Evidence for plasticity in the frequency of skipped breeding opportunities in common toads

Breeding is limited by energetic or environmental constraints and long-lived species sometimes skip breeding opportunities. Environmental conditions may vary considerably across the geographic and elevational range of a species and species that can respond through variation in life history strategies are likely to maintain populations at the extremes of their ranges. The decision to skip breeding enables animals to adjust life history to circumstances, and plasticity in behavior allows implementation of adjustments. Elevational patterns suggest that breeding may be limited physiologically at high elevations (e.g., greater probability of skipped breeding; resources and environmental conditions more variable) in contrast to low elevations (probability of skipping breeding lower; resources and environmental conditions more predictable). We estimated the probabilities of survival and skipped breeding in a high-elevation population of common toads and compared estimates to existing data for common toads at low elevations, and to another toad species inhabiting a similar high elevation environment. Female common toads at high elevations tend to have high probabilities of skipping breeding and survival relative to data for common toads at low elevations, and appear to use a similar strategy of skipping breeding in response to similar environmental constraints as other toads at high elevations. We provide evidence of variability in this aspect of life history for common toads. Understanding variation in life history within widely distributed species is critical. Knowing that certain life history strategies are employed on a continuum informs conservation efforts, especially as impacts of climate change are likely to be different depending on elevation.     

Mesenchymal stem cells in autoimmune diseases: hype or hope?

Intervention with mesenchymal stem cells (MSCs) represents a promising therapeutic tool in treatment-refractory autoimmune diseases. A new report by Schurgers and colleagues in a previous issue of Arthritis Research & Therapy sheds novel mechanistic insight into the pathways employed by MSCs to suppress T-cell proliferation in vitro, but, at the same time, indicates that MSCs do not influence T-cell reactivity and the disease course in an in vivo arthritis model. Such discrepancies between the in vitro and in vivo effects of potent cellular immune modulators should spark further research and should be interpreted as a sign of caution for the in vitro design of MSC-derived interventions in the setting of human autoimmune diseases.     

Polyamine and nitric oxide levels relate with morphogenetic evolution in somatic embryogenesis of <Emphasis Type="Italic">Ocotea catharinensis</Emphasis>

In this study we examined the effect of polyamines (PAs) putrescine (Put), spermidine (Spd) and spermine (Spm) on growth, morphology evolution, endogenous PAs levels and nitric oxide (NO) release in Ocotea catharinensis somatic embryo cultures. We observed that Spd and Spm reduced culture growth, permitted embryo morphogenetic evolution from the earliest to last embryo development stages, increased endogenous PAs levels, and induced NO release in O. catharinensis somatic embryos. On the other hand, Put had little effect on these parameters. Spd and Spm could successfully be used to promote somatic embryo maturation in O. catharinensis. The results suggest that Spd and Spm have an important role during the growth, development and morphogenetic evolution of somatic embryos, through alterations in the endogenous nitric oxide and PAs metabolism in this species.     

Mutual reproductive dependence of distylic Cordia leucocephala (Cordiaceae) and oligolectic Ceblurgus longipalpis (Halictidae, Rophitinae) in the Caatinga

Background and Aims

The close relationship between distylic Cordia leucocephala and the bee Ceblurgus longipalpis, both endemic to the Caatinga, north-east Brazil, was investigated, emphasizing reproductive dependence, morphological adaptations of the partners, and pollen flow.

Methods

In the municipality of Pedra, in the Caatinga of Pernambuco, the breeding system and reproductive success of C. leucocephala, its interaction with flower visitors and inter- and intramorph pollen flow were determined.

Key Results

The bee Ceblurgus longipalpis, the unique flower visitor and effective pollinator of self-incompatible Cordia leucocephala, presents morphological features adapted to exploit hidden pollen and nectar in the long and narrow corolla tubes. Pollen of low-level anthers is collected with hairs on prolonged mouthparts and pollen of high-level anthers with clypeus, mandibles, and labrum, showing pollen removal from both levels with the same effectiveness. In both morphs, this results in similar legitimate, i.e. intermorph cross-pollen flow. Illegitimate pollen flow to stigmas of pin flowers, however, was much higher than to stigmas of thrum flowers. Moreover, more illegitimate pollen was transported to stigmas of pin and less to those of thrum flowers when compared with legitimate pollen flow.

Conclusions

The study reveals a one-to-one reproductive inter-dependence between both partners. Data indicate that this relationship between bee species and plant species is one of the rare cases of monolecty among bees. Monotypic Ceblurgus longipalpis, the only rophitine species of Brazil, evolved prolonged mouthparts rare among short-tongued bees that enable them to access pollen from flowers with short-level anthers hidden for bees of other species, and nectar at the base of the flower tube.     

Chronic hyperhomocysteinemia alters antioxidant defenses and increases DNA damage in brain and blood of rats: protective effect of folic acid

We have previously demonstrated that acute hyperhomocysteinemia induces oxidative stress in rat brain. In the present study, we initially investigated the effect of chronic hyperhomocysteinemia on some parameters of oxidative damage, namely total radical-trapping antioxidant potential and activities of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase), as well as on DNA damage in parietal cortex and blood of rats. We also evaluated the effect of folic acid on biochemical alterations elicited by hyperhomocysteinemia. Wistar rats received daily subcutaneous injection of Hcy (0.3-0.6 micromol/g body weight), and/or folic acid (0.011 micromol/g body weight) from their 6th to their 28th day of life. Twelve hours after the last injection the rats were sacrificed, parietal cortex and total blood was collected. Results showed that chronic homocysteine administration increased DNA damage, evaluated by comet assay, and disrupted antioxidant defenses (enzymatic and non-enzymatic) in parietal cortex and blood/plasma. Folic acid concurrent administration prevented homocysteine effects, possibly by its antioxidant and DNA stability maintenance properties. If confirmed in human beings, our results could propose that the supplementation of folic acid can be used as an adjuvant therapy in disorders that accumulate homocysteine.     

DNA damage in the kidney tissue cells of the fish Rhamdia quelen after trophic contamination with aluminum sulfate

Even though aluminum is the third most common element present in the earth''s crust, information regarding its toxicity remains scarce. It is known that in certain cases, aluminum is neurotoxic, but its effect in other tissues is unknown. The aim of this work was to analyze the genotoxic potential of aluminum sulfate in kidney tissue of the fish Rhamdia quelen after trophic contamination for 60 days. Sixty four fish were subdivided into the following groups: negative control, 5 mg, 50 mg and 500 mg of aluminum sulfate per kg of fish. Samples of the posterior kidney were taken and prepared to obtain mitotic metaphase, as well as the comet assay. The three types of chromosomal abnormalities (CA) found were categorized as chromatid breaks, decondensation of telomeric region, and early separation of sister chromatids. The tests for CA showed that the 5 mg/kg and 50 mg/kg doses of aluminum sulfate had genotoxic potential. Under these treatments, early separation of the sister chromatids was observed more frequently and decondensation of the telomeric region tended to increase in frequency. We suggest that structural changes in the proteins involved in DNA compaction may have led to the decondensation of the telomeric region, making the DNA susceptible to breaks. Moreover, early separation of the sister chromatids may have occurred due to changes in the mobility of chromosomes or proteins that keep the sister chromatids together. The comet assay confirmed the genotoxicity of aluminum sulfate in the kidney tissue of Rhamdia quelen at the three doses of exposure.     

Ventilatory response to helium-oxygen breathing during exercise: effect of airway anesthesia

Krishnan, Bharath S., Ron E. Clemens, Trevor A. Zintel,Martin J. Stockwell, and Charles G. Gallagher. Ventilatory response to helium-oxygen breathing during exercise: effect of airwayanesthesia. J. Appl. Physiol. 83(1):82-88, 1997.The substitution of a normoxic helium mixture(HeO₂) for room air (Air) during exercise results in a sustained hyperventilation, which is present evenin the first breath. We hypothesized that this response is dependent onintact airway afferents; if so, airway anesthesia (Anesthesia) shouldaffect this response. Anesthesia was administered to the upper airwaysby topical application and to lower central airways by aerosolinhalation and was confirmed to be effective for over 15 min. Subjectsperformed constant work-rate exercise (CWE) at 69 ± 2 (SE) % maximal work rate on a cycle ergometer on three separate days: twiceafter saline inhalation (days 1 and3) and once after Anesthesia(day 2). CWE commenced after a briefwarm-up, with subjects breathing Air for the first 5 min (Air-1),HeO₂ for the next 3 min, and Airagain until the end of CWE (Air-2). The resistance of the breathingcircuit was matched for Air andHeO₂. BreathingHeO₂ resulted in a small butsignificant increase in minute ventilation(I) anddecrease in alveolar PCO₂ in both theSaline (average of 2 saline tests; not significant) and Anesthesiatests. Although Anesthesia had no effect on the sustainedhyperventilatory response to HeO₂breathing, theI transientswithin the first six breaths ofHeO₂ were significantly attenuatedwith Anesthesia. We conclude that theI response to HeO₂ is not simply due to areduction in external tubing resistance and that, in humans, airwayafferents mediate the transient but not the sustained hyperventilatoryresponse to HeO₂ breathing duringexercise.