Artemia biodiversity in Asia with the focus on the phylogeography of the introduced American species Artemia franciscana Kellogg, 1906.

Asia harbors a diverse group of sexual and asexual Artemia species, including the invasive Artemia franciscana, which is native to the Americas. The phylogeny of Asian Artemia species and the phylogeography of the introduced A. franciscana from 81 sampling localities in Eurasia, Africa and America were elucidated using mitochondrial (COI) and nuclear DNA (ITS1) sequences. According to a COI phylogeny, 6 distinctive genetic groups were recognized, with a complex phylogeographic structure among Asian Artemia. A haplotype complex which includes parthenogenetic lineages is distributed in 39 inland geographical localities in Asia, illustrating a wide distribution with a narrow genetic structure on this continent. The invasive A. franciscana was discovered in 31 geographical localities along the southern and eastern coastal regions of Asia. Three sexual species (A. sinica, A. tibetiana and A. urmiana) have a restricted distribution in certain geographical localities in Asia. In contrast to COI phylogeny reconstruction, ITS1 sequences showed inconsistency with the COI tree, indicating incomplete lineage sorting which provided the low genetic divergence in the Asian clade. Asian A. franciscana showed higher haplotype diversity as compared to the source population from the Great Salt Lake (USA), which could be attributed to multiple introductions by mass dispersal in Asia via human activities. The invasive success of A. franciscana in Asia could lead to a long-term biodiversity disturbance of the autochthonous Artemia species on the continent.

Metabolic downregulation and inhibition of carbohydrate catabolism during diapause in embryos of Artemia franciscana.

Diapause embryos were collected from ovigerous females of Artemia franciscana at the Great Salt Lake, Utah, and were synchronized to within 4 h of release. Respiration rate for these freshly released embryos across a subsequent 26-d time course showed a rapid decrease during the first several days followed thereafter by a much slower decline. The overall metabolic depression was estimated to be greater than 99%. However, proton conductance of mitochondria isolated from diapause and postdiapause embryos was identical. Because proton leak is apparently not downregulated during diapause, mitochondrial membrane potential is likely compromised because of the very low metabolic rate observed for diapause embryos. Given that trehalose is the primary fuel used by these embryos, we measured metabolic intermediates along the catabolic pathway from trehalose to acetyl-CoA for both diapause and postdiapause (active) embryos in order to identify sites of metabolic inhibition. Comparison of product-to-substrate ratios for sequential enzymatic steps revealed inhibition during diapause at trehalase, hexokinase, pyruvate kinase, and pyruvate dehydrogenase. Measurements of ATP, ADP, and AMP allowed calculations of substantial decreases in ATP:ADP ratio and in adenylate energy charge during diapause. The phosphorylation of site 1 for pyruvate dehydrogenase (PDH) subunit E1α was higher in diapause embryos than in postdiapause embryos, which is consistent with PDH inhibition during diapause. Taken together, our findings indicate that restricted substrate availability to mitochondria for oxidative phosphorylation contributes to downregulating metabolic rate during diapause.

Predictive modeling of selenium accumulation in brine shrimp in saline environments.

Great Salt Lake, Utah, is a large, terminal, hypersaline lake consisting of a northern more saline arm and a southern arm that is less saline. The southern arm supports a seasonally abundant fauna of low diversity consisting of brine shrimp (Artemia franciscana), 7 species of brine flies, and multiple species of algae. Although fish cannot survive in the main body of the lake, the lake is highly productive, and brine shrimp and brine fly populations support large numbers of migratory waterfowl and shorebirds, as well as resident waterfowl, shorebirds, and gulls. Selenium and other trace elements, metals, and nutrients are contaminants of concern for the lake because of their concentrations in municipal and industrial outfalls and runoff from local agriculture and the large urban area of Salt Lake City. As a consequence, the State of Utah recently recommended water quality standards for Se for the southern arm of Great Salt Lake based on exposure and risk to birds. The tissue-based recommendations (as measured in bird eggs) were based on the understanding that Se toxicity is predominately expressed through dietary exposure, and that the breeding shorebirds, waterfowl, and gulls of the lake are the receptors of most concern. The bird egg-based recommended standards for Se require a model to link bird egg Se concentrations to their dietary concentrations and water column values. This study analyzes available brine shrimp tissue Se data from a variety of sources, along with waterborne and water particulate (potential brine shrimp diet) Se concentrations, in an attempt to develop a model to predict brine shrimp Se concentrations from the Se concentrations in surrounding water. The model can serve as a tool for linking the tissue-based water quality standards of a key dietary item to waterborne concentrations. The results were compared to other laboratory and field-based models to predict brine shrimp tissue Se concentrations from ambient water and their diet. No significant relationships were found between brine shrimp and their dietary Se, as measured by seston concentrations. The final linear and piecewise regression models showed significant positive relationships between waterborne and brine shrimp tissue Se concentrations but with a very weak predictive ability for waterborne concentrations<10 µg/L.