Insect photoperiodism: effects of temperature on the induction of insect diapause and diverse roles for the circadian system in the photoperiodic response

This review considers the effects of temperature on insect diapause induction and the photoperiodic response, and includes constant temperature, temperature cycles, pulses and steps in daily light–dark cycles, constant darkness and in constant light, all with reference to various circadian‐based “clock” models. Although it is a comparative survey, it concentrates on two species, the flesh fly Sarcophaga argyrostoma and its pupal parasite Nasonia vitripennis, which possess radically different photoperiodic mechanisms, although both are based upon the circadian system. Particular attention is given to the effects of daily thermoperiod in darkness and to low and high temperature pulses in conjunction with a daily light–dark cycle, treatments that suggest that S. argyrostoma “measures” night length with a “clock” of the external coincidence type. However, N. vitripennis responds to seasonal changes in photoperiod with an internal coincidence device involving both “dawn” and “dusk” oscillators. Other species may show properties of both external and internal coincidence. Although the precepts of external coincidence have been well formulated and supported experimentally, those for internal coincidence remain obscure.     

Activation of upper airway muscles before onset of inspiration in normal humans

Animal studies have shown activation of upper airway muscles prior to inspiratory efforts of the diaphragm. To investigate this sequence of activation in humans, we measured the electromyogram (EMG) of the alae nasi (AN) and compared the time of onset of EMG to the onset of inspiratory airflow, during wakefulness, stage II or III sleep (3 subj), and CO2-induced hyperpnea (6 subj). During wakefulness, the interval between AN EMG and airflow was 92 +/- 34 ms (mean +/- SE). At a CO2 level of greater than or equal to 43 Torr, the AN EMG to airflow was 316 +/- 38 ms (P < 0.001). During CO2-induced hyperpnea, the AN EMG to airflow interval and AN EMG magnitude increased in direct proportion to CO2 levels and minute ventilation. During stages II and III of sleep, the interval between AN EMG and airflow increased when compared to wakefulness (P < 0.005). We conclude that a sequence of inspiratory muscle activation is present in humans and is more apparent during sleep and during CO2-induced hyperpnea than during wakefulness.     

Effect of dose rate on the survival of irradiated human skin fibroblasts.

The survival of cells in density-inhibited, confluent cultures maintained at 37 degrees C was examined following exposure to 137Cs gamma rays at low dose rates (0.023 or 0.153 Gy/h) or to 60Co gamma rays at a single high dose rate (0.70-0.75 Gy/min). Cells from an ataxia telangiectasia (AT) homozygote showed no dose-rate effect, whereas a three- to fivefold increase in D0 was observed for all other cell strains exposed at low dose rates. The magnitude of the dose-rate effect did not differ significantly among cells from persons with hereditary retinoblastoma, basal cell nevus syndrome, or AT-heterozygote compared with normal cell strains, and was not related to the size of the shoulder (extrapolation number) of the survival curve. Furthermore, no differences in the capacity for the repair of potentially lethal damage during confluent holding were observed among these latter cell strains.     

Retinoic Acid signalling and the control of meiotic entry in the human fetal gonad

The development of mammalian fetal germ cells along oogenic or spermatogenic fate trajectories is dictated by signals from the surrounding gonadal environment. Germ cells in the fetal testis enter mitotic arrest, whilst those in the fetal ovary undergo sex-specific entry into meiosis, the initiation of which is thought to be mediated by selective exposure of fetal ovarian germ cells to mesonephros-derived retinoic acid (RA). Aspects of this model are hard to reconcile with the spatiotemporal pattern of germ cell differentiation in the human fetal ovary, however. We have therefore examined the expression of components of the RA synthesis, metabolism and signalling pathways, and their downstream effectors and inhibitors in germ cells around the time of the initiation of meiosis in the human fetal gonad. Expression of the three RA-synthesising enzymes, ALDH1A1, 2 and 3 in the fetal ovary and testis was equal to or greater than that in the mesonephros at 8-9 weeks gestation, indicating an intrinsic capacity within the gonad to synthesise RA. Using immunohistochemistry to detect RA receptors RARα, β and RXRα, we find germ cells to be the predominant target of RA signalling in the fetal human ovary, but also reveal widespread receptor nuclear localization indicative of signalling in the testis, suggesting that human fetal testicular germ cells are not efficiently shielded from RA by the action of the RA-metabolising enzyme CYP26B1. Consistent with this, expression of CYP26B1 was greater in the human fetal ovary than testis, although the sexually-dimorphic expression patterns of the germ cell-intrinsic regulators of meiotic initiation, STRA8 and NANOS2, appear conserved. Finally, we demonstrate that RA induces a two-fold increase in STRA8 expression in cultures of human fetal testis, but is not sufficient to cause widespread meiosis-associated gene expression. Together, these data indicate that while local production of RA within the fetal ovary may be important in regulating the onset of meiosis in the human fetal ovary, mechanisms other than CYP26B1-mediated metabolism of RA may exist to inhibit the entry of germ cells into meiosis in the human fetal testis.     

Temperature Effects on Heterorhabditis megidis and Steinernema carpocapsae Infectivity to Galleria mellonella

The effect of temperature on the infection of larvae of the greater wax moth, Galleria mellonella, by Heterorhabditis megidis H90 and Steinernema carpocapsae strain All, was determined. For both species, infection, reproduction, and development were fastest at 20 to 24 °C. Infection by both H. megidis and S. carpocapsae occurred between 8 and 16 °C; however, neither species reproduced at 8 °C. Among the nematodes used in experiments at 8 °C, no H. megidis and very few S. carpocapsae developed beyond the infective juvenile stage. Compared with H. megidis, S. carpocapsae invaded and killed G. mellonella larvae faster at 8 to 16 °C. By comparing invasion rates, differences in infectivity between the two nematode species were detected that could not be detected in conventional petri dish bioassays where mortality was measured after a specified period. Invasion of G. mellonella larvae by H. megidis was faster at 24 than at 16 °C.     

The effects of 2-aminoethoxydiphenyl borate, a novel inositol 1,4, 5-trisphosphate receptor modulator on myometrial contractions.

These studies were performed to evaluate the effect of 2-aminoethoxydiphenyl borate (2-APB), a novel membrane-permeable inositol 1,4,5-trisphosphate-receptor inhibitor on agonist-induced, spontaneous, and KCl-stimulated in vitro myometrial contractions. 2-APB significantly inhibited spontaneous myometrial contractions as well as phasic contractions induced by various uterotonic agonists. Confiriming its effects on intracellular calcium release, 2-APB inhibited phasic contractions in the absence of extracellular calcium. 2-APB had little effect on the tonic response to KCl stimulation, implicating its insignificant effect on voltage-gated calcium channels. The inhibitory effect of 2-APB on phasic contractions was completely reversed by washout. In summary, 2-APB effectively penetrated uterine tissue and significantly inhibited myometrial events previously shown to be mediated through activation of the PI-signaling pathway.     

Identification of molecular markers in soybean comparing RFLP,RAPD and AFLP DNA mapping techniques

Three different DNA mapping techniques—RFLP, RAPD and AFLP—were used on identical soybean germplasm to compare their ability to identify markers in the development of a genetic linkage map. Polymorphisms present in fourteen different soybean cultivars were demonstrated using all three techniques. AFLP, a novel PCR-based technique, was able to identify multiple polymorphic bands in a denaturing gel using 60 of 64 primer pairs tested. AFLP relies on primers designed in part on sequences for endonuclease restriction sites and on three selective nucleotides. The 60 diagnostic primer pairs tested for AFLP analysis each distinguished on average six polymorphic bands. Using specific primers designed for soybean fromEco RI andMse I restriction site sequences and three selective nucleotides, as many as 12 polymorphic bands per primer could be obtained with AFLP techniques. Only 35% of the RAPD reactions identified a polymorphic band using the same soybean cultivars, and in those positive reactions, typically only one or two polymorphic bands per gel were found. Identification of polymorphic bands using RFLP techniques was the most cumbersome, because Southern blotting and probe hybridization were required. Over 50% of the soybean RFLP probes examined failed to distinguish even a single polymorphic band, and the RFLP probes that did distinguish polymorphic bands seldom identified more than one polymorphic band. We conclude that, among the three techniques tested, AFLP is the most useful.     

Vegetation responses to landscape structure at multiple scales across a Northern Wisconsin,USA, pine barrens landscape

Increasing awareness of the importance of scale and landscape structure to landscape processes and concern about loss of biodiversity has resulted in efforts to understand patterns of biodiversity across multiple scales. We examined plant species distributions and their relationships to landscape structure at varying spatial scales across a pine barrens landscape in northern Wisconsin, U.S.A. We recorded plant species cover in 1×1 m plots every 5 m along a 3575 m transect, along with variables describing macro- and micro-landscape structure. A total of 139 understory plant species were recorded. The distributions of many species appeared to be strongly associated with landscape structural features, such as distinct management patches and roads. TWINSPAN and detrended correspondence analysis (DCA) identified three groups of species that overlapped extensively in the ordination, possibly reflecting the relatively homogeneous nature of disturbance in the pine barrens landscape. Distribution of understory plants did not reflect all of the patch types we identified along the transect; plot ordination and classification resulted in three to five plot groups that differed in niche breadth. Wavelet transforms showed varying relationships between landscape features and plant diversity indices (Shannon–Weiner, Simpson's Dominance) at different resolutions. Wavelet variances indicated that patterns of Shannon diversity were dominated by coarse resolutions ranging from 900–1500 m, which may have been related to topography. Patterns of Simpson's Dominance were dominated by 700 m resolution, possibly associated with canopy cover. However, a strong correspondence between overstory patch type and diversity was found for several patch types at ranges of scales that varied by patch type. Effects of linear features such as roads were apparent in the wavelet transforms at resolutions of about 5–1000 m, suggesting roads may have an important impact on plant diversity at landscape scales. At broad scales, landscape context appeared more important to diversity than individual patches, suggesting that changes in structure at fine resolutions could alter overall diversity characteristics of the landscape. Therefore, a hierarchical perspective is necessary to recognize potential large-scale change resulting from small-scale activities.     

Phylogenetic analyses of anatomical and nuclear SSU rDNA sequence data indicate that the Dasyaceae and Delesseriaceae (Ceramiales,Rhodophyta) are polyphyletic

The aim of the current investigation was to test the general convention that the Dasyaceae, Delesseriaceae and Rhodomelaceae are all monophyletic families of the red algal order Ceramiales. Phylogenetic relationships among 45 ceramialean taxa were determined, including eight ceramiacean, 18 dasyacean, nine delesseriacean and eight rhodomelacean species, plus two of uncertain ceramialean affinities, based on 34 anatomical characters and nuclear small subunit (SSU) rDNA sequences. Results from our ‘total-evidence’ approach were consistent with the notion that the Dasyaceae, Delesseriaceae and Rhodomelaceae have evolved from a common ancestor within a paraphyletic Ceramiaceae. Our data indicate, however, that the Rhodomelaceae alone is monophyletic at the family level, with both the Dasyaceae and Delesseriaceae polyphyletic. In particular we resolved two independent and well-supported lineages for the included Dasyaceae, viz., a Dasya group and a Heterosiphonia group, which were as distinct from one another as they were from the Rhodomelaceae and the various lineages of Delesseriaceae. The molecular data alone were equivocal on the issue of monophyly of the Dasyaceae. We therefore advocate conservative taxonomic revisions as an interim step towards eventual resolution of familial-level taxonomy in the Ceramiales. Based on our results, the Heterosiphonioideae H.-G. Choi, Kraft, I.K. Lee et G.W. Saunders subfam. nov. is proposed for Heterosiphonia and five closely related genera, and the Dasyoideae Schmitz et Falkenberg is emended for the remaining taxa. Although the Dasyoideae is a natural group, it is in need of a thorough systematic reinvestigation at the generic level. Our analyses indicate that the genus Dasya is polyphyletic or paraphyletic in excluding Dasysiphonia, Eupogodon and Rhodoptilum and that Heterosiphonia japonica also has affinities to this group, taxonomic issues that will be addressed in detail elsewhere.