Biparental care in house sparrows: negotiation or sealed bid?

We explored the responses of monogamous house sparrow parentsto deviations in their mates' contributions to nestling provisioning.Following 1-2 days of baseline measurement of parental fooddelivery rates, we applied small lead fishing weights to thetail feathers of either male or female parents. Weighting hadmuch greater immediate impact on male parental care than on female care, but the handicapping had little long-term effecton either male or female provisioning behavior. When parentalperformance of handicapped males was most impaired, their matesdid not show significant increases in parental care as compensation,nor did females mated to handicapped males reduce their provisioningas their mates recovered from weighting. Similarly, males matedto handicapped females did not respond to their partners' recovery with declines in their own efforts; paradoxically, these malesshowed a sustained elevation of provisioning throughout thepost-treatment interval, despite no significant reduction inprovisioning by weighted females. The apparent insensitivityof both males and females to changes in their mates' parentalbehavior, and the ineffectiveness of current partner behaviorat predicting an individual's provisioning effort, fail toconform to assumptions of biparental care models that requirefacultative responses to partner deviations in effort. Instead,the remarkable consistency of each individual's behavior supportsthe notion of "sealed bids" and suggests that variation innestling provisioning is largely attributable to factors thatare independent of the mate's current behavior, such as differencesin individual quality.     

Gene-specific formation and repair of cisplatin intrastrand adducts and interstrand cross-links in Chinese hamster ovary cells

We have used three methods to study the formation and repair of intrastrand adducts and interstrand cross-links in the DNA of Chinese hamster ovary cells induced by the anticancer drug cis-diamminedichloroplatinum II (cisplatin). Using atomic absorption spectroscopy, we found that 21% of the total genomic cisplatin adducts were removed at 8 h and 42% at 24 h. We used ABC excinuclease digestion, coupled with out previously reported methodology to quantify DNA in specific genomic regions. These adducts were removed faster in the transcribed dihydrofolate reductase and c-myc genes compared to a noncoding fragment, a region containing the little or nontranscribed c-fos oncogene, and to the overall genome. Interstrand cross-links in specific sequences were quantified by Southern hybridization of denatured-renatured DNA separated on a neutral gel. We found that cross-links were removed more efficiently from the gene regions than intrastrand adducts and, at high levels of cross-linking, removal was similar from transcribed and from nontranscribed regions.     

Chromosomal assignment of the human genes coding for the major proteins of the desmosome junction, desmoglein DGI (DSG), desmocollins DGII/III (DSC), desmoplakins DPI/II (DSP), and plakoglobin DPIII (JUP)

We have established PCR assays for the genes coding for the major proteins of the desmosome type of cell junction, the desmosomal cadherins DGI (desmoglein) and DGII/III (desmocollins), and the plaque proteins DPI/II (desmoplakin) and DPIII (plakoglobin) and used them to test human-mouse and human-rat somatic cell hybrids with different contents of human chromosomes. From these data we were able to assign DGI to chromosome 18 (DSG), DGII/III to chromosome 9p (DSC), DPI/II to chromosome 6p21-ter(DSP), and DPIII to chromosome 7 (JUP).     

ELECTRON MICROSCOPY OF HELA CELLS AFTER THE INGESTION OF COLLOIDAL GOLD

Tissue cultures of HeLa cells were grown in media containing colloidal gold, and after various intervals, the cells were fixed, embedded, and sectioned for electron microscopy. Uncoated grids with small holes were used in many of the experiments. Intracellular particles of gold were identified in areas surrounded by single membranes, in moderately dense granules, in globoid bodies, and in the cytoplasmic matrix. Gold particles were not found in typical mitochondria, Golgi complex, ergastoplasm (granular forms of endoplasmic reticulum), or nuclei. The phenomenon of pinocytosis was considered to be the most likely means by which the gold particles were ingested, and the locations of gold particles appeared to have significance concerning theories that membranous organelles of the cytoplasm may be derived from the cell membrane.     

Subunit interactions of class I histocompatibility antigens

The kinetics of dissociation of iodinated beta 2-microglobulin (beta 2m) from the papain-solubilized class I histocompatibility antigen HLA-B7 have been investigated. In the presence of unlabeled beta 2m, most of the HLA dissociates according to a single rate constant, whereas in the absence of unlabeled beta 2m, the system approaches an equilibrium dependent upon the initial HLA concentration. When iodinated beta 2m is incubated with unlabeled HLA-B7, the rate of incorporation of beta 2m into the complex is much less dependent on the concentration than is expected for a simple association/dissociation system; instead, the system behaves as if the "activity" (in a thermodynamic sense) of the HLA heavy-chain intermediate cannot surpass a critical concentration. The dissociation rate for each class I specificity is a function of temperature, ionic strength, pH, and the status of the heavy chain (papain solubilized vs. detergent solubilized). High temperature, high ionic strength, and extremes of pH promote dissociation. The intact molecule dissociates about 10 times more slowly than the papain-solubilized molecule. In contrast, the rate of dissociation of all papain-solubilized class I antigens tested falls within the range of about a factor of 2. The presence of the carbohydrate has no effect on the rate of dissociation. The possibility that HLA class I antigen dissociation may occur in vivo within acidic internal vesicles is discussed.     

Rapid Parallel Adaptation to Anthropogenic Heavy Metal Pollution

The impact of human-mediated environmental change on the evolutionary trajectories of wild organisms is poorly understood. In particular, capacity of species to adapt rapidly (in hundreds of generations or less), reproducibly and predictably to extreme environmental change is unclear. Silene uniflora is predominantly a coastal species, but it has also colonized isolated, disused mines with phytotoxic, zinc-contaminated soils. To test whether rapid, parallel adaptation to anthropogenic pollution has taken place, we used reduced representation sequencing (ddRAD) to reconstruct the evolutionary history of geographically proximate mine and coastal population pairs and found largely independent colonization of mines from different coastal sites. Furthermore, our results show that parallel evolution of zinc tolerance has occurred without gene flow spreading adaptive alleles between mine populations. In genomic regions where signatures of selection were detected across multiple mine-coast pairs, we identified genes with functions linked to physiological differences between the putative ecotypes, although genetic differentiation at specific loci is only partially shared between mine populations. Our results are consistent with a complex, polygenic genetic architecture underpinning rapid adaptation. This shows that even under a scenario of strong selection and rapid adaptation, evolutionary responses to human activities (and other environmental challenges) may be idiosyncratic at the genetic level and, therefore, difficult to predict from genomic data.     

Parasitoids in low-level populations ofLymantria dispar [Lep.: Lymantriidae] in different forest physiographic zones

A 2-year study was conducted on the distribution of parasitoids of gypsy moth,Lymantria dispar (L.) (Lep.: Lymantriidae), in mesic and adjacent higher elevation transition and xeric forest habitats in Vermont (U.S.A.). In both years, overall parasitism ranged from 12–18% in each habitat. When analyzed according to the life stage at which the host was collected, parasitism rates of greater than 40% were obtained among the late instars.Parasetigena silvestris (Robineau-Desvoidy) andPhobocampe disparis (Viereck) were recovered most commonly from the mesic habitat, andCotesia melanoscelus (Ratzeburg) andBlepharipa pratensis (= Sturmia scutellata) (Meigen) were most common in collections from the xeric area. Parasitism byCompsilura concinnata (Meigen) occurred at similar levels in all three habitats, and this species was responsible for the highest parasitism rates on the site, reaching 40% among the late instars in 1985. Percent parasitism byC. concinnata increased three-four-fold from 1984 to 1985, while parasitism by other species declined.     

Binocular depth perception and the cerebral cortex

Our ability to coordinate the use of our left and right eyes and to make use of subtle differences between the images received by each eye allows us to perceive stereoscopic depth, which is important for the visual perception of three-dimensional space. Binocular neurons in the visual cortex combine signals from the left and right eyes. Probing the roles of binocular neurons in different perceptual tasks has advanced our understanding of the stages within the visual cortex that lead to binocular depth perception.     

Relative effectiveness of calcium and magnesium in the alleviation of rhizotoxicity in wheat induced by copper,zinc, aluminum,sodium, and low pH

Plant and Soil - Root elongation in short-term experiments with wheat (Triticum aestivum&;nbsp;L.) seedlings demonstrated that the following ions were rhizotoxic in the order Cu2+&;gt;Al...