New penis characters to distinguish between two American Artemia species

Biofilms are an ensemble of autotrophs and heterotrophs, which are highly efficient in removing inorganic and organic compounds, as well as other chemicals, from river water. They are, therefore, key elements in the self-purification processes which occur in rivers. Biofilm function is related to several environmental factors that govern river ecosystems: physical (light, temperature, water current), chemical (nutrient availability, toxicant effects), but also biological. Among the biological factors, community composition (algae, bacteria and fungi), biofilm structure (layer arrangement and biomass accumulation), and the presence of grazers determine variations in the efficiency of the self-depuration function of biofilms in rivers. Algae and bacteria show specific abilities for nutrients and other organic and inorganic compounds, but biofilm thickness may affect these abilities, both through a decrease in diffusion and by enhancing recycling within the biofilm. Nutrient uptake and consequently the capacity of biofilm to ameliorate water quality decreases with biomass. Moreover, biofilm thickness determines the effect of toxicants, since biomass prevents their diffusion through the biofilm. Grazing interferes in the relative efficiency of biofilms, by simplifying the composition of the biofilm community and by decreasing the amount of sorption and uptake of the biofilm. Closer attention should be paid to these aspects, since they unambiguously interfere with the performance of biofilms in the amelioration of the quality of river water.     

Ecology of the brine shrimp Artemia in the Yucatan, Mexico, Salterns

One year of field data on the Yucatan, Mexico, North Coast hypersalinepools and salterns revealed extreme alkalinity, salinity andtemperature conditions, hypoxia and in some instances, totaldesiccation. The four locations were similar in water temperature,nitrites, and phosphates, but differed in salinity, oxygen content,water depth, nitrates, ammonia, silicates, carbonates, sulfates,and pH. The dominant multicellular organism in these hypersalineecosystems is Artemia, the brine shrimp. Artemia abundance andpopulation dynamics were significantly correlated with specificenvironmental conditions, most often water temperature, salinity,and oxygen concentration. The different schedules of Artemiaand cyst production at each location suggest habitat partitioningamong the brine shrimp populations across the North Coast ofthe Yucatan Peninsula. Our results provide an ecological basisfor rational management of these endangered hypersaline ecosystems.     

Cytogenetic variability and differentiation in Artemia (Branchiopoda: Anostraca) populations from the Yucatán Peninsula,México

Chromosome numbers in somatic (naupliar) and germinal (adult male) cells of bisexual Artemia populations from the Yucatán Peninsula, SE México (Celestun, CEL; Chuburna, CHUB; Xtampu, XTAM; and Las Coloradas, COL), were compared to those from San Francisco Bay (SFB) and Great Salt Lake (GSL) individuals. Diploid and haploid counts permitted a double-check on results. SFB and GSL samples had low variability in number of chromosomes, with strong modal values of 2n=42 and n=21, typical for A. franciscana. Chromosome counts in the Yucatán brine shrimp samples indicated deviations from the normal 2n=42 karyotype (heteroploidy): COL had chromosome modes of 2n=42 and n=21; CEL of 2n=40 and n=20; CHUB had 2n=44 and n=22; XTAM 2n=48 and n=24. Chromocenter abundance (heterocromatic blocks of highly repetitive DNA) among populations indicated that the North American brine shrimp from SFB and GSL had a mean of 15.9 and 15.1 chromocenters, respectively. From the Yucatán brine shrimp, COL had a variable number of chromocenters, ranging from 5 to 15 with a mean value of 9.9. The other three Artemia populations had much fewer chromocenters (CEL 1–3, XTAM 1–8, and CHUB 1–4). Heteromorphic sex chromosomes were apparent in some Yucatán karyotypes preparations. The haplotype condition in the Yucatán Artemia populations, though similar to that found in some Italian A. salina populations, is reported for the first time in New World Artemia. This cytological characteristic of the Yucatán Artemia, in conjunction with their morphological and allozyme differentiation, could provide new insight for the role of chromosome rearrangements in the evolutionary process of Artemia in the New World.