Nora Silvia Sidorkewicj

The interaction between Cyprinus carpio L. and Potamogeton pectinatus L. under aquarium conditions

Plants and seedlings of Potamogeton pectinatus were obtained from tubers grown under laboratory conditions. Four plants (mean total length: 14.3 m) and two seedlings (mean height: 10.9 cm) were placed in each of twenty 1001 aquaria illuminated with fluorescent lighting. A 5 cm-thick layer of muddy sediment was then put in each aquarium together with two size-matched fish (mean size classes: 6.8, 14.1 and 23.0 g) of the species Cyprinus carpio. After four weeks, the total length of the plants in the control and small fish aquaria had increased by 71% and 3% respectively, whereas plant total length in the aquaria with medium and large fish had diminished by 33% and 76%, respectively. Few seedlings survived in the presence of the fish. The reduction in plant growth was associated with an increase in water turbidity in all treatments as a result of the benthic feeding habit of C. carpio, and of direct herbivory action in the case of medium- and large-sized fish.

Effects of Cyprinus carpio on Potamogeton pectinatus in experimental culture : the incidence of the periphyton

The effect of one-year-old common carp (Cyprinus carpio L.) on plants and seedlings of Potamogeton pectinatus L., and on periphyton development was studied in 100 l glass aquaria. Two 30-day experiments were conducted using a muddy sediment or a pebbly bottom. In both cases, three treatments based on different fish size (two fish/aquarium) were assayed. The control had no fish. In both experiments, chlorophyll content of the periphyton increased from the beginning to the end of the period, for the three fish treatments. Light attenuation by periphyton was high, with final values 12-30% higher than in the control. Periphytic communities acclimated to reduced light conditions when the bottom was muddy. It can be concluded that, in muddy conditions, small carp affected plant growth by shade stress, which is achieved by a combination of increase in turbidity and the developing of a leaf periphytic cover. Under pebbly conditions, plant damage was caused by collisions and the growth of epiphytic algae. Medium and large fish consumed plants in both experiments. Seedlings were affected by herbivory in all cases.

The Hypertrophy of the Tympanic Bulla in Three Species of Dasypodids (Mammalia, Xenarthra) from Argentina

Fueron estudiados la morfologia y el tamano relativo de la bula timpanica, en tres especies de dasipodidos de la Argentina, Chaetophractus villosus, C. vellerosus and Zaedyus pichiy. Se observaron una morfologia similar y una hipertrofia evidente en la bula en las tres especies. El grado de hipertrofia fue mayor en C. vellerosus y C. villosus que en Z pichiy. Mediante ANCOVA se demostro que, aunque el craneo de C. villosus es mayor que el de C. vellerosus, el tamano relativo de la bula fue similar en ambas especies. Por otra parte, la bula de Z pichiy es relativamente mas pequena que la de C. vellerosus, a pesar que sus craneos son de tamano similar

Cranial Osteology of the Armadillo Chaetophractus villosus (Mammalia, Xenarthra, Dasypodidae)

Realizamos estudios morfologico y morfometrico de los componentes oseos del craneo de Chaetophractus villosus. Los huesos son morfologicamente semejantes en ambos sexos y siguen el patron generalizado de la mayoria de los dasipodidos descritos. El analisis morfometrico, sin embargo, demostro que la mayoria de los huesos ubicados en el plano rostrocaudal son mas largos en las hembras, determinando mayores valores de longitudes total, basal y condilobasal del craneo, que son las principales variables que contribuyen a determinar el dimorfismo sexual en esta especie

Sexual dimorphism in the mandible of the armadillo Chaetophractus villosus (Desmarest, 1804) (Dasypodidae) from northern Patagonia, Argentina

The aim of this study was to study the sexual dimorphism in adult Chaetophractus villosus (Desmarest, 1804), from northern Patagonia, Argentina. Eight mandibular traits were measured in 37 males and 34 females. Univariate and multivariate morphometric analysis were applied to the data set. Results showed that C. villosus was sexually dimorphic, with higher absolute values corresponding to females. The total length of the mandible was the most important variable to discriminate sexes, followed by the height at the level of the last tooth and body length. The percentages of sex discrimination were high, as they were when a new sample (17 males, 13 females) was tested. Females have larger mandibles than males independently of their larger cranial size. They also showed a higher degree of correlation between variables, suggesting a more stable shape for the mandible than in males.

A geometric morphometric study of sex differences in the scapula, humerus and ulna of Chaetophractus villosus (Xenarthra, Dasypodidae)

Sexual diff erences in some of the components of the pectoral girdle and forelimb of Chaetophractus villosus (Desmarest, 1804) were investigated by means of geometric morphometrics. A total of 15 scapulae (7 males, 8 females) and 50 humeri-ulnae complexes (24 males, 26 females) were examined. No size diff erences were detected between sexes for any of the bones, but shape diff erences were found for the humerus and the ulna that enhance the in-forces or the related in-levers. Females had a more robust humerus, with an enlarged deltoid tuberosity, a more spherical head, higher tubercular and epicondylar widths, and more developed supracondylar crests. The ulna of the females was characterised by a more pronounced curvature along its main axis, a caudal displacement of the lateral fossa, a longer olecranon, and a deeper trochlear notch. For both bones, the discriminant analysis classifi ed correctly all the specimens according to their sex. A small percentage of the variance (5.2% for the humerus; 6.8% for the ulna) was explained by allometry. The morphological traits found for the humerus and ulna of the females suggest an increased structural strength that could result in powerful digging strokes while keeping shoulder and elbow stabilisation, suggesting a fossorial advantage over males.

Morphology of the Middle Ear in Three Species of Armadillos (Dasypodidae, Xenarthra) from Argentina

Se estudio cualitativa y cuantitativamente la morfologia del oido medio en adultos de Chaetophractus villosus, C. vellerosus y Zaedyus pichiy. Se observo una gran similitud en las estructuras del oido medio de las tres especies. La bula auditiva, bien desarrollada, se observo formada por la fusion del timpanico y entotimpanico. Internamente se pudo reconocer un recessus meatus y un amplio receso epitimpanico que se extendia dorsalmente en un seno epitimpanico. El promontorio, casi triangular, fue la estructura mas notoria del interior de la cavidad timpanica. Los huesecillos auditivos correspondieron al tipo transicional. Se observo un gran desarrollo en los musculos tensor del timpano y estapedial. Se confirmo la falta de una arteria estapedial en las tres especies. El area del timpano y los huesecillos auditivos fueron relativamente mas grandes en C. vellerosus que en las otras dos especies. Se espera que los resultados del presente trabajo, sumados a la hipertrofia de la bula timpanica reportada previamente, provean una base significativa para futuros estudios sobre la capacidad auditiva en los dasipodidos.

Conservation of Body Sections and Organs of the Narrownose Smooth-hound, Mustelus schmitti (Pisces, Chondrichthyes), by Silicone Injection at Room Temperature to be Used in Comparative Anatomy learning

Comparative Anatomy deals with the study of the ontogenetic and phylogenetic changes of the vertebrates, requiring complementing the theoretical aspects with the observation of structures in specimens belonging to different taxonomic groups. The aim of the present study was to test the injection of silicone at room temperature in organs and trunk sections of Mustelus schmitti as an alternative to the plastination technique. Samples consisted in brain, eyes, heart, proximal end of the ventral aorta, digestiv e tract, spleen, pancreas, kidneys, testis and cross body section at a pre-caudal level. Material was fixed with formalin (10-5 %), dehydrated w ith growing concentrations of isopropyl (30 % 50 % 70 % 90 % 100 % 100 %), impregnated with diluted commercial silicone a nd cured at room temperature. The whole process took 66 days. The brain was the unique organ that could not undergo the complete procedure because it did not resist the injection of silicone. The other pieces resulted in materials that characterised by bei ng off-colour, dry, semi-flexible, lightweight, odourless, and non-toxic. They showed no signs of fungal colonization or bacterial degradation after tw years of being obtained. Shrinkage was observed, which ranged among 2-25 % for total length, and from 5-26 % for maximum width (mean values: 14 and 15 %, respectively), being testicle the organ that suffered greater shrinkage in both dimensions. The degr ee of contraction in length and width for each of the samples was generally similar (difference ≤ 3 %), indicating that not striking deformation occurred. Deformation was observed only for the trunk section, eye, stomach, pancreas and valvular intestine. The technique did not affect the morphology of the structures, allowing the correct visualization of all the basic features required to recognise the m. W conclude that this simple and economic method is an adequate alternative to be implemented for the conservation of small-size m aterial with educational purposes in Comparative Anatomy courses.

Métodos para la Estimación del Volumen de Bula Timpánica en el Quirquincho Grande Chaetophractus villosus (Mammalia, Xenarthra, Dasypodidae)

Two methods of measurement of bullar dimensions (callipers and scaling from digital images) and subsequent application of four volume formulae (rectangular prism, cylinder, ellipse and elliptical cone) were tested to find the most app ropriate non-destructive method for estimating the bullar volume in Chaetophractus villosus . Material for the study consisted in clean adult skull (n=22). Real volume was obtained from latex casts of the tympanic bulla. Each estimation was corrected by a factor based on the differences between the estimated and the real volumes. Highest accuracy (5-7 % of underestimation) and precision (coefficient of variation: 13.27 %) were obtained from callipers and application of rectangular prism, cylinder and ellipse formulae. The corre sponding correction factors were 0.31, 0.39 and 0.58, respectively.

Morphological characterization and sex-related differences of the mandible of the armadillos Chaetophractus vellerosus and Zaedyus pichiy (Xenarthra, Dasypodidae), with consideration of dietary aspects

The morphological characteristics of the mandible of adult Chaetophractus vellerosus (Gray, 1865) and Zaedyus pichiy (Desmarest, 1804) were studied to establish its generalized design and to identify inter- and intra- (sexual) specific differences. Morphological descriptions were complemented with the application of univariate and multivariate (analysis of correlation matrices, PCA, discriminant analysis) techniques. The mandible of both species is very similar, and is characterized by elevated condyle, well developed angular process, distinct coronoid process, tooth row which extends to the rear end of the angle between body and ramus, and unfused but firm symphysis. Although both armadillos are omnivorous, a more slender configuration of the jaw in Z. pichiy could be indicative of a better adaptation of its masticatory apparatus to insectivory. The PCA showed an almost total segregation of both species on PC1 (47.7% of the total variance), with C. vellerosus being associated to mandibles taller and with wider body and ramus. Zaedyus pichiy was characterized by heavy loadings of length parameters on PC2 (22.6% of the variance). A small degree of sexual dimorphism was found, with size-based differences in C. vellerosus (larger mandibles in females) and shape-based differences in Z. pichiy (taller mandibles in males, longer ones in females). Correlations between variables were higher in males of both species, indicating a more stable shape of the mandible than in females. The selected parameters to discriminate sexes were the body length of the mandible in C. vellerosus (correct classification: ca. 86% in males, 81% in females), and the height of the mandible at the level of the last tooth in Z. pichiy (near 85% of right assignment in both sexes). The inclusion of a new variable (body length) in the latter species improved the classification of the females to 100%. Teeth are typically 10 in C. vellerosus and 9 in Z. pichiy, but aberrancies in this basic number, such as unilateral or bilateral extra or fewer teeth, are common.