Power of the scan statistic in detecting a changed segment in a Bernoulli sequence

Fu & Curnow (1990) derive recursive equations to find thelevel of significance and power of a likelihood ratio test fora changed segment of specified length, based on the scan statistic,the maximum number of successes within the specified length.Their method is computationally feasible for segment lengthsof 20 or less. We present and evaluate highly accurate approximationsas well as bounds for the power function of this test that arecomputationally feasible even for very large segment lengths.We also evaluate power when the duration of the increased lengthused in the test statistic does not correspond to the actuallength.     

Physiological factors affecting the rapid decrease in protein assimilation efficiency by a caterpillar on newly‐mature tree leaves

Lymantria dispar L. caterpillars have a decreased ability to assimilate protein from mature leaves of red oak (Quercus rubra) compared with young, expanding leaves. The present study determines whether the drop in protein assimilation efficiency (PAE) occurs during the rapid phase of leaf maturation. Several mechanisms that might account for decreased PAE are also examined: mature leaf tissues could resist being chewed efficiently, protein in mature leaf tissues could become difficult to extract, and other nutrients in mature leaves might become growth limiting. The entire seasonal decrease in PAE occurs rapidly (in less than 2 weeks), when the leaves finished expanding. The maturation process is characterized by increased levels of fibre and decreased levels of water but no significant changes in the levels of protein or carbohydrates. Despite increased fibre in mature leaves, they are not chewed into larger food particles than are immature leaves. Carbohydrate assimilation efficiencies remain high on mature leaves, and signs of limiting water levels in larvae of L. dispar on mature leaves are not observed. The most important finding in the present study is the decreased extractability of protein in food particles from mature leaves, which plays a major role in explaining the rapid decrease in PAE. It is hypothesized that structural changes in cell walls during the rapid process of leaf maturation decrease protein extractability, which, in turn, greatly decreases the nutritional quality of mature oak leaves for caterpillars. The results of the present study therefore suggest a general mechanism to help explain the widely documented decrease in the nutritional quality of the mature leaves of many tree species for herbivorous insects.     

Phylogeographic analysis of the nocturnal velvet ant genus Dilophotopsis (Hymenoptera: Mutillidae) provides insights into diversification in the Nearctic deserts

Understanding the history of diversification in the North American deserts has long been a goal of biogeographers and evolutionary biologists. Although it appears that a consensus is forming regarding the patterns of diversification in the Nearctic deserts in vertebrate taxa, little work has been done exploring the historical biogeography of widespread invertebrate taxa. Before a robust model of geobiotic change in the North American deserts can be proposed, it needs to be determined whether the same historical events affected vertebrate and invertebrate taxa in the same way. We explore the phylogeographic patterns in a widespread nocturnal wasp genus Dilophotopsis using two rDNA loci, the internal transcribed spacer regions 1 and 2 (ITS1 and ITS2). We use Bayesian phylogenetic analysis and haplotype network analysis to determine whether a consistent geographic pattern exists among species and populations within Dilophotopsis. We also used molecular dating techniques to estimate divergence dates of the major phylogenetic clades. Our analyses indicates that the species‐level divergences in Dilophotopsis occurred in the Neogene, and likely were driven by mountain building during the Miocene–Pliocene boundary (approximately 5 Mya) similar to the divergences in many vertebrate taxa. The population‐level divergences within species occurred during the Pleistocene (0.1–1.8 Mya). The present study shows that similar patterns of diversification exist in vertebrate and invertebrate taxa. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 360–375.     

Some Factors Involved in the Control of Microtubule Assembly in Sea Urchins

Some recent evidence is discussed which suggests that the controlof microtubule assembly during the formation of the mitoticapparatus in sea urchins involves three factors. These include:nucleation sites such as the kinetochores, a mechanism for regulatingintracellular calcium, and a heat stable substance which preventsspontaneous, non-nucleated microtubule polymerization.     

The Stability of Cortical Phenotypes in Continuously Growing Cultures of Tetrahymena pyriformis*

Cortical features were analyzed in successive samples of continuously growing stock cultures of amicronucleate strains GL-C and GL-I, and in micronucleate strain WH-6 (syngen 1, mating type I). Thirteen successive samples of strain GL-C, representing a time span of 111 months, 5 samples of WH-6 (43 months) and 2 samples of GL-I (1 month) were examined. The observed range of commonly expressed ciliary row numbers (corticotypes) was 16–20 rows in strain GL-C, 15–20 in strain GL-I, and 16–20 in strain WH-6. These ranges remained constant through time within each strain. The individual samples each included all or a large part of the total range observed in the strain, but the relative abundances of different corticotypes within this range shifted through time. The shifts appeared random, with no discernible trends. Mean contractile vacuole pore (CVP) position and number of CVP meridians were assayed in the 2 “GL” strains. Mean CVP position was an apparently stable character, with only slight fluctuations through time, while the distribution of number of CVP meridians was somewhat less constant. The CVP parameters of strains GL-C and GL-I were considerably different, and both of these strains were very different from the GL strain which had been studied by Nanney. In fact, these 3 “GL” strains have, among them, virtually the entire gamut of known CVP characteristics. The possible significance of these wide differences among strains presumed to be closely related is considered in the Discussion.     

Immunoprecipitation Assay of Alpha-fetoprotein Synthesis by Cultured Mouse Hepatoma Cells Treated with Estrogens and Glucocorticords

This investigation was to study the biosynthesis of ³H-labeled alpha-fetoprotein (AFP) by cultured mouse hepatoma (HEPA-2) cells. Both the function and regulation of this oncodevelopmental gene are unknown. However, evidence indicates that mechanisms controlling the expression of AFP involve aspects of both normal embryonic development and neoplastic transformation. The secretion of AFP was analyzed during different phases of the growth cycle to provide information on AFP production using standard culture conditions. The highest rate of secretion occurred during the stationary phase, followed by the late logarithmic and early logarithmic phases of growth, respectively. The production of AFP was then determined following the addition of glucocorticords and estrogens in an attempt to understand hormonal factors that may be involved. Studies utilizing estradiol-17β indicated that the secretion of AFP did not appear to be sensitive to this steroid even though sucrose density gradient analysis of HEPA-2 cytosol, for estrogenic receptors, revealed competitive binding moieties in the 8S and 4S regions of the gradient. In contrast, the secretion of the total complement of proteins, including AFP, was significantly stimulated by the glucocorticords, dexamethasone and corticosterone. Analysis of HEPA-2 cytosol for glucocorticord receptors revealed binding components in the 7S and 3–4S regions of the gradient. The ³H-dexamethasone binding appeared to be stereospecific since nonlabeled dexamethasone, but not nonlabeled estradiol-17β, effectively displaced the bound radioactivity. The glucocorticoid-binding component in HEPA-2 therefore displayed characteristics reported for glucocorticord receptors in normal liver and other hepatomas.