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= Gammarus roeseli = Gammarus roeseli is a species of freshwater amphipod native to Europe and are specifically adapted to the summer-warm waters of Northern Italy. This species is easily identified by the presence of dorsal carinae on metasome segments. G. roeseli are a successful invasive species due to their high reproductive rate, tolerance to changing environmental conditions and unique anti-predation characteristics. Gammarus roeseli are detritivores and scavengers and It's food sources commonly include decaying tree leaves, aquatic macrophytes and other aquatic plants. G. roeseli are often used in experiments to study the effect that a stress, such as salinity and water temperature, have on ecotoxicology.

Distribution
Gammarus roeseli are found in freshwater environments such as ponds, oxbow lakes and small streams. Populations tend to be highest in rivers with moderate water flow and ample plants to be used as shelter. G. roeseli originated in the Balkan area of Europe, but increased the distribution area to into Northern Italy. Populations can even be found in the sub-lacustrine area known as the Ticino River basin, which is the furthest region from it origin that this species has invaded thus far. In Northern Italy, the invasive G. roeseli shares the same geographic location as the native Echinogammarus stammeri, but G. roeseli is more successful in reaching the adult stage. G. roeseli's original mechanism of invasion is still unknown but it is most likely due to human activities such as aquaculture or fish repopulation. G. roeseli were once used as a food source in commercial fisheries, so it is possible that some individuals escaped and were able to populate new areas. G. roeseli are a successful invasive species due to their high reproductive rate, tolerance to changing environmental conditions and unique anti-predation characteristics. G. roeseli have the ability to easily attach their bodies to substrates by using the spines on its metasomes. These organisms are also able to survive out of water for several days at a time, making the transfer of G. roeseli feasible over land.

Description
Gammarus roeseli is a species belonging to the amphipod order, which characterized by lacking a carapace and having laterally compressed bodies. As with all other arthropods, G. roeseli have a segmented body that is protected by a hard exoskeleton. The most distinctive features of G. roeseli are the setae present on the antennae, pereiopods, and third uropod. These setae function as spines for protection against predators and allow the organism to attach itself to surfaces. As an individual get older, the number and length of setae increase, this characteristic is essential when doing research on this species. The urosome is divided into 3 segments, where the middle segment is laterally compressed and at a different elevation than the 2 neighboring segments. G. roeseli mouthparts are highly specialized for omnivorous feeding. Individuals have rasp-like mandibles used for grinding solid plant material and can also used setae present on maxillipeds to grind food off of surfaces.

Reproduction
Gammarus roeseli reproduce sexually, but individuals must moult 9-10 times before they reach sexual maturity. The relationship between maturation time and water temperature can be described as a power function because as water temperature increased, maturation times dramatically decrease. Females can better resist highly polluted environments compared to males, specifically in the spring because the warmer waters cause females to reach sexual maturity faster. In fall and winter months, female's enzyme levels decreased and lipid levels increase because the excess energy to breed is not needed. G. roeseli commonly exhibit strategic sperm investment, meaning that an unhealthy female will receive less sperm when mated with a healthy male. Reproduction is easily influenced by vertically-transmitted parasites. The parasite Nosema granulosis can cause males to feminize and become infertile, causing a change in the sex ratio of a population.

Predation
G. roeseli practice predator avoidance by choosing microhabitat with the lowest predator density. This species has the ability to detect the high infochemical concentrations that are dispersed by G. roeseli's freshwater predators. Individuals use the presence of different to non-visually detect changing conditions of it's environment and adapt its behavior in order to increase its change of survival. For example, in an area when fish kairomones are present, G. roeseli increase activity in pebble-like substrates in order to more effectively hide from predators.