Local and ecoregion effects on fish assemblage structure in tributaries of the Rio Paraíba do Sul, Brazil

1.  We examined the effects of physical and chemical habitat variables and ecoregions on species occurrence and fish assemblage structure in streams of the Paraíba do Sul basin, in southeast Brazil.
2.  Fish and environmental data were collected from 42 sites on 26 first to fourth order streams (1 : 50 000 map scale) in three ecoregions. The sites occurred in one valley and two plateau ecoregions at altitudes of 40–1080 m and distances of 0.1–188 km from the main channel of the Rio Paraíba do Sul. Physical habitat (substratum, riparian cover, habitat types) and water quality (dissolved oxygen, pH, temperature and conductivity) variables were measured at each sampling site.
3.  A total of 2684 individuals in 16 families and 59 species were recorded.
4.  Ecoregion was a better predictor of the fish assemblage than the other environmental variables, according to the differences between the mean within-class and mean between-class similarities in assemblage data.
5.  Differing landscape characteristics were associated with differing local variables and thereby with differing fish assemblage structures. Riffles, shrub, grass, dissolved oxygen, conductivity and temperature were closely related to fish assemblage structure.
6.  Fish assemblages in sites far from the main river and at higher altitudes also differed from those near the Paraíba do Sul main channel, presumably as a result of differences in connectivity, covarying environmental factors and anthropogenic influence.
7.  These results reinforce the importance of understanding how stream communities are influenced by processes and patterns operating at local and regional scales, which will aid water resource managers to target those factors in their management and rehabilitation efforts.     

Purine Metabolism in Trypanosomatids*

SYNOPSIS. Purine nucleotide biosynthesis was studied in culture forms of Trypanosoma cruzi strain Y, Crithidia deanei (a reduviid trypanosomatid with an endosymbiote) and an aposymbiotic strain of C. deanei (obtained by curing C. deanei with chloramphenicol). Trypanosoma cruzi was found to synthesize purine nucleotides only from the preformed bases adenine and guanine (“salvage” pathway), adenine being incorporated into both adenine and guanine nucleotides. Similar results were obtained with guanine, indicating that this flagellate has a system for the interconversion of purine nucleotides. Crithidia deanei was able to synthesize purine and pyrimidine nucleotides from glycine (“de novo” pathway) and purine nucleotides from adenine and guanine (“salvage” pathway). Adenine was incorporated into both adenine and guanine nucleotides, while guanine was incorporated into guanine nucleotides only, indicating the presence of a metabolic block at the level of GMP reducaase. The aposymbiotic C. deanei strain was unable to utilize glycine for the synthesis of purine nucleotides, although glycine was utilized for synthesizing pyrimidine nucleotides. These results suggest that the endosymbiote is implicated in the de novo purine nucleotide pathway of the C. deanei-endosymbiote complex. The incorporation of adenine and guanine by aposymbiotic C. deanei strain followed a pattern similar to that observed for C. deanei.     

新热带区两种潮虫的生态特征(甲壳纲:等足目)

对体型大小不同的两种陆生等足类动物进行形态特征和行为特征研究,探讨环境变化对其繁殖特征和种群结构的影响。自2004年5月至2005年4月,在巴西Parque Estadual de Itapua进行野外采样,其中每月采集12个凋落物和土壤样品,实验室手拣法收集等足类,共获得2540只,同时进行个体性别鉴定与测量。结果表明,Atlantoscia floridana平均密度为114只Pm2,Balloniscus glaber平均密度为133只Pm2。A.floridana雌性个体全年可育,B.glaber雌性个体只在早春至初夏时段可育,其中春季这两种动物雌性可育个体数量高。2005年夏季干旱,该气候因子对两种动物种群影响存在差异,其中干旱使A.floridana种群减少,而B.glaber种群基本保持稳定,两种动物间形态结构不同是上述差异的主要原因,尤其是B.glaber,特殊的体型和腹肢肺的存在使其更能忍耐干燥。此外,B.glaber可能也依赖行为策略适应环境,例如挖掘活动,在不利气候条件下挖掘活动能够增加年轻个体生存的机会,也可能对成年个体起到保护作用。对于A.floridana来说,它具有连续繁殖、性成熟时间短和高雌性生育比率的特征,这些策略是对其幼体死亡率高的一种反应     

Phylogeography and conservation genetics of endangered European Margaritiferidae (Bivalvia: Unionoidea)

Margaritifera margaritifera and M. auricularia are among the most endangered freshwater mussels in the world, and the only species of the genus found in Europe. Our genetic study explores allozymic variability (27 loci) and differentiation at the mitochondrial sequence level (partial COI and 16S rRNA gene sequences). The Spanish M. auricularia population showed genetic parameters of variation that were of the same order as those of other freshwater molluscs (though at the lower end of the range), probably permitting its potential recovery. The difference between this species and M. margaritifera was clearly established (ten diagnostic allozymic loci, Nei = 0.462, and mean nucleotide divergence around 9.4%). The M. margaritifera populations analysed showed a certain degree of population genetic structure (according to allozyme data) that was not, however, related to a geographical cline. Nevertheless, two mitochondrial lineages (albeit very closely related) were identified: a northern lineage extending from Ireland to the Kola Peninsula including the western Atlantic coast, and a second cluster distributed from Ireland to the Iberian Peninsula. The phylogenetic relationships between these two species and other related taxa were established. The putative M. m. durrovensis could be considered an 'ecophenotype'. Palaeobiogeographical scenarios are presented and indicate unexpected 'recent' gene flow between M. margaritifera populations that were theoretically isolated in the early Tertiary.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society 2003, 78, 235–252.     

Antigenic Similarity Between the Coccidian Parasites Toxoplasma gondii and Hammondia hammondi1

The antigens that are present in the coccidian parasites Toxoplasma gondii and Hammondia hammondi were demonstrated and defined by using SDS-PAGE and immunoenzymatic techniques with ¹²⁵I-labeled and unlabeled antigens of T. gondii and sera of mice infected orally or intraperitoneally with H. hammondi. All cell surface antigens of T. gondii that were labeled with ¹²⁵I were recognized by antibodies in the sera of the mice infected with H. hammondi except the antigen of approximate molecular weight of 21.5 Kd. This suggests that this antigen is specific for T. gondii. Various antigens in the T. gondii-lysed antigen preparations were recognized by antibodies to H. hammondi. The number of recognized antigens increased as the infection of the mice with H. hammondi progressed. Oral infection with H. hammondi appeared to induce the formation of antibodies that recognized more T. gondii antigens than infection by intraperitoneal inoculation.     

Binding of Lectins to the Cell Surface of Trypanosoma cruzi*

SYNOPSIS. Differences in the composition and distribution of cell membrane carbohydrates were demonstrated in the 3 life cycle forms of 3 Trypanosoma cruzi strains by using lectins with different specificities. The results suggest that lectin binding may be useful in characterization of the parasite strains.     

THE GONADS OF MARGARITIFERA AURICULARIA (SPENGLER, 1793) AND M. MARGARITIFERA (LINNAEUS, 1758) (BIVALVIA: UNIONOIDEA).

A detailed study of the gonads of two endangered species of thegenus Margaritifera living in the Iberian Peninsula, Margaritiferaauricularia (Spengler, 1793) and Margaritifera margaritifera(Linnaeus 1758), based on macroscopic and histological observationsis presented. In both species, gonadal tissue occurs withinthe visceral mass without a specific location. In hermaphrodite specimens,male and female acini are mixed in the visceral mass but canbe clearly distinguished by detailed macroscopic study. The gonadaltopography and cycle of Margaritifera auricularia is described forthe first time, indicating that the species is a female hermaphroditeand that gametogenesis occurs from December to March. Fiftypercent of Margaritifera margaritifera specimens studied werehermaphrodites and 50% females. (Received 6 March 2000; accepted 5 June 2000)