Do changes in skull size of South American sea lions reflect changes in population density?

Populations of the South American sea lion (SASL, Otaria byronia) have been intensely exploited for leather and oil in different parts of its distribution range throughout the 19th and 20th centuries, generating large changes in abundance. In Patagonia, the SASL population was reduced by more than 90% of its original abundance, and it began to recover after sealing ended. The aim of this work was to assess changes in size and shape of the skull related to changes in population abundance during the last 100 years. Using geometric morphometry techniques, we analyzed 145 individuals (68 males and 77 females) from Patagonia. Skulls were classified by sex, time period (harvest vs. postharvest), and decades of individual's birth. Results indicated that there were differences in skull size but not in shape discriminated by time period. Moreover, individuals of the postharvest period showed a decrease in the skull size during the last two decades, coinciding with the recovery in population abundance. Our results suggest the existence of a density-dependence response in somatic growth of SASL population of Patagonia.     

Are RB proteins a potential substrate of Pin1 in the regulation of the cell cycle?

RB family members are post-transductionally regulated proteins and phosphorylation at Ser/Thr residues leads to their gradual inactivation. Cyclin/cdk complexes are mainly responsible for the regulation of these pocket proteins, which is crucial for release of E2F factor. Despite the fact that E2F release is a phosphorylation-dependent process, it is still not evident how phosphorylation physically determines the shift from the active to the inactive feature of RB molecules. We would like to put forward the hypothesis that Pin1 is involved in RB proteins phosphorylation and E2F release, suggesting an additional post-translational level of control on this family of molecules.     

Do evolutionary changes in cytochrome c structure reflect functional adaptations?

Following the demonstration that the rate of evolutionary change in the amino acid sequences of cytochromes c of eukaryotic species was not constant either for a single line of phylogenetic descent during different evolutionary intervals or for separate lines of descent, the concept that neutral mutations account for the vast majority of the evolutionary variations could no longer be accepted. Previous studies had shown that all eukaryotic cytochromes c tested appeared to be functionally indistinguishable in their reaction with mitochondrial respiratory chain components. However, an examination of the kinetics at low ionic strength led to the discovery of a high affinity reaction of cytochrome c with cytochrome c oxidase that revealed large differences in activity between the cytochromes of the horse, baker's yeast and the protist Euglena. Observed Km values for this reaction of 10(-7) to 10(-8) M appear to represent actual dissociation constants, as demonstrated by direct binding studies of cytochrome c with purified cytochrome c oxidase. The high affinity reaction is sensitive to ionic strength and inhibited by ADP and ATP in the range of physiological concentrations, ATP being three times as effective as ADP. The possibility is discussed that this effect of ATP on cytochrome c binding to its oxidase could provide the basis of a mechanism for mitochondrial respiratory control. The demonstration of differences between cytochrome c of various species in this kinetic system opens the way to a systematic study of the possible evolutionary adaptations of cytochromes c to their oxidases.     

Can a Ca2+ pump in the endoplasmic reticulum of the Lepidium root be the trigger for rapid changes in membrane potential after gravistimulation?

Since gravistimulation is followed by alterations in the external current symmetry (Behrens et al., 1982), the effect of gravistimulation on cellular membrane potential was investigated using conventional glass microelectrode techniques. The resting potential of statocytes in a vertically oriented root is approx. -118 mV. Upon gravistimulation, the membrane potential is temporarily depolarized (lag time = 2 s) to a potential of approx. -93 mV. This depolarization is only observed in statocytes located on the physically lower root flank while those on the corresponding upper flank become weakly hyperpolarized (approx. -13 mV). These results reflect altered ion fluxes across the plasma membrane. The perception of gravistimulus was suggested to result from a pressure of the amyloplasts on the distal endoplasmic reticulum (ER) of the statocytes (Sievers and Volkmann, 1972). A causal relationship between changes in ER-amyloplast interactions and the rapid alterations in plasma membrane potential described above is not known. A candidate for such an intracellular messenger is Ca2+. As a first step in establishing the validity of such an assumption, we have isolated ER membranes from roots. When incubated with micromolar concentrations of Ca2+, the vesicular membrane fraction accumulates Ca2+. The accumulation is ATP-dependent and -specific and is directly coupled to ATP hydrolysis since a protonophore shows no inhibitory effect. Thus, in analogy to the sarcoplasmic reticulum of muscle, regulation of an ER-localized Ca2+ compartment might be an important step in such complex processes as stimulus-transduction in gravitropism.     

Do seasonal changes in numbers of aerially dispersing spiders reflect population density on the ground or variation in ballooning motivation?

Groups of linyphiid spiders (Erigone spp.) (Araneae, Linyphiidae), collected at intervals from arable land, were tested in laboratory bioassays to determine the proportion of individuals that exhibited ballooning behaviour on each field sampling occasion. There was no significant variation in the proportions of spiders in each test group ballooning in the laboratory over a year. Investigations of ground density and aerial dispersal, in a grass field and a winter-wheat field, confirmed that peaks in numbers of spiders observed ballooning in the field generally coincided with population peaks in the summer and autumn. Significant correlations between ground populations and aerial catches were found for total spiders, immature spiders, and Bathyphantes gracilis (Blackwall) in both fields, adult spiders in the grass field, Erigone spp. in the grass, and Meioneta rurestris (C.L. Koch) in the wheat. The other groups analysed, Lepthyphantes tenuis (Blackwall) in both fields, Erigone spp. in wheat, and M. rurestris in grass, showed similar but non-significant trends. No significant difference was found between overall ground-to-air ratios for males compared to females, but adult spiders were more likely to balloon than immatures.     

Do the long-term changes in zooplankton biomass indicate changes in fish stock?

The narrow, 53.5 m deep and 42 km long Slapy reservoir was sampled at 3-week intervals at a standard sampling station 9 km from the dam during the years 1964–2001. The chlorophyll-a increased relatively more than the total phosphorus concentration. The relative increase in the biomass of crustaceoplankton larger than 0.2 mm and also that of its cladoceran and copepod component was in-between. The biomass of copepods nearly equaled that of cladocerans. The seasonal maximum of copepods preceded that of cladocerans. The increase of the means of these maxims in subsequent decennia did not fully follow the general increase. In the last decennium compared to previous decennia there has been a clear increase of both taxonomical groups in the second half of summer and in the first half of autumn. The percentage of cladocerans larger than 0.71 mm determined in the period 1985–2001 decreased. In connection with the increase of the biomass of zooplankton this indicates an increase in the fishstock, especially of the fraction of small fish. The decrease in large cladocerans was distributed nearly uniformly over the season and is larger between the means of the 3-week intervals in the 1985–1990 period and 1991–1995 period than between the last one and the 1996–2001 period. The broad spring maximum is not uniform in individuals years. There are two subsequent high values the relation of which differs in different years in height and date. The two spring values for the impact of fish on the zooplankton are probably due to the spawning activities of two groups of fish, probably percids and cyprinids. The minimum percentage of the large cladocerans in autumn can be connected with the increasing size and therefore increased feeding activity of the yearlings in the period of decreasing biomass of zooplankton. The later mild increase can be connected to the decreased activity of cyprinids in the period of decreasing low temperature.     

Are there changes in postural regulation across the lifespan?

Abstract

The purpose was to obtain parameters of postural regulation (n?=?1724) of asymptomatic subjects (6–97 years). The maximum postural stability and capacity of postural subsystems were calculated for the age ranges from 34 to 35 years (men) and from 38 to 44 years (women). A significant decline in postural performance was observed in the 40s (men) and 50s (women). Data can be used in the evaluation of dizziness and balance disorders in people of all ages.     

Mitochondrial membrane potential: a trait involved in organelle inheritance?

Which mitochondria are inherited across generations? Are transmitted mitochondria functionally silenced to preserve the integrity of their genetic information, or rather are those mitochondria with the highest levels of function (as indicated by membrane potential Δψm) preferentially transmitted? Based on observations of the unusual system of doubly uniparental inheritance of mitochondria and of the common strictly maternal inheritance mode, I formulate a general hypothesis to explain which mitochondria reach the primordial germ cells (PGCs), and how this happens. Several studies indicate that mitochondrial movements are driven by microtubules and that mitochondria with high Δψm are preferentially transported. This can be applied also to the mitochondria that eventually populate embryonic PGCs, so I propose that Δψm may be a trait that allows for the preferential transmission of the most active (and healthy) mitochondria. The topics discussed here are fundamental in cell biology and genetics but remain controversial and a subject of heated debate; I propose an explanation for how a Δψm-dependent mechanism can cause the observed differences in mitochondrial transmission.     

New mechanism for post-translational processing during assembly of a cytoplasmic membrane protein?

Insertion of nitrate reductase into the Escherichia coli cytoplasmic membrane was examined by following the fate of pulse-labeled enzyme in both the membrane and cytoplasm during various times after the addition of an unlabeled chase. The polypeptide composition of this labeled enzyme was determined by autoradiography of immunoprecipitated material after separation on sodium dodecyl sulfate-polyacrylamide gels. The data presented here indicate that immediately after appropriate insertion of the enzyme into the membrane, a post-translational event occurs which converts the cytoplasmically synthesized form of subunit B (B') to the form found in the completely assembled enzyme (B). B' is distinguished from B by its more rapid electrophoretic mobility. B' was found in the cytoplasm of all strains tested, in the membrane of strains with defects in enzyme insertion (hemA and chlE), and as a transient component in the membrane of wild-type cells.     

Apparent “mild depolarization of the inner mitochondrial membrane” as a result of a possible generation of the outer membrane potential

Recently reported kinase-linked mild depolarization of mitochondria, which prevents the generation of the reactive oxygen species (ROS) and disappears in various organs of the old mice, has been assumed to represent a crucial component of the mitochondrial anti-aging program. To measure mitochondrial inner membrane potential (IMP), the authors used fluorescent probe safranin O⁺. It is widely accepted that the accumulation of such cationic probes in the mitochondrial matrix depends exclusively on IMP, thus completely ignoring the possibility of the outer membrane potential (OMP) generation. However, computational analysis performed in the presented work suggests that the kinase-linked generation of the positive OMP might take place under the described conditions, because the measured potential includes the algebraic sum of both IMP and OMP. Alternatively to the suggested mild depolarization of mitochondria, the reported experimental data might reflect mainly a change of the positive OMP generated by the VDAC-kinase complexes. We also demonstrate that the reported in the literature mitochondrial hyperpolarization induced by erastin (known to prevent VDAC-tubulin interactions) and the depolarization caused by the mitochondrial VDAC knockdowns in the cancer cells might actually represent a decrease or increase, respectively, of the magnitude of the kinase-linked positive OMP. This is consistent with our hypothesis that VDAC voltage gating by the kinase-linked metabolically-dependent OMP plays a very important physiological role in regulating the cell energy metabolism under normal and pathological conditions, in the maintenance of the cell death resistance and even in the genetic aging program.     

Does a lateral gradient of membrane potential on the plasma membrane of growing pollen tube of germinating pollen grain exist?

The data presented in the article by Breigina et al. (2009) "Changes in the membrane potential during pollen grain germination and pollen tube growth" (Tsitologiya. 51 (10): 815-823) and concerning the measurement of electric membrane potential (Delta Psi) on the plasma membrane of growing pollen tube of germinating pollen grain with the use of fluorescent potential-sensitive dye, di-4-ANEPPS, were critically analyzed in order to clarify whether a lateral gradient of Delta Psi on this membrane indeed exists. This analysis showed that the main conclusion of the authors of the above article on the existence of polar distribution of Delta Psi along the pollen tube plasma membrane is not in accordance with a number of known peculiarities of di-4-ANEPPS behavior in biological membranes and requires a significant revision. The findings in question reported by the authors, in my opinion, might be interpreted as evidence for the presence on the plasma membrane of growing pollen tube not only the membrane potential Delta Psi but also lateral gradient of so called intra-membrane dipole potential. Based on the comments made, another interpretation of the experimental results described by Breigina et al. has been offered. In addition, some drawbacks in the methodology used by the authors for measurement of Delta Psi with other fluorescent potential-sensitive dye, DiBAC3(3), are also shortly considered.     

Strain-specific differences in the regulation of the hepatic cytoplasmic 17β-hydroxysteroid dehydrogenase activity of the rat

• 1.1. The effect of prepuberal gonadectomy of Sprague-Dawley/NIH/HAN rats on cytoplasmic 17β-hydroxysteroid dehydrogenase was examined on day 30, 45, 60, 75, 90 and 105 of life.
• 2.2. The activity in male rats was not significantly affected by gonadectomy, whereas the activity in females showed an age-dependent oestrogen dependency.
• 3.3. This age-dependent oestrogen dependency could also be demonstrated in 5α-dihydrotestosterone treated intact females.
• 4.4. Cytoplasmic 17β-hydroxysteroid dehydrogenase activity of female Chbb:THOM rats also showed an age-dependent oestrogen dependency, whereas the enzyme activity of male rats of this strain showed a distinct androgen dependency absent in Sprague-Dawley/NIH/HAN rats.
• 5.5. On the basis of previous investigations it is concluded that the androgen dependency of the enzyme activity of male Chbb:THOM rats has been bred into this strain in the period 1974–1977.

     

Do New Zealand invertebrates reflect the dominance of birds in their evolutionary history?

Pre-human New Zealand had some unusual feeding guilds of birds (e.g. the herbivorous moa fauna), thought to have developed as a result of the absence of a ?normal? mammal fauna. Insectivorous birds, on the other hand, are an integral part of all the world?s ecosystems, regardless of the presence or absence of mammals. While it is acknowledged the overall predation impact from birds in New Zealand is unlikely to have differed greatly from elsewhere, the low impact of mammalian insectivores (apart from microbats), coupled with the presence of a specialised avian feeding guild that concentrated on ground-active prey, might have exerted certain unique selection pressures. Do New Zealand invertebrates reflect this? It would be necessary to compare the New Zealand invertebrate fauna with that of mammal-dominated lands in greater detail than is available today before we could assert whether any unique anti-predator characteristics have evolved. Knowledge of the insects that succumbed to extinction when mammals invaded New Zealand should provide clues to avian-adapted features that might have rendered them particularly vulnerable to introduced rodents. Predation by kiwi (Apteryx spp.), an extraordinarily mammal-like nocturnal bird, may to some extent have prepared the invertebrate fauna for the arrival of small mammals.     

Do faunal assemblages reflect the exchange intensity in groundwater zones?

The exchange of water with groundwater is a key determinant of water quality and faunal assemblage. Water exchange not only occurs with running waters, but also through percolation, interception (soil, porous alluvium), and evaporation. The aim of this study was to identify how different types of exchange were related to the groundwater faunal assemblage of an alluvial aquifer. Hydrological exchange is largely governed by pore space and thus ultimately by geological formation. In the Marbling Brook catchment of Western Australia the different geological formations did not eventuate in hydrochemically distinct groundwater zones. The cluster analysis of faunal assemblages revealed five groups within the faunal samples which did not reflect spatial patterns such as geological, chemical or topographic features. Discriminant analysis showed that these five groups were best characterized by a range of abiotic features including dissolved oxygen, land-use, and temperature. These variables signal different types and intensities of exchange with the surface. Handling editor: K. Martens     

Do peptide-induced changes in feeding occur because of changes in motivation to eat?

The usual paradigm in which peptides are tested for their effect on food intake involves measuring intake of readily available food. In the lever press apparatus, the subjects must "work" to get food. Such work has traditionally been used as a means of measuring motivation. Mice were trained to press a lever for milk reinforcement. After achieving a stable level of performance, we tested the effects of gastrin-related peptide (GRP), bombesin (BBS) and cholecystokinin octapeptide (CCK-8) on lever pressing. All three peptides suppressed lever pressing for milk reinforcement. Prefeeding mice with milk increased the suppression of lever pressing to a greater extent in peptide-treated mice than in saline-treated mice. As the duration of prefeeding increased, lever pressing decreased. When mice were required to make more lever presses to obtain milk, both saline- and CCK-8-treated mice increased their lever pressing. However, saline-treated mice pressed at a higher rate than CCK-8-treated mice. Unlike the results obtained with saline and CCK-8, administration of a known gustatory adversant, lithium chloride, suppressed lever pressing to the same degree in mice fed or not fed prior to training. The results are consistent with the hypothesis that these peptides act as satiety agents.     

Allosterism in membrane binding: a common motif of the annexins?

Annexins are a family of proteins generally described as Ca(2+)-dependent for phospholipid binding. Yet, annexins have a wide variety of binding behaviors and conformational states, some of which are lipid-dependent and Ca(2+)-independent. We present a model that captures the cation and phospholipid binding behavior of the highly conserved core of the annexins. Experimental data for annexins A4 and A5, which have short N-termini, were globally modeled to gain an understanding of how the lipid-binding affinity of the conserved protein core is modulated. Analysis of the binding behavior was achieved through use of the lanthanide Tb(3+) as a Ca(2+) analogue. Binding isotherms were determined experimentally from the quenching of the intrinsic fluorescence of annexins A4 and A5 by Tb(3+) in the presence or absence of membranes. In the presence of lipid, the affinity of annexin for cation increases, and the binding isotherms change from hyperbolic to weakly sigmoidal. This behavior was modeled by isotherms derived from microscopic binding partition functions. The change from hyperbolic to sigmoidal binding occurs because of an allosteric transition from the annexin solution state to its membrane-associated state. Protein binding to lipid bilayers renders cation binding by annexins cooperative. The two annexin states denote two affinities of the protein for cation, one in the absence and another in the presence of membrane. In the framework of this model, we discuss membrane binding as well as the influence of the N-terminus in modifying the annexin cation-binding affinity by changing the probability of the protein to undergo the postulated two-state transition.     

Do single mitochondria contain zones with different membrane potential?

Observations of Lan Bo Chen’s group using a mitochondria-selective fluorochrome 5,5’,6,6’- tetrachloro- 1,1’,3,3’- tetraethylbenzimidazolocarbocyanine iodide (JC-1) indicate that mitochondria in situ may have zones of different electrochemical potential along their length. This was indicated by the formation of J-aggregates of this dye at distinct sites along a single mitochondrion. Also, intensity variations along single mitochondria were found with diamino-styryl-pyridinium methiodide (DASPMI), another fluorochrome that selectively stains mitochondria depending on their electrochemical potential. DASPMI exchanges easily with the cytoplasm and changes its quantum yield when bound to mitochondrial membranes. Therefore, fluorescence intensity is primarily controlled by the membrane environment rather than by mass accumulation. Two possible explanations of intramitochondrial fluorescence intensity variations have to be discussed: variations in the amount of mitochondrial inner membrane per unit of projection area (or voxel), and differences in the electrochemical gradient. This problem has been approached by comparing fluoro-micrographs of mitochondria in endothelial cells stained with either JC-1 or DASPMI with electron micrographs of the same mitochondria after fixation with glutardialdehyde and osmium tetroxide and ultrathin sectioning. JC-1 red fluorescence (revealing J-aggregate formation) as well as high-intensity staining with DASPMI correlate roughly with the local thickness of mitochondria; no differences in the crista organization are revealed for those areas or mitochondria exhibiting red JC-1 fluorescence and those with green fluorescence. The distance between red fluorescing areas in a single mitochondrion seem to be caused by competition for dye molecules placed in between centres of JC-1 aggregation. Isolated mitochondria are of uniform small size and spherical shape; therefore, no differences in shape interfere with JC-1 staining. Thus JC-1 may be an appropriate indicator of membrane potential in isolated mitochondria. In living cells mitochondria often are large and elongated, and thus the situation is not straightforward to interpret. However, evidence is provided that there are submitochondrial zones, which differ in membrane potential from one adjacent area to another, because DASPMI staining of intramitochondrial zones reveals differences in fluorescence intensity and preferred photodamage of these areas. In some cases separation of the zones of higher membrane potential by cristae traversing the whole diameter of a mitochondrion has been observed. Local photobleaching of stained mitochondria results in a loss of fluorescence along the total length of a mitochondrion. However, this type of bleaching develops over tens of seconds, not in the very short time range (e.g. ms) expected from the discharge of all the membranes if they were electrically coupled.     

Do leaf margins of the temperate forest flora of southern South America reflect a warmer past?

Aim   Our aims were: (1) to characterize the linear relationship between the proportion of woody dicotyledonous species with entire-margined leaves ( E ) and mean annual temperature (MAT) from a southern temperate flora that still harbours many lineages that originated under warmer climates; (2) to compare this relationship with those developed from floras of different regions of the world; and (3) to contrast temperature predictions based on leaf margins of the native southern flora versus the naturalized alien flora, mostly of boreal origin.
Location   The temperate forest of southern South America (TFSA).
Methods   At each 1° latitudinal band, we estimated E based on species latitudinal ranges and MAT from both an isotherm map and a global temperature grid. We also calculated E from five local floras located between 40 and 43° S, and from the naturalized alien flora of Nahuel Huapi National Park in southern Argentina.
Results   We found a close relationship between E and MAT for the TFSA. Equations developed from floras of the Northern Hemisphere overestimated extant temperatures of this biome by 6–10 °C at both geographical and local spatial scales. On the other hand, MAT predictions from leaf margins of the alien flora were similar to the actual MAT. A published regression between E and MAT from tropical South America was remarkably similar to the one we estimated from the TFSA. This tropical equation predicted accurately the temperatures observed for this temperate biome based on leaf margins of the native flora.
Main conclusions   Despite massive plant extinction due to environmental cooling and biogeographical isolation during the Tertiary, leaf-margin analysis reveals that the flora of the TFSA still reflects its original development under the warmer conditions of western Gondwana and its past connections with low-latitude forest floras of tropical South America.