Why Do Females Store Sperm?
Females store sperm to decouple mating from ovulation and fertilization. This allows for several reproductive advantages.
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Timing Flexibility: Sperm storage enables females to mate when opportunities arise, regardless of their current ovulatory cycle. This is particularly advantageous in environments with unpredictable mating opportunities or seasonal breeding patterns. As stated in the provided text, "Because sperm storage enables mating and fertilization to be asynchronous, it could be extremely advantageous to females, who could thus mate before it is time for ovulation and seize the opportunity for post-copulatory sexual selection."
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Post-Copulatory Sexual Selection: Sperm storage allows for competition between sperm from different males, influencing which sperm fertilizes the egg. This mechanism is a key component of post-copulatory sexual selection, shaping the evolution of male reproductive traits.
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Increased Reproductive Success: By storing sperm, females can increase the chances of fertilization, even if mating opportunities are limited or if sperm viability is affected by environmental factors. This is exemplified by the observation of sea turtles capable of storing sperm to produce clutches over multiple seasons, as indicated by the various sources including one study which states that: "In female painted turtles, stored sperm evidently can be sufficient to produce clutches over multiple seasons. Thus, these genetic data imply…"
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Protection from Polyspermy: In some species, sperm storage mechanisms help regulate polyspermy, the fertilization of an egg by multiple sperm, which is often detrimental to embryo development. One source mentions this by saying that sperm storage "Decreasing the incidence of polyspermy (e.g., some mammals such as pigs)."
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Supporting Sperm Viability: The female reproductive tract provides a supportive environment for stored sperm, maintaining their viability until fertilization occurs. This is elaborated on in several articles which mention the “Supporting the sperm” capabilities within the female reproductive tract. For instance, one source highlights how "Sperm that females receive during mating are stored in special places in the females' reproductive tracts. These storage sites serve to support…" the sperm.
Mechanisms of Sperm Storage
Sperm is stored in specialized structures within the female reproductive tract, such as seminal receptacles and spermathecae, which provide protection and nourishment for the stored sperm. These structures are species-specific, reflecting the diversity of reproductive strategies across the animal kingdom.
