Thermal Dependence of Tongue-flicking and Comments on Use of Tongue-flicking as an Index of Squamate Behavior

Tongue-flicking rate has often been used as a dependent variable or a component of a dependent variable taken as a measure of responsiveness to chemical stimuli by lizards and snakes. Because temperature has been controlled in most studies, effects of temperature have been largely overlooked. In this study, a constant stimulus, the adult cloacal odor of a conspecific female, was presented to adult scincid lizards (Eumeces laticeps) and temperature was from 15 ° to 35 °C. Tongue-flicking rates by adult Eumeces laticeps in response to cloacal odors of conspecific females were strongly thermally dependent in 20 s and 60 s trial periods. The tongue-flick-temperature curve appears to be roughly quadratic over the entire 15 °-35 °C range studied, with very low rates at 15 ° and 20 °C followed by a rapid rise to maximum tongue-flicking rate at 30 ° and rapid decline to 35 °C. Presumably, similar relationships apply to other lizards and snakes with modifications related to ecological characteristics such as diel activity cycle and foraging mode, to relative position on a scale of eurythermy-stenothermy, and to taxon. Thermal response curves for other stimuli, especially prey odors, are likely to have the same basic form, but have not been determined.     

AdaptivSearch: A Novel Iterative Algorithm for the Generation of n-dimensional Hypersurfaces Using an Adaptive Numerical Strategy

AdaptivSearch is the first adaptive strategy based algorithm for the rational and economical construction of n-dimensional hypersurfaces. AdaptivSearch works iteratively: At each step it parcels out the definition range into several triangles, evaluates the worst according to a built-in error criterion, and refines the approximation to the unknown function by choosing the barycenter of this partial area as the node to be calculated next. Based upon the error criterion, AdaptivSearch selectively approaches those parts of the hypersurface in which the curvature exhibits the strongest changes. Some examples of AdaptivSearch applications for both analytical functions and chemical model surfaces are given in order to demonstrate the behavior of the algorithm. These show its broad applicability and the usefulness, especially for chemical problems.     

Low codon bias and high rates of synonymous substitution in Drosophila hydei and D. melanogaster histone genes

We have evaluated codon usage bias in Drosophila histone genes and have obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat unit. This repeat contains genes for all five histone proteins (H1, H2a, H2b, H3, and H4) and differs from the previously reported one by a second EcoRI site. These D. hydei repeats have been aligned to each other and to the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from D. melanogaster. In each species, base composition at synonymous sites is similar to the average genomic composition and approaches that in the small intergenic spacers of the histone gene repeats. Accumulation of synonymous changes at synonymous sites after the species diverged is quite high. Both of these features are consistent with the relatively low codon usage bias observed in these genes when compared with other Drosophila genes. Thus, the generalization that abundantly expressed genes in Drosophila have high codon bias and low rates of silent substitution does not hold for the histone genes.      

Reduction of food intake and weight gain by the ob protein requires a specific secondary structure and is reversible.

BACKGROUND: Obesity, the condition of excessive accumulation of fat is a poorly understood disorder and is a risk factor for type II diabetes, hypertension, and hyperlipidaemia. Recently, a putative mouse obese gene was cloned and its product, termed ob protein, was shown to be involved in the regulation of body weight. MATERIALS AND METHODS: Bacterial and insect cells were used for expression of recombinant mouse ob protein. Amino-terminal sequence analysis and site-directed mutagenesis were used to identify and characterize the mature form of ob protein. Genetically obese mice and wild-type rats were used to determine the biological activity of ob protein. RESULTS: Mouse ob protein is synthesized as a precursor molecule, the mature form of which was found in mouse serum. Biochemical analysis identified the processing site in the ob precursor molecule and an intramolecular disulfide bond in the mature form that is necessary for activity. Reduction of food intake and weight gain after administration of ob protein to genetically obese mice and wild-type rats is reversible. DISCUSSION: This study demonstrates that ob protein is a secreted satiety factor which regulates body weight and reduces food intake even in animals with no genetic body weight abnormalities. The failure of ob protein to effect these parameters in db/db mice supports the hypothesis that these mice are deficient in a signaling molecule that normally responds to the ob protein.     

Local differentiation and plasticity in size and sex expression in jack-in-the-pulpit, Arisaema triphyllum (Araceae)

The size advantage hypothesis suggests that natural selection will favor size-dependent sex expression when one sex gains more than the other by being large. But members of a minority sex will also have a higher reproductive value, on average. Thus, an individual's reproductive success depends on the reproductive decisions made by neighboring individuals. As a result, the optimal relationship between size and sex may differ among populations. In Arisaema triphyllum, the probability for an individual to be female increases with size, regardless of the character measured. A reciprocal transplant experiment showed the relationship between size and sexual expression is environmentally plastic. Plants originating from our two study sites became female at a larger average size when grown at one site than when grown at the other. In addition to environmental influence on sex expression, the experiment demonstrated genetic differences in the relationship between size and sex. Plants collected from one site became female at a larger size than those from the other, regardless of where they were grown. Thus, while the environment in which an individual was grown had a substantial influence on its sex expression, populations only a few kilometers apart have genetically different relationships between size and sex.     

Growth differentiation factor-9 stimulates proliferation but suppresses the follicle-stimulating hormone-induced differentiation of cultured granulosa cells from small antral and preovulatory rat follicles

In addition to pituitary gonadotropins and paracrine factors, ovarian follicle development is also modulated by oocyte factors capable of stimulating granulosa cell proliferation but suppressing their differentiation. The nature of these oocyte factors is unclear. Because growth differentiation factor-9 (GDF-9) enhanced preantral follicle growth and was detected in the oocytes of early antral and preovulatory follicles, we hypothesized that this oocyte hormone could regulate the proliferation and differentiation of granulosa cells from these advanced follicles. Treatment with recombinant GDF-9, but not FSH, stimulated thymidine incorporation into cultured granulosa cells from both early antral and preovulatory follicles, accompanied by increases in granulosa cell number. Although GDF-9 treatment alone stimulated basal steroidogenesis in granulosa cells, cotreatment with GDF-9 suppressed FSH-stimulated progesterone and estradiol production. In addition, GDF-9 cotreatment attentuated FSH-induced LH receptor formation. The inhibitory effects of GDF-9 on FSH-induced granulosa cell differentiation were accompanied by decreases in the FSH-induced cAMP production. These data suggested that GDF-9 is a proliferation factor for granulosa cells from early antral and preovulatory follicles but suppresses FSH-induced differentiation of the same cells. Thus, oocyte-derived GDF-9 could account, at least partially, for the oocyte factor(s) previously reported to control cumulus and granulosa cell differentiation.     

ADP-ribosylation of the ras-related, GTP-binding protein RhoA inhibits lymphocyte-mediated cytotoxicity.

The Rho proteins are identified as a subgroup of the Ras superfamily of low molecular weight GTP-binding proteins. We have studied the expression of these proteins in human cytotoxic natural killer cells and found that RhoA is the most abundantly expressed member of the Rho family. The Rho proteins are specific substrates for ADP-ribosylation catalyzed by the C3 exoenzyme from Clostridium botulinum. We report here that introduction of recombinant C3 in electropermeabilized natural killer cells or in cytotoxic T lymphocytes resulted in a dose-dependent inhibition of their cytolytic function. Furthermore, a single substrate is efficiently ADP-ribosylated by C3 in extracts from cytotoxic cells. Biochemical analyses indicate that this substrate is RhoA, and subcellular fractionation experiments demonstrate that it is essentially present in the cytosol of the cells. Western blot analysis, however, revealed that a small proportion of the Rho protein can be found associated with the cell membrane as well as with the cytotoxic granules. These results indicate that the low molecular weight GTP-binding protein RhoA is present in cytotoxic lymphocytes and plays a critical role in cell-mediated cytotoxicity.     

Role of XIAP protein, a human member of the inhibitor of apoptosis (IAP) protein family, in phytohemagglutinin-induced apoptosis of human T cell lines

A new family of human genes xiap, hiap-1 and hiap-2, which are homologous to the baculovirus iap (inhibitor of apoptosis) genes cp-iap and op-iap, has been recently cloned and shown to suppress apoptosis after serum withdrawal or exposure to a free radical inducer. In order to examine the role of one of these human genes, namely xiap, in lymphoid cells, we studied XIAP expression, after PHA stimulation in three different human T cell lines. We report here that stimulation with PHA resulted in the human T cell lines undergoing apoptosis, as assessed by DNA fragmentation and by propidiumiodide (PI) staining and flow cytometry. When XIAP protein expression was evaluated by Western blot, we observed that the induction of apoptosis by PHA was associated with a parallel decrease of XIAP expression. We also provide evidence that stably transfected Jurkat cells containing the xiap open reading frame became resistant to PHA-induced apoptosis. These data suggest a role for XIAP protein in the regulation of apoptosis in lymphoid cells. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optimal foraging constrains macroecological patterns: body size and dietary niche breadth in lizards

Aim  To explore and identify probable mechanisms contributing to the relationships among body size, dietary niche breadth and mean, minimum, maximum and range of prey size in predaceous lizards.
Location  Our data set includes species from tropical rainforests, semi-arid regions of Brazil, and from deserts of the south-western United States, Australia and the Kalahari of Africa.
Methods  We calculated phylogenetic and non-phylogenetic regressions among predator body size, dietary breath and various prey size measures.
Results  We found a negative association between body size and dietary niche breadth in 159 lizard species sampled across most evolutionary lineages of squamate reptiles and across major continents and habitats. We also show that mean, minimum, maximum and range of prey size were positively associated with body size.
Main conclusions  Our results suggest not only that larger lizards tend to eat larger prey, but in doing so offset their use of smaller prey. Reduction of dietary niche breadth with increased body size in these lizards suggests that large predators target large and more profitable prey. Consequently, the negative association between body size and niche breadth in predators most likely results from optimal foraging. Though this result may appear paradoxical and runs counter to previous studies, resources for predators may be predictably more limited than resources for herbivores, thus driving selection for more profitable prey.