page_title: Mating of gastropods
section_title: Courtship
hierarchical_section_title: Mating of gastropods / Courtship
caption_attribution_description: English: The mating dance of two banana slugs. This picture was taken in August 2003 in en:El Corte de Madera Creek Open Space Preserve in Northern California. Part of the Midpeninsula Regional Open Space District system.
context_page_description: The mating of gastropods is a vast and varied topic, because the taxonomic class Gastropoda is very large and diverse, a group comprising sea snails and sea slugs, freshwater snails and land snails and slugs. Gastropods are second only to the class Insecta in terms of total number of species. Some gastropods have separate sexes, others are hermaphroditic. Some hermaphroditic groups have simultaneous hermaphroditism, whereas some sequential hermaphroditism. In addition, numerous very different mating strategies are used within different taxa.
  Land slugs can be thought of as land snails that over evolutionary time have either lost the shell completely, have a very reduced external shell, or have retained only internal remnants of a shell. Land slugs are a highly polyphyletic group, which means that many land slug families are not at all closely related to one another.
  The majority of land slugs are simultaneous hermaphrodites, meaning they possess both male and female reproductive organs that are functional at the same time. Some species regularly self-fertilise. Uniparental reproduction may also occur by apomixis, an asexual process.
context_section_description: Once a mate is found, land slugs undergo a prolonged courtship phase prior to copulation. Courtship can and usually does last for several hours. The two individuals get into position along the periphery of an imaginary circle with their heads towards the other's tail, and circle one another. The slugs crawl in a clockwise direction so that their right sides, containing the genital pores, continually face each other. This circling may serve to assess whether the other is ready to mate; the speed of circling generally decreases as courtship progresses. The slugs then lie close together, remaining in the antiparallel configuration. Each protrudes from its genital pore a sarcobelum, a highly manoeuvrable penile structure, with which it strokes its mate.
  Secretions, presumably from the glandular part of the penis wall, are probably transferred by the sarcobela during this mutual stroking. These secretions have several possible functions, including physiological stimulation and synchronisation, partner labelling or manipulation. Labelling may benefit the donor by helping it to avoid mating with individuals it has already mated with. Alternatively or additionally, labelling may serve as an indication to conspecifics that this individual has recently mated and therefore should be avoided, either because its sperm reserves are possibly depleted or, more likely, because of sperm competition. In the latter case, the secretion transferrer's risk of being subjected to sperm competition is also reduced. Besides labelling, another possibility is that the secretion is absorbed by the partner, in whom it acts as a manipulative allohormone. An allohormone is a substance that is transferred from one member of a species to another and that "induces a direct behavioural or physiological response". The secretion may then cause the recipient to refrain from mating with additional partners, to uptake more of the donor's sperm and to digest less of it, or to increase egg fertilisation and laying using the donated sperm. For more information on one use of this kind of hormone, see the article love dart.
  Species differ in the way stroking occurs and the duration of stroking, but all species get progressively closer during courtship and stroking intensity increases until it stops just before the start of mating. At this point, the sarcobela slightly contract and point upwards. The anterior parts of the slugs swell and roll slightly over to the left. There may be biting and touching around the genital pore areas with mouths and tentacles, as well as mutual head swinging. The slugs press their genital pores against each other and pull their mantles backwards. It is also during courtship that the ejaculate is prepared; sperm flows from storage into the penis and, in some species, is assembled into packages such as spermatophores.
caption: A pair of banana slugs in antiparallel configuration prior to mating.
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