Edge effects on palm diversity in rain forest fragments in western Ecuador

At the edges of tropical rain forest fragments, altered abiotic and biotic conditions influence the structure and dynamics of plant communities. In Neotropical rain forests, palms (Arecaceae) are important floristic and ecological elements. Palms’ responses to edge effects appear to be idiosyncratic and to depend on the level of disturbance at edges. This paper explores how variation in forest structure at the edges of two old-growth forest fragments in a tropical rain forest in western Ecuador affects palms of different species, life-forms, and size classes. We investigate (1) how edge effects influence the relative proportion of palm adults and juveniles, (2) how distance from the forest edge affects palm density and species richness, (3) how altered forest structure along edges affects palm density. We found that at edges (1) palm communities had a lower proportion of adults relative to juvenile individuals compared to continuous forests, (2) the density of two species of palms and the overall species richness of the palm community tended to decrease toward the edges within forest fragments, and, (3) altered forest structure decreased the density of adult palms. Hence, edge effects on palms were controlled by the degree of modification of the forest structure, and by species responses to edge-related disturbance.     

mtDNA diversity in rhesus monkeys reveals overestimates of divergence time and paraphyly with neighboring species

Reconstructions of the human-African great ape phylogeny by using mitochondrial DNA (mtDNA) have been subject to considerable debate. One confounding factor may be the lack of data on intraspecific variation. To test this hypothesis, we examined the effect of intraspecific mtDNA diversity on the phylogenetic reconstruction of another Plio- Pleistocene radiation of higher primates, the fascicularis group of macaque (Macaca) monkey species. Fifteen endonucleases were used to identify 10 haplotypes of 40-47 restriction sites in M. mulatta, which were compared with similar data for the other members of this species group. Interpopulational, intraspecific mtDNA diversity was large (0.5%- 4.5%), and estimates of divergence time and branching order incorporating this variation were substantially different from those based on single representatives of each species. We conclude that intraspecific mtDNA diversity is substantial in at least some primate species. Consequently, without prior information on the extent of genetic diversity within a particular species, intraspecific variation must be assessed and accounted for when reconstructing primate phylogenies. Further, we question the reliability of hominoid mtDNA phylogenies, based as they are on one or a few representatives of each species, in an already depauperate superfamily of primates.      

Evidence for a catalytic Mg2+ ion and effect of phosphate on the activity of Escherichia coli phosphofructokinase-2: regulatory properties of a ribokinase family member

Phosphofructokinase-2 (Pfk-2) from Escherichia coli belongs to the ribokinase family of sugar kinases. One of the signatures observed in amino acid sequences from the ribokinase familiy members is the NXXE motif, which locates at the active site in the ribokinase fold. It has been suggested that the effect of Mg2+ and phosphate ions on enzymatic activity, observed in several adenosine kinases and ribokinases, would be a widespread feature in the ribokinase family, with the conserved amino acid residues in the NXXE motif playing a role in the binding of these ions at the active site [Maj, M. C., et al. (2002) Biochemistry 41, 4059-4069]. In this work we study the effect of Mg2+ and phosphate ions on Pfk-2 activity and the involvement of residue E190 from the NXXE motif in this behavior. The kinetic data are in agreement with the requirement of a Mg2+ ion, besides the one present in the metal-nucleotide complex, for catalysis in the wild-type enzyme. Since the response to free Mg2+ concentration is greatly affected in the E190Q mutant, we conclude that this residue is required for the proper binding of the catalytic Mg2+ ion at the active site. The E190Q mutant presents a 50-fold decrease in the kcat value and a 15-fold increment in the apparent Km for MgATP(2-). Inorganic phosphate, typically considered an activator of adenosine kinases, ribokinases, and phosphofructokinases (nonhomologous to Pfk-2) acted as an inhibitor of wild-type and E190Q mutant Pfk-2. We suggest that phosphate can bind to the allosteric site of Pfk-2, producing an inhibition pattern qualitatively similar to MgATP(2-), which can be reversed to some extent by increasing the concentration of fructose-6-P. Given that the E190Q mutant presents alterations in the inhibition by MgATP(2-) and phosphate, we conclude that the E190 residue has a role not only in catalysis but also in allosteric regulation.     

Formation of reactive oxygen species during one-electron reduction of noradrenochrome catalyzed by NADPH-cytochrome P-450 reductase

One-electron reduction of noradrenochrome catalyzed by NADPH-cytochrome P-450 reductase resulted primarily in the formation of o-semiquinone and, probably, also o-hydroquinone. Under aerobic conditions these reduced form(s) autoxidize, accompanied by the formation of reactive oxygen species, as revealed by continuous NADPH oxidation and oxygen consumption.

The presence of manganese-pyrophosphate complex contributed to autoxidation of the o-semiquinone during the reduction of noradrenochrome catalyzed by NADPH-cytochrome P-450 reductase, since the addition of the metal chelator diethylenetriamine pentaacetic acid (DETAPAC) resulted in a 34% inhibition of NADPH oxidation.

Oxygen in the ground state was found to be predominantly involved in the autoxidation of o-semiquinone during the reduction of noradrenochrome catalyzed by NADPH-cytocbrome P-450 reductase, since the addition of superoxide dismutase (SOD) to the incubation mixture only inhibited NADPH oxidation 13% and 6% in the absence and presence of DETAPAC, respectively.

The addition of catalase to the incubation mixture resulted in a slight increase in NADPH oxidation, both in the absence and in the presence of diethylenetriamine pentaacetic acid. However, no effect of catalase and SOD together on NADPH oxidation was observed, either in the absence or presence of DETAPAC.     

Genus delimitation,biogeography and diversification of Choristoneura Lederer (Lepidoptera: Tortricidae) based on molecular evidence

Widely known for pest species that include major modulators of temperate forests, the genus Choristoneura is part of the species‐rich tribe Archipini of leafroller moths (Tortricidae). Delimitation of the genus has remained unresolved because no phylogeny has included species endemic to Africa and studies have often omitted the type species of the genus. Further taxonomic confusion has been generated by the transfer of Archips occidentalis (Walsingham) to Choristoneura, creating a homonym with Choristoneura occidentalis Freeman, an important defoliator of North American forests. To define the limits of the genus, we reconstructed a phylogeny using DNA sequences for mitochondrial cytochrome oxidase subunit I and nuclear ribosomal 28S genes. Our ingroup included 23 Choristoneura species‐level taxa, complemented by a large sample of outgroups comprising 82 species of Archipini and other Tortricidae. We generated a time‐calibrated tree using fossil and secondary calibrations and we inferred biogeographic and diversification processes in Choristoneura. Our analysis recovered the genus as polyphyletic, with Archips occidentalis, Choristoneura simonyi and Choristoneura evanidana excluded from the main clade. Based on the recovered phylogenies and a redefinition, we restrict Choristoneura primarily to species with a northern hemisphere distribution. Our analysis supports A. occidentalis as the sister group of Cacoecimorpha pronubana, C. simonyi as the sister of ‘Xenotemna’ pallorana, and C. evanidana as the sister of Archips purpurana. A new combination is proposed: Archips evanidana comb.n. ; the availability of ‘Xenotemna’ as a valid name is discussed and A. occidentalis is considered as an orphaned name within the Archipini. We found support for a Holarctic origin of Choristoneura about 23 Ma, followed by early divergence in the Palearctic region. The main divergence occurred at 16 Ma, with one clade in the Nearctic and another in the Palearctic. Subsequent cladogenetic events were synchronous and related to herbivorous specialization, with each clade divided into coniferophagous and polyphagous lineages. Their specialization as conifer feeders temporally matched the expansion of boreal forest during the Miocene.