DIFFERENTIAL SEED PRODUCTION IN MIMULUS GUTTATUS IN RESPONSE TO INCREASING CONCENTRATIONS OF COPPER IN THE PISTIL BY POLLEN FROM COPPER TOLERANT AND SENSITIVE SOURCES

Selection can occur in the pistil, during a series of stages that include both pre-zygotic (pollen germination, pollen tube growth, and fertilization) and post-zygotic events. This study explores the extent to which selection, at this level, could be due to the environmental conditions under which the maternal parent is growing. Five plants of Mimulus guttatus, tolerant to copper, were vegetatively cloned and each clone was grown in control and in solutions to which copper was added. The maternal plants received pollen from plants either tolerant or sensitive to copper. Seeds and ovules were counted to estimate the number of seeds/capsule, the seed/ovule ratio, the percent fertilization, and the proportion of zygotes aborting for each clone, treatment and pollen source combination. There were large differences among the pollen recipients for each of the measurements. However, there was a consistent pattern to seed production depending on the pollen source and copper treatment. The seed/ovule ratio was unaffected if pollen came from tolerant sources but was reduced by an average of 24% for both copper supplemented treatments if pollen came from copper sensitive sources. Thus, the data indicated that selection due to environmental factors could occur within the pistil. Differences in percent fertilization were not statistically significant, but the seed/zygote ratio showed a pattern that was similar to seed production suggesting that abortion of immature seeds was responsible for most of the difference in seed production.     

Geographic song discrimination in relation to dispersal distances in song sparrows

Whether geographic variation in signals actually affects communication between individuals depends on whether discriminable differences in signals occur over distances that individuals move in their lifetimes. We measure the ability of song sparrows (Melospiza melodia) to discriminate foreign from local songs using foreign songs recorded at a series of increasing distances and compare the results with previous measurements of dispersal distances. We test discrimination in males using playback of songs on territories and measuring approach and in females using playback to estradiol-treated captives and measuring courtship display. Females fail to discriminate against foreign songs recorded at 18 km but do discriminate against foreign songs recorded at 34, 68, 135, and 540 km. Males fail to discriminate against foreign songs recorded at 18, 34, 68, 135, and 270 km but do discriminate against foreign songs from 540 km. Females are more discriminating, but even they do not discriminate at a distance three times the root-mean-square dispersal distance, as estimated from mtDNA variation. We suggest that female preference for local songs benefits females not because it allows them to reject foreign males but because accurate production of local song serves as a test of song-learning ability.     

Occult Glucose Intolerance: Incidence in a General Population

A survey of two-hour postprandial glycemic responses to an oral dose of 100 gm of glucose was conducted in 456 appparently healthy adult members of a small Southern California community. Serum glucose levels of 32 per cent of the men and 36 per cent of the women exceeded 140 mg per 100 ml at the two-hour sampling period.In both sexes, there was a tendency for hyperglycemia to become more conspicuous with age.Under the age of 50, a much higher percentage of women than men had seemingly excessive serum glucose values.These findings may suggest a need for modifying criteria currently used for interpreting glycemic responses to oral glucose challenges.     

Female swamp sparrows do not show evidence of discriminating between the songs of peak‐aged and senescent males

Sexual selection theory predicts that females face contrasting selection pressures when choosing the age of their mate. On the one hand, older males have demonstrated their ability to survive and they may be more experienced than younger males. At the same time, however, younger males are expected to have accumulated fewer deleterious mutations in their germline as compared to older males. These contrasting pressures on female preference may result in a preference for intermediate‐aged males. A preference for males of a particular age can only be expressed, however, if females are able to identify males of different ages. We have previously shown that male swamp sparrows display age‐related changes in vocal quality, such that males display sharp increases in vocal quality in early adulthood, followed by gradual senescent declines thereafter. We have also shown that territorial males discriminate these within‐individual differences, giving stronger aggressive responses to songs of peak‐aged males than to those of senescent males. Here, we use a copulation solicitation assay to test whether females also discriminate these within‐signaler markers of senescence in song. Contrary to our prediction, females did not show any evidence of discriminating between songs recorded from peak‐aged males as compared to songs from the same males following song senescence. We suggest that this difference in demonstrated discrimination between males and females may be the result of the two sexes attending to different song characteristics.     

Genome sequence of the stramenopile <Emphasis Type="Italic">Blastocystis</Emphasis>, a human anaerobic parasite

Background

Blastocystis is a highly prevalent anaerobic eukaryotic parasite of humans and animals that is associated with various gastrointestinal and extraintestinal disorders. Epidemiological studies have identified different subtypes but no one subtype has been definitively correlated with disease.

Results

Here we report the 18.8 Mb genome sequence of a Blastocystis subtype 7 isolate, which is the smallest stramenopile genome sequenced to date. The genome is highly compact and contains intriguing rearrangements. Comparisons with other available stramenopile genomes (plant pathogenic oomycete and diatom genomes) revealed effector proteins potentially involved in the adaptation to the intestinal environment, which were likely acquired via horizontal gene transfer. Moreover, Blastocystis living in anaerobic conditions harbors mitochondria-like organelles. An incomplete oxidative phosphorylation chain, a partial Krebs cycle, amino acid and fatty acid metabolisms and an iron-sulfur cluster assembly are all predicted to occur in these organelles. Predicted secretory proteins possess putative activities that may alter host physiology, such as proteases, protease-inhibitors, immunophilins and glycosyltransferases. This parasite also possesses the enzymatic machinery to tolerate oxidative bursts resulting from its own metabolism or induced by the host immune system.

Conclusions

This study provides insights into the genome architecture of this unusual stramenopile. It also proposes candidate genes with which to study the physiopathology of this parasite and thus may lead to further investigations into Blastocystis-host interactions.

     

Optimal risky choice in humans: effects of amount of variability

The present study investigated whether the predictions of an optimal risk-sensitive foraging model (the energy-budget rule) would extend to humans’ choices between high- and low-variance monetary response options. In Experiment 1, participants were presented with repeated choices between two options that had the same mean values but different variances across positive- and negative-budget conditions. In Experiment 2, a within-subject comparison was conducted to investigate choice under positive- and negative-budget conditions when the options were either (a) a fixed option and a high-variance option, or (b) a low-variance option and a high-variance option. Session-wide choices were analyzed in relation to the predictions of the energy-budget rule and sequential choices were analyzed with dynamic optimization modeling. When both options were variable choice was generally consistent with predictions of the energy-budget rule and was more risk prone under negative-budget than positive-budget conditions. Sequential choices were sensitive to local budget conditions, but choices were less consistent with optimality when both options were variable, possibly because of the greater similarity in expected earnings for optimal and nonoptimal choices in these conditions. Overall, the results provide further evidence that the energy-budget rule may have broad applicability and that it can extend to human risky choice between multiple variable response options.