Sequencing of the CO1 mitochondrial gene (barcoding) highlighted a possible different species in the semi-desert region of Mexico. After a detailed morphological analysis we describe Scapholeberis duranguensis n. sp. (Cladocera: Anomopoda: Daphniidae). Specimens from the type locality, El Chupadero, Durango, were compared with specimens of S. armata armata Herrick, 1882 and S. armata freyi Dumont and Pensaert, 1983 from Canada and southeastern, central and northern Mexico. The main characters that differentiate the new species are: (1) a thicker denticulate membrane with a conspicuous underlying hyaline membrane at the posterior rim of the valves, (2) fewer setae in the gnathobase of trunk limb II and (3) longer and more rectilinear ejector hooks in trunk limb I. The presence of a pore-like structure at the top of the head was also observed, however we are not certain whether this can be considered as a distinctive character, as it was not consistent in all SEM scanned organisms. The denticulate membrane, the number of setae in the gnathobase of trunk limb II and the length of the ejector hooks are characters shared with other species, however, the combination of them and in particular the structure and thickness of the double membrane at the posterior rim of the valves lead us to conclude that S. duranguensis is a species different from S. armata and from other members of this genus. The CO1 sequences of S. armata freyi and S. duranguensis n. sp. showed a mean divergence of 12.02%, thus supporting the morphological differences between them. Finally, a comparison of the CO1 sequences of Scapholeberis duranguensis n.sp. with other Scapholeberinae available in GenBank supported our results.
The epifaunal community associated with eelgrass beds in San Quintin Bay, Baja California, Mexico, was studied from April to November 1993. Taxonomic identification, univariate community descriptors, and biomass data were obtained for each sample. Multivariate analyses of community composition were also performed, and plant-animal relationships were analyzed. The epifaunal community was characterized by the high abundance of a few dominant species, with the mollusk Assiminea dubiosa representing 70% of the total abundance. Summer samples had the highest similarity, as indicated by the Analysis of Similarity (ANOSIM) test. Polychaetes and amphipod abundances seemed to follow the variations in eelgrass aboveground biomass.
a b s t r a c tDissolved aluminium (Al) is generally at low concentrations in neutral freshwater due to its insolubility. However, a fall in pH resulting from acid deposition and mining alters the mobility of Al and so entry to adjacent neutral waters. The present study examines the environmental behaviour, cell-associated surface adsorption/absorption and toxicity of Al at neutral pH to the alga Chlamydomonas gigantea in the presence and absence of the key Al-binding ligand silica. We then examined transfer of Al from C. gigantea to the planktonic crustacean Daphnia pulex. Finally, the effect of Al on the elemental composition (and hence nutritional value) of the two organisms was compared to unexposed controls. C. gigantea increased the amount of Al in the algal culture medium. Binding of Al to extracellular glycoprotein is probably the reason why only one-third of the biosorbed Al was absorbed (accumulated) by C. gigantea. Aluminium concentrations between 50 and 500 mg l À 1 reduced growth of C. gigantea at 16 days exposure to the metal. Silica reduced biosorption, accumulation and toxicity of Al by C. gigantea. The concentration of Al in D. pulex fed Al-contaminated C. gigantea for 16 days did not differ from those fed alga grown in the absence of added Al. C. gigantea contaminated with Al contained less sulphur, magnesium, potassium and sodium although only sulphur fell in D. pulex subsequently fed the contaminated alga. Chloride, calcium, iron and silicon were significantly higher in D. pulex.
This study was carried out to monitor and relate seasonal Al, Si and transition metal (Mn, Fe, Ni and Cu) concentrations in lake water and phytoplankton within an unpolluted lake. Lake water concentrations of Al and Mn showed seasonal (high winter-low summer) variation. The clear annual correlation pattern had significant links among transition metals, but not Si-Al. Within phytoplankton biomass, separate analyses of acid (soluble) and carbonate (insoluble) constituents showed that most elements (Si, Ni, Cu and Fe) occurred in bound form, but insoluble Al and Mn concentrations were \50% total. Diatom abundance was characterised by high Si and low Al biomass concentration, with substantial amounts of Si also occurring during phases of bluegreen dominance. The elemental correlation pattern of phytoplankton acid digests (soluble material) was different from carbonate digests, which had significant correlations among the three transition metals (Mn, Ni, and Cu)-but no relationships involving Si, Al and Fe. Data show that phytoplankton biomass accumulates high levels of Al, Si and transition metals, irrespective of taxonomic composition. The different correlation patterns seen for aquatic, soluble biomass and insoluble biomass elemental concentrations indicate that external availability, soluble uptake and insoluble deposition are distinct aspects of the pelagic ecosystem.
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