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, [1] and can be thought of as functioning on three different levels: individuals, colonies, and populations within an area. [2]
The amount of space accessible and the time both male and female usually determines the site of copulation. Many hymenopteran males constantly fly around specific sites, usually the tops of tall trees, summits, or along hedges, where approachable females are found as they can also be resources visited by females for the purpose of feeding. In honey bee the queens join the mating area alone and are then pursued by a dynamic swarm of males. Those located in the front of the line usually achieve reproduction success. A queen usually mates with twelve males on an average of two mating flights and stores the sperm throughout her entire lifetime. Colonies sustain many males but only a few queens, so only very few males are able to successfully mate with the queen. [3]
Onthophagus taurus is a species of dung beetle. Competition for fertilisation of females occurs when males engage in trials of strength over the possession of breeding tunnels. This competition is a prominent feature of the mating system of these beetles. When ionizing radiation is applied to males, mutations are induced that reduce the expression of strength-related precopulatory sexual traits such as competition for breeding tunnels. [4] However, sexual selection by females proved sufficient to remove such mutations from progeny after two generations.
Males can be choosier than females. As an offering, males are capable of providing nuptial gifts secretions, which can be more expensive than female reproductive investment, [1] parental care, where the reproductive costs in males are higher than in females because they invest large quantities of resources and time after egg fertilization, and foraging and nesting sites to the females. Moreover, these factors decrease their subsequent male reproductive opportunities, and the availability of males. An example of male parental care can be found in belostomatid water bugs, where the male, after fertilizing the eggs, allows the female to glue her eggs onto his back. He broods them until the nymphs hatch 2–4 weeks later. The eggs are large and reduce the ability of the male to fertilize other females and catch prey, and increases its predation risk. [5] [6]
Females are usually in conflict over the acquisition of resources and also tend to compete for male provided resources, thus generating a sex role reversal. Females compete to monopolize parental care, [7] and displace rivals with claspers that appear to be specialized in keeping their hold on males, avoiding takeover attempts by other females.
Male-to-male competition for access to females and for resources that the females require for themselves and their offspring is common and can explain the morphological phenotypic traits and behaviors, such as large body size, weapons, territoriality, and early sexual maturation that increase their possibilities of gaining access to the females. [8] In many social insects, larger males are more competitive and tend to monopolize females or the resources that they need. In bees, females may choose males who are faster, more agile, or more persistent fliers. Sequestering of females and forced copulation may also favor large male size. Males with longer horns and mandibles can use them to fight, or for take over attempts when rivals are copulating. In beetle species, the male horns can be as long as the male's body. Early sexually mature males can start their reproductive life before the rest of the male population. Under scramble competition to inseminate females, the early matured males are smaller but can be favored in some cases where courtship occurs on the ground and attain the highest reproductive success. Thus, in the fly Drosophila suboscura , smaller males are better than large males at tracking females during the courtship dance. [9]
The effect of mating on female fitness may vary depending upon the kind of benefit that the females receive from males through of their choices. Direct benefits include nutritional resources to be used by females, donation of foods to mates, males offering prey to the female, seen in scorpion flies and dance flies. Several orthopteran species, butterflies, flies, and beetle males can donate secretions or nutritional substances to the females which are transferred in the ejaculate or produced by male glands which can contribute to increase female fecundity. In the green-veined white (Pieris napi), a virgin male can transfer an ejaculate containing 14% nitrogen by dry mass. Females utilize the nutrients transferred from the male in order to increase their nutrients. These nutrients essentially contribute to ensure successful egg production. A positive relationship between the amount of ejaculate material received and lifetime reproductive output, as male-transferred material increases female longevity. In some insect species, males can donate some body parts to females such as the leg spurs or the fleshy hindwings of jumped-winged crickets, or they may be completely cannibalized, as occurs in mantis and some dipterous, as well as in some Arachnida scorpions and spider species. [2]
Sexual pheromones are defined as odors and are one of the prevalent ways in which social male insects find females to mate with. They can be produced in either males or females. The central roles of pheromones are to trigger behavioral interactions between the two sexes. [10] Ultimately, this brings the sexes together for mating purposes. In addition, females discriminate against mates by the judgment of their sex pheromones. [11] Courtship pheromones are issued in many cases by males. In the queen butterfly Danaus gilippus and the Arctic moth Utetheisa ornatrix , the chemical stimulation of the female is necessary for male mating success. [1]
In species such as the Coleopteran family Lampyridae, the males fly in the darkness and emit a species-specific pattern of light flashes, which are answered by perching receptive females. The color and temporal variation of the flash contribute to the success in attracting females. [12] Acoustic signals are produced by many groups including several orthopteran species, neuropterida, cicadas, flies, cave planthroppers, leaf hoppers, and tree hoppers. In crickets and other Orthopeterans, loudness and/or uninterrupted songs often attract more females. In other insects, females may choose a mate in relation to aspects of his songs. In any case, it is possible that females compare the songs of several males before making a choice. [13]
Female calling syndrome occurs when female social insects emit a typical call to the males in close proximity to their natal nests. Males that are attracted by the callings fly extensively in pursuit of potential mates. Their gasters raise and stings start to protrude. The venom glands are a basis of a chemical male attractant. In Xenomyrmex floridanus , the queen's venom glands and gasters both attracted males and prompted copulation. [11]
Callosobruchus maculatus is a species of beetle, also known as the cowpea seed beetle. Recessive deleterious mutations of this beetle are generally directly selected against in males but not in females. [14] Mutations with deleterious effects on population growth due to their effects on females can be indirectly selected against and efficiently purged by way of their male siblings. [14]
Tribolium castaneum is a species of beetle also known as the red flour beetle. When experimental populations of the red flour beetle were subjected to strong sexual selection for multiple years they became resilient to extinction. Furthermore when such beetles were subjected to inbreeding, they maintained fitness for up to 20 generations. [15] However experimental lineages derived form populations that had either no or weak sexual selection experienced rapid fitness decline under inbreeding, and all of these populations became extinct within 10 generations. It was concluded from these findings that sexual selection reduces mutational load, and by doing so improves population viability.
Sexual selection is a mode of natural selection 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.
Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when studying animal behaviors: What are the proximate causes, ontogeny, survival value, and phylogeny of a behavior?
Pseudocopulation describes behaviors similar to copulation that serve a reproductive function for one or both participants but do not involve actual sexual union between the individuals. It is most generally applied to a pollinator attempting to copulate with a flower. Some flowers mimic a potential female mate visually, but the key stimuli are often chemical and tactile. This form of mimicry in plants is called Pouyannian mimicry.
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.
Reproductive success is an individual's production of offspring per breeding event or lifetime. This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves.
Parental investment, in evolutionary biology and evolutionary psychology, is any parental expenditure that benefits offspring. Parental investment may be performed by both males and females, females alone or males alone. Care can be provided at any stage of the offspring's life, from pre-natal to post-natal.
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.
Parental care is a behavioural and evolutionary strategy adopted by some animals, involving a parental investment being made to the evolutionary fitness of offspring. Patterns of parental care are widespread and highly diverse across the animal kingdom. There is great variation in different animal groups in terms of how parents care for offspring, and the amount of resources invested by parents. For example, there may be considerable variation in the amount of care invested by each sex, where females may invest more in some species, males invest more in others, or investment may be shared equally. Numerous hypotheses have been proposed to describe this variation and patterns in parental care that exist between the sexes, as well as among species.
Drosophila pseudoobscura is a species of fruit fly, used extensively in lab studies of speciation. It is native to western North America.
The red flour beetle is a species of beetle in the family Tenebrionidae, the darkling beetles. It is a worldwide pest of stored products, particularly food grains, and a model organism for ethological and food safety research.
Eusociality is the highest level of organization of sociality. It is defined by the following characteristics: cooperative brood care, overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups. The division of labor creates specialized behavioral groups within an animal society which are sometimes referred to as 'castes'. Eusociality is distinguished from all other social systems because individuals of at least one caste usually lose the ability to perform behaviors characteristic of individuals in another caste. Eusocial colonies can be viewed as superorganisms.
Bateman's principle, in evolutionary biology, is that in most species, variability in reproductive success is greater in males than in females. It was first proposed by Angus John Bateman (1919–1996), an English geneticist. Bateman suggested that, since males are capable of producing millions of sperm cells with little effort, while females invest much higher levels of energy in order to nurture a relatively small number of eggs, the female plays a significantly larger role in their offspring's reproductive success. Bateman's paradigm thus views females as the limiting factor of parental investment, over which males will compete in order to copulate successfully.
Sexual antagonistic co-evolution is the relationship between males and females where sexual morphology changes over time to counteract the opposite's sex traits to achieve the maximum reproductive success. This has been compared to an arms race between sexes. In many cases, male mating behavior is detrimental to the female's fitness. For example, when insects reproduce by means of traumatic insemination, it is very disadvantageous to the female's health. During mating, males will try to inseminate as many females as possible, however, the more times a female's abdomen is punctured, the less likely she is to survive. Females that possess traits to avoid multiple matings will be more likely to survive, resulting in a change in morphology. In males, genitalia is relatively simple and more likely to vary among generations compared to female genitalia. This results in a new trait that females have to avoid in order to survive.
Eusociality evolved repeatedly in different orders of animals, notably termites and the Hymenoptera. This 'true sociality' in animals, in which sterile individuals work to further the reproductive success of others, is found in termites, ambrosia beetles, gall-dwelling aphids, thrips, marine sponge-dwelling shrimp, naked mole-rats, and many genera in the insect order Hymenoptera. The fact that eusociality has evolved so often in the Hymenoptera, but remains rare throughout the rest of the animal kingdom, has made its evolution a topic of debate among evolutionary biologists. Eusocial organisms at first appear to behave in stark contrast with simple interpretations of Darwinian evolution: passing on one's genes to the next generation, or fitness, is a central idea in evolutionary biology.
Interlocus sexual conflict is a type of sexual conflict that occurs through the interaction of a set of antagonistic alleles at two or more different loci, or the location of a gene on a chromosome, in males and females, resulting in the deviation of either or both sexes from the fitness optima for the traits. A co-evolutionary arms race is established between the sexes in which either sex evolves a set of antagonistic adaptations that is detrimental to the fitness of the other sex. The potential for reproductive success in one organism is strengthened while the fitness of the opposite sex is weakened. Interlocus sexual conflict can arise due to aspects of male–female interactions such as mating frequency, fertilization, relative parental effort, female remating behavior, and female reproductive rate.
A nuptial gift is a nutritional gift given by one partner in some animals' sexual reproduction practices.
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.
Cryptic female choice is a form of mate choice which occurs both in pre and post copulatory circumstances when females in certain species use physical or chemical mechanisms to control a male's success of fertilizing their ova or ovum; i.e. by selecting whether sperm are successful in fertilizing their eggs or not. It occurs in internally-fertilizing species and involves differential use of sperm by females when sperm are available in the reproductive tract.
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 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.
Prochyliza xanthostoma, the waltzing fly, is a species of carrion-feeding cheese skipper, insects in the family Piophilidae and the order Diptera. P. xanthostoma is a member of the genus Prochyliza, which contains eleven species. The adult flies are found through North America and are brown-bodied, with orange and black coloring. Mating occurs on animal carcasses and male perform mating rituals; females engage in ejaculate feeding. The waltzing fly is known for its exaggerated sexual dimorphism and has thus become a prominent model for sexual dimorphism and larval behavior. These organisms are known as cheese skippers because when startled, the larvae can leap several inches into the air. P. xanthostoma is an important model organism for sexual selection, larval behavior, and adult reproductive success and survivability.
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