzidae. The fly is found through various areas in the Northern hemisphere and has brown and orange coloration with distinctive large red eyes. The life span of the fly is not known, but laboratory-reared males can live 28–178 days. D. anilis has recently been placed back in the genus Dryomyza, of which it is the type species. Dryomyzidae were previously part of Sciomyzidae but are now considered a separate family with two subfamilies.
Sexual selection in birds concerns how birds have evolved a variety of mating behaviors, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and color differences are energetically costly attributes that signal competitive breeding situations. Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signaling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behavior are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviors.
Sexual selection in scaled reptiles studies how sexual selection manifests in snakes and lizards, which constitute the order Squamata of reptiles. Each of the over three thousand snakes use different tactics in acquiring mates. Ritual combat between males for the females they want to mate with includes topping, a behavior exhibited by most viperids in which one male will twist around the vertically elevated fore body of its opponent and forcing it downward. It is common for neck biting to occur while the snakes are entwined.
Sexual selection in insects is about how sexual selection functions in insects. The males of some species have evolved exaggerated adornments and mechanisms for self-defense. These traits play a role in increasing male reproductive expectations by triggering male-male competition or influencing the female mate choice, and can be thought of as functioning on three different levels: individuals, colonies, and populations within an area.
Sexual selection in amphibians involves sexual selection processes in amphibians, including frogs, salamanders and newts. Prolonged breeders, the majority of frog species, have breeding seasons at regular intervals where male-male competition occurs with males arriving at the waters edge first in large number and producing a wide range of vocalizations, with variations in depth of calls the speed of calls and other complex behaviours to attract mates. The fittest males will have the deepest croaks and the best territories, with females making their mate choices at least partly based on the males depth of croaking. This has led to sexual dimorphism, with females being larger than males in 90% of species, males in 10% and males fighting for groups of females.
Sexual selection in spiders shows how sexual selection explains the evolution of phenotypic traits in spiders. Male spiders have many complex courtship rituals and have to avoid being eaten by the females, with the males of most species surviving only a few matings and consequently having short life-spans.
In behavioral ecology, polyandry is a class of mating system where one female mates with several males in a breeding season. Polyandry is often compared to the polygyny system based on the cost and benefits incurred by members of each sex. Polygyny is where one male mates with several females in a breeding season . A common example of polyandrous mating can be found in the field cricket of the invertebrate order Orthoptera. Polyandrous behavior is also prominent in many other insect species, including the red flour beetle, the adzuki bean weevil, and the species of spider Stegodyphus lineatus. Polyandry also occurs in some primates such as marmosets, mammal groups, the marsupial genus' Antechinus and bandicoots, around 1% of all bird species, such as jacanas and dunnocks, insects such as honeybees, and fish such as pipefish.
Inbreeding in fish is the mating of closely related individuals, leading to an increase in homozygosity. Repeated inbreeding generally leads to morphological abnormalities and a reduction in fitness in the offspring. In the wild, fish have a number of ways to avoid inbreeding, both before and after copulation.
