Speculations on enigmatic structures in relation to associated copepod phylogeny

A median exoskeletal structure, lying between the maxillipeds, is described in the female of Lichomolgides cuanensis (Poecilostomatoida: Lichomolgidae) a copepod symbiont of the compound ascidian Trididemnum tenerum. This structure is compared with the intermaxillipedal process of the primitive copepod order Platycopioida. It is tentatively suggested that despite the evolutionarily advanced status of poecilostomatoids, the structure might represent a plesiomorphic feature of considerable antiquity. Some speculative implications for the phylogeny of associated copepods are briefly discussed.     

Two Stage Sampling for Simultaneously Testing Main and Side Effects in Clinical Trials

In clinical trials for the comparison of two treatments it seems reasonable to stop the study if either one treatment has worked out to be markedly superior in the main effect, or one to be severely inferior with respect to an adverse side effect. Two stage sampling plans are considered for simultaneously testing a main and side effect, assumed to follow a bivariate normal distribution with known variances, but unknown correlation. The test procedure keeps the global significance level under the null hypothesis of no differences in main and side effects. The critical values are chosen under the side condition, that the probability for ending at the first or second stage with a rejection of the elementary null hypothesis for the main effect is controlled, when a particular constellation of differences in mean holds; analogously the probability of ending with a rejection of the null hypotheses for the side effect, given certain treatment differences, is controlled too. Plans “optimal” with respect to sample size are given.     

Fine Structure of the Cyst and Some Sporulation Stages of Ichthyosporidium (Microsporida)*

SYNOPSIS. Ichthyosporidium sp. Schwartz, 1963, apparently identical with the type species, I. giganteum (Thélohan, 1895) Swarczewsky, 1914, was studied with the electron microscope. Only late stages, a mature cyst containing sporulation stages and a cyst in the terminal (necrotic) stage were observed. The cyst, originating from host tissue, is a highly organized structure that is integrated with the surrounding connective tissue by means of numerous conspicuous processes. It is interpreted as essentially a manifestation of a defensive reaction of the host that is elicited by the parasite and then used to its advantage. Eventually the cyst dies and disintegrates. This type of cyst, peculiar among those associated with microsporidia, may be regarded as a distinctive character of the poorly defined genus Ichthyosporidium. Other observations let to an hypothesis which reconciles several different views regarding the identity of the Golgi complex. According to this new interpretation, these different views concern different aspects af the total complex. When all such views are integrated, a “classical Golgi” can be recognized in the presporoblastic stages and the “primitive Golgi” concept disappears. This “classical Golgi” then becomes highly modified during spore morphogenesis, giving rise to many of the internal organelles that are peculiar to the spore.     

Response properties of CO2-sensitive receptors in tsetse flies (Diptera: Glossina Palpalis)

Abstract. Extracellular single cell recordings of CO₂-sensitive receptors in tsetse flies revealed a steep dose response over a range of stimuli of two to three orders of magnitude and a maximum response of approximately 70 impulses/s after exposure to a high, but naturally feasible, C0₂ concentration of 5%. These receptor neurones are slightly sensitive to C0₂ levels occurring in air (-0.03%); the sensitivity to CO² above that level may be used to locate potential hosts. The C0₂-sensitive neurones did not respond to some other biologically relevant odours such as octenol, butanone or p-cresol; however, other receptor cells, some in the same sensillum, are sensitive to some of these odours.
A striking feature of the C0₂ receptors is that they appear not to adapt in their response frequencies. The spike numbers of the phasic-tonic response remain constant in the tonic portion during continuous (or repetitively pulsed) long-term stimulation (1 min). This unusual physiological ability would allow continuous monitoring of C0₂ values as well as detecting potential hosts that exhale CO₂. These electrophysiological results are compared to the behavioural findings in tsetse flies and to the physiological data on C0₂ receptors of other, non-bloodsucking insects.     

An iterative method to protect the type I error rate in bioequivalence studies under two‐stage adaptive 2×2 crossover designs

Bioequivalence studies are the pivotal clinical trials submitted to regulatory agencies to support the marketing applications of generic drug products. Average bioequivalence (ABE) is used to determine whether the mean values for the pharmacokinetic measures determined after administration of the test and reference products are comparable. Two‐stage 2×2 crossover adaptive designs (TSDs) are becoming increasingly popular because they allow making assumptions on the clinically meaningful treatment effect and a reliable guess for the unknown within‐subject variability. At an interim look, if ABE is not declared with an initial sample size, they allow to increase it depending on the estimated variability and to enroll additional subjects at a second stage, or to stop for futility in case of poor likelihood of bioequivalence. This is crucial because both parameters must clearly be prespecified in protocols, and the strategy agreed with regulatory agencies in advance with emphasis on controlling the overall type I error. We present an iterative method to adjust the significance levels at each stage which preserves the overall type I error for a wide set of scenarios which should include the true unknown variability value. Simulations showed adjusted significance levels higher than 0.0300 in most cases with type I error always below 5%, and with a power of at least 80%. TSDs work particularly well for coefficients of variation below 0.3 which are especially useful due to the balance between the power and the percentage of studies proceeding to stage 2. Our approach might support discussions with regulatory agencies.     

On Significance Testing in Comparative Epidemiologic Research

The choice of the referent entity in comparative epidemiologic studies is, of course, crucial to the attainment of a valid and sharp contrast. A commonplace procedure in large sample significance testing for (multiple) fourfold (and extended) tables is to base the estimation of the expected value (and/or the variance) on the combined study and comparison experience. This procedure is, however, deplorable in that in interim stages of the study it may hide the underlying difference in rates. The notion that the probability of the realization of the observed number of exposed cases be evaluated unconditionally assuming a binomial model with the Bernoulli parameter estimated solely by the rate in the referent series is considered. This outlook is carried over to bilateral testing. A chi square criterion accommodating this viewpoint could be used to canvass the accrued data for deciding on the prospects of continuing the data collection. A test employing exact variance estimates is derived and various methods for computing an ‘exact’ significance probability are developed. The procedure is exemplified by artificial data and accompanied by a discussion of its applicability.     

Ecology and Bioproduction in the Microphytobenthos of the Chain of Shallow Inlets (Boddens) South of the Darss-Zingst Peninsula (Southern Baltic Sea)

The significance of epipsammic microphytobenthos bioproduction in a shallow estuary was investigated by the oxygen method. Bioproduction reached a maximum in May or June. A close correlation was found between the gross production rate and algal biomass at station K. The biomass and production rates were distinctly lower at station B than at station K as station B was more exposed. Circadian variations and depth profiles of the gross production rate correlated best with irradiation intensity. Mean gross production from April to October was 1761 O₂.m⁻² and 75 g C·m⁻².     

P-values For Discrete Test Statistics

This paper considered the relative merits of the P-value and the mid-P-value. It is shown that inference based on the mid-P-value is in a certain sense on firmer ground. In particular the expected mid-P-value does not change under an irrelevant breakup in the test statistic.     

How to Use the Two Sample t-Test

This work discusses how two sample t-tests behave when applied to data that may violate the classical statistical assumptions of independence, heteroscedasticity and Gaussianity. The usual two sample t-statistic based on a pooled variance estimate and the Welch-Aspin statistic are treated in detail. Practical “rules-of-thumb” are given along with their applications to various examples so that readers will easily be able to use such tests on their own data sets.     

The Cultural Keystone Concept: Insights from Ecological Anthropology

The concept of the keystone species has a long history in ecological analysis, although its validity remains controversial. Anthropological researchers have recently coined the term cultural keystone species, but have not demonstrated any significant differences from existing treatments of culturally important species. We define cultural keystones according to their systemic function, as having essential roles in maintaining any level of complexity within a social–ecological system. Examples include bitter cassava consumption among lowland South American groups such as the Wapishana in Guyana, and commercial cultivation of carrots in Rurukan Village in Minahasa, Indonesia. These examples are both essential at one level of systemic reproduction: within the domestic and village economy in the cassava case, and carrots within regional markets. While each is centred upon a single biological species, the cultural keystone itself is not this species, but a complex incorporating several material and non-material system elements.