Hyalella azteca

Appearance

''Hyalella azteca'' grows to a length of 3–8 millimetres , with males being larger than females. Their colour is variable, but the most frequent hues are white, green and brown.

Distribution

''Hyalella azteca'' is found across Central America, the Caribbean and North America, as far north as the Arctic tree line. It lives among vegetation in permanent bodies of freshwater, including lakes and rivers, extending into tidal fresh water, and freshwater barrier lagoons. It is "the most abundant amphipod of lakes [in North America]", with golf course ponds sometimes supporting large populations.

Behavior

''Hyalella azteca'' passes through a minimum of nine instars during its development. Sexes can first be distinguished at the 6th instar, with the first mating occurring in the 8th instar. Subsequent instars, of which there may be 15–20, are considered adulthood.

Habitat

In contrast to other species of ''Hyalella'', ''H. azteca'' is extremely common and has wide ecological tolerances. It can tolerate alkaline waters and brackish waters, but cannot tolerate a pH lower than 6.0.

The main foodstuffs of ''H. azteca'' are filamentous algae and diatoms, although they may also consume organic detritus. It cannot assimilate either cellulose or lignin, even though these biomolecules are a major component of the leaf litter. It can, however, assimilate 60%–90% of the bacterial biomass that it ingests.

''Hyalella azteca'' is an important food for many waterfowl. In Saskatchewan, 97% of the diet of female white-winged scoters was observed to be ''H. azteca'', and it also makes up a significant part of the diet of lesser scaup.

Evolution

''Hyalella azteca'' was first described by Henri Louis Frédéric de Saussure in 1858, under the name ''Amphitoe aztecus'', based on material collected by Aztecs from a "cistern" near Veracruz, Mexico. It has also been described under several junior synonyms, including:
⤷ ''Hyalella dentata'' S. I. Smith, 1874
⤷ ''Hyalella fluvialis'' Lockington, 1877
⤷ ''Hyalella inermis'' S. I. Smith, 1875
⤷ ''Hyalella knickerbockeri'' Bate, 1862
⤷ ''Hyalella ornata'' Pearse, 1911
When Sidney Irving Smith erected the genus ''Hyalella'' in 1874, ''H. azteca'' was the only included species, and therefore the type species. The genus now includes dozens of species, mostly in South America.

''H. azteca'' is now thought to represent a species complex, since there is little gene flow between populations, and different morphotypes are known to coexist in some areas. Two local populations have been described as separate species – ''Hyalella texana'' from the Edwards Plateau of Texas, and ''Hyalella montezuma'' from Montezuma Well, Arizona.

Uses

''Hyalella azteca'' is used in various aquatic bioassays. Because of their wide distribution, ease of captive reproduction, and its niche in lake sediments, ''Hyalella azteca'' is used in aquatic toxicology assays in sediments