Comparison of Ribosomal and Isozymic Phylogenies of Tetrahymenine Ciliates

A recent analysis of sequence variations in ribosomal RNA's from 31 species of tetrahymenine ciliates groups them into 9 sets referred to as "ribosets." These species associations are not well correlated with the distributions of distinctive morphological characteristics. The phylogenetic structure suggests that modem "pyriform" tetrahymenines may be paraphyletic survivors of primitive design and that the morphologically distinctive forms may include examples of convergent evolution of derived forms. Alternatively, the common ancestor may have been a polymorphic species that has lost its plasticity in some derived lineages. In an attempt to test the ribosomal phylogeny, we here compare it with a phytogeny based on isozymic variation. The main features of the ribosomal and isozymic phylogenies are similar. The carnivorous (macrostome-forming) species are widely scattered in both, as are the bacteriophagous pyriform species. Isozymic and ribosomal analyses are optimally useful, however, in different contexts. Isozymic variations can distinguish species that are ribosomally identical. Ribosomal variations provide more secure evaluations of distant relationships.     

Parallel foraging cycles for different resources in leaf‐cutting ants: a clue to the mechanisms of rhythmic activity

1. Leaf‐cutting ants display regular diel cycles of foraging, but the regulatory mechanisms underlying these cycles are not well known. There are, however, some indications in the literature that accumulation of leaf tissue inside a nest dampens recruitment of foragers, thereby providing a negative feedback that can lead to periodic foraging. We investigated two foraging cycles occurring simultaneously in an Atta colombica colony, one involving leaf harvesting and the other exploiting an ephemeral crop of ripe fruit. 2. Leaf harvesting followed a typical diel pattern of a 10–12 h foraging bout followed by a period of inactivity, while fruit harvesting occurred continuously, but with a regular pre‐dawn dip in activity that marked a 24 h cycle. 3. Although the results of the present study are drawn from a single field colony, the difference found is consistent with a mechanism of negative feedback regulation acting in parallel on two resources that differ in their rates of distribution and processing, creating cycles of formation and depletion of material caches. 4. This hypothesis should provoke further interest from students of ant behaviour and some simple manipulative experiments that would begin to test it are outlined. Any role of resource caches in regulating foraging by Atta colonies may have similarities to the logistics of warehouse inventories in human economic activity.     

POWER AND SENSITIVITY OF THE SAME-DIFFERENT TEST: COMPARISON WITH TRIANGLE AND DUO-TRIO METHODS

Same-different, duo-trio and triangle discrimination methods were compared using vanilla flavored yogurt with and without added sugar as the medium. Two experiments were performed, one in controlled laboratory conditions and the other in conditions approximating more to consumer testing. A modification of the same-different test had greater power than the duo-trio of triangle tests. At higher sugar concentrations, d'values for the three methods were equivalent. Yet, at lower sugar concentrations, the same-different d'tended to be higher. The results are discussed in terms of Sequential Sensitivity Analysis, memory effects and changes between β and criteria.     

The Fine Structure of the Flagellum and Kinetoplast-Chondriome of Trypanosoma (Schizotrypanum) cruzi in Tissue Culture*

SYNOPSIS. Trypanosoma cruzi in tissue cultures was studied with the electron microscope after double fixation in glutaraldehyde and osmium tetroxide, and embedding in Epon. Previous findings on its fine structure were confirmed, and some new structures were found in the flagellum and kinetoplast-chondriome. In the flagellum, an intraflagellar body was found, similar to that observed in other trypanosomes, beginning at the base of the flagellum and running along the axial fibre bundle thruout its length. The axial fibre bundle is formed by interconnecting tubules, the outer ones apparently smooth, the inner ones with a helical substructure. Lateral extensions from the outer tubules in the flagellar bundle seem to enter the intraflagellar body. The kinetopiast in the leishmania bodies has the same electrondense structure described before. In the trypanosome form it has assumed a large spherical shape, in which the formerly short, compressed fibres have grown in length, are more dispersed and have an irregular shape. They are oriented in the direction of the body's length in parallel array. The whole formation is continuous with a long mitochondrion which begins in the region of the nucleus and extends up almost to the tip of the trypanosome. The matrix of the kinetoplast in these forms is electron-transparent; the matrix of the mitochondria is rather dense. In a few extracellular trypanosomes, a special structure was found in which the kinetoplast is composed of electron-transparent formations, arranged in orderly horizontal lines quite similar to the mitochondrial cristae of the parasite. The significance of this structure is uncertain.     

Dynamic subcellular localization of isoforms of the folate pathway enzyme serine hydroxymethyltransferase (SHMT) through the erythrocytic cycle of Plasmodium falciparum

Background

The folate pathway enzyme serine hydroxymethyltransferase (SHMT) converts serine to glycine and 5,10-methylenetetrahydrofolate and is essential for the acquisition of one-carbon units for subsequent transfer reactions. 5,10-methylenetetrahydrofolate is used by thymidylate synthase to convert dUMP to dTMP for DNA synthesis. In Plasmodium falciparum an enzymatically functional SHMT (PfSHMTc) and a related, apparently inactive isoform (PfSHMTm) are found, encoded by different genes. Here, patterns of localization of the two isoforms during the parasite erythrocytic cycle are investigated.

Methods

Polyclonal antibodies were raised to PfSHMTc and PfSHMTm, and, together with specific markers for the mitochondrion and apicoplast, were employed in quantitative confocal fluorescence microscopy of blood-stage parasites.

Results

As well as the expected cytoplasmic occupancy of PfSHMTc during all stages, localization into the mitochondrion and apicoplast occurred in a stage-specific manner. Although early trophozoites lacked visible organellar PfSHMTc, a significant percentage of parasites showed such fluorescence during the mid-to-late trophozoite and schizont stages. In the case of the mitochondrion, the majority of parasites in these stages at any given time showed no marked PfSHMTc fluorescence, suggesting that its occupancy of this organelle is of limited duration. PfSHMTm showed a distinctly more pronounced mitochondrial location through most of the erythrocytic cycle and GFP-tagging of its N-terminal region confirmed the predicted presence of a mitochondrial signal sequence. Within the apicoplast, a majority of mitotic schizonts showed a marked concentration of PfSHMTc, whose localization in this organelle was less restricted than for the mitochondrion and persisted from the late trophozoite to the post-mitotic stages. PfSHMTm showed a broadly similar distribution across the cycle, but with a distinctive punctate accumulation towards the ends of elongating apicoplasts. In very late post-mitotic schizonts, both PfSHMTc and PfSHMTm were concentrated in the central region of the parasite that becomes the residual body on erythrocyte lysis and merozoite release.

Conclusions

Both PfSHMTc and PfSHMTm show dynamic, stage-dependent localization among the different compartments of the parasite and sequence analysis suggests they may also reversibly associate with each other, a factor that may be critical to folate cofactor function, given the apparent lack of enzymic activity of PfSHMTm.     

The influence of elevated nitrate concentration on rate of leaf decomposition in a stream

SUMMARY.

• 1 Leaf decomposition was compared in two streams at the Coweeta Hydrologic Laboratory, North Carolina. U.S.A. One stream drains an undisturbed hardwood watershed, while the other drains a successional watershed subject to an insect outbreak. The successional watershed has elevated nitrate concentrations in the streamwater.
• 2 Both black locust (Robinia pseudo-acacia) and sweet birch (Betula lenta) leaf litter decomposed 2.8 times more rapidly in the stream with high nitrate concentrations.
• 3 The more rapid decay rates appeared to be partly due to accelerated microbial processing in response to nitrate enrichment, because microbial biomass (as ATP) was higher in the nitrate-enriched stream.
• 4 At each point in time, nitrogen and phosphorus content of the litter was lower in the high nitrate stream; however, there was no significant difference in nitrogen or phosphorus content at the same state of leaf decay in the two streams.

     

Evolution of Dendrocolaptes platyrostris (Aves: Furnariidae) between the South American open vegetation corridor and the Atlantic forest

The open vegetation corridor of South America is a region dominated by savanna biomes. It contains forests (i.e. riverine forests) that may act as corridors for rainforest specialists between the open vegetation corridor and its neighbouring biomes (i.e. the Amazonian and Atlantic forests). A prediction for this scenario is that populations of rainforest specialists in the open vegetation corridor and in the forested biomes show no significant genetic divergence. We addressed this hypothesis by studying plumage and genetic variation of the Planalto woodcreeper Dendrocolaptes platyrostris Spix (1824) (Aves: Furnariidae), a forest specialist that occurs in both open habitat and in the Atlantic forest. The study questions were: (1) is there any evidence of genetic continuity between populations of the open habitat and the Atlantic forest and (2) is plumage variation congruent with patterns of neutral genetic structure or with ecological factors related to habitat type? We used cytochrome b and mitochondrial DNA control region sequences to show that D. platyrostris is monophyletic and presents substantial intraspecific differentiation. We found two areas of plumage stability: one associated with Cerrado and the other associated with southern Atlantic Forest. Multiple Mantel tests showed that most of the plumage variation followed the transition of habitats but not phylogeographical gaps, suggesting that selection may be related to the evolution of the plumage of the species. The results were not compatible with the idea that forest specialists in the open vegetation corridor and in the Atlantic forest are linked at the population level because birds from each region were not part of the same genetic unit. Divergence in the presence of gene flow across the ecotone between both regions might explain our results. Also, our findings indicate that the southern Atlantic forest may have been significantly affected by Pleistocene climatic alteration, although such events did not cause local extinction of most taxa, as occurred in other regions of the globe where forests were significantly affected by global glaciations. Finally, our results neither support plumage stability areas, nor subspecies as full species. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 801–820.     

Benthic macroinvertebrate community structure, function and production with respect to habitat type, reach and drainage basin in the southern Appalachians (U.S.A.)

1. Benthic macroinvertebrates were sampled for 1 year to assess functional and taxonomic differences in invertebrate biomass and production with respect to habitat types, reaches and catchments in Wine Spring Basin, western North Carolina. Quantitative samples were collected from depositional, cobble-riffle and bedrock outcrop habitats at four stream reaches (two headwater sites, one second order, and one third order). Other measures included physical parameters, periphyton and organic matter standing crops. Invertebrate data from the Wine Spring catchment were also compared with data from another catchment (Ball Creek) within the same region. 2. The three habitat types had different current velocities and mean substratum particle sizes; both measures were greatest in bedrock outcrop habitats and lowest in depositional habitats. Organic matter standing crops, invertebrate functional group productivity and biomass also differed significantly with respect to habitat type. Cobble-riffle areas had the lowest standing crops of organic matter, invertebrate productivity and biomass. 3. Both invertebrate communities and organic matter standing crops differed significantly between the two headwater reaches. First- to third-order reaches differed in taxonomic composition at the genus level, yet had similar relative functional group productivity and biomass. 4. Annual mean invertebrate biomass and secondary production were greater in the Wine Spring Basin than in Ball Creek. Sites in both the Wine Spring and Ball Creek catchments, however, exhibited similar functional group distributions per habitat type. 5. Local geomorphology and related physical parameters influenced the structure of invertebrate functional group composition, and the distribution of organic matter standing crops. Furthermore, comparison of community structure in Wine Spring with that in Ball Creek suggested that taxonomic composition was more related to catchment-specific parameters (e.g. thermal regime, evolutionary history) than stream size.