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Banana Slug Biology

Guest lecture by John Pearse and Janet Leonard, from Long Marine Laboratory, University of California-Santa Cruz. They did research on Banana Slugs for several years and talked about their findings in the class.
John talked about habitat, color, general characteristics, predators, and taxonomy of hermaphrodites. Janet talked mostly about sexual behavior of slugs.

General Characteristics

  • Habitat : Banana Slugs are slimy, spineless gastropods which live on forest floor in moist places. They are part of animals of forest of North West. They are also found in conifer forest, open forest, and unexpected habitats like UC Davis reserve dry area, and also in Springs. Pacific grove has lots of ice plants in which Banana Slugs live.
  • Diet : Some slugs are predators. They eat other slugs, snails and earthworms. Banana Slugs eat feces. They are fond of mushrooms, but it is not their major diet. In labs they are fed lettuce.
  • Color : They are mostly yellow in color, but they are also found in brown, and black colors.
  • Predators : Raccoons, garter snakes, ducks, geese and salamanders eat banana slugs.
  • Taxonomy : Banana Slug belongs to genus Ariolimax. Three species are included in these genus : A. californicus, A. columbianus, and A. dolichophallus. These species have opening either on top or on the right side called as pneumostome. Everything is done through this opening. Mead classified A.californicus and A.dolichophallus as two separate species based on their penis and vaginal muscle size. A.californicus has a huge vaginal muscle and penis, whereas A.dolichophallus has thinner vaginal muscle. Although the species of Ariolimax family are morphologically apart, they are not distinct at molecular level.
  • Reproductive morphology : Slugs are hermaphrodites (have both male and female organs), but they also get involved in mating. They have a ovisperm duct, and possess a complex mechanism to keep the external and internal sperm separate. They have vesicle to store sperm. They have vaginal muscle and some species have large vaginal muscle. Have a penis sheath with penis inside it.

Sexual behavior & Sexual selection

  • Sexual selection : These species can be distinguished through genitalia. In 1985 it was hypothesized that the genitalia distinguishes species and sub-species, and hence it is probably a feature of sexual selection. At molecular level all the slugs are indistinct.
  • Sexual behavior : Slugs get involved in elaborate mating and sperm is exchanged through genitalia. They often get involved in apophallation, a mechanism where the mating partners chew off their penis. Ariolimax stramineus has a blunt penis and no biting or chewing of penis is observed. A.californicus and A.dolichophallus show apophallation. 5 in 100 copulations end in apophallation. Although apophallation is not that often but it happens.
  • Copulation and egg laying habits : Copulation starts during foggy nights of July, August, and September. Egg laying starts when it begins to rain sometime during October, November, and December. Slugs lay eggs in moist places under things like leaves. In labs they lay eggs on surfaces at 18 - 19 degrees celsius. Low pressure seems to be a stimulus for egg laying. On an average 75 eggs are laid in a week, and it takes 7 weeks for hatching. A.dolichophallus lays big eggs, and A.californicus lays tiny eggs. A.dolichophallus is the youngest to copulate at about 6 months and youngest to lay eggs at about 10-1/2 months, and the life span is about 7 years.


Jeffrey Long has slides from Janet Leonard and he will be uploading them.

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lecture_notes/04-23-2010.1272305918.txt.gz · Last modified: 2010/04/26 11:18 by svasili