Ornament size and colour as alternative strategies for effective communication in gliding lizards

Sexual ornamentation needs to be conspicuous to be effective in attracting potential mates and defending territories and indeed, a multitude of ways exists to achieve this. Two principal mechanisms for increasing conspicuousness are to increase the ornament's colour or brightness contrast against the background and to increase the size of the ornament. We assessed the relationship between the colour and size of the dewlap, a large extendible throat‐fan, across a range of species of gliding lizards (Agamidae; genus Draco) from Malaysia and the Philippines. We found a negative relationship across species between colour contrast against the background and dewlap size in males, but not in females, suggesting that males of different species use increasing colour contrast and dewlap size as alternative strategies for effective communication. Male dewlap size also increases with increasing sexual size dimorphism, and dewlap colour and brightness contrast increase with increasing sexual dichromatism in colour and brightness, respectively, suggesting that sexual selection may act on both dewlap size and colour. We further found evidence that relative predation intensity, as measured from predator attacks on models placed in the field, may play a role in the choice of strategy (high chromatic contrast or large dewlap area) a species employs. More broadly, these results highlight that each component in a signal (such as colour or size) may be influenced by different selection pressures and that by assessing components individually, we can gain a greater understanding of the evolution of signal diversity.     

Repair replication and unscheduled DNA synthesis in mammalian cell lines showing differential sensitivity to alkylating agents

Repair replication has been measured by CsCl density gradient centrifugation in cell lines showing differential sensitivity to mono- and bifunctional alkylating agents. A correlation between cellular sensitivity as measured by the D₀ value and amount of repair replication was demonstrated after exposure of Yoshida cells to nitrogen mustard (HN2) and methylene dimethanesulphonate (MDMS). No differences in the amount of repair replication after methyl methanesulphonate (MMS) were observed in two L5178Y cell lines which differed in sensitivity by virtue of the shoulder size only. The Yoshida cell lines showed no difference in sensitivity to MMS and no difference in amount of repair replication. Incorporation of tritiated thymidine 9[³H]TdR) after drug treament was also measured by autoradiography. The qualitative differences observed between the two cell lines were similar to those obtained in density gradient experiments. The temporal pattern of [³H]TdR uptake indicated that the reduced repair replication observed in the sensitive line after HN2 and MDMS is not due to slower synthesis. The kinetics of [^3H]TdR incorporation differed for all three mutagens suggesting that different enzymes may be involved in each case.     

Bioactivity and molecular modelling of diphenylsulfides and diphenylselenides

Bis(2-bromo-4,5-dimethoxyphenyl)sulfide (5) and bis(2-bromo-4,5-dimethoxyphenyl) selenide (7) have been shown to block cells in the G2/M phase of the cell cycle, whereas the debromo (4, 6) equivalents do not. The dibromoselenide (7) is cytotoxic to tumour cells in vitro and has been shown to increase the mitotic index of treated cells. These biological effects are consistent with disruption of the mitotic apparatus. This agent does not inhibit microtubule assembly in vitro, but does bind to tubulin. Molecular modelling of these structures indicates that their spatial and electronic structures may make an important contribution to the biological activity.     

Beta‐Adrenoceptor Activation Reduces Both Dermal Microvascular Endothelial Cell Migration via a cAMP‐Dependent Mechanism and Wound Angiogenesis

Angiogenesis is an essential process during tissue regeneration; however, the amount of angiogenesis directly correlates with the level of wound scarring. Angiogenesis is lower in scar‐free foetal wounds while angiogenesis is raised and abnormal in pathophysiological scarring such as hypertrophic scars and keloids. Delineating the mechanisms that modulate angiogenesis and could reduce scarring would be clinically useful. Beta‐adrenoceptors (β‐AR) are G protein‐coupled receptors (GPCRs) expressed on all skin cell‐types. They play a role in wound repair but their specific role in angiogenesis is unknown. In this study, a range of in vitro assays (single cell migration, scratch wound healing, ELISAs for angiogenic growth factors and tubule formation) were performed with human dermal microvascular endothelial cells (HDMEC) to investigate and dissect mechanisms underpinning β‐AR‐mediated modulation of angiogenesis in chick chorioallantoic membranes (CAM) and murine excisional skin wounds. β‐AR activation reduced HDMEC migration via cyclic adenosine monophosphate (cAMP)‐dependent and protein kinase A (PKA)‐independent mechanisms as demonstrated through use of an EPAC agonist that auto‐inhibited the cAMP‐mediated β‐AR transduced reduction in HDMEC motility; a PKA inhibitor was, conversely, ineffective. ELISA studies demonstrated that β‐AR activation reduced pro‐angiogenic growth factor secretion from HDMECs (fibroblast growth factor 2) and keratinocytes (vascular endothelial growth factor A) revealing possible β‐AR‐mediated autocrine and paracrine anti‐angiogenic mechanisms. In more complex environments, β‐AR activation delayed HDMEC tubule formation and decreased angiogenesis both in the CAM assay and in murine excisional skin wounds in vivo. β‐AR activation reduced HDMEC function in vitro and angiogenesis in vivo; therefore, β‐AR agonists could be promising anti‐angiogenic modulators in skin. J. Cell. Physiol. 230: 356–365, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.     

The in vitro lifespan of MRC-5 cells is shortened by 5-azacytidine-induced demethylation

The minor base 5-methylcytosine (5mC) in DNA may be important for the regulation of gene expression. Random loss of 5mC may occur during pre-replicative DNA synthesis in mortal cell strains, and thus give rise to biochemical aberrations in aging cells. 5-Azacytidine (5azaC) was used to induce loss of 5mC in DNA of human diploid fibroblasts (MRC-5) in an attempt to accelerate in vitro senescence. The 5mC content of DNA was measured by incorporation of [3H]uridine into dividing cells, hydrolysis of DNA and separation of bases by HPLC. In untreated MRC-5 cells, 5mC was 3.6% of the total cytosine (C+5mC) at population doubling (PD) 20 (28% of lifespan) and fell to 1.6% at PD 67 (97% of lifespan). A single pulse treatment with 5azaC (1 microgram/ml) induced demethylation and shortened the lifespan by 10% (6.8 PDs loss). Pulse-treated cells showed temporary growth inhibition, though they subsequently regained normal growth rate and morphology. However, uniform treatment with 0.1 microgram/ml 5azaC between PD 20 and 23 produced no immediate growth inhibition, but a 22% loss of 5mC and 25% decrement in lifespan (16.6 PDs loss). The present results indicate that 5mC levels fall during normal aging of MRC-5 cells and accelerated 5mC loss shortens the in vitro lifespan of these cells. Hypomethylation may thus be responsible for some aspects of in vitro aging.     

Synthetic peptides used to locate the alpha-bungarotoxin binding site and immunogenic regions on alpha subunits of the nicotinic acetylcholine receptor

Synthetic peptides corresponding to 57% of the sequence of alpha subunits of acetylcholine receptors from Torpedo californica electric organ and extending from the NH2 to the COOCH terminus have been synthesized. The alpha-bungarotoxin binding site on denatured alpha subunits was mapped within the sequence alpha 185-199 by assaying binding of 125I-alpha-bungarotoxin to slot blots of synthetic peptides. Further studies showed that residues in the sequence alpha 190-194, especially cysteines-alpha 192, 193, were critical for binding alpha-bungarotoxin. Reduction and alkylation studies suggested that these cysteines must be disulfide linked for alpha-bungarotoxin to bind. Binding sites for serum antibodies to native receptors or alpha subunits were mapped by indirect immunoprecipitation of 125I-peptides. Several antigenic sequences were identified, but a synthetic peptide corresponding to the main immunogenic region (which is highly conformation dependent) was not identified.     

Larval host plant affects fitness consequences of egg size variation in the seed beetle Stator limbatus

Egg size variation often has large effects on the fitness of progeny in insects. However, many studies have been unable to detect an advantage of developing from large eggs, suggesting that egg size variation has implications for offspring performance only under adverse conditions, such as during larval competition, periods of starvation, desiccation, or when larvae feed on low-quality resources. We test this hypothesis by examining the consequences of egg size variation for survivorship and development of a seed-feeding insect, Stator limbatus, on both a low-quality (Cercidium floridum) and a high-quality (Acacia greggii) host plant. Our results are consistent with the hypothesis. S. limbatus larval performance was affected by egg size only when developing on the poor-quality host (C. floridum); larvae from large eggs survived better on C. floridum than those from small eggs, while there was no evidence of an effect of egg size on progeny development time, body weight, or survivorship when larvae developed on A. greggii. These results indicate intense selection for large eggs within C. floridum-associated populations, but not in A. greggii-associated populations, so that egg size is predicted to vary among populations associated with different hosts. Our results also support this hypothesis; females from a C. floridum-associated population (Scottsdale) laid larger eggs than females from an A. greggii-associated population (Black Canyon City).     

Trophic Tangles through Time? Opposing Direct and Indirect Effects of an Invasive Omnivore on Stream Ecosystem Processes

Omnivores can impact ecosystems via opposing direct or indirect effects. For example, omnivores that feed on herbivores and plants could either increase plant biomass due to the removal of herbivores or decrease plant biomass due to direct consumption. Thus, empirical quantification of the relative importance of direct and indirect impacts of omnivores is needed, especially the impacts of invasive omnivores. Here we investigated how an invasive omnivore (signal crayfish, Pacifastacus leniusculus) impacts stream ecosystems. First, we performed a large-scale experiment to examine the short-term (three month) direct and indirect impacts of crayfish on a stream food web. Second, we performed a comparative study of un-invaded areas and areas invaded 90 years ago to examine whether patterns from the experiment scaled up to longer time frames. In the experiment, crayfish increased leaf litter breakdown rate, decreased the abundance and biomass of other benthic invertebrates, and increased algal production. Thus, crayfish controlled detritus via direct consumption and likely drove a trophic cascade through predation on grazers. Consistent with the experiment, the comparative study also found that benthic invertebrate biomass decreased with crayfish. However, contrary to the experiment, crayfish presence was not significantly associated with higher leaf litter breakdown in the comparative study. We posit that during invasion, generalist crayfish replace the more specialized native detritivores (caddisflies), thereby leading to little long-term change in net detrital breakdown. A feeding experiment revealed that these native detritivores and the crayfish were both effective consumers of detritus. Thus, the impacts of omnivores represent a temporally-shifting interplay between direct and indirect effects that can control basal resources.     

Testing a simple rule for dominance in resource competition

Competition for limiting resources long has been considered an important factor generating community structure. A minimal model of resource competition predicts that the species that reduces the limiting resource R to the lowest level ([Formula: see text]) will exclude its competitors. Whether this "[Formula: see text] rule" is robust to violations of model assumptions remains largely unknown. I conducted a competition experiment with four species of bacterivorous protists in laboratory microcosms and predicted the outcome from each species' [Formula: see text] value. I also examined how the outcome of competition, species abundances, and the effect of protists on bacterial density varied with productivity. Microcosms were unstirred batch cultures containing a variety of bacteria, challenging the robustness of the simplest competition models. Protists with low [Formula: see text] values were less affected by competition, although competing protists often coexisted. The values of [Formula: see text] can predict competitive dominance, even in the absence of competitive exclusion. Other model predictions were less robust. Contrary to expectation, densities of grazed bacteria increased with productivity, and the effect of some protists on bacterial density did not vary with productivity. Bacterial heterogeneity may account for deviations from model predictions. Further experiments should examine the conditions under which simple rules can be expected to identify dominant species.