Genetic incompatibility
Exactly how females determine compatible genes prior to mating is not completely understood, but various mechanisms have been proposed, such as pheromones and male appearance and/or courtship behavior.
It is also surmised that sexual selection can continue after copulation, the so called 'cryptic female choice', so named because it takes place within the body and cannot be directly observed.
Introduced to the scientific community in the early 1990s, the concept of cryptic female choice is complicated and offers a new explanation for infertility.
[2] Multiple studies have shown that the physical contact between the sperm and the egg can cause a chemical reaction in the female.
[7] Not only are offspring of heterozygous males less genetically competitive, if both the male and female are heterozygous, their offspring will be either inviable or infertile[7] One example of how indirect non additive genes impact fertility comes from a team of researchers who investigated how female rhodeus ocellatus (rosy bitterlings) employ mate choice and the role of the MHC gene in that decision.
[3] Although these researchers did not test this theory, they speculated that perhaps during the male's courtship, he dissipates odor cues from the MHC gene that assist the female in her decision-making process[3] DDK is a lethal phenotype in Mus Domesticus (house mice) that leads to developmental abnormalities and eventually deterioration of the embryo when females with the phenotype mate with males who carry other inbred strains.
[10] A group of researchers investigated how the survival rates of offspring of Erythrura Gouldiae (Gouldian finch) are impacted when the mating pair have genes for different colors.
[7] Partaking in polyandry allows her to ensure that the offspring that she will be providing for is going to be viable, and not be a waste of her time, energy, and resources.
[13] They discovered that by participating in "extra-pair" mating relationships, the females were able to more accurately target compatible genes, thus increasing the amount of viable offspring that they produce.
[13] Although females are unable to tell the difference between compatible and incompatible partners, by participating in polyandry, their likelihood of yielding more and healthier offspring is increased.
[15] There has been some debate over whether these selfish genetic elements can actually influence the post-copulatory sperm selection that some females go through in order to determine the best (most compatible) match for her genes.
[17] If they were to mate with a heterozygous partner, it could potentially lead to half of their offspring dying as a result of the lethal allele[17]
[18] Because the EGI males are equal rivals to their wild counterparts, they are able to use the female's time and energy reproducing but only to create non-viable offspring.
[18] A team of researchers from the University of Minnesota were successful in genetically engineering a population of fruit flies that would not be able to generate viable progeny when mating with wild-types specifically.
[18] A great deal of research has gone into trying to use this technology as a tool in order to try and control the spread of diseases that are carried by mosquitoes such as Dengue, Zika, and Chikungunya.
