Paracerceis sculpta
Encyclopedia
Paracerceis sculpta is a species of marine isopod between 1.3 millimetre (0.0511811023622047 in) and 10.3 mm (0.405511811023622 in) in length. The species lives mainly in the intertidal zone
, and is native to the Northeast Pacific from Southern California
to Mexico
, but has since been introduced
to many other countries. Adults are herbivorous
and consume algae
but juveniles are carnivorous
and consume moulting
females. They reproduce in sponges but do not feed near them.
and exist in 3 forms, α, β, and γ of different sizes. Of the three, α males are the largest and most dominant; they mate with multiple females
in a harem
. The β males mimic
the females and therefore manage to mate with some of the females in an α male's harem. The γ form is much smaller and mimics the juvenile form, also allowing it to escape detection. Relatively speaking, the γ males invest the most energy in their testes, followed by the β males and the α males. Other species in which alternative reproductive strategies caused by a genetic polymorphism occur are the swordtail (Xiphophorus nigrensis) , the tree lizard (Urosaurus ornatus
) , the ruff (Philomachus pugnax) and the side-blotched lizard (Uta stansburiana).
The α males guard a spongocoel
into which females (as many as 19) enter to mate. Females brood their offspring internally within a brood pouch and use their bodies to provide nutrition to their developing young before they are released. Females only reproduce once, with larger females producing more eggs. Shortly before females become fertile, they can be cannibalistic
. They then undergo a sexual moult
, losing their mouthparts in the process. The eggs are fertilised inside the female, though how the sperm
enter the female is unclear since the sperm of this, and other related species, are apparently immotile. The length of gestation
depends on the temperature of the water – the cooler the water, the longer it takes. The female provides nutrition
directly, her internal organs and muscles degrading throughout the gestation. This gives the juveniles a headstart, before they begin feeding on intertidal algae. The females die shortly after juveniles are released.
s involved in international trade. The sponges they reproduce in grow on the hulls
of ships and this allows Paracerceis sculpta to be transported easily. There is also a high potential for them to be spread through ballast water. Through these mechanisms Paracerceis sculpta has spread to Australia
, Brazil
, the Atlantic coast of Europe
, Hawaii
, Hong Kong
, the Mediterranean and Japan
. The wide range of water temperatures in its native range is thought to contribute to its ability to be spread by shipping.
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
, and is native to the Northeast Pacific from Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
to Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, but has since been introduced
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
to many other countries. Adults are herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
and consume algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
but juveniles are carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
and consume moulting
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
females. They reproduce in sponges but do not feed near them.
Reproduction
Their reproductive strategy is of interest, as both males and females are unusual among animals. Males are polymorphicPolymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
and exist in 3 forms, α, β, and γ of different sizes. Of the three, α males are the largest and most dominant; they mate with multiple females
Polygyny
Polygyny is a form of marriage in which a man has two or more wives at the same time. In countries where the practice is illegal, the man is referred to as a bigamist or a polygamist...
in a harem
Harem
Harem refers to the sphere of women in what is usually a polygynous household and their enclosed quarters which are forbidden to men...
. The β males mimic
Mimic
In evolutionary biology, mimicry is the similarity of one species to another which protects one or both. This similarity can be in appearance, behaviour, sound, scent and even location, with the mimics found in similar places to their models....
the females and therefore manage to mate with some of the females in an α male's harem. The γ form is much smaller and mimics the juvenile form, also allowing it to escape detection. Relatively speaking, the γ males invest the most energy in their testes, followed by the β males and the α males. Other species in which alternative reproductive strategies caused by a genetic polymorphism occur are the swordtail (Xiphophorus nigrensis) , the tree lizard (Urosaurus ornatus
Urosaurus ornatus
The Tree lizard or Ornate Tree Lizard is a species of lizard that is native to the southwestern United States and northern Mexico. The species has been used to research the physiological changes in the body during the fight-or-flight response as related to stress and aggressive competition...
) , the ruff (Philomachus pugnax) and the side-blotched lizard (Uta stansburiana).
The α males guard a spongocoel
Spongocoel
A spongocoel is the large, central cavity of sponges. Water enters the spongocoel through hundreds of tiny pores and exits through the larger opening . Depending on the body plan of the sponge , the spongocoel could be a simple interior space of the sponge or a complexly branched inner structure...
into which females (as many as 19) enter to mate. Females brood their offspring internally within a brood pouch and use their bodies to provide nutrition to their developing young before they are released. Females only reproduce once, with larger females producing more eggs. Shortly before females become fertile, they can be cannibalistic
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
. They then undergo a sexual moult
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
, losing their mouthparts in the process. The eggs are fertilised inside the female, though how the sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
enter the female is unclear since the sperm of this, and other related species, are apparently immotile. The length of gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
depends on the temperature of the water – the cooler the water, the longer it takes. The female provides nutrition
Nutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
directly, her internal organs and muscles degrading throughout the gestation. This gives the juveniles a headstart, before they begin feeding on intertidal algae. The females die shortly after juveniles are released.
Introductions
Paracerceis sculpta is thought to have been spread around the world by shipShip
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
s involved in international trade. The sponges they reproduce in grow on the hulls
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
of ships and this allows Paracerceis sculpta to be transported easily. There is also a high potential for them to be spread through ballast water. Through these mechanisms Paracerceis sculpta has spread to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, the Atlantic coast of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
, the Mediterranean and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. The wide range of water temperatures in its native range is thought to contribute to its ability to be spread by shipping.