The Ariolimax Dolicophallus is a relatively unstudied species. Here we aim to provide concise and accurate biological information about the Ariolimax Dolicophallus.
The term “banana slug” refers to any member of the genus Ariolimax, of which there are three species. They are part of the mollusk superfamily Arionoidea, which contains most terrestrial air-breathing slugs. Within Ariolimax, there are three species: A. columbianus, A. californicus, and A. dolichophallus, which is the UC Santa Cruz mascot.
Snails and slugs belong to the gastropod class in the mollusc phylum. The term “slug” is polyphyletic, does not refer to a specific phylogenetic group but rather have a converged body shape not inherited from common ancestors. Slugs are gastropods that through the course of evolution have lost their functional shell. The term “banana slug” is the common name for members of the Ariolimax genus. The Ariolimax genus were first described in publication by Otto Andreas Lowson Mörch in 1859. The species A. dolichophallus was first described in publication, here, by Albert R. Mead in 1943.
Ariolimax dolichophallus, the slender banana slug, can grow up to 7“ long. As the name suggests, banana slugs are usually bright yellow in color, although they can also be green, black, brown, or white. The scientific name, dolichophallus given by Mead in 1943 literally translates into “long slender penis.” Because the outside appearance of banana slugs are so similar Mead decided the most prominent distinction for this species was the reproductive anatomy.
Banana slugs are similar to other terrestrial species in their anatomy. They have two sets of retractable tentacles on their head. The top pair of larger tentacles are frequently referred to as eyestalks, and are used for light-sensing. The smaller lower pair of tentacles provide the slug with a sense of smell. The slug's mouth is on the underside of the head.
Directly behind the head is the slug's mantle. The mantle is a fleshy structure that serves to protect the slug's anal and genital pores. The pneumostome is also found in this area, and is used for gas exchange. It connects to the banana slug's single lung.1)
The remainder of the banana slug's body is the foot. Banana slugs move, as do other slugs, through contraction and expansion of this foot. Like some other terrestrial slugs, banana slugs have a backbone-like keel that runs along the foot.2)
Banana slugs are known for the thick mucous that they excrete from their skin. This mucous performs several functions. It keeps their skin lubricated, which is necessary for gas exchange. During mating season, banana slugs release pheromones in their mucous that signals their location to potential mates. In addition, the mucous provides some protection against predators, as it has anesthetic properties when it contacts a wet surface, such as the inside of a predator's mouth.3)
The internal anatomy of gastropods is very asymmetrical and contorted. This is an artifact of packing their internal organs into a shell. Even though slugs have adapted to life without a shell their internal organs are still asymmetrical and contorted. The image on the left, provided by Lander University here, was diagramed from a dissected Limax maximus which is a close relative of banana slugs. This illustration is sufficiently accurate to banana slugs with exceptions to the reproductive anatomy. The illustration bellow details the “extremely attenuate apical phallus which not infrequently is of greater length than the slug itself!” (Mead 1943)
When searching for a banana slug specimen to ensure that the species is a true A. dolichophallus the genital anatomy must look very similar to what is illustrated above.
Banana slugs are detritivorous, eating dead and decomposing plant and animal matter. They also eat living plant material and have a special fondness for mushrooms. Since banana slugs are prone to desiccation in hot, arid environments, they are typically nocturnal, and come out during the day only when the weather is acceptable. During particularly dry periods of time, banana slugs can estivate by burying themselves in debris, secreting an especially thick coat of protective mucous, and going dormant until the conditions become more hospitable.4)
Banana slugs have been shown to have a mutually symbiotic relationship with the redwood tree, Sequoia sempervirens. The slugs do not eat the seedlings of the redwood tree, preferring even cardboard over redwood trees. Instead, they eat plant species that compete with redwoods for light, water, and nutrients. In exchange for this, the redwoods provide the slugs with the cool, moist habitat that they need.5)
Many animals are predators of the banana slug, including birds, raccoons, snakes, and salamanders. However, due to the mucous secreted by the slug, most such predators will roll the slug around in the dirt to remove the slime before eating the slug.6)
Banana slugs are hermaphroditic, possessing both male and female genitalia. Banana Slugs like many gastropods are capable of self fertilization, however it has been generally regarded that slugs prefer cross mating. When a slug is ready to mate, it will release pheromones into its slime as a signal to other slugs. The slugs release sperm into each other and is coated with secretions from the albumen gland and walls of the spermoviduct before fertilizing the eggs. Sperm can be collected and stored internally in the seminal receptacle for several months, to allow immature eggs to fully develop before fertilization.
The mating ritual in banana slugs has been studied by Dr. Brook Miller for her Ph.D. dissertation, ”Sexual conflict and partner manipulation in the banana slug, Ariolimax dolichophallus.“ in evolutionary biology. Her research describes the complex sperm competition observed in banana slugs. The normal ritual is similar to the Deroceras invadens ritual illustrated below. Both Ariolimax and Deroceras genus have been observed to have an aggressive courtship that involves striking and biting.
In Ariolimax the phenomenon of apophallation, the removal of a penis, has been studied by many researchers. Rather than simply withdrawing after copulation as illustrated above one banana slug will bite off and eat the other's penis. A video recording of apophallation by Dr. Miller can be found here. Dr. Miller also recorded an A. dolichophallus specimen consuming its own penis, autoapophallation, found here.
Every animal has a genome, and almost every genome is stored in multiple copies. Some plants keep as many as 100 different copies of their genome (with small changes between each) but many animals are diploid, meaning they have two copies of their genome. Heterozygosity is a term that describes the difference between the two copies of the genome. Most diploid organisms are heterozygous since they get one copy of their genome from each parents. While the ploidy of the banana slug is unknown, we suspect that it is diploid. At the end of the spring 2015 class professor Ed Green performed a heterozygosity analysis on the kolossus Discovar de novo banana slug assembly. The result showed that the slug that was sequenced was entirely homozygous.
This is very strange, normally organisms are heterozygous because they get a copy of their genome from each parent. While the level of heterozygosity changes between organisms, it is very odd to see an organism that has no heterozygosity at all. The lack of variation in the slug can be explained by one of their odder behaviors, 'selfing'. It has been proven that the banana slug can 'self', a process in which the organism impregnates itself. By repeating this process over many generations, a homozygous slug would be born.
Our findings suggest that the slugs do indeed self in nature, and it may be their preferred way of reproducing. Our project sequenced a wild caught slug, and the fact that this wild caught slug was homozygous heavily implies that it is the result of several generations of selfing.
Presented to the BME235 Slug Genome class on April 23, 2010, this website http://compbio.soe.ucsc.edu/slugGenome/ contains a pdf “All About Banana Slugs”. A similar presentation was given to the Spring 2015 class, notes can be found here.
To find the rather sparse literature on A. dolichophallus requires doing sensitive literature searches, then weeding the results to get higher specificity. This section should list searches tried, how many hits they got, and what sort of specificity they had. The results should be collected in the Annotated Bibliography section.
Uploaded is a long bibliography by Janet Leonard ariolimax_bibliography_janet_leonard.doc Please extract citations from there and work them into this bibliography. She has a lot of older works that would be difficult to find electronically, but does not include anything newer than 2002, when she created the bibliography.