Female sperm storage

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. 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 (bird anatomy), 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: 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. 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 (bird anatomy), 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: One important advantage female insects that store sperm gain is increased genetic diversity in their offspring. There are many ways that females can alter offspring genetics to increase their success and diversity. An example of how this can be accomplished is in female Scathophaga that preferentially fertilize eggs to survive in different environments. Since many environments require different traits for success, females are somehow able to match sperm (acquired from multiple mates) that have the best genes for whichever environment in which they will develop. Many of the different properties of the environment, including temperature and thermal properties affect the female's sperm choice. Studies have also shown that ovipositing is nonrandom and females lay eggs with varying PGM(phosphoglucomutase) genotypes in different environments in order to optimize offspring success. Females are acutely aware to their environment and manipulate the genetic diversity of their offspring in appropriate ways to ensure their success. Another way sperm-storing females can alter the diversity of their offspring is controlling the relatedness to the males that provide them with sperm. Inbreeding depression can have a deleterious impact on populations of organisms and is due to mating of closely related individuals. To combat this effect, female insects appear to be able to sort out the sperm of relatives from the sperm of non-relatives to choose the best option to fertilize their eggs. Female crickets are able to preferentially store sperm of multiple unrelated males to that of their siblings; this results in more of the offspring having unrelated parentage. Being able to choose between sperm after coupling might be advantageous to females because choosing between mates precopulation may be more costly, or it may just be too difficult to tell males apart before mating. Females possess remarkable abilities to select sperm to store and to fertilize their eggs that will make their offspring diverse. Though it has been shown that a majority of female insect species can store sperm, specific examples that have been studied could include field crickets, dung flies and Mediterranean fruit flies. Females largely benefit from this mechanism, but males often can experience low fitness because their paternity is not secure. Sperm stored often determines which male ends up fertilizing the most eggs. An example of this is seen in Red Flour Beetles, where most of the sperm is stored in the first mating. Another male can remove previously stored sperm to better chances of successful mating. Antagonistic coevolution is the relationship between males and females where sexual morphology changes over time to change with the opposite's sex traits in order to achieve the maximum reproductive success. One such development is alternative sperm storage sites, such as seminal receptacles, spermathecae, and pseudospermathecae, that are complex and extremely variable to allow for more choice in sperm selection. In some cases, sperm storage sites can produce proteases that break down various proteins in male seminal fluid resulting in female selection in sperm. Like females, males have developed responses to counter evolutionary adaptations of the opposite sex. Responses in insects can vary in both genitalia and sperm structures, along with variations in behavior. Spiny male genitalia help to anchor the male to the female during copulation and remove sperm of previous males from female storage structures. Males have also developed alternative ways to copulate. In the case of the bed bug, males traumatically inseminate females, which allows faster passage of sperm to female sperm storage sites. The sperm are received by the mesospermalege and eventually reach the spermathecae, also referred to as seminal conceptacles. At the microscopic level, Drosophila males have differing sperm tail lengths that correspond to various sizes of female seminal receptacles. Longer male sperm tail length has shown a greater reproductive success with a larger female seminal receptacle while sperm with short tail lengths have been found to be more successful in smaller seminal receptacles. The ability to store and separate sperm from multiple males enables females to manipulate paternity by choosing which sperm fertilize their eggs, a process known as cryptic female choice. Evidence for this ability exists in many different taxa, including birds, reptiles, gastropods, arachnids, and insects. In combining long-term sperm storage with polyandrous behavior, female members of the tortoise family Testudinidae have access to sperm from a range of genetically different males and can potentially influence a clutch’s paternity during each fertilization event, not just through her mating choices alone. As a result of clutches with greater variation in paternal genes and increased sperm competition, females can maximize both the genetic quality and number of offspring. Cryptic choice allows females to preferentially choose sperm. Females are thus able to mate multiple times and allocate sperm to their eggs according to paternal phenotype, or according to other characteristics. In some cases, such as in the yellow dung fly, certain male traits will affect the fitness of eggs laid in particular environmental conditions. Females can choose sperm based on male quality as a function of its interaction with the environment. In other species, such as the fly Dryomyza anilis, females preferentially choose sperm from one storage location over another. Males of this species have developed behaviors, such as abdominal tapping, to increase their number of sperm stored in the favored storage site. Evidence for this pattern of storage, cryptic choice, and male behavior also exists in the flour beetle Tribolium castaneum.