Song discrimination by nestling collared flycatchers during early development

Pre-zygotic isolation is often maintained by species-specific signals and preferences. However, in species where signals are learnt, as in songbirds, learning errors can lead to costly hybridization. Song discrimination expressed during early developmental stages may ensure selective learning later in life but can be difficult to demonstrate before behavioural responses are obvious. Here, we use a novel method, measuring changes in metabolic rate, to detect song perception and discrimination in collared flycatcher embryos and nestlings. We found that nestlings as early as 7 days old respond to song with increased metabolic rate, and, by 9 days old, have increased metabolic rate when listening to conspecific when compared with heterospecific song. This early discrimination between songs probably leads to fewer heterospecific matings, and thus higher fitness of collared flycatchers living in sympatry with closely related species.     

Evolution of the elaborate male intromittent organ of Xiphophorus fishes

Internally fertilizing animals show a remarkable diversity in male genital morphology that is associated with sexual selection, and these traits are thought to be evolving particularly rapidly. Male fish in some internally fertilizing species have “gonopodia,” highly modified anal fins that are putatively important for sexual selection. However, our understanding of the evolution of genital diversity remains incomplete. Contrary to the prediction that male genital traits evolve more rapidly than other traits, here we show that gonopodial traits and other nongonopodial traits exhibit similar evolutionary rates of trait change and also follow similar evolutionary models in an iconic genus of poeciliid fish (Xiphophorus spp.). Furthermore, we find that both mating and nonmating natural selection mechanisms are unlikely to be driving the diverse Xiphophorus gonopodial morphology. Putative holdfast features of the male genital organ do not appear to be influenced by water flow, a candidate selective force in aquatic habitats. Additionally, interspecific divergence in gonopodial morphology is not significantly higher between sympatric species, than between allopatric species, suggesting that male genitals have not undergone reproductive character displacement. Slower rates of evolution in gonopodial traits compared with a subset of putatively sexually selected nongenital traits suggest that different selection mechanisms may be acting on the different trait types. Further investigations of this elaborate trait are imperative to determine whether it is ultimately an important driver of speciation.     

Some aspects of substrate specificity in biological demethylation at C4 of steroids

In order to ascertain some of the structural requirements for substrate activity in the oxidative demethylation at C4 of steroids by rat liver enzymes, several steroids have been synthesized, labeled with tritium, and incubated with rat liver enzyme preparations. These include 4α-formyl-4β-methylcholestan-3β-ol (4), 4-methylcholest-3-ene (14), 3β,4β-epoxy-4α-methylcholestane (20), 3α,4α-epoxy-4β-methylcholestane (18), 4α-ethyl-4β-methylcholestan-3β-ol (21), and 4β-ethyl-4α-methylcholestan-3β-ol (22). Enzymic incubation demethylates 4 with an efficiency consistent with its being an intermediate in the biological demethylation of 4,4-dimethyl sterols, but all of the other substrates are recovered unchanged.     

Inhalation Therapy

Joint Accord on the Role of Respiratory (Inhalation) Therapy Personnel in Airway Management and Endotracheal Intubation endorsed by the California Medical Association, the California Hospital Association, the California Society for Respiratory Therapy, the California Society of Anesthesiologists and the California Thoracic Society.     

Determination of the Length of the V Colicinogenic Factor and a Derivative Fertility Factor

Plasmid deoxyribonucleic acid from Escherichia coli harboring either the V colicinogenic factor (Col V) or the derivative fertility factor (Fv), (a non-colicin-producing fertility factor derived from Col V) were separated by cesium chloride-ethidium bromide centrifugation and examined by electron microscopy. Results indicate a deletion of 11 mum of deoxyribonucleic acid in the transition from Col V to Fv.     

Effect of an inhibitor of DNA methylation on T cells. I. 5-Azacytidine induces T4 expression on T8+ T cells

Maturing thymocytes express a series of cell surface glycoproteins which can be identified by monoclonal antibodies. The stage II or common thymocyte expresses the phenotype T4+T8+T6+T3-. In response to unknown signals, but presumably involving interactions with products of the major histocompatibility complex, the thymocyte suppresses either the T8 or T4 gene, becoming committed to the T4+T8- or T4-T8+ phenotype. With maturation, the thymocyte also becomes T6-T3+. To study whether DNA methylation may be involved in regulating expression of these determinants in mature T cells, we treated cloned interleukin 2-dependent T8- and T4-bearing T cells with 5-azacytidine (5-azaC), a nucleoside analog which inhibits methylation of newly synthesized DNA. In this report, we show that T8+ T cells treated with 5-azaC express the phenotype T8+T4+T6-T3+. Treatment of the same cells with hydroxyurea, an inhibitor of DNA synthesis, failed to induce T4 on T8+ cells. These results suggest that expression of the T4 gene may be suppressed by DNA methylation in mature T8+ cells.