Hierarchical genetic structure and gene flow in three sympatric species of Amazonian rodents

The population genetic structure of three species of Amazonian rodents ( Oligoryzomys microtis, Oryzomys capito , and Mesomys hispidus ) is examined for mtDNA sequence haplotypes of the cytochrome b gene by hierarchical analysis of variance and gene flow estimates based on fixation indices ( N _ST) and coalescence methods. Species samples are from the same localities along 1000 km of the Rio Juruá in western Amazonian Brazil, but each species differs in important life history traits such as population size and reproductive rate. Average haplotype differentiation, hierarchical haplotype apportionment, and gene flow estimates are contrasted in discussing the current and past population structure. Two species exhibit isolation by distance patterns wherein gene flow is largely limited to geographically adjacent localities. Mesomys exhibits this pattern throughout its range along the river. More than 75% of haplotype variation is apportioned among localities and regions, and estimates of Nm for pair-wise comparisons are nearly always less than 1. Oligoryzomys shows weak isolation by distance, but only over the largest geographical distances. Nm values for this species are nearly always above 1 and most (about 80%) of haplotype variation is contained within local populations. In contrast, Oryzomys exhibits no genetic structure throughout its entire distribution; Nm values average 17 and nearly 90% of the total haplotype variance is contained within local populations. Although gene flow estimates are high, the pattern of Nm as a function of geographical distance suggests that this species experienced a more recent invasion of the region and is still in genetic disequilibrium under its current demographic conditions.     

Phylogenetic relationships among marsupial frog genera (Anura: Hylidae: Hemiphractinae) based on evidence from morphology and natural history

We reassess the phylogenetic relationships of genera of hemiphractine hylid frogs (Marsupial Treefrogs) and discuss the evolution of several distinctive characters within this group using parsimony analysis. Fifty-one morphological and life-history characters were sampled from two species of Cryptobatrachus , three species of Flectonotus , 17 species of Gastrotheca , all five species of Hemiphractus , and one species of Stefania as the ingroup and three hyline, one phyllomedusine, and one pelodryadine species as outgroups. Our results support the mon-ophyly of Flectonotus, Cryptobatrachus , and Hemiphractus. Gastrotheca is paraphyletic with respect to Hemiphractus , dorsal pouches were lost in the ancestor of Hemiphractus. Direct development is a synapomorphy for Hemiphractinae and tadpoles were regained independently several times. These results stand in stark contrast to the prevailing paradigm regarding marsupial frog relationships.     

The effects of Anabaena spiroides (Cyanophyceae) exopolysaccharide on copper toxicity to Simocephalus serrulatus (Cladocera, Daphnidae)

1. This work investigated the consumption of a microalgal (Anabaena spiroides) exopolysaccharide by the cladoceran Simocephalus serrulatus (Cladocera, Daphnidae) and its effect on copper toxicity. 2. Total organic carbon concentration was used to quantify the microalgal exopolysaccharide. Both copper‐complexed exopolysaccharides and copper‐free exopolysaccharides were taken up by S. serrulatus. 3. A reduction of free copper ions was obtained in the presence of A. spiroides exopolysaccharide. Copper toxicity (EC₅₀) and zooplankton concentrations were inversely correlated to exopolysaccharide concentration in experimental media. 4. An increase of free copper ions in experimental media was obtained after exopolysaccharide consumption, suggesting that S. serrulatus excreted copper to the surrounding environment.     

锁阳和肉苁蓉寄生方式的区别

锁阳和肉苁蓉都是中医药里重要的补益类药材,但由于过度采挖和采挖方式不当,目前它们的野生资源已濒临枯竭。肉苁蓉和锁阳分别是我国濒危和易危珍稀植物,研究二者寄生方式的特点与区别不仅可以促进锁阳和肉苁蓉的人工栽培,从而使野生药材得到一定的保护,而且对了解寄生植物在荒漠地区等极端严酷环境中的适应机制具有重要的生态学意义。该研究采用形态学观察结合常规石蜡切片法,对锁阳和肉苁蓉分别在各自寄主植物上的寄生方式进行了研究。结果表明：(1)锁阳的营养繁殖体在寄主植物根部呈串状分布,与寄主植物的连接方式属于非末端寄生;锁阳的吸器侵入寄主根系韧皮部和木质部的一部分区域,但是韧皮部和木质部大部分区域未被锁阳吸器占据,即有部分营养物质被锁阳“截取”。(2)肉苁蓉在其肉质茎基部长出新的芽体,与寄主植物的连接方式属于末端寄生;肉苁蓉的吸器侵入寄主根韧皮部和木质部全部区域。因此,锁阳寄生后,被寄生的寄主根依然能够向前生长,具有正常的功能;肉苁蓉寄生后,寄生点的寄主根失去根系的正常功能,成为一个为肉苁蓉生长发育提供营养物质的“输送通道( Transport channel)”。     

Structural and functional differentiation of two clinally distributed glucosephosphate isomerase allelic isozymes from the teleost Fundulus heteroclitus

The teleost Fundulus heteroclitus (L.) possesses two loci, Gpi-A and Gpi-B, for the glycolytic enzyme, glucose-phosphate isomerase (GPI; D- glucose-6-phosphate ketol-isomerase; E.C. 5.3.1.9). The Gpi-B locus is polymorphic in Fundulus, with two common alleles, Gpi-Bb and Gpi-Bc, distributed in a clinal manner in populations along the east coast of North America. Since this clinal distribution is strongly correlated with a temperature gradient, we asked whether the GPI-B2 allozymes were functionally adapted to the thermal environment in which a given phenotype predominated. The two major GPI-B2 allozymes were purified to homogeneity and were characterized as to molecular weight, isoelectric pH, thermal denaturation, and kinetic parameters. Both GPI-Bb2 and GPI- Bc2 allozymes have molecular masses of 110 kD, and they have isoelectric pHs of 6.4 and 6.6, respectively. The GPI-Bb2 allozyme was more stable to thermal denaturation than was the GPI-Bc2 enzyme. Kinetic properties of the allelic isozymes were investigated both as a function of pH and as a function of temperature. At 25 degrees C, over the pH range considered, there were no significant differences between allozymes, either in Km for fructose-6-phosphate or in Ki for 6- phosphogluconate, but apparent Vmax values differed between pH 7.5 and pH 8.5. All steady-state kinetic parameters showed strong temperature dependence, but the allozymes differed only in the Ki for 6- phosphogluconate at temperatures greater than 30 degrees C. On the basis of the observed structural and functional differences alluded to above, the hypothesis that the major allelic isozymes of the Gpi-B locus were functionally equivalent was rejected. However, it is not yet known whether these structural and functional differences have any significance at higher levels of biological organization.      

Correlation of thrombin-induced glycoprotein V hydrolysis and platelet activation

To assess the possibility that hydrolysis of the platelet surface thrombin substrate, glycoprotein V, is a necessary step in thrombin-induced platelet activation, thrombin-catalyzed hydrolysis of glycoprotein V was correlated with thrombin-induced platelet activation. Hydrolysis of tritium-labeled glycoprotein V on washed human platelets was measured by the appearance of a labeled supernatant fragment, and platelet activation was measured as secretion of ATP. Hydrolysis of glycoprotein V was linear with respect to both thrombin concentration and time of incubation. The extent of platelet activation was correlated with the rate of hydrolysis but not with the amount hydrolyzed. Maximum platelet activation could be obtained with thrombin treatments resulting in hydrolysis of as little as 4% of glycoprotein V per min. Glycoprotein V was partially removed from platelets by pretreatment with either platelet calcium-dependent protease or chymotrypsin. The rate of thrombin-catalyzed hydrolysis of the remaining glycoprotein V from these pretreated platelets was as little as 1.5% the rate from control platelets, but there was no impairment of the extent of platelet activation. Thus, these protease-pretreated platelets compared with control platelets showed a different correlation of glycoprotein V hydrolysis with platelet activation. Glycoprotein V was also partially removed by pretreatment of prostacyclin-inhibited platelets with thrombin. After removal of thrombin and prostacyclin, these platelets were desensitized to subsequent activation by thrombin. Incubation of desensitized platelets with nonsaturating levels of thrombin led to less than 25% of the activation seen with control platelets but to a slightly greater hydrolysis of glycoprotein V. Thus, the desensitization to thrombin was not due to loss of ability of the activating thrombin to hydrolyze glycoprotein V. These results do not exclude a role for glycoprotein V as a component of the platelet thrombin receptor, but they indicate that there is no simple relationship between thrombin-induced hydrolysis of glycoprotein V and platelet activation.     

Regulation of platelet phosphorylase.

A sensitive fluorimetric enzyme assay was developed for study of activation of glycogen phosphorylase (EC 2.4.1.1) in intact platelets and in platelet extracts. Activity was calculated as AMP independent (activity in the absence of AMP), total (activity in the presence of 1 mM AMP), and AMP dependent (difference between AMP independent and total). The following observations were made with intact rat platelets. (1) Stimulation of platelets with thrombin caused a 7-fold increase in total activity, with increases in both AMP-dependent and AMP-independent activities. Maximum activation was obtained within 10 s after addition of thrombin. (2) The divalent cation ionophore A23187 caused a similar, though less pronounced, activation of phosphorylase. (3) Acceleration of glycogenolysis by inhibition of respiration with cyanide caused similar changes in phosphorylase activity but with the maximum effect observed only after 45 s. (4) Dibutyryl cyclic AMP had two effects; it partially activated phosphorylase and blocked further activation by thrombin, but not A23187. Similar effects were observed with human platelets, but low resting levels of phosphorylase activity could not be maintained so that changes were not as large as with rat platelets. Experiments with extracts of rat platelets gave the following results. (1) Phosphorylase activity in many extracts of non-stimulated platelets could be increased by incubation with Mg2+-ATP and Ca2+; ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) partially inhibited. (2) In some extracts there was essentially no activation by incubation with Mg2+-ATP and Ca2+, but addition of cyclic AMP GAVE PARTIAL ACTIVATIon while addition of rabbit muscle phosphorylase kinase gave full activation. (3) Incubation of extracts of thrombin-stimulated platelets caused conversion of AMP-dependent to AMP-indeptndent activity. It is concluded that platelet phosphorylase exists in an inactive and two active forms. Conversion of the inactive to the active forms and of the AMP-dependent to the AMP-independent form is catalyzed by a kinase(s) that requires Ca2+ for full activity and is activated through a cyclic AMP-mediated process. The major change following physiological stimulation is an increase in both active forms, with little change in their ratio.     

Hair Cell Interactions in the Statocyst of Hermissenda

Hair cells in the statocyst of Hermissenda crassicornis respond to mechanical stimulation with a short latency (<2 ms) depolarizing generator potential that is followed by hyperpolarization and inhibition of spike activity. Mechanically evoked hyperpolarization and spike inhibition were abolished by cutting the static nerve, repetitive mechanical stimulation, tetrodotoxin (TTX), and Co⁺⁺. Since none of these procedures markedly altered the generator potential it was concluded that the hyperpolarization is an inhibitory synaptic potential and not a component of the mechanotransduction process. Intracellular recordings from pairs of hair cells in the same statocyst and in statocysts on opposite sides of the brain revealed that hair cells are connected by chemical and/or electrical synapses. All chemical interactions were inhibitory. Hyperpolarization and spike inhibition result from inhibitory interactions between hair cells in the same and in opposite statocysts.