Quaternary origin and genetic divergence of the endemic cactus Mammillaria pectinifera in a changing landscape in the Tehuacán Valley, Mexico.

The endemic Mexican cactus, Mammillaria pectinifera, shows low dispersal capabilities and isolated populations within the highly dissected landscape of Tehuacán Valley. These characteristics can restrict gene flow and act upon the genetic divergence and speciation in arid plants. We conducted a phylogeographic study to determine if the origin, current distribution, and genetic structure of M. pectinifera were driven by Quaternary geomorphic processes. Sequences of the plastids psbA-trnH and trnT-trnL obtained from 66 individuals from seven populations were used to estimate genetic diversity. Population differentiation was assessed by an analysis of molecular variance. We applied a stepwise phylogenetic calibration test to determine whether species origin and genetic divergence among haplotypes were temporally concordant with recognizable episodes of geomorphic evolution. The combination of plastid markers yielded six haplotypes, with high levels of haplotype diversity (h = 0.622) and low nucleotide diversity (π = 0.00085). The populations were found to be genetically structured (F(ST) = 0.682; P < 0.00001), indicating that geographic isolation and limited dispersal were the primary causes of genetic population differentiation. The estimated origin and divergence time among haplotypes were 0.017-2.39 and 0.019-1.237 mya, respectively, which correlates with Pleistocene tectonics and erosion events, supporting a hypothesis of geomorphically-driven geographical isolation. Based on a Bayesian skyline plot, these populations showed long term demographic stability, indicating that persistence in confined habitats has been the main response of this species to landscape changes. We conclude that the origin and haplotype divergence of M. pectinifera were a response to local Quaternary geomorphic evolution.

Photosynthetically active radiation and carbon gain drives the southern orientation of Myrtillocactus geometrizans fruits.

The equatorial orientation of reproductive structures is known in some columnar cacti from extratropical deserts. It has been hypothesised that photosynthetically active radiation (PAR) interception is the main reason for this orientation, because of its key effect on nocturnal CO2 uptake. However, there are no studies addressing both the effect of PAR and its consequence, carbon gain, on fruit orientation. Accordingly, we tested whether PAR and carbon gain could explain the southern fruit orientation of Myrtillocactus geometrizans, an inter-tropical columnar cactus. We studied three populations of M. geometrizans in Mexico. For each population, azimuth of fruits, total daily PAR, nocturnal acid accumulation (NAA) and fruit production were measured. The relationships between rib orientation and number of fruits, as well as total daily PAR, were evaluated using periodic regressions. The effect of total daily PAR and NAA on number of fruits was assessed using generalised linear models. During spring, mean fruit orientation had a south azimuth for three populations. Likewise, rib orientation had a significant effect on fruit production, with the south-facing ribs having the maximum number of fruits. Total daily PAR was highest in the south-facing ribs, at least for those in the northern and central populations. Furthermore, during spring, there was a significant positive effect of total daily PAR and NAA on fruit production. Our results provide strong evidence that the higher carbon gain in equatorial ribs, through a highest interception of PAR, would be the responsible factor for equatorial orientation of fruits in an inter-tropical columnar cactus.

A new species of the genus periglischrus (Acari: Mesostigmata: Spinturnicidae) on Choeronycteris mexicana (Chiroptera: Phyllostomidae) in Central Mexico.

Periglischrus leptosternus new species was found on the bat Choeronycteris mexicana in the central part of Mexico. The female, male, and protonymph are described and illustrated.

Uptake of phenytoin by tissues of Mongolian gerbils.

1. Radioactive phenytoin was extracted from brain, cerebellum liver and kidney of i.p. injected Mongolian gerbils that were killed at hourly intervals. 2. The drug was extracted by two procedures. Procedure I involved acidification and chloroform extraction, the other, procedure II, an alkaline extraction, acidification and solubilization in chloroform (II). 3. Procedures I and II yielded 98 and 93% recoveries, respectively, from experiments performed either in vivo or in vitro. 4. Concentrations of labeled phenytoin found in brain, cerebellum, liver and kidney from the first to the fifth hour were 7.7, 7.8, 5.2, 4.0 and 2.2% (I) and 10.6, 8.5, 7.2, 4.0 and 2.8% (II) of the amount injected, correspondingly. 5. Concentrations of phenytoin in cerebellum were greater by a statistically significant margin than were those in other tissue at the third hour following the time of injection of radioactive phenytoin but liver and kidney concentrations were greater than cerebellum uptake at the fourth and fifth hour. 6. Brain showed the lowest incorporation of phenytoin throughout five hours.

Phenytoin effects on tissues of Mongolian gerbils (Meriones unguiculatus).

1. Phenytoin was intraperitoneally injected in six different experimental groups of adult Mongolian gerbils of both sexes at doses of 5, 100 and 150 mg/kg of body wt during 7 and 14 days. 2. Their brain, cerebellum, liver and kidney DNA, RNA and protein content were measured by conventional procedures. 3. The reference values of these rodents' cellular DNA were calculated through hepatocytes isolated following an intracardiac perfusion with collagenase in Hanks solution. 4. A concentration of 7.2 micrograms of DNA per 10(6) cells was found. 5. Phenytoin did not affect tissues of groups of animals receiving daily doses of 5 mg/kg of weight during 7 and 14 days of treatment; although a slight increase of protein concentration was observed in liver (P less than 0.01) and kidney (P less than 0.05). 6. RNA values were found to be significantly decreased in cerebellum (P less than 0.001), brain (P less than 0.05) and kidney (P less than 0.05) of those animals receiving the drug throughout 14 days. 7. DNA concentration was found to be decreased in all four tissues obtained from animals treated with daily doses of phenytoin of 100 (P less than 0.001) and 150 (P less than 0.001) mg/kg of body wt throughout 14 days. 8. These results indicate that phenytoin affected tissue cellularity only when administered at high doses and 14 days of interval of drug administration (P less than 0.001).

Conjugacion de hierro con difenilhidantoinato sodico. / Iron binding with sodium diphenylhydantoinate

Se pretende demostrar la union de la difenilhidantoina (DFH) y el difenilhidantoinato sodico (DFH-Na) con hierro (59 Fe y Fe) mediante un procedimiento radiometrico y uno colorimetrico. La ciclohexanona extrae totalmente el DFH-Na y DFH desde pH 2.0 hasta pH 13.0. En amortiguador de fosfatos se disolvieron 0.1 micrograma de 59 Fe, 59 Fe (0.1 micrograma) -DFH (0.1 micrograma) y 59 Fe (0.1 micrograma) DFH (1.0 micrograma/ml). Se seleccionaron valores de pH 2.0, 7.0 y 9.0. Solamente 28 por ciento del 59 Fe se desplazo hacia la ciclohexanona (Cx) a pH 9.0; en cambio, pasaron 30.5 y 95.9 por ciento (p < 0.00l) a la Cx a pH 7.5 y 9.0 en presencia de DFH -Na utilizados, unicamente se encontraron 12 +/- 4 micrograma/ml en solucion salina glucosada (S.S.G.) y en amortiguadora de fosfatos (PO4), ajustados a pH 6.4. En S.S.G. se encontraron 1.5 y 0.67 por ciento de union; en cambio, de hierro se encontraron unidos a DFH y DFH-Na en fosfatos 0.5 y 0.7 por ciento. Mediante ambos procedimientos queda comprobada la union de Fe a DFH