Estimations of the joint distribution of failure time and failure type with dependent truncation

In biomedical studies involving survival data, the observation of failure times is sometimes accompanied by a variable which describes the type of failure event (Kalbeisch and Prentice, 2002). This paper considers two specific challenges which are encountered in the joint analysis of failure time and failure type. First, because the observation of failure times is subject to left truncation, the sampling bias extends to the failure type which is associated with the failure time. An analytical challenge is to deal with such sampling bias. Second, in case that the joint distribution of failure time and failure type is allowed to have a temporal trend, it is of interest to estimate the joint distribution of failure time and failure type nonparametrically. This paper develops statistical approaches to address these two analytical challenges on the basis of prevalent survival data. The proposed approaches are examined through simulation studies and illustrated by using a real data set.     

The control of Myrmica rubra workers by queens of their own and other Myrmica species and the interaction between queenless groups of workers

ABSTRACT. Queens of two species of the ant genus Myrmica bonded to workers of the species M. rubra L. as the latter emerge from the pupal skin can use these workers nearly 6 months later to arrest gyne formation in sex-competent larvae of the same species. Queens of M. ruginodis Nylander var. microgyria (Brian & Brian, 1949) are as good at this as the natural M. rubra , but those of M. sabuleti Meinert (of a race close to M. scabrinodis) are not. Though the M. sabuleti queens induce normal aggression against sexualizing larvae, they are unable to prevent some or all of the workers feeding larvae as though they were queenless. However, queens from different colonies of M. rubra adopted by queenless populations of workers in spring, control their brood-rearing behaviour perfectly. M. rubra workers from different colonies bring gynes to maturity from female sexual larvae at different average sizes. When workers from two such sources are mixed in equal proportions, the size of gyne larva produced after a week's culture corresponds with that of one of the worker populations; it is not intermediate in size. Also, large workers can rear larger gyne-larvae than small workers of the same age. This is only true if the workers have been living with queens all the time from emergence as an imago to the moment the experiment was set. Size mixtures only achieve the same size larvae as a pure culture of small workers would. A possible reason for this is that small workers exclude the larger ones from the nursery areas of the nest.     

Sexual dimorphism in scales of marbled flounder Pseudopleuronectes yokohamae (Pleuronectiformes: Pleuronectidae), with comments on the relevance to their spawning behaviour

Variation of scales on the blind side of Pseudopleuronectes yokohamae in relation to sex, maturity and body size was examined. Immature males often have cycloid scales, while mature males have mostly ctenoid scales. Large females also often have ctenoid scales (but with fewer spines compared with males), and small females have mostly cycloid scales. The number of spines (ctenii) on the blind‐side scale increases with body size in both sexes, indicating an ontogenetic change in scale morphology. As P. yokohamae spawn demersal eggs with males positioning themselves above the females on the ocular side, it is hypothesized that ctenoid scales on the blind side in mature males function for maintaining contact with females during spawning.     

SOCIAL SELECTION AND THE EVOLUTION OF ANIMAL SIGNALS

Social selection is presented here as a parallel theory to sexual selection and is defined as a selective force that occurs when individuals change their own social behaviors, responding to signals sent by conspecifics in a way to influence the other individuals' fitness. I analyze the joint evolution of a social signal and behavioral responsiveness to the signal by a quantitative-genetic model. The equilibria of average phenotypes maintained by a balance of social selection and natural selection and their stability are examined for two alternative assumptions on behavioral responsiveness, neutral and adaptive. When behavioral responsiveness is neutral on fitness, a rapid evolution by runaway selection occurs only with enough genetic covariance between the signal and responsiveness. The condition for rapid evolution also depends on natural selection and the number of interacting individuals. When signals convey some information on signalers (e.g., fighting ability), behavioral responsiveness is adaptive such that a receiver's fitness is also influenced by the signal. Here there is a single point of equilibrium. The equilibrium point and its stability do not depend on the genetic correlation. The condition needed for evolution is that the signal is beneficial for receivers, which results from reliability of the signal. Frequency-dependent selection on responsiveness has almost no influence on the equilibrium and the rate of evolution.     

Folic acid reverses nitric oxide synthase uncoupling and prevents cardiac dysfunction in insulin resistance: Role of Ca2+/calmodulin-activated protein kinase II

Nitric oxide synthase (NOS) may be uncoupled to produce superoxide rather than nitric oxide (NO) under pathological conditions such as diabetes mellitus and insulin resistance, leading to cardiac contractile anomalies. Nonetheless, the role of NOS uncoupling in insulin resistance-induced cardiac dysfunction remains elusive. Given that folic acid may produce beneficial effects for cardiac insufficiency partially through its NOS recoupling capacity, this study was designed to evaluate the effect of folic acid on insulin resistance-induced cardiac contractile dysfunction in a sucrose-induced insulin resistance model. Mice were fed a sucrose or starch diet for 8 weeks before administration of folic acid in drinking water for an additional 4 weeks. Cardiomyocyte contractile and Ca²⁺ transient properties were evaluated and myocardial function was assessed using echocardiography. Our results revealed whole body insulin resistance after sucrose feeding associated with diminished NO production, elevated peroxynitrite (ONOO⁻) levels, and impaired echocardiographic and cardiomyocyte function along with a leaky ryanodine receptor (RYR) and intracellular Ca²⁺ handling derangement. Western blot analysis showed that insulin resistance significantly promoted Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) phosphorylation, which might be responsible for the leaky RYR and cardiac mechanical dysfunction. NOS recoupling using folic acid reversed insulin resistance-induced changes in NO and ONOO⁻, CaMKII phosphorylation, and cardiac mechanical abnormalities. Taken together, these data demonstrated that treatment with folic acid may reverse cardiac contractile and intracellular Ca²⁺ anomalies through ablation of CaMKII phosphorylation and RYR Ca²⁺ leak.     

Bayesian Quantile Regression for Longitudinal Studies with Nonignorable Missing Data

Summary .  We study quantile regression (QR) for longitudinal measurements with nonignorable intermittent missing data and dropout. Compared to conventional mean regression, quantile regression can characterize the entire conditional distribution of the outcome variable, and is more robust to outliers and misspecification of the error distribution. We account for the within-subject correlation by introducing a   ℓ₂   penalty in the usual QR check function to shrink the subject-specific intercepts and slopes toward the common population values. The informative missing data are assumed to be related to the longitudinal outcome process through the shared latent random effects. We assess the performance of the proposed method using simulation studies, and illustrate it with data from a pediatric AIDS clinical trial.     

Eight-year study of social and ecological correlates of mortality among immature baboons of Mikumi National Park,Tanzania

The Cox Proportional Hazards Regression Model was used to examine ecological and sociodemographic correlates of mortality among 164 immature yellow baboons born over an 8-year period at Mikumi National Park, Tanzania. Ecological correlates were derived from seasonal rainfall. Mortality was lowest for immatures born during the late rainy season, when it was likely that nourishment for pregnant and lactating females was greatest. High mortality was associated with above-average rainfall early in the immature's first complete rainy season. This association may result from one or more of the following: exposure, increased ranging, or accelerated vegetation growth, each of which is thought to increase hazards for weanlings. When births for the 8 years of the study were pooled, a birth peak occurred during the early dry season. The larger number of births during a birth peak should intensify competition among mothers and among immatures. Mortality was greatest for immature females born during the season immediately following the birth peak, while lowest for immature females born during the season immediately preceding the peak. Immature female mortality was greatest when the troop size at birth was large, and was most severe for females born to low ranking mothers. The sociodemographic results are consistent with Wasser's hypothesis that cooperative attacks of female baboons upon other troop females suppress the others' reproduction and the vitality of their infants, thereby improving the relative competitive position of the attackers' own young.