CEO Pay-for-Performance Heterogeneity Using Quantile Regression (CRI 2009-002)

We provide some examples of how quantile regression can be used to investigate heterogeneity in pay–firm size and pay-performance relationships for U.S. CEOs. For example, do conditionally (predicted) high-wage managers have a stronger relationship between pay and performance than conditionally low-wage managers? Our results using data over a decade show, for some standard specifications, there is considerable heterogeneity in the returns to firm performance across the conditional distribution of wages. Quantile regression adds substantially to our understanding of the pay-performance relationship. This heterogeneity is masked when using more standard empirical techniques

Biology, ecology, and evolution of chewing lice

Book ChapterChewing lice are small, dorsoventrally compressed insects and are parasites of virtually all birds (Fig. 1) and some mammals (Fig. 2). Many chewing lice are host specific, being found on only a single species of host. All chewing lice are permanent ectoparasites and complete their entire life cycle on the body of the host, where they feed mainly on feathers, dead skin, blood, or secretions. Chewing lice on mammals apparently do not ingest hair, rather they feed on skin and skin products (Waterhouse 1953). Some species of lice feed on the eggs and molting stages of mites and other lice, including members of their own species (Nelson and Murray 1971). Lice also ingest microbes, such as bacteria and fungi, which are of unknown nutritive value

Molecular phylogeny of the dove genus Zenaida: mitochondrial and nuclear DNA sequences

Journal ArticleWe reconstructed a phylogeny for the seven species of doves in the genus Zenaida on the basis of a combined analysis of mitochondria (ND2 and cytochrome b) and nuclear (fibrinogen intron 7) DNA sequences. This phylogeny, which is completely resolved, is well supported with all nodes showing greater than 50% bootstrap support. There was no significant conflict between trees based on each gene independently, although trees produced from fibrinogen intron 7 did not resolve relationships among five of the Zenaida species. The species status of Z. graysoni, as well as that of Z. meloda, is suggested based on their divergence from sister taxa (about 1% and 4%, respectively) and other differences. Zenaida can be divided into two major groups: Zenaida asiatica and Z. meloda versus Z. aurita, Z. galapagoensis, Z. auriculata, Z. graysoni, and Z. macrour

Swiftlets on islands: genetics and phylogeny of the Seychelles and Mascarene swiftlets

Journal ArticlePopulations on islands are isolated from mainland populations and are thus expected to diverge and speciate from mainland relatives. We investigated die phylogenetic position and taxonomic rank of the Seychelles and Mascarene swiftlets using nuclear (fibrinogen intron 7) and mitochondrial (cytochrome b) DNA sequences. Both sequences recovered a placement for these two swiftlets within a group of other echolocating swiftlets (Aerodramus)

Testing species limits of non-echolocating Philippine swiftlets (Collocalia spp.) using molecular genetic data

Journal ArticleSwiftlets are small, insectivorous birds that are distributed from the Indian Ocean, through southeast Asia and north Australia, to the Pacific. About 22 species of swiflets nest in caves or other dark places, where they navigate using a crude form of echolocation (Chantler and Driessens 1995). Three additional species, which are incapable of echolocation, do not nest in the dark. The 25 species of swiftlets are considered by many authors to represent the most difficult problem in the taxonomy of birds (e.g., Mayr 1937). This is because swiftlets show extreme morphological similarity, making species limits extremely difficult to decipher. Lee et a/. (1996) used DNA sequence data to show that morphologically-based species concepts are seriously flawed for swiftlets. They also showed that the echolocating species (Aerodramus spp.) are not closely related to the non-echolocating species (Collocalia spp.)

Molecular phylogeny of the dove genera Streptopelia and Columba

Journal ArticleEvolutionary history of the dove genus Streptopelia has not been examined with rigorous phylogenetic methods. We present a study of phylogenetic relationships of Streptopelia based on over 3,600 base pairs of nuclear and mitochondrial gene sequences

Coevolutionary history of ecological replicates: comparing phylogenies of wing and body lice to Columbiform hosts

Book ChapterPhylogenies depict the history of speciation for groups of organisms. Comparing the phylogenies of interacting groups can reveal instances of tandem speciation, or "cospeciation" (Brooks and McLennan, 1991; Hoberg et al., 1997; Paterson and Gray, 1997). Understanding the conditions under which cospeciation takes place is a challenging task. In the case of hosts and their parasites, cospeciation occurs when isolation of host populations also isolates the parasites on those hosts. Patterns of cospeciation can break down owing to dispersal of parasites among host populations, sympatric speciation of parasites on a single host population, or extinction of parasites on a host population (Page and Charleston, 1998). All else being equal, ecologically similar parasites living on the same host should respond to isolation of host populations in the same way, yielding similar coevolutionary histories. In this chapter we compare cospeciation events in two such "replicate" groups of lice living on the same hosts. If forces promoting speciation, such as host speciation, act on these parasites in similar ways, then we would expect cospeciation events to be correlated between these parasite groups. On the other hand, if the parasites respond to isolation differently, then cospeciation events should be independent in the two groups

Stable incidence rates of tuberculosis (TB) among human immunodeficiency virus (HIV)-negative South African gold miners during a decade of epidemic HIV-associated TB.

During the last decade, annual tuberculosis (TB) case-notification rates increased 4-fold, to >4000 cases/100000 person-years, in the study workforce, among whom prevalence of human immunodeficiency virus (HIV) was 30% in 2000. Three separate cohort studies, totalling 6454 HIV-negative participants, were combined and analyzed for time trends. Observed incidence of TB varied between 962 (1991-1994) and 1589 (1999-2000) cases/100000 person-years (P=.17, test for trend). There was, however, a progressive increase in age, and, for each period, older age was associated with increased incidence rates of TB (P<.001). Having adjusted for age differences, there was no significant association between incidence of TB and calendar period (P=.81, test for trend). Relative to 1991-1994, multivariate-adjusted incidence-rate ratios were 0.94, for 1995-1997, 0.96, for 1998-1999, and 1.05, for 1999-2000. Preventing a secondary epidemic of TB among HIV-negative individuals may be achievable with conventional means, even in settings with a high burden of HIV-associated TB

Amyloid plaque deposition accelerates tau propagation via activation of microglia in a humanized app mouse model

Alzheimer’s disease is characterized by the formation of two major pathological hallmarks: amyloid plaques and neurofibrillary tangles. Although there have been many studies to understand the role of microglia in Alzheimer’s disease, it is not yet known how microglia can promote disease progression while actively phagocytosing amyloid plaques or phosphorylated tau (p-tau). Through stereotaxic injection of adeno-associated virus expressing mutant P301L tau (AAV-P301L-tau) into the medial entorhinal cortex (MEC) of both wild-type (WT) and APPNL-G-F mice, we demonstrate how amyloid plaques exacerbate p-tau propagation to the granule cell layer (GCL) of the hippocampus. However, in mice receiving the colony-stimulating factor 1 receptor inhibitor (PLX5622), ~95% of microglia were depleted, which dramatically reduced p-tau propagation to the GCL. Although microglia depletion curtailed p-tau propagation, it also led to reduced plaque compaction and an increase in overall amyloid-beta (Aβ) plaque presence. Additionally, we found microglia depletion resulted in greater p-tau aggregation in dystrophic neurites surrounding amyloid plaques. We investigated neurodegenerative microglia (MGnD), which are activated in response to amyloid plaques, for their propensity to release extracellular vesicles in comparison to homeostatic microglia. We discovered that MGnD, identified by Clec7a or Mac2 staining, strongly express Tumor susceptibility gene 101 (Tsg101), which is an ESCRT-1 protein and a marker for extracellular vesicles (EVs). To further investigate EV release and MGnD, a novel lentivirus expressing fluorescent mEmerald conjugated to CD9 (mE-CD9) was constructed and injected into the MEC of both WT and APPNL-G-F mice which allowed for visualization of mE-CD9+ puncta around individual microglia. CD9 is a tetraspanin and also a marker for EVs. We observed that the number of mEmerald+ particles surrounding MGnD was three-fold higher compared to non-diseased, homeostatic microglia. Sequential injection of mE-CD9 and AAV-P301L-tau into the MEC revealed that microglia-derived EVs encapsulate pathologic p-tau, which is augmented by the MGnD phenotype. Taken together, these data provide strong evidence that MGnD exhibit increased secretion of tau-containing EVs, providing a possible mechanism for how amyloid deposition indirectly exacerbates tau propagation

A potential role for a novel ZC3H5 complex in regulating mRNA translation in Trypanosoma brucei

In Trypanosoma brucei and related kinetoplastids, gene expression regulation occurs mostly post-transcriptionally. Consequently, RNA-binding proteins play a critical role in the regulation of mRNA and protein abundance. Yet, the roles of many RNA-binding proteins are not understood. Our previous research identified the RNA-binding protein ZC3H5 as possibly involved in gene repression, but its role in controlling gene expression was unknown. We here show that ZC3H5 is an essential cytoplasmic RNA-binding protein: RNAi targeting ZC3H5 causes accumulation of pre-cytokinetic cells followed by rapid cell death. Affinity purification and pair-wise yeast 2-hybrid analysis suggest that ZC3H5 forms a complex with three other proteins, encoded by genes Tb927.11.4900, Tb927.8.1500 and Tb927.7.3040. RNA immunoprecipitation revealed that ZC3H5 is preferentially associated with poorly translated, low-stability mRNAs, the 5´-untranslated regions and coding regions of which are enriched in the motif (U/A)UAG(U/A). As previously found in high-throughput analyses, artificial tethering of ZC3H5 to a reporter mRNA or other complex components repressed reporter expression. However, depletion of ZC3H5 in vivo caused only very minor decreases in a few targets, marked increases in the abundances of very stable mRNAs, an increase in monosomes at the expense of large polysomes, and appearance of "halfmer" disomes containing two 80S subunits and one 40S subunit. We speculate that the ZC3H5 complex might be implicated in quality control during the translation of sub-optimal open reading frames.Fil: Bajak, Kathrin. Universität Heidelberg; AlemaniaFil: Leiss, Kevin. Universität Heidelberg; AlemaniaFil: Clayton, Christine. Universität Heidelberg; AlemaniaFil: Erben, Esteban Daniel. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Biotecnológicas; Argentin