Love mucus

Ground belly snails for themselves Cupids. Many of them have “love arrows” with which they pierce the attracted partner. The goal of this shooting, as it turned out, is very prosaic: snails seek to leave as much offspring as possible.

Brush -legged lung snails - hermaphrodites. Representatives of some species, mating, chop each other with hard sharp needles, consisting of aragonite - a crystalline form of calcium carbonate. These needles are called love arrows. They are in a special muscle bag, which opens in the sexual cloak. During mating, the bag turns out, and the snails poke each other with arrows, piercing the skin. Such behavior has not left without attention, naturalists have been discussing it since the middle of the 17th century. They put forward the hypotheses rather strange: for example, it was assumed that an injection with an Aragonite needle supplies a coil-recipient with calcium, encourages it to lay eggs or gives a different signal. However, observations show that arrows practically do not excite snails, their external effect is too insignificant for such a complex device. But the action of the arrows can be not only mechanical, but also chemical, they are covered with a dense layer of mucus, which may contain biologically active substances that fall into the bloodstream of mollusk. This hypothesis has been checked since the 80s of the twentieth century.

The reproductive system of snails has a complex structure, but all the sexual holes, including the egg, the seed, and the bag with arrows open into the sex cloak. During mating, it is twisted and looks like white growth on the right side of the body. Love arrows are covered with mucus, which produce finger -shaped glands. Having stumbled them into each other, mollusks simultaneously introduce penis into the genital canal of the partner and exchange spermatophores: “pills” with sperm. Spermians have two destinies. Some of them leave the spermatofor and rushes along the egg in the spermate, where it is stored until fertilization. According to estimates, the spermatex reaches no more than 0.1% of the sperm, everything else and the sperm itself on a special duct falls into the bursa copulatrix, in which they are lyowned.

The influence of mucus on the reproductive system was checked by the specialists of the Canadian University of McGill University (McGill University) Joris Cohen and Ronald Chase (Joris Koene, Ronald Chase [1]. Researchers worked with the Cornu Aspersum Garden, which is also Helix Aspersa . The mucus is present in the finger -shaped glands of the snail throughout the reproduction season. Scientists calculated that each love arrow carries 2.2 mg of mucus. The selected organs of the reproductive system were placed in a small cup of Petri in a salt solution and added there the extract of the finger -shaped. It turned out that the extract changes the configuration of the female reproductive system in such a way that it becomes more convenient for taking a spermatophore, blocking his path to a consumer receiver. After a few minutes, the growth of the reproductive system into which the sperm gets into, begins to contract. This peristalsis holds the spermatofor on the spot and gives sperm more time to get to the sperm, before the initial configuration recovers, the channel in the Bursa Copulatrix will open and the excess sperm will be destroyed. In the control drugs where the researchers added a physiological solution, no changes occurred.

Before the snail lays eggs, it mating several times with different partners. Therefore, it is beneficial for the sperm to increase the safety of his gametes, to ensure their participation in fertilization. The mucus covering the love arrow just facilitates the fulfillment of this task.

Subsequently, other researchers have repeatedly proved that the use of love arrows or simply injection of mucus helps to preserve sperm and, therefore, increase its chances of its donor for paternity. And the specialists of the Japanese University Tahoku showed that the action of the mucus of love arrives is not limited to this. Working with the Euhadra Quaesita snail from the Bradybaenidae family, they found that mollusks who were injected with mucus, later start the next mating than control snails [2].
The use of arrows is an obligatory element of sexual behavior, but the virgin E. Quaesita does not prick your partner. Crossing snails with experienced and virgin partners, the researchers observed whether the use of love arrows affect the interval between subsequent mating. In addition, anesthetic snails were injured by the extract of the finger -shaped or saline solution in the area next to the floor cloak, that is, to where the snails themselves usually pierce the arrows. It turned out that after an injection of an arrow or injection of mucus, the snails abstain from subsequent mating about three times longer than control mollusks. Moreover, this effect does not cause an injection itself, but precisely mucus, since injections with a saline solution do not affect the frequency of mating. The mechanism of this phenomenon has yet to be studied.

Although representatives of at least nine families of pulmonary snails have love arrows, most studies were conducted on the mollusks of the Helicidae family, mainly on C. aspersum . Moreover, it turned out that one of the snails of this family, Arianta Arbustorum , does not affect the safety of sperm.

To determine how universal mucus is for arrow -bearing ground snails, Japanese scientists have joined the efforts with Joris Cohen, who by that time moved to Amsterdam Free University (Vrije University Amsterdam). This time, they chose an endemic Japanese landlide to the Euhadra Pelomphala from the Bradybaenidae family [3]. Snails, anesthetized injections of magnesium chloride, introduced plastic tubes with a diameter of 0.5 mm into the germ cloak. A suspension of the homogenized finger of another adult snail in a solution of salt was injected into the body of the snail around the floor opening. Then, through the inserted tube, a solution of salt was inserted into the reproductive system, painted with Altian blue. A minute later, snails were dissected and watched the distribution of dye in the reproductive system. Where the paint was in the experiment, there should be sperm in real life. All 15 snails, which made mucus injections, stained the oviduct. In 11 out of 15 control mollusks, the paint fell into the sequin, where the gametes are destroyed, and in the remaining four and into the seven receiver and into the egg. Apparently, the mucus changes the shape of the ducts of the female reproductive system of the snail. This means that in E. Peliomphala , like C. aspersum , it provides a seed entering the egg and does not let it into the gametolytic organ. The mucus concentration necessary for this is approximately the same for both species and is 1.0-1.75 mg/ml of blood.

Obviously, the emergence of funds that protect sperm from digestion played an important role in the evolution of pulmonary ground snails. It is possible that arrows and mucus arose during evolution several times. Scientists came to this opinion, since C.ASPERSUM and E. Peliomphala have a different “shelling” strategy. The Garden Snail Knoets the partner once, and the Japanese does it several times, and the processing lasts 10 minutes. In addition, E. Peliomphala uses arrows even during copulation, and not just before it.

Researchers write that since many hermaphrodites have a gametolytic body, a decrease in its accessibility can be a general strategy for the struggle to preserve sperm. This assumption has yet to be checked. And now we, at least, know what a love arrow is. Just a syringe!

1. Koene, JM, Chase, R. (1998) “Changes in the Reproductive System of the Snail Helix Aspersa Caused from the Love Dart”, The Journal of Experiental Biology 201, 2313-2319
2. Kimura, K., Shibuya, K. and Chiba, S. (2013) “The Mucus of a Land Snail Love-Dart Suppresses Subsequent Matings in Darted Individuals”. Animal Behavior, 85, 631-635, DOI: 10.1016/J.ANBEHAV 2012.12.026.
3. Kimura, K., Chiba, S., Koene, JM (2014) “Common Effect of the Mucus Transferred During Mating In Two Dart-Shooting Snail Species from Different Families”, the Journal of Experimental Biology 217, 1150-1153, DOI: 10.1242/JEB.095935