The incredible shrinking dewlap: signal size,skin elasticity,and mechanical design in the green anole lizard (Anolis carolinensis)

The expression of male secondary sexual traits can be dynamic, changing size, shape, color, or structure over the course of different seasons. However, the factors underlying such changes are poorly understood. In male Anolis carolinensis lizards, a morphological secondary sexual signal called the dewlap changes size seasonally within individuals. Here, we test the hypothesis that seasonal changes in male dewlap size are driven by increased use and extension of the dewlap in spring and summer, when males are breeding, relative to the winter and fall. We captured male green anole lizards prior to the onset of breeding and constrained the dewlap in half of them such that it could not be extended. We then measured dewlap area in the spring, summer, and winter, and dewlap skin and belly skin elasticity in summer and winter. Dewlaps in unconstrained males increase in area from spring to summer and then shrink in the winter, whereas the dewlaps of constrained males consistently shrink from spring to winter. Dewlap skin is significantly more elastic than belly skin, and skin overall is more elastic in the summer relative to winter. These results show that seasonal changes in dewlap size are a function of skin elasticity and display frequency, and suggest that the mechanical properties of signaling structures can have important implications for signal evolution and design.     

Metabolism of norepinephrine during nerve stimulation in dog trachea

We determined the relative importance of neuronal and extraneuronal uptake in the metabolism of norepinephrine (NE) released during electrical stimulation (ES) of isolated canine tracheal smooth muscle (TSM). Strips of TSM were labeled with L-[3H]NE (2 X 10(-7) M) and mounted for superfusion. Superfusate was collected continuously before, during, and after ES (15 V, 0.5 ms, 5 Hz). Measurements were made of [3H]NE and its metabolites in superfusate and in tissue. Neuronal uptake followed by metabolism was estimated by measuring the amount of 3,4-dihydroxyphenylglycol (DOPEG). Extraneuronal uptake was estimated by measuring O-methylated metabolites (OMM). ES caused large increases in the efflux of NE, DOPEG, and OMM from TSM. However, the overflow of OMM was six times greater than that of DOPEG. Cocaine (10(-5) M) abolished the increased efflux of DOPEG during ES and enhanced the overflow of NE and OMM. We conclude that extraneuronal uptake constitutes the primary metabolic pathway for NE released from adrenergic nerves innervating TSM.     

Amplification of three threonine biosynthesis genes inCorynebacterium glutamicum and its influence on carbon flux in different strains

Summary The hom-thrB operon (homoserine dehydrogenase/homoserine kinase) and the thrC gene (threonine synthase) of Corynebacterium glutamicum ATCC 13 032 and the hom _FBR (homoserine dehydrogenase resistant to feedback inhibition by threonine) alone as well as hom _FBR-thrB operon of C. glutamicum DM 368-3 were cloned separately and in combination in the Escherichia coli/C. glutamicum shuttle vector pEK0 and introduced into different corynebacterial strains. All recombinant strains showed 8- to 20-fold higher specific activities of homoserine dehydrogenase, homoserine kinase, and/or threonine synthase compared to the respective host. In wild-type C. glutamicum, amplification of the threonine genes did not result in secretion of threonine. In the lysine producer C. glutamicum DG 52-5 and in the lysine-plus-threonine producer C. glutamicum DM 368-3 overexpression of hom-thrB resulted in a notable shift of carbon flux from lysine to threonine whereas cloning of hom _FBR-thrB as well as of hom _FBR in C. glutamicum DM 368-3 led to a complete shift towards threonine or towards threonine and its precursor homoserine, respectively. Overexpression of thrC alone or in combination with that of hom _FBR and thrB had no effect on threonine or lysine formation in all recombinant strains tested. Offprint requests to: B. J. Eikmanns     

Longevity of seven species of cactophilic Drosophila and D. melanogaster on carbohydrates

Adults of 6 species of Drosophila that use decaying prickly pear cactus (Opuntia sp.) as breeding and feeding sites were compared to each other and to D. nigrospiracula, whose host is saguaro cactus, and to the cosmopolitan D. melanogaster, in their utilization of 21 sugars for longevity (time to 50% mortality). In general, the utilization of sugars by these flies for longevity followed the pattern observed with the other insects. None of the species were able to live very long on solutions of pentoses, uronic acids, inositol, rhamnose, sorbose or the β-linked disaccharides, lactose and cellobiose. Althogh all could use glucose, fructose, sucrose, maltose and melezitose well, their life spans on galactose, mannose, trehalose and raffinose were more variable. Two of the Opuntia feeders were also tested on a number of other carbohydrates. Ribitol, mannitol, sorbitol and xylitol significantly prolonged the life of D. arizonensis but not that of D. wheeleri. Neither species lived long on solutions of arabitol, galactitol, starch, inulin or on arabogalactan.     

Intramolecular uncoupling of chromophore photoconversion from structural signaling determinants drive mutant phytochrome B photoreceptor to far-red light perception

The phytochrome (phy) photoreceptor family regulates almost all aspects of plant development in a broad range of light environments including seed germination, onset of the photomorphogenic program in seedling stage, the shade avoidance syndrome in competing plant communities, flowering induction and senescence of adult plants. During evolution two clearly distinct classes of phy-s emerged covering these very different physiological tasks.¹ PhyA is rapidly degraded in its activated state. PhyA functions in controlling seed germination at very low light intensities (very low fluence response, VLFR) and seedling establishment under photosynthetic shade conditions (high irradiance response, HIR) where the far-red portion of the transmitted light to understorey habitats is substantially enhanced. Arabidopsis phyB together with phyC, D and E belongs to the relatively stable sensor class in comparison to the light labile phyA. PhyB functions at all stages of development including seed germination and seedling establishment, mediates classical red/far-red reversible low fluence responses (LFR) as well as red light high irradiance responses, and it is considered to be the dominating phytochrome sensor of its class.