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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.

Additional notes

Additional notes from Jonathan follow.

John Pearse talk

John originally worked with sea urchins and sea stars primarily. Janet joined the lab about twelve years ago to study marine slugs.
She was interested in hermaphrodite mating behavior. Banana slugs' rare behavior of apophallation became a research focus. No one had
really studied banana slugs [academically] since the forties. Alice Bryant Harper (Aptos naturalist, works with Santa Cruz Museum of
Natural History) wrote The Banana Slug (1988), the best book on them.

Despite Chancellor Sinsheimer's desire to keep the sea lion as the UCSC mascot, students voted 95% for the banana slug.

There are just two complete mollusc genomes, [California sea hare and giant owl limpet], and neither are very complete.

Banana slugs habitat is very diverse. Though often found in conifer forests and considered an animal of the Northwest (first found in
Washington or Oregon), they've been found in drier habitats: San Diego, Napa's McLaughlin Reserve (by small springs), abandoned rice
patties in the Sacramento River Delta, oceanside iceplants in Pacific Grove. High variation in the numbers you'll see on any day/site: none
or dozens.

They eat feces, hemlock, poison oak, mushrooms (reported but John has not seen), sorrel, ferns, ice plants, humus soil. In the lab
they eat hamburger, cat food, apples, beans, zucchini, mushrooms, yams, lettuce and milk.

Colors may camouflage them, e.g. dead leaves often turn bright yellow, the color of species in Santa Cruz and the SF Bay area. In
other areas you'll find spotted slugs – but they may be a different species.

There predators may include [seemed uncertain] garter snakes, salamanders and newts, birds and some small mammals. It is possible
that some specific carnivorous snails and slugs eat banana slugs.

Aphallarion buttoni originally thought to be a different species because no penes were found when dissected (late 19th century).
However, a Stanford professor later found some with penes and so sent students into the field to study. They observed apophallation. That
was the end of buttoni as a separate taxon. It became Ariolimax columbianus.

All banana slugs have an opening on the right side of the “head” for defecation, breathing, and copulation. The only way to distinguish
species is by dissection of the genitalia. [See slide *Ariolimax Arilimax columbians genitalia* for overview of genitalia.] The
gonad has a mix of testes and ovaries, and they can play both roles at same time curing copulation. How is sperm kept separate during
copulation? It is not necessarily. They can fertilize themselves.

And aphalon are born without a penis [sometimes?].

Ariolimax Meadarion californicus is found in San Mateo county. Santa Cruz has dolichophallus. [See slide comparing their
genitalia.] Mead thoought dolichophallus and californicus were sufficiently different to be a separate species.

A collaborator in Belgium has been sequencing banana slug mitochrondrial DNA. They see at least five clades but cannot yet
connect them. ~“Morphologically distinct and molecularly distinct are not the same thing.” [See slide.]

Interestingly the distribution of the salamander genus Ensatia is similar to that of banana slug [dolichophallus? – see slide]. Is
this a remnant of five million years ago when there were islands in the Monterey Bay? Morphologically distinct but molecularly
[mito. DNA] indistict suggests recent change.

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lecture_notes/04-23-2010.1272473888.txt.gz · Last modified: 2010/04/28 09:58 by jmagasin