Hypselodoris

Diversity

This genus of nudibranchs (also known as sea slugs) has approximately 50 described species, which are commonly divided into two major clades. Eastern Pacific and Atlantic nudibranchs are often grouped together into a single clade, which is a sister clade to the Indo-Pacific nudibranchs. It is thought that these two groups reflect allopatric divergence events, such as the formation of the Panama isthmus and the expansion of the Pacific Ocean (Valdes, 2001). The effects of vicariance often appear in the form of color - the eastern Pacific and Atlantic clade often have a dark blue base color and a variety of spot and stripe patterns. They are found in both the Pacific and Atlantic coasts of North and South America, and in the Atlantic coasts of Europe and Africa. Morphologically, they have larger sperm storage structures than those in their sister clade. The Indo-Pacific species vary more in their coloration and have more compact sperm storage structures (Alejandrino and Valdes, 2006; Gosliner and Johnson, 1999). (Alejandrino and Valdes, 2006; Gosliner and Johnson, 1999; Valdes, 2001)

Geographic Range

Hypselodoris is found throughout the world. The species included in the eastern Pacific and Atlantic clade can be found along both the Pacific and Atlantic coasts of The Americas and along the Atlantic coasts of Europe and Africa. This clade also expands into the Mediterranean Sea. The other major clade of Hypselodoris can be found in the oceans that make up the Indo-Pacific region of the world - the Indian Ocean and the western Pacific (Alejandrino and Valdes, 2006; Alvia et. al., 1991). (Alejandrino and Valdes, 2006; Avila, et al., 1991)

Habitat

Hypselodoris is found in the benthic zone of tropical and temperate regions of the ocean. Nudibranchs are carnivores that prey on sessile organisms and are found near food sources such as coral, sponges, or anemones (Alejandrino and Valdes, 2006; Wagner, Kahng, and Toonen, 2009). (Alejandrino and Valdes, 2006; Wagner, et al., 2009)

Physical Description

The genus Hypselodoris is comprised of bilaterally symmetrical, soft-bodied slugs without shells. They are known for their vibrant colors and patterns. The east Pacific and Atlantic clade tend to be blue with spots or stripes of numerous colors, excluding red. Species in the Indo-Pacific clade are more varied in their coloration - they range from pink/purple to orange/yellow, and also have a wide variety of spot and stripe patterns. Because these two clades are thought to have diverged after an allopatric speciation event, Hypselodoris is a genus that scientists use to study the effects of vicariance on the evolution of color patterns (Alejandrino and Valdes, 2006; Galvao et. al., 2015; Gosliner and Johnson, 1999).

Morphologically, members of this genus have a high body profile and laterally-opening glands along the edge of the mantle. Generally, they have teeth with curved points which include bicuspid lateral teeth, however Hypselodoris lacks a rachidian row of radular teeth. This genus has branched vestibular glands, which are primarily used for lubrication of female sex organs. Nudibranchs are also characterized by the presence of receptaculum seminis, or sperm storage structures, that open in the middle of the vaginal duct. The eastern Pacific and Atlantic clade are thought to have larger receptaculum seminis than the Indo-Pacific clade (Rudman, 1984). (Alejandrino and Valdes, 2006; Galvao, et al., 2015; Gosliner and Johnson, 1999; Rudman, 1984)

Reproduction

Sea slugs are simultaneous hermaphrodites, but do not often self-fertilize because they have the ability to store sperm. Copulation is preceded by what is thought to be courtship behavior, which is expressed in a variety of behaviors such as head contact, or contact with the edges of the mantle (Hamel, Sargent, and Mercier, 2008; Pola and Gonzalez Duarte, 2008). (Hamel, et al., 2008; Pola and González Duarte, 2008)

Sea slugs are internally-fertilized simultaneous hermaphrodites. During copulation, a mating pair will align their gonopores to exchange gametes. Individuals are usually in fixed position side-by-side during copulation, and have been observed both during the day and at night. Egg dispersal is low, and survival rates of egg clutches is approximately 5-7% (Hamel, Sargent, and Mercier, 2008; Pola and Gonzalez Duarte, 2008). (Hamel, et al., 2008; Pola and González Duarte, 2008)

Nudibranchs lay egg ribbons that are often attached to rocks or sessile marine organisms. Other than choosing suitable locations for egg masses, nudibranchs are not known to have parental investment in their offspring (Hamel, Sargent, and Mercier, 2008; Pola and Gonzalez Duarte, 2008). (Hamel, et al., 2008; Pola and González Duarte, 2008)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Sea slugs have a lifespan of up to 1 year in the wild and 1 month in captivity. Their reduced lifespan in captivity is attributed to the components of their diet that are difficult to rear in captivity because of their toxicity and danger to other organisms (e.g. sponges, hydroids) (National Geographic Society, 2018; Willin and Coleman, 1984). (National Geographic Society, 2018; Willin and Coleman, 1984)

Behavior

Species in Hypselodoris are typically solitary, but aggregate behaviors are observed during mating. Nudibranchs are motile but sedentary, usually sticking close to environments that meet their dietary requirements. Because they occupy the benthic zone, they rarely swim, although they are able to. Swimming behavior is not advantageous to Hypselodoris because they rarely encounter predators, and because ocean currents can displace individuals from their preferred habitat. Sea slugs are more often seen crawling across benthic substrates. Motionless floating behaviors are observed in some nudibranchs, which allows them to remain in the water column without the high energy expenditure of swimming. Floating is also a function of foraging behavior - since individuals cannot swim and feed at the same time, this allows them to open their oral hood to sample the environment for prey or potential mates (Lawrence and Watson, 2002; MacLeod and Valiela, 1975; Wyeth and Willows, 2006). (Lawrence and Watson, 2002; MacLeod and Valiela, 1975; Wyeth and Willows, 2006)

Communication and Perception

Nudibranchs in the genus Hypselodoris are known for their bright aposematic or warning coloration. This coloration is used as a visual cue to warn predators that most of Hypselodoris is toxic if ingested. Several species of Hypselodoris are considered Müllerian mimics, meaning that they share similar coloration with another species, but each species is equipped with its own chemical defense mechanism. Typically, chemical defenses in Hypselodoris are derived from their diet, but can also be produced internally. Defensive allomones are typically located in the mantle and have toxic properties that deter other animals from feeding on nudibranchs. However, some species in Hypselodoris do not have chemical deterrents and some are considered to be Bayesian mimics of other species (Avila et. al., 1991; Haber et. al., 2010)

Despite using visual signals to communicate with predators, sea slugs have relatively low visual acuity. Tactile signals are more commonly used for communication with conspecifics, specifically during mating behaviors. Nudibranchs approach other individuals by touching their head, tail, or the sides of the body. Species in Hypselodoris often utilize chemoreception structures, called rhinopores, to obtain information about the location of food and mates. Slugs intraspecifically communicate their location in the form of pheromones, which are 1000x stronger than pheromones found in the human bloodstream (Wyeth and Willows, 2006). (Avila, et al., 1991; Haber, et al., 2010; Wyeth and Willows, 2006)

Food Habits

Sea slugs are specialized carnivores that feed on sessile animals that are not heavily exploited by other taxa - such as sponges, corals, bryozoans, or hydroids. Some species are cannibalistic and will feed on other nudibranchs. Typically, sea slugs practice stenophagy, meaning that different species have a specialized diet of one or two kinds of food. Nudibranchs appear to graze on sessile food items and strike at more formidable prey, such as cnidarians (Megino and Cervera, 2003; National Geographic Society, 2018; Wagner, Kahng, and Toonen, 2009; Wyeth and Willows, 2006). (Megino and Cervera, 2003; National Geographic Society, 2018; Wagner, et al., 2009; Wyeth and Willows, 2006)

Predation

Despite their lack of a protective shell, nudibranchs display a wide variety of anti-predatator strategies. Several species use crypsis as a form of predator avoidance, but most sea slugs are known for their striking aposematic coloration. Some scientists suggest that several species in Hypselodoris form a Mullerian mimetic circle, which indicates that many species in this taxa are poisonous to predators. Some species, however, use Bayesian mimicry in order to benefit from the toxicity of other species without synthesizing chemical defenses themselves (Haber et. al., 2010). Most nudibranchs rely on chemical defenses that are typically derived from their diet, and have the ability to select food items containing furanosesquiterpenoids, or toxic essential oils. The combination of chemical defenses and aposematic coloration in Hypselodoris is why they are rarely predated on, except by other cannibalistic species of sea slugs (Avila et. al., 1991; Harris, 1973; (Avila, et al., 1991; Fontana, et al., 1993; Haber, et al., 2010; Harris, 1973)

Ecosystem Roles

With formidable anti-predator defense strategies, Hypselodoris serves as a predator within the ecosystem more so than prey. Because they are carnivorous and their prey is sessile, nudibranchs approach an ecto-parasitic relationship with animals such as sponges, coral, and hyroids. They graze on these sessile organisms, extracting nutrients without causing immediate death (Haber et. al., 2010; Megino and Cervera, 2003; Wagner, Kahng, and Toonen, 2009). (Haber, et al., 2010; Megino and Cervera, 2003; Wagner, et al., 2009)

Economic Importance for Humans: Positive

Several FDA-approved chemical products were originally isolated from mollusks and are further used in drugs and in clinical trials. The genus Hypselodoris is of interest to scientists because of the chemical properties of their toxic oils, and Hypselodoris jacksoni is first known natural source of the metabolite (−)-(5R,6Z)-dendrolasin-5-acetate. Sea slugs have much to offer in terms of unexplored chemical synthesis research, which has many applications in education and medicine (Mudianta et. al., 2013).

Recent research has suggested that total nudibranch abundance along the coast of California is highly correlated with warming. This relationship suggests the potential use of nudibranchs as an indicator taxa of climate change (Goddard, Pearse, and Gosliner, 2011). (Goddard, et al., 2011; Mudianta, et al., 2013)

Economic Importance for Humans: Negative

There are no known adverse effects of Hypselodoris on humans.

Conservation Status

There is no listing of the conservation status of Hypselodoris, nor any of its species.

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

Sea slugs are used in the aquarium trade and are typically recommended for advanced aquarists because of the difficulty involved with rearing supporting organisms (e.g. sponges, hydroids, and byrozoans) (Willin and Coleman, 1984).

Nudibranchs do not often appear in museum collections because there is no known technique to preserving the shape, size, or color of a non-living specimen. Because color morphology is so distinct in Hypselodoris, it is recommended that a color photograph of a living specimen be included along with the preserved specimen (Willin and Coleman, 1984). (Willin and Coleman, 1984)

Contributors

Megan Jones (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

mimicry

imitates a communication signal or appearance of another kind of organism

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

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