Chronotropism and blood flow patterns following teratogenic doses of catecholamines in 5-day-old chick embryos.

In vivo heart rates of 5-day-old chick embryos were recorded from electrodes placed in close proximity to the heart. L-epinephrine (4X10(-10) mole), 1-norepinephrine (1X10(-9)mole) and 1-isoproterenol (1.6X10(-10)mole) in 5 microliter of isotonic saline transiently accerlerated the mean heart rate by almost 9 percent. L-phenylephrine (2X10(-9)mole/5microliter) and the experimental procedure produced no appreciable effect. The positive chronotropic effect of the catecholamines was found to be highly significant (P less than 0.0005) as computed by Student's t test. However, no direct relationship could be established between the chronotropic response and the aortic arch anomalies produced. A prolonged reduction of blood flow in the primitive heart tube and the sixth aortic arch after administration of epinephrine and isoproterenol is apparently related to the induction of hypoplastic right pulmonary artery with absent or hypoplastic right ductus arteriosus.     

Fine‐scale habitat heterogeneity explains the local distribution of two Amazonian frog species of concern for conservation

To test the hypothesis that subtle differences in abiotic requirements can result in almost total spatial segregation, we sampled two species of diurnal frogs, Atelopus spumarius and Allobates sumtuosus, in a primary forest reserve in central Brazilian Amazonia. We conducted visual and acoustic surveys on three occasions over 2 months, in 40 streamside (riparian) plots distributed throughout the reserve's two major drainage basins, using a grid system that covers 64 km². On average, drainages differed in the pH of stream water and the number of connected and isolated streamside pools. Differences in abiotic characteristics of drainages were associated with the spatial distribution of frog species. The occurrence and density of Allobates sumtuosus was negatively related to stream pH and discharge and positively related to the number of isolated pools in plots. The occurrence and density of Atelopus spumarius was associated with streams with high discharge and pH near neutral. These results indicate that although very large reserves will probably contain sufficient landscape heterogeneity to accommodate different species of diurnal frogs, due to strongly patchy distributions, in situ studies using fine‐scale species‐distribution models will be necessary to assess the adequacy of small reserves in Amazonia that cover hundreds of square kilometers or less for the conservation of some anuran species.     

A Matter of Scale: Historical and Environmental Factors Structure Anuran Assemblages from the Upper Madeira River,Amazonia

Biogeographical history and current ecological interactions have usually been addressed separately to explain the spatial distribution of patterns of biodiversity. In this study, we evaluated the integrated effects of biogeographical and environmental factors in structuring the diurnal amphibian anuran assemblages of the upper Madeira River, southwestern Amazonia. We used a sampling design involving 98 standardized units, distributed across seven locations covering both banks of the river's course in the state of Rondônia, Brazil. We conducted searches for frogs in three campaigns between February 2010 and February 2011, aiming to: (1) evaluate the effect of the Madeira River as a biogeographic barrier at the species‐assemblage level, and (2) test the influence of seven environmental variables (vegetation structure, vegetation cover, soil nutrients, soil structure, slope, elevation, and distance from the river bank) on the spatial structure of the frog assemblages, separately on each riverbank. Thirteen species of diurnal frogs were recorded, six of which were restricted to one of the river margins. Multivariate analysis of variance indicated a significant effect of the river as a barrier. Multiple regression analyses suggested that the environmental variables structuring frog assemblages differ on either side of the river. We found that both historical elements (on a regional scale) and environmental factors (at a local scale) shaped the occurrence and distribution of frog species in the study area.     

Masking interference and the evolution of the acoustic communication system in the Amazonian dendrobatid frog Allobates femoralis

The efficacy of communication relies on detection of species-specific signals against the background noise. Features affecting signal detection are thus expected to evolve under selective pressures represented by masking noise. Spectral partitioning between the auditory signals of co-occurring species has been interpreted as the outcome of the selective effects of masking interference. However, masking interference depends not only on signal's frequency but on receiver's range of frequency sensitivity; moreover, selection on signal frequency can be confounded by selection on body size, because these traits are often correlated. To know whether geographic variation in communication traits agrees with predictions about masking interference effects, we tested the hypothesis that variation in the male-male communication system of the Amazonian frog, Allobates femoralis, is correlated with the occurrence of a single species calling within an overlapping frequency range, Epipedobates trivittatus. We studied frogs at eight sites, four where both species co-occur and four where A. femoralis occurs but E. trivittatus does not. To study the sender component of the communication system of A. femoralis and to describe the use of the spectral range, we analyzed the signal's spectral features of all coactive species at each site. To study the receiver component, we derived frequency-response curves from playback experiments conducted on territorial males of A. femoralis under natural conditions. Most geographic variation in studied traits was correlated with either call frequency or with response frequency range. The occurrence of E. trivittatus significantly predicted narrower and asymmetric frequency-response curves in A. femoralis, without concomitant differences in the call or in body size. The number of acoustically coactive species did not significantly predict variation in any of the studied traits. Our results strongly support that the receiver but not the sender component of the communication system changed due to masking interference by a single species.     

Chromosomal Study of Colostethus brunneus from the Type Locality and Two Related Species (Anura – Dendrobatidae)

In this paper, we report a chromosomal study of three Brazilian species of Colostethus, C. brunneus from the type locality, Colostethus sp. (aff. trilineatus), and Colostethus sp., which is morphologically similar to C. brunneus. The diploid number for C. brunneus was 2n = 24 chromosomes, in agreement with that previously described for specimens from Peru. Colostethus sp. (aff. trilineatus) and Colostethus sp. showed a very similar karyotype with 22 chromosomes. The NOR was located on pair 3 in C. brunneus, on pair 4 in Colostethus sp. (aff. trilineatus), and on pair 2 in Colostethus sp. In one specimen of Colostethus sp., an additional NOR site was located on pair 7 in only one of the homologs. This extra Ag-NOR site was confirmed by FISH using an rDNA probe. In addition to the NOR location, the C-banding pattern was also species-specific, despite the similar chromosomal morphology of the species. These results indicate that although these species may be closely related, there is a clear dichotomy in their chromosome number.     

Beyond the river: underlying determinants of population acoustic signal variability in Amazonian direct-developing Allobates (Anura: Dendrobatoidea)

The multidimensional nature of animal signals makes acoustic traits potentially subject to different determinants. The Amazonian frogs Allobates nidicola and Allobates masniger have an allopatric distribution, occurring along the left and right sides of the Madeira River, respectively. These are two sister, phenotypically similar species whose eggs are deposited and develop entirely in a terrestrial nest. In this study, we analyzed 2,000 advertisement calls recorded from ten localities across Central Amazonia, in order to understand the role of determinants of acoustic signal variability at the population and species levels. We assessed, through nested analyses of variance, the differentiation of six characters of this sexual signal among populations and between interfluves. Moreover, we measured the degree of variability and the extent of temperature- and body size-induced plasticity in call traits. We also tested for isolation-by-distance effects in phenotypic differentiation through Mantel tests. Coefficients of variation were higher among than within populations for all call measurements. Spectral call properties were more distinctive than temporal traits among populations and species. Advertisement call traits showed strong temperature-induced plasticity (e.g., 45?% of the variation in note duration). In contrast, the effects of body size were restricted to frequency-related characters. The river barrier effect was significant among all the acoustic variables analyzed even after controlling for male body size. Geography (sampling locality) and body size also jointly affected call variability. No correlation between geographical and acoustic distances among populations was observed, suggesting that local stabilizing selective pressures have an important role in the evolution of call differentiation.     

Structure-anti-leukemic activity relationship study of ortho-dihydroxycoumarins in U-937 cells: Key role of the δ-lactone ring in determining differentiation-inducing potency and selective pro-apoptotic action

Previous studies indicated the need of at least one phenolic hydroxyl group in the coumarin core for induction of cytotoxicity in different cell lines. Herein, we present an exhaustive structure-activity relationship study including ortho-dihydroxycoumarins (o-DHC) derivatives, cinnamic acid derivatives (as open-chain coumarin analogues) and 1,2-pyrones (representative of the δ-lactone ring of the coumarin core), carried out to further identify the structural features of o-DHC required to induce leukemic cell differentiation and apoptosis in U-937 cells. Our results show for the first time that the δ-lactone ring positively influences the aforementioned biological effects, by conferring greater potency to compounds with an intact coumarin nucleus. Most tellingly, we reveal herein the crucial role of this molecular portion in determining the selective toxicity that o-DHC show for leukemic cells over normal blood cells. From a pharmacological perspective, our findings point out that o-DHC may be useful prototypes for the development of novel chemotherapeutic agents.