Amorous acrobatics To mate, the slugs hang upside down from a string of mucus they have secreted because they need the help of gravity to extend their large penises from openings in their heads. When an individual of a species with external sperm transfer lacks a penis, it can still reproduce uniparenterally, such as by self-fertilisation, provided it possesses the other components of a normal reproductive system. They separate and crawl away from each other as soon as their genitals are untangled. For a long time scientists thought this was the Deroceras panormitanum, originally from southern Italy, but a few were starting to suspect that several species were being mistaken for them. Once a penis is severed, it is usually eaten by the partner. There is usually an exchange of sperm, but one-way sperm transfer can occur in certain cases. Reise and colleagues are also hoping their research will yield answers to how the slugs proliferate, why they are so successful, and how to better combat them. Way too fast, in other words, for the eyes of curious researchers -- so video makes it possible "to analyze exactly the interaction of the genitalia," Reise says.
This can lead to a co-evolutionary cycle in which the amount of sperm digested and male allocation both increase until eventually, male and female gametes are equally invested in. That's why researchers analyze coupling behaviors. Apophallation is most widely found in Ariolimax species,  which have internal sperm exchange. This is particularly helpful because field slugs are otherwise difficult to distinguish. For a long time scientists thought this was the Deroceras panormitanum, originally from southern Italy, but a few were starting to suspect that several species were being mistaken for them. They separate and crawl away from each other as soon as their genitals are untangled. It is not yet known whether tail waving is a visual cue or whether it wafts chemical attractants in the direction of the follower. The penial gland is filled during early courtship and its secretions are transferred onto the skin of the partner slug. Mating of marine gastropods[ edit ] For example, in mating of sea slugs Siphopteron quadrispinosum there occur traumatic mating. Apophallation may be made necessary in order for separation to occur by the partner tightly gripping the penis via a special muscle of the female reproductive tract. Reise and her colleagues have already been able to identify several as yet unidentified slug species. In addition to Ariolimax species, autoapophallation self-amputation has been documented in Deroceras laeve. They spend hours engaged in foreplay, but the act of sex is very quick. A penis will suddenly emerge, and it takes less than a second to ejaculate. The leading slug seemingly pauses to wait for the follower, tail waving, if the follower falls too far behind. Twisting their slimy bodies together, the large slugs dangle upside down from a glittering rope of mucus, slowly rotating. According to risk-averse models, when this is the case, it would be more prudent for an individual to invest in eggs. Using mucus trails to find a mate involves the discrimination between conspecific and heterospecific trails. Simultaneous reciprocal mating versus unilateral mating[ edit ] In simultaneous reciprocal mating, both slugs act as males and females at the same time. The researchers leave the slugs — hermaphrodites possessed of both male and female sex organs — on their own for a few days in individual receptacles. At least one species, the grey field slug Deroceras reticulatum , shows a primitive degree of sperm packaging. Finding a mate[ edit ] Deroceras panormitanum leaving behind a mucus trail. After this, it is common for one or both slugs to engage in mucus consumption; they may return to the mating site and lick the mucus off the ground, or lick it from their own body surface. However, there is much intraspecific variation. The slugs often switch roles after sperm transfer for a second round of mating. The slugs then lie close together, remaining in the antiparallel configuration. They can only shake their heads in wonder at the love games of the great, grey slug Limax maximus, for example.
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