Heterospecific pollen deposition: does diversity alter the consequences?

? In natural communities, plants can receive pollen from multiple heterospecifics as well as conspecifics. However, studies on the effects of interspecific pollen transfer have focused on interactions between species pairs. The potential exists for diverse interactions among heterospecific pollen (HP) grains on the stigma, and for these to affect plant reproduction, alone or in combination with conspecific pollen (CP) loss, but these interactions have not yet been explored. ? We used hand-pollinations to simulate increasing community diversity and CP loss on Mimulus guttatus stigmas. We used pollen mixes of one to three heterospecific donors to determine how species composition and CP load size affect seed production and to characterize the mechanisms underlying fertilization failure. ? Heterospecific pollen deposition reduced M. guttatus seed production and while the effect increased with the number of heterospecific donors, the strength depended on species composition and was independent of conspecific load size. Different types of interactions (additive and synergistic) are hypothesized to underlie the diverse effects on M. guttatus reproductive success. ? Our results suggest that an increase in the diversity of heterospecific donors will not always lead to a greater decrease in fitness because multispecies effects depend on the interacting species.     

Nocturnal masseter electromyographic activity of complete denture wearers

doi: 10.1111/j.1741‐2358.2011.00528.x Nocturnal masseter electromyographic activity of complete denture wearers Objective: Collection of normative data on activity patterns of the masseter during sleep in elderly denture wearers by portable electromyography (EMG) recorders. Background: Complete denture wearers might suffer from orofacial pain caused by myoarthropathies of the masticatory system. Indeed, denture instability may precipitate parafunctional habits and consequently muscle soreness and/or temporomandibular pain. Materials and methods: We collected normative masseter EMG data during sleep in 15 complete denture wearers (five women, 10 men, 56–88 years) by portable recorders in their natural environment. Activity periods (AP) were signal portions including subthreshold intervals ≤5 s. Signal amplitude was expressed in per cent of maximum voluntary contraction (%MVC). For this reason, maximum bite force was assessed. Twenty age‐matched dentate controls were also recorded for the maximum bite force. Results: We found 157.2 ± 86.5 AP per night, i.e. 24.0 ± 12.2 AP/h. Mean amplitude was 15.1 ± 4.3%MVC. AP lasted 6.8 ± 4.1 s, and their time integral was 126.3 ± 112.5%MVC?s. Maximum bite force was 116.8 ± 69.6 N in the edentulous, significantly lower than in controls (344.8 ± 150.4 N). Conclusions: Healthy complete denture wearers showed intermittent periods of nocturnal masseter activity of very low intensity and short duration.     

Hypothesis testing of the aging male gonadal axis via a biomathematical construct

Neuroendocrine axes are feedback- and feedforward-coupled dynamic ensembles. Disruption of selected pathways in such networklike organizations may explicate loss of orderly hormonal output as observed in aging. To test this notion more explicitly, we implemented an earlier computer-assisted biomathematical model of the interlinked male hypothalamo [gonadotropin-releasing hormone (GnRH)]-pituitary [luteinizing hormone, (LH)]-testicular [Leydig cell testosterone (Te)] axis (Am J Physiol Endocrinol Metab Physiol 275: E157--E176, 1988; Keenan D., W. Sun, and J. D. Veldhuis, SIAM J Appl Math 61: 934--965, 2000). Thereby, we appraise mechanistic hypotheses for more disorderly LH and Te secretion in aging men. We compare model predictions with monitored abnormalities in the older male, namely, irregular patterns of individual and synchronous LH and Te release, reduced 24-h rhythmic Te output, and variably elevated LH secretion. Among the mechanisms examined, the most parsimonious aging hypothesis would entail impaired LH feedforward on Te without or with attenuated Te feedback on GnRH/LH secretion. This investigative strategy should aid in exploring new postulates of disrupted feedback networks in pathophysiology.     

Developmental evolution of sexual ornamentation: model and a test of feather growth and pigmentation

A tremendous diversity of avian color displays has stimulatednumerous studies of natural and sexual selection. Yet, the developmentalmechanisms that produce such diversification, and thus the proximatetargets of selection pressures, are rarely addressed and poorlyunderstood. In particular, because feathers are colored duringgrowth, the dynamics of feather growth play a deterministicrole in the variation in ornamentation. No study to date, however,has addressed the contribution of feather growth to the expressionof carotenoid-based ornamentation. Here, we examine the developmentalbasis of variation in ornamental feather shapes in male housefinches (Carpodacus mexicanus)—a species in which carotenoiddisplays are under strong natural and sexual selection. First,we use geometric morphometrics to partition the observed shapevariation in fully grown feathers among populations, ages, degreesof elaboration, ornamental body parts, and individuals. Second,we use a biologically informed mathematical model of feathergrowth to predict variation in shape of ornamental feathersdue to simulated growth rate, angle of helical growth of featherbarbs, initial number of barb ridges, rate of addition of newbarbs, barb diameter, and ramus-expansion angle. We find closeconcordance between among-individual variation in feather shapeand hue of entire ornament, and show that this concordance canbe attributed to a shared mechanism—growth rate of featherbarbs. Predicted differences in feather shape due to rate ofaddition of barbs and helical angle of feather growth explainedobserved variation in ornamental area both among individualsand between populations, whereas differences in helical angleof growth and the number of barbs in the feather follicle explaineddifferences in feather shape between ornamental parts and amongmales of different ages. The findings of a close associationof feather growth dynamics and overall ornamentation identifythe proximate targets of selection for elaboration of sexualdisplays. Moreover, the close association of feather growthand pigmentation not only can reinforce condition-dependencein color displays, but can also enable phenotypic and geneticaccommodation of novel pigments into plumage displays providinga mechanism for the observed concordance of within-populationdevelopmental processes and between-population diversificationof color displays.     

The influence of neonatal ketamine injection on pain sensitivity and audiogenic seizures in adult rats

The remote effects of neonatal (on the 3d-to-9th postnatal days) ketamine injections (10 and 50 mg/kg in 20 microliters of distilled water, s.c.) were analyzed in adult Wistar, WAG/Rij, and KM (a strain with high audiogenic sensitivity) rats. Both ketamine and water injections increased pain sensitivity in adult rats. Neonatally injected water increased the mean score of seizures in Wistar and WAG/Rij, whereas ketamine water solution injected in the dose of 50 mg/kg did not change the seizure intensity (as compared to the intact control). Consequently, ketamine significantly reduced the mean score of the audiogenic seizure fit without change in its latency. In highly sensitive KM rats the neonatally injected ketamine (50 mg/kg) significantly shortened the mean latency of the fit onset, and fit stages developed faster. Thus, the neonatal ketamine injection increased the audiogenic seizure susceptibility of brain structures in KM rats.     

Ascorbate inhibits the carbethoxylation of two histidyl and one tyrosyl residues indispensable for the transmembrane electron transfer reaction of cytochrome b561

Cytochrome b(561) from bovine adrenal chromaffin vesicles contains two heme B prosthetic groups and transports electron equivalents across the vesicle membranes to convert intravesicular monodehydroascorbate radical to ascorbate. We found previously that treatment of oxidized cytochrome b(561) with diethyl pyrocarbonate caused specific N-carbethoxylation of three fully conserved residues (His88, His161, and Lys85) located at the extravesicular side. The modification lead to a selective loss of the electron-accepting ability from ascorbate without affecting the electron donation to monodehydroascorbate radical [Tsubaki, M., Kobayashi, K., Ichise, T., Takeuchi, F., and Tagawa, S. (2000) Biochemistry 39, 3276-3284]. In the present study, we found that these modifications lead to a drastic decrease of the midpoint potential of heme b at the extravesicular side from +60 to -30 mV. We found further that the O-carbethoxylation of one tyrosyl residue (Tyr218) located at the extravesicular side was significantly enhanced under alkaline conditions, leading to a very slow reduction process of the oxidized heme b with ascorbate. On the other hand, the presence of ascorbate during the treatment with diethyl pyrocarbonate was found to suppress the carbethoxylation of His88, His161, and Tyr218, whereas the modification level of Lys85 was not affected. Concomitantly, the final reduction level of heme b with ascorbate was protected, although the fast reduction phase was not fully restored. These results suggest that the two heme-coordinating histidyl residues (His88 and His161) are also a part of the ascorbate binding site. Tyr218 and Lys85 may have a role in the recognition/binding process for ascorbate and are indispensable for the fast electron transfer reaction.