The timing of resource availability does not affect reproductive allotment or the rate of oocyte development in the flesh fly,Sarcophaga crassipalpis

1. The flesh fly, Sarcophaga crassipalpis, is anautogenous and largely relies on adult‐acquired income resources for reproduction, but allocates some larvally derived capital into the first clutch. Therefore, the timing of adult resource acquisition may be important for both reproductive timing and magnitude of capital vs. income resources allocated to reproduction. Specifically, we predict that flesh flies that wait longer to acquire adult income resources will allocate greater quantities of larvally derived capital to the first clutch. 2. To test how reproductive allocation in flesh flies responds to the timing of adult protein availability, we provided pulses of protein only on day 3, 6, 9, or 12 after eclosion, a series of times equivalent to the onset of oogensis and early, middle and late oogenic development in individuals fed ad libitum. Protein pulses contained isotopically distinct carbon (¹³C), allowing us to distinguish between larval capital and adult‐income resources allocated towards reproduction. 3. Neither the timing of oocyte development nor reproductive allotment (egg number by egg size) was altered by the timing of protein availability. 4. There was no effect of adult protein acquisition timing on the quantity of larvally derived somatic capital vs. adult‐acquired income carbon allocated to reproduction. While flesh flies have remarkable pre‐feeding plasticity in reproductive timing, they appear to have little post‐feeding plasticity in allocation of stored reserves towards reproduction.     

Mechanics and Growth Form of the MossHylocomium splendens

The mossHylocomium splendenshas two different growth forms.Sympodial growth occurs where the apical meristem ceases activityannually and growth is continued by a lateral bud. Sympodialplants are vertical and self-supporting. Monopodial growth occurswhen the apex continues growth. Monopodial plants are prostrate.The aims of the study were to examine stem mechanics of thedifferent growth forms and to compare mechanical propertiesalong stems. Stems of annual segments were subjected to threepoint bending tests. In sympodial plants the stiffness of thestem material increased significantly with segment age. Flexuralrigidity increased significantly with age in segments from 1to 4 years old, and then declined. Segment diameter decreasedsignificantly with age in sympodial plants. Monopodial plantsshowed no significant effects of segment age on the diameter,material stiffness or flexural rigidity of stems. Sympodialsegments were significantly wider, stronger, more rigid andcomposed of stiffer material with a higher stress at yield thanmonopodial segments, but did not have a larger proportion ofstrengthening material. Sympodial stems had significantly morecellulose than monopodial stems. The mossHylocomium splendensshowsa range of mechanical adaptations, as a self-supporting or aprostrate plant, which suit it to life in very different environments.Copyright1998 Annals of Botany Company. Hylocomium splendens, growth form, mechanics, cellulose, stiffness, flexural rigidity, bending, monopodial, sympodial, adaptation, anatomy, stems, plant.     

Concurrent changes in plant weight and soil water regimes in herbaceous communities in Central Australia

Two studies of arid zone plant communities are described. In the first, the perennial grass Eragrostis eriopoda was sampled over 8 months for dry weight and water stress of tops, and water content and tension of soil to a depth of 150 cm. In the second, lasting 2 years, pure Eragrostis and pure Aristida con-torta (annual) communities were sampled for dry weight of tops and roots and soil water content. Plots of naturally occurring mixtures of Eragrostis and Aristida were also studied. During periods of prolonged high soil water content, perennial communities greatly out-yielded annuals (1200 and 260gm^-2 respectively). During prolonged droughts all communities yielded less than 100 gm^-2. Perennial root systems were larger than for annuals. The weight of annual roots varied little with season as distinct from perennials which varied greatly. Maximum weight of annual roots occurred in the top 10 cm of soil; the zone of maximum rooting by perennials was 10–30 cm. Water loss from annual, perennial and bare plots was similar and extended throughout the measured profile. Two gradients of soil water tension of opposite signs developed during prolonged drought. The greater was due to evapo-transpiration and the lesser developed below the zone of recharge. On average. Eragrostis grew 4.6 times faster than the annuals which enjoyed a marginally more favourable water regime. In a mixture which had received one heavy simulated grazing the presence of annuals reduced the growth of Eragrostis by 68%, suggesting that the invasion of Eragrostis by annuals would seriously reduce productivity.     

Ants and the enigmatic Namibian fairy circles – cause and effect?

1. Parts of the Namibian landscape show extensive surface perturbation in the form of long‐lived, yet dynamic ‘fairy circles'. While exerting profound ecological effects on 7.3% of the land surface, the origin and nature of these large bare discs embedded in an arid grassland matrix remains unresolved. 2. We found no evidence to support the current hypothesis of a termite origin for fairy circles but instead observed a strong spatial association between fairy circles and large nests of the ant Black pugnacious ant Anoplolepis steingroeveri Forel, with much higher ant abundances on the circles compared with the matrix. 3. Aggression trials showed that different colonies of A. steingroeveri were located on different circles, and that the species was polydomous. 4. Fairy circles and Pogonomyrmex ant nests both have a bare disc surrounding the nest, are overdispersed (evenly spaced), and are associated with elevated soil moisture. Fairy circle soils exhibited a five‐fold increase in soil moisture when compared with the matrix. 5. Senescent Stipagrostis obtusa (Delile) Nees seedlings were only observed on the circles and not in the matrix, and were found to have a reduction in both root length and number of roots. 6. Anoplolepis steingroeveri excavated the root system of both S. obtusa seedlings on the disc and Stipagrostis ciliata (Desf.) de Winter grasses on the perimeter of the circles, where they tended honeydew‐secreting Meenoplidae bugs that fed on grass roots and culms. The bugs occurred almost exclusively on grasses associated with the circles. This ant–bug interaction is a possible mechanism for the observed reduction in root length and number of senescent grass seedlings on the circles.     

Colony genetic structure and queen mating frequency in fire ants of the subgenus Solenopsis (Hymenoptera: Formicidae)

Colony genetic structure was studied in natural populations of three fire ant taxa, Solenopsis richteri Forel, S. geminata (Fabr.), and hybrid S. invicta/richteri , using allozyme markers. All colonies studied exhibited arrays of female genotypes predicted under a model of monogyny (single functional queen) and monoandry (single insemination of queens). Males produced in the colonies appear to originate exclusively from the foundress queen, rather than from any virgin females present in the colonies. Thus these social insect colonies represent simple, albeit enormous, family groups. Single insemination and foundress parentage of males appear to be conserved reproductive traits in the subgenus Solenopsis , whereas another major determinant of colony genetic structure, the number of functional queens, is evolutionarily labile in this group.     

Effect of Dominant-Negative Epidermal Growth Factor Receptors on Cardiomyocyte Hypertrophy

Angiotensin II (AngII) induces heart growth via cardiomyocyte hypertrophy, and central to this is the capacity of the type 1 AngII receptor (AT₁R) to “transactivate” epidermal growth factor receptors (EGFRs)—a family with four main subtypes (HER1-4)—although the exact molecular mechanism remains unresolved. In this study, the pharmacological inhibition of AngII-stimulated ERK1/2 activation and cardiomyocyte hypertrophy by increasing concentrations of an EGFR inhibitor, AG1478, indicated that other EGFR subtypes, in addition to HER1, may be involved. We constructed expression vectors and adenoviruses expressing truncated mutant versions of HER1, HER2, and HER4 and determined their capacity to act as dominant-negative inhibitors when co-transfected with full-length EGFRs. It is surprising that adenoviral-mediated expression of these truncated EGFRs in cardiomyocytes led to paradoxical, ligand-independent increases in cardiomyocyte hypertrophy and unusual morphological changes. These results challenge our perception of AT₁R-mediated EGFR transactivation and imply that truncated EGFRs may affect cell function through unconventional mechanisms.     

A psychosomatic approach to the climacteric

Two major aspects of the climacteric in women are endocrinological changes with their effects upon the sympathetic nervous system, and psychological factors leading to anxiety with its effect upon the sympathetic nervous system. Depending upon the circumstances in each case, the interruption of the vicious cycle thereby established may require hormonal therapy, psychotherapy, or both. The mere correction of hormonal imbalance may fall far short of effective treatment.