Seminal fluid proteins (SFPs) or accessory gland proteins (Acps) are one of the non-

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

components of semen. In many animals with internal fertilization, males transfer a complex cocktail of proteins in their semen to females during copulation. These seminal fluid proteins often have diverse, potent effects on female post-mating phenotypes. SFPs are produced by the male accessory glands. Seminal fluid proteins frequently show evidence of elevated evolutionary rates and are often cited as an example of sexual conflict.

Proteomics

SFPs are best studied in

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s and insects, especially in the common fruit fly, '' Drosophila melanogaster''. Most species produce a wide variety of proteins that are transferred to females. For example, approximately 150 SFPs have been identified in ''D. melanogaster'', 46 in the mosquito '' Anopheles gambae'', and around 160 in humans.

Elevated evolution

Even between closely related species, the seminal fluid proteome can vary greatly. SFPs show elevated rates of

DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...

change compared to non-reproductive genes (measured by K_a/K_s ratio) in many orders, including

Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...

(flies),

Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...

(butterflies and moths), Rodentia, and Primates. Additionally, SFPs show high rates of gene turnover compared to non-reproductive genes.

Function

The function of SFPs is best understood in '' D. melanogaster''. SFPs play a role in male-male sperm competition. One study that manipulated the amount of SFPs male ''D. melanogaster'' produced found that when males were in competition, males that produced more SFPs sired a larger proportion of offspring. In many insect species, significant changes occur in female behavior and physiology following mating; the isolated receipt of SFPs has been shown to be responsible for many of these changes. In ''D. melanogaster'' females, over 160 genes show either up or down-regulation following isolated SFP receipt. These

transcriptomic Transcriptomics technologies are the techniques used to study an organism's transcriptome, the sum of all of its RNA transcripts. The information content of an organism is recorded in the DNA of its genome and expressed through transcription. He ...

changes are not limited to the female's reproductive tract. SFPs lengthen the refractory period (when the female is disinterested in mating) and stimulate ovulation; additionally they can affect processes such as

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 f ...

, metabolism, and activity levels. Though SFPs seem to play a role in coordinating male and female reproductive efforts (e.g. in timing of ovulation), SFPs may also be a source of sexual conflict. Studies of ''D. melanogaster'' have revealed that females who received SFPs suffered decreased lifespan and fitness. Frequent mating in ''D. melanogaster'' is associated with a reduction in female lifespan, and this cost of mating in females has been shown to be primarily mediated by receipt of SFPs. As SFPs play an important role in reproductive processes in disease-carrying species of mosquito and additionally tend to be highly species-specific, manipulation of SFPs may hold potential for highly targeted control of these mosquito populations.

References

{{reflist Semen Proteins by location Evolutionary biology