Fitness costs of resistance to \u3ci\u3eBacillus thuringiensis\u3c/i\u3e in the Indianmeal moth, \u3ci\u3ePlodia interpunctella\u3c/i\u3e

Genetic changes in insects that result in insecticide resistance can also affect their fitness. Here, we report measurements of development time and survival of the Indianmeal moth, Plodia interpunctella (Hübner), to compare the relative fitness of Bacillus thuringiensis (Bt)-susceptible and -resistant colonies. Measurements of larval development time and survival indicated that a fitness cost was associated with resistance to Bt in some Bt-resistant colonies but not others. Comparisons of geographically different populations revealed inherent differences in development time and survival. In most cases, Bt-resistant moths suffered no disadvantage when feeding on a Bt-treated diet. In many cases, the development of Bt-resistant moths on Bt-treated diet was slower than the unselected moths on untreated diet, but it is unclear whether these differences would affect the successful mating of susceptible and resistant moths

Synchronization-Induced Rhythmicity of Circadian Oscillators in the Suprachiasmatic Nucleus

The suprachiasmatic nuclei (SCN) host a robust, self-sustained circadian pacemaker that coordinates physiological rhythms with the daily changes in the environment. Neuronal clocks within the SCN form a heterogeneous network that must synchronize to maintain timekeeping activity. Coherent circadian output of the SCN tissue is established by intercellular signaling factors, such as vasointestinal polypeptide. It was recently shown that besides coordinating cells, the synchronization factors play a crucial role in the sustenance of intrinsic cellular rhythmicity. Disruption of intercellular signaling abolishes sustained rhythmicity in a majority of neurons and desynchronizes the remaining rhythmic neurons. Based on these observations, the authors propose a model for the synchronization of circadian oscillators that combines intracellular and intercellular dynamics at the single-cell level. The model is a heterogeneous network of circadian neuronal oscillators where individual oscillators are damped rather than self-sustained. The authors simulated different experimental conditions and found that: (1) in normal, constant conditions, coupled circadian oscillators quickly synchronize and produce a coherent output; (2) in large populations, such oscillators either synchronize or gradually lose rhythmicity, but do not run out of phase, demonstrating that rhythmicity and synchrony are codependent; (3) the number of oscillators and connectivity are important for these synchronization properties; (4) slow oscillators have a higher impact on the period in mixed populations; and (5) coupled circadian oscillators can be efficiently entrained by light–dark cycles. Based on these results, it is predicted that: (1) a majority of SCN neurons needs periodic synchronization signal to be rhythmic; (2) a small number of neurons or a low connectivity results in desynchrony; and (3) amplitudes and phases of neurons are negatively correlated. The authors conclude that to understand the orchestration of timekeeping in the SCN, intracellular circadian clocks cannot be isolated from their intercellular communication components

VARIETAL RESISTANCE

Production of all classes of wheat grown in the United States totaled 2.5 billion bushels in 1997. Common wheat, Triticum aestivum L. subsp. aestivum, is the primary source of all wheat varieties grown in the United States, with over 200 varieties known and over 100 varieties cultivated. These 100 varieties constitute over 95% of all wheat cultivated in the United States. Five general wheat classes are predominant in the United States: hard red winter, hard red spring, soft red winter, white, and durum

Two major cuticular proteins are required for assembly of horizontal laminae and vertical pore canals in rigid cuticle of Tribolium castaneum

The insect exoskeleton is composed of cuticle primarily formed from structural cuticular proteins (CPs) and the polysaccharide chitin. Two CPs, TcCPR27 and TcCPR18, are major proteins present in the elytron (highly sclerotized and pigmented modified forewing) as well as the pronotum (dorsal sclerite of the prothorax) and ventral abdominal cuticle of the red flour beetle, Tribolium castaneum. Both CPs belong to the CPR family, which includes proteins that have an amino acid sequence motif known as the Rebers & Riddiford (R&R) consensus sequence. Injection of double-stranded RNA (dsRNA) for TcCPR27 and TcCPR18 resulted in insects with shorter, wrinkled, warped and less rigid elytra than those from control insects. To gain a more comprehensive understanding of the roles of CPs in cuticle assembly, we analyzed for the precise localization of TcCPR27 and the ultrastructural architecture of cuticle in TcCPR27- and TcCPR18-deficient elytra. Transmission electron microscopic analysis combined with immunodetection using goldlabeled secondary antibody revealed that TcCPR27 is present in dorsal elytral procuticle both in the horizontal laminae and in vertical pore canals. dsRNA-mediated RNA interference (RNAi) of TcCPR27 resulted in abnormal electron-lucent laminae and pore canals in elytra except for the boundary between these two structures in which electron-dense molecule(s) apparently accumulated. Insects subjected to RNAi for TcCPR18 also had disorganized laminae and pore canals in the procuticle of elytra. Similar ultrastructural defects were also observed in other body wall regions with rigid cuticle such as the thorax and legs of adult T. castaneum. TcCPR27 and TcCPR18 are required for proper formation of the horizontal chitinous laminae and vertical pore canals that are critical for formation and stabilization of rigid adult cuticle

Functional specialization among members of knickkopf family of proteins in insect cuticle organization.

Citation: Chaudhari SS, Moussian B, Specht CA, Arakane Y, Kramer KJ, Beeman RW, et al. (2014) Functional Specialization Among Members Of Knickkopf Family Of Proteins In Insect Cuticle Organization. PLoS Genet 10(8): e1004537. doi:10.1371/journal.pgen.1004537Our recent study on the functional analysis of the Knickkopf protein from T. castaneum (TcKnk), indicated a novel role for this protein in protection of chitin from degradation by chitinases. Knk is also required for the laminar organization of chitin in the procuticle. During a bioinformatics search using this protein sequence as the query, we discovered the existence of a small family of three Knk-like genes (including the prototypical TcKnk) in the T. castaneum genome as well as in all insects with completed genome assemblies. The two additional Knk-like genes have been named TcKnk2 and TcKnk3. Further complexity arises as a result of alternative splicing and alternative polyadenylation of transcripts of TcKnk3, leading to the production of three transcripts (and by inference, three proteins) from this gene. These transcripts are named TcKnk3-Full Length (TcKnk3-FL), TcKnk3-5′ and TcKnk3-3′. All three Knk-family genes appear to have essential and non-redundant functions. RNAi for TcKnk led to developmental arrest at every molt, while down-regulation of either TcKnk2 or one of the three TcKnk3 transcripts (TcKnk3-3′) resulted in specific molting arrest only at the pharate adult stage. All three Knk genes appear to influence the total chitin content at the pharate adult stage, but to variable extents. While TcKnk contributes mostly to the stability and laminar organization of chitin in the elytral and body wall procuticles, proteins encoded by TcKnk2 and TcKnk3-3′ transcripts appear to be required for the integrity of the body wall denticles and tracheal taenidia, but not the elytral and body wall procuticles. Thus, the three members of the Knk-family of proteins perform different essential functions in cuticle formation at different developmental stages and in different parts of the insect anatomy

Budget Processes: Theory and Experimental Evidence

This paper studies budget processes, both theoretically and experimentally. We compare the outcomes of bottom-up and top-down budget processes. It is often presumed that a top-down budget process leads to a smaller overall budget than a bottom-up budget process. Ferejohn and Krehbiel (1987) showed theoretically that this need not be the case. We test experimentally the theoretical predictions of their work. The evidence from these experiments lends strong support to their theory, both at the aggregate and the individual subject level

The impact of interactions, bars, bulges, and AGN on star formation efficiency in local massive galaxies

Using observations from the GASS and COLD GASS surveys and complementary data from SDSS and GALEX, we investigate the nature of variations in gas depletion time observed across the local massive galaxy population. The large and unbiased COLD GASS sample allows us to assess the relative importance of galaxy interactions, bar instabilities, morphologies and the presence of AGN in regulating star formation efficiency. Both the H2 mass fraction and depletion time vary as a function of the distance of a galaxy from the main sequence in the SFR-M* plane. The longest gas depletion times are found in below-main sequence bulge-dominated galaxies that are either gas-poor, or else on average less efficient than disk-dominated galaxy at converting into stars any cold gas they may have. We find no link between AGN and these long depletion times. The galaxies undergoing mergers or showing signs of morphological disruptions have the shortest molecular gas depletion times, while those hosting strong stellar bars have only marginally higher global star formation efficiencies as compared to matched control samples. Our interpretation is that depletion time variations are caused by changes in the ratio between the gas mass traced by the CO(1-0) observations, and the gas mass in high density star-forming cores, with interactions, mergers and bar instabilities able to locally increase pressure and raise the ratio of efficiently star-forming gas to CO-detected gas. Building a sample representative of the local massive galaxy population, we derive a global Kennicutt-Schmidt relation of slope 1.18+/-0.24, and observe structure within the scatter around this relation, with galaxies having low (high) stellar mass surface densities lying systematically above (below) the mean relation, suggesting that gas surface density is not the only parameter driving the global star formation ability of a galaxy.Comment: 19 pages, 12 figures, accepted for publication in Ap

Low CO Luminosities in Dwarf Galaxies

[Abridged] We present maps of CO 2-1 emission covering the entire star-forming disks of 16 nearby dwarf galaxies observed by the IRAM HERACLES survey. The data have 13 arcsec angular resolution, ~250 pc at our average distance of 4 Mpc, and sample the galaxies by 10-1000 resolution elements. We apply stacking techniques to perform the first sensitive search for CO emission in dwarfs outside the Local Group ranging from single lines-of-sight, stacked over IR-bright regions of embedded star formation, and stacked over the entire galaxy. We detect 5 dwarfs in CO with total luminosities of L_CO = 3-28 1e6 Kkmspc2. The other 11 dwarfs remain undetected in CO even in the stacked data and have L_CO < 0.4-8 1e6 Kkmspc2. We combine our sample of dwarfs with a large literature sample of spirals to study scaling relations of L_CO with M_B and metallicity. We find that dwarfs with metallicities of Z ~ 1/2-1/10 Z_sun have L_CO about 1e2-1e4x smaller than spirals and that their L_CO per unit L_B is 10-100x smaller. A comparison with tracers of star formation (FUV and 24 micron) shows that L_CO per unit SFR is 10-100x smaller in dwarfs. One possible interpretation is that dwarfs form stars much more efficiently, however we argue that the low L_CO/SFR ratio is due to significant changes of the CO-to-H2 conversion factor, alpha_CO, in low metallicity environments. Assuming a constant H2 depletion time of 1.8 Gyr (as found for nearby spirals) implies alpha_CO values for dwarfs with Z ~ 1/2-1/10 Z_sun that are more than 10x higher than those found in solar metallicity spirals. This significant increase of alpha_CO at low metallicity is consistent with previous studies, in particular those which model dust emission to constrain H2 masses. Even though it is difficult to parameterize the metallicity dependence of alpha_CO, our results suggest that CO is increasingly difficult to detect at lower metallicities.Comment: Accepted for publication in the Astronomical Journal, 19 pages, 7 figure

COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties

We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30m telescope, we measure the CO(1-0) line in a sample of ~350 nearby (D=100-200 Mpc), massive galaxies (log(M*/Msun)>10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with SDSS photometry and spectroscopy, GALEX imaging and high-quality Arecibo HI data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. The overall CO detection rate is 54%, but our survey also uncovers the existence of sharp thresholds in galaxy structural parameters such as stellar mass surface density and concentration index, below which all galaxies have a measurable cold gas component but above which the detection rate of the CO line drops suddenly. The mean molecular gas fraction MH2/M* of the CO detections is 0.066+/-0.039, and this fraction does not depend on stellar mass, but is a strong function of NUV-r colour. Through stacking, we set a firm upper limit of MH2/M*=0.0016+/-0.0005 for red galaxies with NUV-r>5.0. The average molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with significant scatter from one galaxy to the next. The existence of strong detection thresholds in both the HI and CO lines suggests that "quenching" processes have occurred in these systems. Intriguingly, atomic gas strongly dominates in the minority of galaxies with significant cold gas that lie above these thresholds. This suggests that some re-accretion of gas may still be possible following the quenching event.Comment: Accepted for publications in MNRAS. 32 pages, 25 figure