Hyalella azteca
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| Hyalella azteca | |
|---|---|
 | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Amphipoda |
| Family: | Hyalellidae |
| Genus: | Hyalella |
| Species: | H. azteca |
| Binomial name | |
| Hyalella azteca (Saussure, 1858) | |
Hyalella azteca is a widespread and abundant species complex of amphipod crustacean in North America. It reaches 3–8 mm (0.12–0.31 in) long, and is found in a range of fresh and brackish waters. It feeds on algae and diatoms and is a major food of waterfowl.
Hyalella azteca has body plan similar to most amphipods and is a classic freshwater example of the order. They grow to a length of 3–8 millimetres (0.12–0.31 in), with males being larger than females.[1] Their color is variable, but the most frequent hues are white, green and brown.[1]
They are identified from other similar species by antenna 1 being equal or shorter than antenna 2, 1 spine on pleosome 1 and pleosome 2, Pereopod I and II are gnathopod with males having a visibly larger gnathopod.
Distribution
Hyalella azteca is found across Central America, the Caribbean and North America,[2] as far north as the Arctic tree line.[1] It lives among vegetation and sediments in permanent bodies of freshwater, including lakes and rivers,[1] extending into tidal fresh water, and freshwater barrier lagoons.[2] It is "the most abundant amphipod of lakes [in North America]",[3] with golf course ponds sometimes supporting large populations.
Ecology
In contrast to other species of Hyalella, H. azteca is extremely common and has wide ecological tolerances.[4] It can tolerate alkaline waters and brackish waters, but cannot tolerate a pH lower (more acidic) than 6.0.[4]
The main foodstuffs of H. azteca are filamentous algae and diatoms, although they may also consume organic detritus.[1] It cannot assimilate either cellulose or lignin, even though these biomolecules are a major component of the leaf litter.[5] It can, however, assimilate 60%–90% of the bacterial biomass that it ingests.[5]
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.[6]
Insecticide resistance
Hyalella azteca is widely used in ecotoxicology due to its sensitivity to pollutants; however, recent studies suggest that populations may develop tolerance to insecticides over few generations. For instance, a 2024 study found that after just two generations of exposure to thiacloprid, tolerance levels increased significantly, highlighting the potential role of developmental plasticity in rapid adaptation to pesticide pollution.[7] However, evolved resistance to insecticides may conflict with the species' ability to adapt to climate change. Fulton et al. (2021) demonstrated that some resistance mechanisms in H. azteca impose a fitness cost under higher temperatures, raising concerns about the trade-offs between pesticide tolerance and thermal adaptability in a changing environment. Some H. azteca have evolved insecticide resistance. This does however conflict with their need to adapt to climate change: Fulton et al 2021 finds some of their mechanisms of resistance impose a fitness cost under higher temperatures.[8]
Life cycle
Uses
Hyalella azteca are used in various aquatic bioassays [9][10] (also called toxicity tests). Because of their wide distribution, ease of captive reproduction, and its niche in lake sediments, Hyalella azteca are used in aquatic toxicology assays in sediments [11] Hyalella azteca have been used to test bioaccumulation of different contaminants such as manufactured nanomaterials , pesticides , and metals .
Taxonomic history
Hyalella azteca was first described by Henri Louis Frédéric de Saussure in 1858, under the name Amphitoe aztecus, based on material collected by Aztecs[12] from a "cistern" near Veracruz, Mexico.[13] It has also been described under several junior synonyms, including:[14]
- 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.[15] The genus now includes dozens of species, mostly in South America.[15]
H. azteca is now thought to represent a species complex,[16] since there is little gene flow between populations, and different morphotypes are known to coexist in some areas.[12] Two local populations have been described as separate species – Hyalella texana from the Edwards Plateau of Texas, and Hyalella montezuma from Montezuma Well, Arizona.[12] In addition to being a species complex, laboratory work sequencing and analyzing the genome of lab populations of Hyalella azteca revealed Hyalella azteca shares characteristics of other model organisms. [8]. How these crustaceans interact with contaminants can provide insight about how other species will interact with those same contaminants.