) Copulatory Plug Displacement Evidences Sperm Competition in Lemur Catta

During two mating seasons, two groups were studied of free-ranging ring-tailed lemurs on St. Catherines Island. There were twenty-two mating pairs. Copulatory (sperm) displacement by males occurred in nine cases. The first group contained five adult (over 2 years) females and four adult males and the second group contained 8 adult females and 3 adult males.

A copulation plug (or mating plug) is gelatinous secretion used in the mating of some species. It is deposited by a male into a female's genital tract and later hardens into a plug or glues the tract together. It plays an important role in sperm competition and may serve as an alternative and more advantageous strategy to active mate guarding.

Male and Female are preparing for mating.

Because there is a tendency for first-mating males to mate-guard for longer periods of time in Lemur catta, the latency period between the first mate’s ejaculation and that of subsequent mates may be an important determinant of male fertilization success.
Sperm competition occurs In Lemur catta several traits indicate sperm competition: copulatory plugs form in female vaginas within minutes following ejaculation; females typically mate with more than one male during extremely short estrous periods that usually last less than a day; males have the largest relative testes of any strepsirhine primate; and males engage in  post-ejaculatory mate guarding.

 

A mating plug.

As for the results, a single bout of copulation between a pair of ring-tailed lemurs may involve several separate mounts with intromission before ejaculation, and the males mounted several times before placing the plug. They would also mount again and ejaculate once more after the plug was displaced. Displaced plugs were left on the forest floor. The plugs were displaced anywhere from thirty minutes to 3 hours after they were deposited. The general trend is for first-mating males that do no sneak copulations to guard females after copulation for longer periods of time than non-first-mating males.

Although a copulatory plug visible in the vagina confirms that a female has mated and that ejaculation has occurred, a lack of plug visibility cannot be used to assume that a plug is not present. Females showing no sign of having mated later had plugs displaced from their vaginas by subsequently-mating males. The appearance of (or lack of visibility of) copulatory plugs may just indicate how deeply the plug was deposited into the female’s vaginal tract. The depth at which a plug is deposited inside the vagina may greatly affect male reproductive success.

It remains to be seen whether plugs effectively preclude subsequent males from achieving fertilization. However, the finding that copulatory plugs do not impede intromission by subsequent males, and furthermore, that they are routinely displaced by different males provides further support for the suggestion hat copulatory plugs function in sperm competition and that male copulatory plug displacement may be a successful mating strategy for males that are not first to mate with estrous females.

Parga, J. (2002) Copulatory Plug Displacement Evidences Sperm Competition in Lemur Catta. International Journal of Primatology, Vol. 24, No. 4.