Analysis of the time to sustained progression in Multiple Sclerosis using generalised linear and additive models

The course of multiple sclerosis (MS) is generally difficult to predict. This is due to the great inter-individual variability with respect to symptoms and disability status. An important prognostic endpoint for MS is the expected time to sustained disease progression. Using the Expanded Disability Status Scale (EDSS) this endpoint is here defined as a rise of 1.0 or 0.5 compared to baseline EDSS (5.5) which is confirmed for at least six months. The goal of this paper was threefold. It aimed at identifying covariates which significantly influence sustained progression, determining size and form of the effect of these covariates and estimating the survival curves for given predictors. To this end a piecewise exponential model utilizing piecewise constant hazard rates and a Poisson model were devised. In order to improve and simplify these models a method for piecewise linear parameterization of non-parametric generalized additive models (GAMs) was applied. The models included fixed and random effects, the posterior distribution was estimated using Markov Chain Monte Carlo methods (MCMC) as well as a penalized likelihood approach and variables were selected using Akaikes information criterium (AIC). The models were applied to data of placebo patients from worldwide clinical trials that are pooled in the database of the Sylvia Lawry Centre for Multiple Sclerosis Research (SLCMSR). Only with a pure exponential model and fixed effects, baseline EDSS and the number of relapses in the last 12 month before study entry had an effect on the hazard rate. For the piecewise exponential model with random study effects there was no effect of covariates on the hazard rate other than a slightly decreasing effect of time. This reflects the fact that unstable patients reach the event early and are therefore eliminated from the analysis (selection effect)

Environmental influences on the gametic investment of yellow dung fly males

The energetic investment per spermatozoon and in spermatogenesis is central to a male's reproductive strategy. Relatively little, however, is known about environmental influences on variation in male allocation decisions and associated trade-offs. Plasticity in sperm length and testis size in response to variable food and temperature conditions either before or after adult eclosion was investigated in Scathophaga stercoraria, a classic model organism for sperm competition. Both measures showed interesting and clear environmental effects and also a heritable component. Testis length, and thus presumably sperm production, showed a hypoallometric (b < 1), but non-linear increase with body size, indicating that the allometric relationship changed with size. Like body size, testis length decreased with increasing developmental temperatures, but also showed a complex cubic relationship with adult temperatures. In contrast, sperm length increased or showed a negative quadratic relationship with increasing temperatures. The increase of within-male variation in sperm length with increasing developmental temperature and decreasing adult food indicates that some of our treatments were stressful. Nevertheless, there was no evidence of a trade-off between testis size and sperm length. The missing effect of adult or larval food availability on testis and sperm length, despite strong effects of larval food on body size, suggests that investment into reproduction is less sensitive to food restriction than investment into growt

Fertilization competence and sperm size variation in sperm-heteromorphic insects

Between species, variation in sperm size has been related to male-female coevolution and male-male competition. In contrast, variation within species is poorly understood. A particular case of intraspecific sperm-size variation occurs in sperm-heteromorphic species, where males produce distinct sperm morphotypes, usually only one of which is fertile. This allows to investigate sperm size variation under different selection regimes. Nonfertile morphotypes, whose role is aside from fertilization, may have other functions, and this may be reflected by changes in developmental processes and a different phenotype compared to fertile sperm. We show that the intraspecific coefficient of variation in sperm length is up to four times lower for fertile than nonfertile morphotypes across 150 sperm-heteromorphic species (70 butterfly, 71 moth, 9 diopsid fly species). This is in agreement with a previous study on 11 species in the Drosophila obscura group. Significantly lower variation in fertile than nonfertile sperm morphometry may result from fertilization-related selection for optimal sperm size, novel functions of nonfertile sperm, or from tighter control of fertile sperm development. More data are needed to clarify the consequences and adaptive significance of within-morph variation, and its consistent pattern across sperm-heteromorphic insect

Repeatability of sperm size in outbred and inbred Scathophaga stercoraria (Diptera: Scathophagidae)

Variability in male gametic traits can depend on several genetic and environmental factors such as developmental instability as a consequence of inbreeding, developmental noise during spermatogenesis, or age- or condition-dependent changes in allocation to sperm cells. Variation in sperm size is particularly evident in species that produce more than one sperm morph but also occurs among males in sperm-monomorphic species. Both discrete and continuous sperm size variation have been implicated in male fertilization success when the sperm of several males directly compete for fertilization of the same set of ova. In this study, we investigated among-male variation in sperm length in field-collected, outbred male Scathophaga stercoraria (L.) flies, as well as in flies from the same natural population that had been subjected to 15 and 16 generations of inbreeding under laboratory conditions. Among-male variation in sperm length was significant and repeatable over subsequent matings in both inbred and outbred flies. We conclude that sperm length can be used as an individual male marker in sperm competition studies and that significant repeatability of sperm length supports heritability for this trai

Sperm survival in the female reproductive tract in the fly Scathophaga stercoraria (L.)

While sperm competition risk favours males transferring many sperm to secure fertilizations, females of a variety of species actively reduce sperm numbers reaching their reproductive tract, e.g. by extrusion or killing. Potential benefits of spermicide to females include nutritional gains, influence over sperm storage and paternity, and the elimination of sperm bearing somatic mutations that would lower zygote fitness.We investigated changes in sperm viability after in vivo and in vitro exposure to the female tract in the polyandrous fly, Scathophaga stercoraria. Sperm viability was significantly lower in the females' spermathecae immediately after mating than in the experimental males' testes. Males also varied significantly in the proportion of live sperm found in storage in vivo. However, the exact mechanism of sperm degradation remains to be clarified. In vitro exposure to extracts of the female reproductive tract, including female accessory glands, failed to significantly lower sperm viability compared to controls. These results are consistent either with postcopulatory sperm mortality in vivo depending entirely on the male (with individual differences in sperm viability, motility or longevity) or with postcopulatory sperm mortality being subtly affected by female effects which were not detected by the in vitro experimental conditions. Importantly, we found no evidence in support of the hypothesis that female accessory glands contribute to sexual conflict via spermicide. Therefore, female muscular control remains to date the only ascertained mechanism of female influence on sperm storage in this species

Fertilization competence and sperm size variation in sperm-heteromorphic insects

Between species, variation in sperm size has been related to male-female coevolution and male-male competition. In contrast, variation within species is poorly understood. A particular case of intraspecific sperm-size variation occurs in sperm-heteromorphic species, where males produce distinct sperm morphotypes, usually only one of which is fertile. This allows to investigate sperm size variation under different selection regimes. Nonfertile morphotypes, whose role is aside from fertilization, may have other functions, and this may be reflected by changes in developmental processes and a different phenotype compared to fertile sperm. We show that the intraspecific coefficient of variation in sperm length is up to four times lower for fertile than nonfertile morphotypes across 150 sperm-heteromorphic species (70 butterfly, 71 moth, 9 diopsid fly species). This is in agreement with a previous study on 11 species in the Drosophila obscura group. Significantly lower variation in fertile than nonfertile sperm morphometry may result from fertilization-related selection for optimal sperm size, novel functions of nonfertile sperm, or from tighter control of fertile sperm development. More data are needed to clarify the consequences and adaptive significance of within-morph variation, and its consistent pattern across sperm-heteromorphic insect

Environmental influences on the gametic investment of yellow dung fly males

The energetic investment per spermatozoon and in spermatogenesis is central to a male's reproductive strategy. Relatively little, however, is known about environmental influences on variation in male allocation decisions and associated trade-offs. Plasticity in sperm length and testis size in response to variable food and temperature conditions either before or after adult eclosion was investigated in Scathophaga stercoraria, a classic model organism for sperm competition. Both measures showed interesting and clear environmental effects and also a heritable component. Testis length, and thus presumably sperm production, showed a hypoallometric (b < 1), but non-linear increase with body size, indicating that the allometric relationship changed with size. Like body size, testis length decreased with increasing developmental temperatures, but also showed a complex cubic relationship with adult temperatures. In contrast, sperm length increased or showed a negative quadratic relationship with increasing temperatures. The increase of within-male variation in sperm length with increasing developmental temperature and decreasing adult food indicates that some of our treatments were stressful. Nevertheless, there was no evidence of a trade-off between testis size and sperm length. The missing effect of adult or larval food availability on testis and sperm length, despite strong effects of larval food on body size, suggests that investment into reproduction is less sensitive to food restriction than investment into growt

Applied immuno-epidemiological research: an approach for integrating existing knowledge into the statistical analysis of multiple immune markers.

BACKGROUND: Immunologists often measure several correlated immunological markers, such as concentrations of different cytokines produced by different immune cells and/or measured under different conditions, to draw insights from complex immunological mechanisms. Although there have been recent methodological efforts to improve the statistical analysis of immunological data, a framework is still needed for the simultaneous analysis of multiple, often correlated, immune markers. This framework would allow the immunologists' hypotheses about the underlying biological mechanisms to be integrated. RESULTS: We present an analytical approach for statistical analysis of correlated immune markers, such as those commonly collected in modern immuno-epidemiological studies. We demonstrate i) how to deal with interdependencies among multiple measurements of the same immune marker, ii) how to analyse association patterns among different markers, iii) how to aggregate different measures and/or markers to immunological summary scores, iv) how to model the inter-relationships among these scores, and v) how to use these scores in epidemiological association analyses. We illustrate the application of our approach to multiple cytokine measurements from 818 children enrolled in a large immuno-epidemiological study (SCAALA Salvador), which aimed to quantify the major immunological mechanisms underlying atopic diseases or asthma. We demonstrate how to aggregate systematically the information captured in multiple cytokine measurements to immunological summary scores aimed at reflecting the presumed underlying immunological mechanisms (Th1/Th2 balance and immune regulatory network). We show how these aggregated immune scores can be used as predictors in regression models with outcomes of immunological studies (e.g. specific IgE) and compare the results to those obtained by a traditional multivariate regression approach. CONCLUSION: The proposed analytical approach may be especially useful to quantify complex immune responses in immuno-epidemiological studies, where investigators examine the relationship among epidemiological patterns, immune response, and disease outcomes