The spermatheca is a structure of the reproductive tract in female animals. It is found primarily in invertebrates but also appears in some vertebrates. The organ also is known as the receptacula seminis, sperm pouch or seminal receptacle.
The purpose of the spermatheca is to hold sperm from the male of a species. Fertilization also can take place in this organ. Sperm pouches vary in size and shape even within species, and thus the amount of sperm that females can contain in spermathecae is not consistent. The cause for these variances is not entirely known. Multiple spermathecae are present in some species.
Insects are the primary examples of species that have spermathecae. In particular, spermathecae of queen bees has been a focus of study because of the ramifications for hive preservation. Recepticle organs for sperm are also found in other organisms. Examples include some species of mollusks, fish, frogs and worms.
Scientists have focused attention on spermathecae in part because of the role that they play in natural selection and evolution. Members of species that do not have sperm pouches are at an evolutionary disadvantage, because sperm survives only for a short period within the reproductive tract. Where spermathecae are present, fertilization might take place long after the males and females have separated from each other, because the female can store the sperm necessary until her oocytes, or egg cells, mature. This is particularly an advantage when there are a limited number of males in a population.
The function of the spermatheca is to contain sperm in the female for later use, but like any other cell, sperm cells are subject to damage by multiple factors. Studies of spermathecae have shown that particular proteins extend the longevity of the sperm. The proteins essentially act like a preservative. In some species, sperm is preserved in the spermatheca for years.
Although the presence of spermathecae is helpful to species from the standpoint of natural selection, it is not by itself a guarantee of fertilization. Problems with egg production still might occur in the female for instance. As in humans, the quality of sperm also can fluctuate based on genetic mutations and the overall health of the fertilizing male.
Scientists have studied spermathecae through simple physical dissection. Those performing dissection have been able to determine whether insemination has been successful by looking at the appearance of the spermatheca. A spermatheca that has not been involved in insemination looks clearer when compared with one that has, because of the presence of the sperm.