All About Banana Slugs April 1, 2015
Guest Lecturers: John Pearse and Jan Leonard
Slug Overview
Habitat
Wide range of habitats: conifer forests, open woodlands, dry-land springs, coastal ice plants
Diet
Lab: lettuce, yams, hamburger, milk, cat food
Field: mushrooms, plants, seem to prefer animal feces
Color
Different species have different colors, but colors are not species specific
Not sure why they have their color
Predators
Garter snakes, birds
No main predator in particular
Their slime serves as a protection against predation
Distribution
Found along Pacific Coast line
5 major clades seem to have geographical specific ranges with little overlap
Similar distribution as salamanders
Slug Taxonomy
mtDNA doesn’t separate our local Meadarion species, but they are known to differ based on social cues, egg size and morphology
2 subgenera based on penis morphology
1) Meadarion with epiphallus A.(A.)
2) Ariolomax with no epiphallus and thin-walled apical end of penis A.(M.)
5 clades in the genus: 2 within columbianus (A.(A.) columbianus and A.(A.) buttoni), A.(A.) stramineus, a 4th clade in San Diego County that is as of yet undescribed, and 5th clade (Meadarion) comprising of at least 4 subclades (A. (M.) californicus, A. (M.) brachyphallus, A.(M.) dolicophallus and a 4th undescribed species found in Fremont Peak)
Further molecular taxonomy only performed with three genes CO1-16S-CytB
Slug Sex: The Basics
Simultaneous hermaphrodites; can’t distinguish sex until dissection
Complex mating behavior with apophallation at times
Copulate: internal fertilization, either simultaneous or alternating copulation
Eggs are laid underground, take 1-2months to develop, requires humid envirnoment to protect from dessication
Hatch as small individuals
Same reproductive system as all terrestrial gastropods
Slug Sex Behavior: Apophallation
During copulation, penis of one and/or both slugs is bit off, this process is termed apophallation
Penis does not regenerate, but slug continue its sex life as a “female” or “male” (incomplete apophallation)
Does not occur until copulation has occurred for an extended period of time already
Unknown if has effect on mating behavior/preference thereafter
Apophallation rarely occurs (~5% observed by Jan Leonard), only seen in A. (M.) californicus and A. (M.) dolichophallus species in Meadarion subgenera
Species differ in courtship and copulation behavior: A. (M.) californicus have longest courtship, A. (M.) dolicophallus have longest intromession, and A. (M.) bracyphallus display penile loop (distinguishing feature observed initially by Mead in 1943)
Other phallus polymorphisms (developmental) are very common among gastropods and can associate with a certain environmental signal (eg. increased water temperatures)
Goal of Sequencing Project
Assemble and compare slug genomes to identify genes related to their rapid evolution of sexual phenotypes:
Genital morphology
Sexual behavior
Pally polymoprhism
Egg size
Species recognition molecules
Self-fertilization
