This amphipod species is found in freshwater drainages throughout North America. It is a native of the Mississippi River and its drainages, as well as most river systems in the Atlantic River Plain, including the Delaware, Hudson and Chesapeake. It also occurs throughout the Great Lakes of the United States and their drainages, although it is unclear if it is native to these areas. These amphipods are also found throughout drainages in northeastern Canada (St. Lawrence River and its drainages and gulf), as far north as Prince Edward Island. Recently there have been reports of this species from the United Kingdom and Finland, where they were likely introduced via shipping. ("Gammarus fasciatus", 2013; Kipp, 2013; Lowry, 2012; Pennak, 1989; Van Overdijk, et al., 2003)
This species prefers unpolluted, clear, cold waters, including springs, streams, pools, ponds, and lakes. They prefer highly oxygenated, shallow, still areas, with lots of vegetation or debris for coverage, as they tend to avoid light. When found in rivers, they cluster near the bottom at the edges of backwaters. This species can tolerate some salinity (only up to 1%) and is sometimes found in estuaries. Many scientists categorize them as cold water stenotherms, meaning that they require a narrow range of cold temperatures in order to survive (10-15°C, with temperatures of 20-24°C being tolerable, and temperatures above 34°C causing death). (Bronmark and Hansson, 1998; Kipp, 2013; Lowry, 2012; Pennak, 1989; Van Overdijk, et al., 2003)
Individuals are white or clear in color (variations likely dependent on diet, water temperature and/or age), with brown or green stripes on their bodies and proximal appendage segments. Their bodies are laterally compressed, and they have two pairs of antennae on their cephalophorax. This species is distinguished from others in its family by its accessory flagellum, which has 2-7 segments, on the first set of antennae. The first set of antennae are longer than the second set. The body has seven free thoracic segments, an abdomen with six segments, and a minute telson at the end of the organism. Each of the seven thoracic segments have segmented legs; one segment, the coxa, plays an important role in reproductive activity. The coxa also marks the beginning of the gills, which run from the second to the sixth pair of legs. The first two sets of legs are specialized for grasping, and are called gnathopods. The rest of the legs are relatively unspecialized, and are called pereiopods. The first three abdominal segments have paired pleopods (legs used for swimming), and the last three abdominal segments bear paired uropods, which form a fin with dorsal spines. The eyes are unstalked, well-developed, medium-sized, and kidney shaped. ("Gammarus fasciatus", 2013; Pennak, 1989)
Females have large pouches called oostegites on the the inside of the legs (coxal area) used to carry eggs. Males usually have larger gnathopods (appendages used in feeding and mating) than females. Paired testes or ovaries are found ventrally on either side of the heart, appearing as long strands. (Pennak, 1989)
Newly fertilized eggs develop and are carried in their mother's oostegites until they have hatched and their appendages have formed; this can take from 2-4 weeks, depending on water temperature and other environmental conditions. Young are released into the water after the mother molts into her tenth instar. This species grows and achieves new phases of its life cycle through a series of molting and instars (periods between molting). The first five instar phases are considered to be juvenile phases, in which the sexes are indistinguishable. Once the sixth instar is reached, males and females are visually distinguishable (though their sexes are determined at fertilization). Once reaching their eighth instar, usually within 2 months of hatching, males and females enter the nuptial phase and pair for the first time, only mating once before dying. They typically complete their life cycle within a year. (Kestrup and Riccardi, 2010; Pennak, 1989)
Mating occurs following a female's molt and ovulation. Males attracts females by performing a mating dance. Once they have paired, the male grasps his partner and swims with her, using his appendages to maneuver her body so that he can use his pleopods to insert sperm into her brood pouch, where eggs are fertilized. This species is monogamous, though a male and female may mate multiple times during one pairing. ("Gammarus fasciatus", 2013; Clemans, 1950; Kestrup and Riccardi, 2010; Pennak, 1989; Van Overdijk, et al., 2003)
A ninth phase male will typically pair with a female in her eighth instar who is about to molt. The female, who remains passive throughout, is seized by the male. He carries her on his back, holding her with his gnathopods. If the female has not molted yet, the pair will remain together until she does, separating briefly in order for her to molt. The pair may copulate several times over the next 24 hours, each time taking less than a minute. Once his uropods have come into contact with her oostegites, a male ejaculates sperm and his partner uses her pleopods to sweep them into her pouch. Her oviducts then open, allowing the eggs to be fertilized; females do not store sperm. Males disperse following mating; females carry eggs in their pouches until they have hatched and juveniles have grown appendages. Egg clutches are known to have as many as 23 and as few as 8 eggs. (Clemans, 1950; Kestrup and Riccardi, 2010; Pennak, 1989)
Females carry their eggs until they have hatched and juveniles have grown appendages. Once this has happened, she molts, releasing them into the open water and ending her parental care. Males exhibit no parental investment following mating. (Bronmark and Hansson, 1998; Dawes and Campbell, 2005; Kestrup and Riccardi, 2010; Pennak, 1989)
These amphipods typically complete their life cycle within a year and reproduce once. They undergo 15-20 molts during their lives; length of instars (and therefore longevity) depends largely on water temperature. (Bronmark and Hansson, 1998; Clemans, 1950; Pennak, 1989)
This species avoids light; therefore individuals typically stay hidden beneath vegetation or debris/stones during the day. They are known to hold on to vegetation or dig themselves into the substrate, in order to avoid being moved by water currents. At night, they may crawl on the bottom, using their appendages to propel themselves. When swimming, these amphipods rely heavily on their pleopods for locomotion. Because they often roll on their sides while swimming, members of the family Gammaridae are sometimes called "sideswimmers" or "scuds". This species uses its first set of legs to generate currents at the bottom to bring food near the mouth, drawing it in using its gnathopods, which are specialized for grasping food and transferring it to the mouth. (Clemans, 1950; Pennak, 1989)
There is currently no information available regarding the home range of this species.
This species is highly sensitive to water disturbances, which it senses with its antennae and other appendages. They sense predators through movement and chemical cues. Their eyes are highly developed as well, and potential mates communicate through a mating dance. (Bronmark and Hansson, 1998; Brusca and Brusca, 1990)
These amphipods prefer benthic regions of water bodies because they feed on the detritus, zooplankton and microplantae found there as well as the feces of Dreissena species (freshwater mussels). They are categorized as scavengers, and though they eat meat, they very rarely attack living animals to feed (though they will eat newly dead aquatic animals). They are even known to chew on and eat cotton or linen threads (parts of fishing nets). There are some records of cannibalism in this species, particularly amongst males. Recent research has indicated that types of food consumed may shift throughout the life cycle, with smaller individuals feeding mainly on detritus and larger individuals having a more varied diet. ("Gammarus fasciatus", 2013; Bronmark and Hansson, 1998; Clemans, 1950; Limén, et al., 2005; Meglitsch and Schram, 1991; Pennak, 1989; Summers, et al., 1997)
Fishes (such as yellow perch) are the main predators of this species. They are also prey to birds, insects, and amphibians. These amphipods are very sensitive to any water movement and will quickly dart away and/or burrow into substrate as an escape mechanism. ("Gammarus fasciatus", 2013; Bronmark and Hansson, 1998; Brusca and Brusca, 1990; Pennak, 1989)
This species of amphipod is an important detritivore in its ecosystem and a key food source for many other species. It has commensalistic relationships with a number of algae and sessile protozoan which live on its body. They also form an important relationship with Dreissena sp. (freshwater zebra mussels), feeding on their fecal matter. The mussels also excrete mucous on which algae, an important food source for these shrimp, feed. This species is also an intermediate host for a number of parasites, including tapeworms, acanthocephalan, and nematodes, and is host to a parasitic water mold (currently undescribed). ("Gammarus fasciatus", 2013; Kestrup, et al., 2010; Limén, et al., 2005; Olsen, 1986; Pennak, 1989; Stewart, et al., 1998; Van Overdijk, et al., 2003)
This amphipod species is considered a good biomonitor, as its health can indicate the presence and toxicity of pesticides and chemicals. It absorbs nickel, cadmium, and lead and so, by looking at the levels of these compounds in their systems, scientists can evaluate water toxicity, and potentially locate sources of polluting run off. (Lee and Jones-Lee, 1999; Van Overdijk, et al., 2003)
There are no known adverse effects of this species on humans.
This species has no special conservation status. (IUCN, 2012)
Meghan Hendershot (author), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
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.
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.
helps break down and decompose dead plants and/or animals
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
flesh of dead animals.
uses smells or other chemicals to communicate
an animal that mainly eats the dung of other animals
an animal that mainly eats decomposed plants and/or animals
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
parental care is carried out by females
union of egg and spermatozoan
mainly lives in water that is not salty.
An animal that eats mainly plants or parts of plants.
fertilization takes place within the female's body
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
Having one mate at a time.
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
an animal that mainly eats plankton
breeding is confined to a particular season
remains in the same area
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
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).
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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