Morphological variation and covariation in mandibular molars of platyrrhine primates

Molars are highly integrated biological structures that have been used for inferring evolutionary relationships among taxa. However, parallel and convergent morphological traits can be affected by developmental and functional constraints. Here, we analyze molar shapes of platyrrhines in order to explore if platyrrhine molar diversity reflects homogeneous patterns of molar variation and covariation. We digitized 30 landmarks on mandibular first and second molars of 418 extant and 11 fossil platyrrhine specimens to determine the degree of integration of both molars when treated as a single module. We combined morphological and phylogenetic data to investigate the phylogenetic signal and to visualize the history of molar shape changes. All platyrrhine taxa show a common shape pattern suggesting that a relatively low degree of phenotypic variation is caused by convergent evolution, although molar shape carries significant phylogenetic signal. Atelidae and Pitheciidae show high levels of integration with low variation between the two molars, whereas the Cebinae/Saimiriinae, and especially Callitrichinae, show greater variation between molars and trend toward a modular organization. We hypothesize that biomechanical constraints of the masticatory apparatus, and the dietary profile of each taxon are the main factors that determine high covariation in molars. In contrast, low molar shape covariation may result from the fact that each molar exhibits a distinct ecological signal, as molars can be exposed to distinct occlusal loadings during food processing, suggesting that different selective pressures on molars can reduce overall molar integration.     

Bacterioplankton Dynamics in the McMurdo Dry Valley Lakes, Antarctica: Production and Biomass Loss over Four Seasons

Abstract Research of the microbial ecology of McMurdo Dry Valley lakes has concentrated primarily on phototrophs; relatively little is known about the heterotrophic bacterioplankton. Bacteria represent a substantial proportion of water column biomass in these lakes, comprising 30 to 60% of total microplankton biomass. Bacterial production and cell numbers were measured 3 to 5 times, within four Antarctic seasons (October to January), in Lakes Fryxell, Hoare, and Bonney. The winter-spring transition (September to October) was included during one year. Lake Fryxell was the most productive, but variable, lake, followed by Lakes Bonney and Hoare. Bacterial production ranged from 0 to 0.009 μg C ml-1 d-1; bacterial populations ranged from 3.2 x 10(4) to 4.4 x 10(7) cells ml-1. Bacterial production was always greatest just below the ice cover at the beginning of the season. A second maximum developed just above the chemocline of all the lakes, as the season progressed. Total bacterioplankton biomass in the lakes decreased as much as 88% between successive sampling dates in the summer, as evidenced by areal integration of bacterial populations; the largest decreases in biomass typically occurred in mid-December. A forward difference model of bacterial loss in the trophogenic zone and the entire water column of these lakes showed that loss rates in the summer reached 6.3 x 10(14) cells m-2 d-1 and 4.16 x 10(12) cells m-2 d-1, respectively. These results imply that bacteria may be a source of carbon to higher trophic levels in these lakes, through grazing.     

Genetic relationships within and among Iberian fescues (Festuca L.) based on PCR-amplified markers.

The genus Festuca comprises approximately 450 species and is widely distributed around the world. The Iberian Penninsula, with more than 100 taxa colonizing very diverse habitats, is one of its main centers of diversification. This study was conducted to assess molecular genetic variation and genetic relatedness among 91 populations of 31 taxa of Iberian fescues, based on several molecular markers (random amplified polymorphic DNA, amplified fragment length polymorphisms, and trnL sequences). The analyses showed the paraphyletic origin of the broad-leaved (subgenus Festuca, sections Scariosae and Subbulbosae, and subgenus Schedonorus) and the fine-leaved fescues (subgenus Festuca, sections Aulaxyper, Eskia, and Festuca). Schedonorus showed a weak relationship with Lolium rigidum and appeared to be the most recent of the broad-leaved clade. Section Eskia was the most ancient and Festuca the most recent of the fine-leaved clade. Festuca and Aulaxyper were the most related sections, in concordance with their taxonomic affinities. All taxa grouped into their sections, except F. ampla and F. capillifolia (section Festuca), which appeared to be more closely related to Aulaxyper and to a new independent section, respectively. Most populations clustered at the species level, but some subspecies and varieties mixed their populations. This study demonstrated the value in combining different molecular markers to uncover hidden genetic relationships between populations of Festuca.     

Dehydration rate and time of desiccation affect recovery of the lichenic algae <Emphasis Type="Italic">Trebouxia erici</Emphasis>: alternative and classical protective mechanisms

The mechanisms involved in desiccation tolerance of lichens and their photobionts are still poorly understood. To better understand these mechanisms we have studied dehydration rate and desiccation time in Trebouxia, the most abundant chlorophytic photobiont in lichen. Our findings indicate that the drying rate has a profound effect on the recovery of photosynthetic activity of algae after rehydration, greater than the effects of desiccation duration. The basal fluorescence (F′_o) values in desiccated algae were significantly higher after rapid dehydration, than after slow dehydration, suggesting higher levels of light energy dissipation in slow-dried algae. Higher values of PSII electron transport were recovered after rehydration of slow-dried Trebouxia erici compared to rapid-dried algae. The main component of non-photochemical quenching after slow dehydration was energy dependent (q _E), whereas after fast dehydration it was photoinhibition (q _I). Although q _E seems to play a role during desiccation recovery, no significant variations were detected in the xanthophyll cycle components. Desiccation did not affect PSI functionality. Classical antioxidant activities like superoxide dismutase or peroxidase decreased during desiccation and early recovery. Dehydrins were detected in the lichen-forming algae T. erici and were constitutively expressed. There is probably a minimal period required to develop strategies which will facilitate transition to the desiccated state in this algae. In this process, the xanthophyll cycle and classical antioxidant mechanisms play a very limited role, if any. However, our results indicate that there is an alternative mechanism of light energy dissipation during desiccation, where activation is dependent on a sufficiently slow dehydration rate.     

Fluorescence resonance energy transfer and molecular modeling studies on 4',6-diamidino-2-phenylindole (DAPI) complexes with tubulin

The goal of this work was to determine the binding properties and location of 4',6-diamidino-2-phenylindole (DAPI) complexed with tubulin. Using fluorescence anisotropy, a dissociation constant of 5.2+/-0.4 microM for the DAPI-tubulin complex was determined, slightly lower than that for the tubulin S complex. The influence of the C-terminal region on the binding of DAPI to tubulin was also characterized. Using FRET experiments, and assuming a kappa2 value of 2/3, distances between Co2+ bound to its high-affinity binding site and the DAPI-binding site and 2',3'-O-(trinitrophenyl)guanosine 5'-triphosphate bound to the exchangeable nucleotide and the DAPI-binding site were found to be 20+/-2 A and 43+/-2 A, respectively. To locate potential DAPI-binding sites on tubulin, a molecular modeling study was carried out using the tubulin crystal structure and energy minimization calculations. The results from the FRET measurements were used to limit the possible location of DAPI in the tubulin structure. Several candidate binding sites were found and these are discussed in the context of the various properties of bound DAPI.     

Complex binding interactions between multicomponent mixtures and odorant receptors in the olfactory organ of the Caribbean spiny lobster Panulirus argus

Our study was designed to examine how components of complex mixtures can inhibit the binding of other components to receptor sites in the olfactory system of the spiny lobster Panulirus argus. Biochemical binding assays were used to study how two- to six-component mixtures inhibit binding of the radiolabeled odorants taurine, L-glutamate and adenosine-5'-monophosphate to a tissue fraction rich in dendritic membrane of olfactory receptor neurons. Our results indicate that binding inhibition by mixtures can be large and is dependent on the nature of the odorant ligand and on the concentration and composition of the mixture. The binding inhibition by mixtures of structurally related components was generally predicted using a competitive binding model and binding inhibition data for the individual components. This was not the case for binding inhibition by most mixtures of structurally unrelated odorants. The binding inhibition for these mixtures was generally smaller than that for one or more of their components, indicating that complex binding interactions between components can reduce their ability to inhibit binding. The magnitude of binding inhibition was influenced more by the mixture's precise composition than by the number of components in it, since mixtures with few components were sometimes more inhibitory than mixtures with more components. These findings raise the possibility that complex binding interactions between components of a mixture and their receptors may shape the output of olfactory receptor neurons to complex mixtures.      

Evaluating the forced oscillation technique in the detection of early smoking-induced respiratory changes

Background  

Early detection of the effects of smoking is of the utmost importance in the prevention of chronic obstructive pulmonary disease (COPD). The forced oscillation technique (FOT) is easy to perform since it requires only tidal breathing and offers a detailed approach to investigate the mechanical properties of the respiratory system. The FOT was recently suggested as an attractive alternative for diagnosing initial obstruction in COPD, which may be helpful in detecting COPD in its initial phases. Thus, the purpose of this study was twofold: (1) to evaluate the ability of FOT to detect early smoking-induced respiratory alterations; and (2) to compare the sensitivity of FOT with spirometry in a sample of low tobacco-dose subjects.