Molecular and morphological divergence in the inland silverside (<Emphasis Type=Italic>Menidia beryllina</Emphasis>) along a freshwater-estuarine interface

Populations that vary across ecological gradients or that have invaded novel habitats are important to elucidate the association between adaptive divergence and gene flow, factors that may play an important role in speciation of silverside fishes. The inland silverside, Menidia beryllina, is an ideal organism for this kind of research, displaying a great diversity in morphology among freshwater and coastal brackish habitats. Using a combination of geometric morphometrics and mitochondrial (mt) DNA, we investigated patterns of variation within and among the nominal freshwater Menidia audens and coastal M. beryllina, spanning the transition from freshwater to tidally influenced semi-brackish waters of the lower Mississippi River to brackish waters of the Lake Pontchartrain estuary. Although we found no evidence for a phylogenetic split between M. audens and M. beryllina, our results indicate that significant genetic divergence corresponds with body shape differences among the two, with a clear distinction at the interface of freshwater and brackish water. Patterns in mtDNA suggest that freshwater populations referred to as M. audens are of recent origin with evidence for habitat-based divergence compared to coastal populations referred to as M. beryllina. Our findings add to a growing body of evidence that ecological shifts, following colonization of novel habitats, may promote rapid adaptive divergence and reduced gene flow among silverside populations in adjacent environmental regimes.     

Short and long courses of ofloxacin therapy of Klebsiella pneumoniae sepsis following irradiation.

Exposure to whole-body irradiation is associated with fatal gram-negative sepsis. The optimal length of therapy of such infection is not established. The effect of short and long courses of oral therapy with the quinolone ofloxacin for orally acquired Klebsiella pneumoniae infection was tested in B6D2F1 mice exposed to 8.0 Gy of bilateral radiation from 60Co. A dose of 10(8) organisms was given orally 4 days after irradiation, and therapy was started 1 day later. Cultures of the ileum 7 days after irradiation showed the recovery of K. pneumoniae in 7 of 10 untreated mice and in 3 of 20 treated with ofloxacin. However, 14 days after irradiation K. pneumoniae was isolated in 5 of 6 untreated mice, in 7 of 9 that received the short course of therapy, and in one of those that received the long course of therapy (P less than 0.05). At Day 7, K. pneumoniae was isolated from the livers of 6 of 10 untreated mice, and from none of those receiving ofloxacin (P less than 0.05). At 14 days, K. pneumoniae was isolated in 4 of 6 untreated animals, in 4 of 9 that received the short course of therapy, and in none of the mice that received the long course of therapy (P less than 0.05). Only 3 of 20 (15%) untreated mice survived for 30 days as compared to 11 of 20 (55%) mice treated for 7 days with ofloxacin and 18 of 20 (90%) mice treated for 21 days with ofloxacin (P less than 0.05). These survival data illustrate the efficacy of a 21-day course over a 7-day course of ofloxacin therapy for orally acquired K. pneumoniae infection in irradiated hosts.     

ARE POPULATIONS ISLANDS? ANALYSIS OF CHLOROPLAST DNA VARIATION IN AQUILEGIA

The degree to which conspecific populations are interconnected via ongoing gene flow remains an important focus of evolutionary biology. One major difficulty in distinguishing ongoing gene flow from historical subdivision is that either process can generate similar estimates of apparent gene flow. Thus, gene flow estimates themselves are insufficient to distinguish between these alternatives. However, genetic data coupled with additional information about demography and distribution do allow a distinction to be made. Here we address the specific question, does gene flow link populations of Aquilegia? In a survey of a 525 B.P. chloroplast DNA fragment sampled from 251 individual plants from 18 populations of three taxa, five haplotypes were identified. No significant relationship between geographic distance and apparent gene flow between population pairs existed. Further, the estimated level of gene flow was entirely compatible with a historical subdivision of Aquilegia populations during the late Pleistocene or early Holocene. Therefore, these patterns of variation are due not to ongoing gene flow, but rather to historical association among populations. Thus Aquilegia populations may be considered as distinct evolutionary entities with regard to seed-mediated processes. As a result, comparative analysis of ecological traits undergoing potentially rapid evolution (e.g., life histories, mating systems, inbreeding depression) should be possible in these taxa.     

REPRODUCTION IN ZONARIA FARLOWII II. CYTOLOGY AND ULTRASTRUCTURE1

The development of spores and eggs of Zonaria farlowii was studied with light and electron microscopy. Oogonia require a lunar month to develop and are produced in periodic crops. The sporangia, on the other hand, are longer in developing and on a particular plant do not become mature all at the same time. Differences in size, content, and products of sporangia and oogonia have been found. One of the quantifiable differences is in the amount of osmiophilic substance, presumably oil, present in the 2 cells. This substance is more abundant in the sporangium, a cell which produces 8 reproductive spores. These differences are particularly interesting since the embryology of sporic and zygotic germlings has been found to be identical, while ontogeny of spores and eggs differs. The findings of this study are discussed in view of possible relationships between microstrtrclitral features of spores and fertilized eggs and their subsequent development.     

Effect of Loading History on Airway Smooth Muscle Cell-Matrix Adhesions

Integrin-mediated adhesions between airway smooth muscle (ASM) cells and the extracellular matrix (ECM) regulate how contractile forces generated within the cell are transmitted to its external environment. Environmental cues are known to influence the formation, size, and survival of cell-matrix adhesions, but it is not yet known how they are affected by dynamic fluctuations associated with tidal breathing in the intact airway. Here, we develop two closely related theoretical models to study adhesion dynamics in response to oscillatory loading of the ECM, representing the dynamic environment of ASM cells in vivo. Using a discrete stochastic-elastic model, we simulate individual integrin binding and rupture events and observe two stable regimes in which either bond formation or bond rupture dominate, depending on the amplitude of the oscillatory loading. These regimes have either a high or low fraction of persistent adhesions, which could affect the level of strain transmission between contracted ASM cells and the airway tissue. For intermediate loading, we observe a region of bistability and hysteresis due to shared loading between existing bonds; the level of adhesion depends on the loading history. These findings are replicated in a related continuum model, which we use to investigate the effect of perturbations mimicking deep inspirations (DIs). Because of the bistability, a DI applied to the high adhesion state could either induce a permanent switch to a lower adhesion state or allow a return of the system to the high adhesion state. Transitions between states are further influenced by the frequency of oscillations, cytoskeletal or ECM stiffnesses, and binding affinities, which modify the magnitudes of the stable adhesion states as well as the region of bistability. These findings could explain (in part) the transient bronchodilatory effect of a DI observed in asthmatics compared to a more sustained effect in normal subjects.     

Confirmation and refinement of the localisation of the c-MEL locus on chromosome 19 by physical and genetic mapping

Summary The human gene locus c-MEL was identified following transfection of genomic DNA from the human melanoma cell line NK14; it has previously been assigned to chromosome 19 (p13.2–q13.2) by analysis of somatic cell hybrids. We have further refined the position of this gene to the proximal region of 19p (cen-p13.2), using cell hybrids containing only fragments of human chromosome 19. We have confirmed this physical localisation by linkage analysis with a recently described restriction fragment length polymorphism for the c-MEL gene, and mapped the locus within the region of the low density lipoprotein receptor gene (LDLR) (Lod 4.43, ) and the anonymous marker D19S11 (13.1.25) (Lod 9.33, ). This gene thus maps to a region of chromosome 19 involved in karyotypic abnormalities in a variety of malignancies including melanomas and leukaemias.     

Influence of heredity and environment in determination of skinfold thickness in children.

Triceps and subscapular skinfold thicknesses were measured in 222 pairs of like-sex twins (78 monozygotic and 144 dizygotic) aged 3-15 years. Log transformations of the measurements were standardized for age and sex and the results used to estimate heritability--that is, the proportion of total variation determined by genetic factors. The overall contribution of non-genetic familial effects was small. There were appreciable differences in heritability between limb and trunk fat and between the sexes and at different ages. Over the age of 10 heritability was high for both sites in boys and girls. In younger children environmental factors contributed more to the variation.     

Testing for the chemical induction of aneuploidy in the male mouse

Dyad scores of metaphase II spermatocytes in the mouse have been used as an end point to assess the aneuploidy-inducing potential of three different chemicals; p-fluorophyalanine, phenylalanine and 6-mercaptopurine. The sensitivities of three different spermatogenic stages have been tested; pre-leptotene, zygotene and metaphase I. No effect was found at any treated stage for 6-mercaptopurine and phenylalanine. p-Fluorophenylalanine, when compared to control treatments, did, however, induce non-disjunction when applied at metaphase I. It also caused a delay to spermatogenesis when applied at this stage. The potential of mammalian test systems for the routine screening of chemicals as non-disjunction inducers, is discussed.