Banana Slug Genomics

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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. 

====== Slides ======
The slides from the presentation of John and Jan can be dowloaded here,[[http://compbio.soe.ucsc.edu/slugGenome/|http://compbio.soe.ucsc.edu/slugGenome/]] .\\


====== 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.

===== Janet Leonard talk =====

Janet's interest is in sex selection.  Eberhard's hypothesis: [That we
can ] classif[y] based on genitalia (as done with insects, spiders,
//etc.//) suggests the importance of sex selection.  Genitalia
differences in nearby counties are not explicable by natural
selection, //e.g.// how would NS explain [improved fitness by a
different vaginal muscle in the same geographical area.]

The talk focused on courtship behavior:  much effort/expense in banana slug mating.

//Ariolimax stramineus// courtship: antiparallel alignment of slugs is
standard.  They line up right sides of their heads until the alignment
allows copulation.  The first copulation takes place in about twenty
minutes with subsequent occuring over about two hours.  No apophallation in the
one shown on film.

Mating film for //brachyphallus//: This is one of the three under
//Ariolimax Meadarian//.  Note the initial biting and head swinging
which seem to cause no damage.  The biting helps line up the head
regions.  Banana slugs cannot reverse so the cirlcing helps get them
get into position for mating.

Mating film for //californicus//: Unilateral copulation (after two hours
biting, head swinging).  It is hard to tell which plays the role of
male and female but Janet thinks they alternate over a copulation
session.

Mating film for //dolicophallus//: Example of apophallation (by the
first to withdraw).  How costly is this for a hermaphrodite?  It is
pretty rare: 5 out of 100 copulations end in apophallation.

Why does apophallation occur and when?  They have observed it only nine
times and never by virgins.  Is it done as retaliation if one partner does not give
any sperm?  Do they run out, and perhaps later in life focus on egg laying?

Note in the table comparing copulations that //dolicophallus// and
//californicus// are indistinguishable by mitochondrial DNA.

The rapid morphological changes are among the evidence for sex
selection, as well as the high cost of courtship/mating.  There is
some evidence for sperm competition.

Soon we should have based on microsatellite data (nuclear DNA) ...

It is unknown how many chromosomes they have, though chromosome
variation is usually not seen till "quite high" taxonomic levels.


Their egg laying habits in the field are uncertain.  Perhaps under
leaflitter.  They do not dig holes in moist soil like garden
snails. In the lab at 19^C, they take seven weeks to hatch,
sometimes two to three weeks longer.  The record for a clutch is
seventy-five eggs (but this could have been multiple clutches since
they don't check every day).  Egg size varies.  //Dollicophallus//
eggs are almost the size of jellybelly and weigh up to half a gram.
For //californicus// they're usually under 0.3g.

Egg laying starts in fall and copulation is associated with foggy
nights (late summer, Santa Cruz).  Eggs are laid October through
December when the rains come and usually finished by February.
Hypothesis: Low pressure systems trigger egg laying.  (This is based
on lab observations, and makes sense since dehydration is the highest
mortality source.  You want to lay eggs at the start of the rainy season
in a moist place.)

They have observed copulation for slugs as young as six months and egg
laying as young as ten.

How long do they live?  No one knows but perhaps two to three years.
Some have lived thirty months in the lab (when sacrificed).
Banana Slug Genomics

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