Is male back space limiting? An investigation into the reproductive demography of the giant water bug,Abedus indentatus (Heteroptera: Belostomatidae)

Because male giant water bugs in the subfamily Belostomatinae provide parental care by brooding eggs on their back, an accurate assessment can be made of both the actual and potential reproductive capacity of males. Two operational sex-ratio (OSR) indices were developed and empirically measured for a population of giant water bug, Abedus indentatus,in California. One index was based on reproductive rates measured in the laboratory; the other index was based on reproductive resources observed in the field. Both OSR indices suggest that the operational sex ratio fluctuates between maleskewed ratios in the summer and femaleskewed ratios in the winter. This pattern appears to be the consequence of two factors. First, the adult sex ratio is significantly female biased. Second, although males can outreproduce females at high ambient temperatures, the reverse is true at low temperatures. Possible reasons for the female-skewed adult sex ratio are examined, including differential recruitment, differential mortality, and sampling bias.     

Two substrate sites in the renal Na+-d-glucose cotransporter studied by model analysis of phlorizin binding and-d-glucose transport measurements

Summary Time courses of phlorizin binding to the outside of membrane vesicles from porcine renal outer cortex and outer medulla were measured and the obtained families of binding curves were fitted to different binding models. To fit the experimental data a model with two binding sites was required. Optimal fits were obtained if a ratio of low and high affinity phlorizin binding sites of 1:1 was assumed. Na⁺ increased the affinity of both binding sites. By an inside-negative membrane potential the affinity of the high affinity binding site (measured in the presence of 3 mM Na⁺) and of the low affinity binding site (measured in the presence of 3 or 90 mM Na⁺) was increased. Optimal fits were obtained when the rate constants of dissociation were not changed by the membrane potential. In the presence of 90 mM Na⁺ on both membrane sides and with a clamped membrane potential,K _D values of 0.4 and 7.9 M were calculated for the low and high affinity phlorizin binding sites which were observed in outer cortex and in outer medulla. Apparent low and high affinity transport sites were detected by measuring the substrate dependence ofd-glucose uptake in membrane vesicles from outer cortex and outer medulla which is stimulated by an initial gradient of 90 mM Na⁺(out>in). Low and high affinity transport could be fitted with identicalK _m values in outer cortex and outer medulla. An inside-negative membrane potential decreased the apparentK _m ofhigh affinity transport whereas the apparentK _m of low affinity transport was not changed. The data show that in outer cortex and outer medulla of pighigh and low affinity Na⁺-d-glucose cotransporters are present which containlow and high affinity phlorizin binding sites, respectively. It has to be elucidated from future experiments whether equal amounts of low and high affinity transporters are expressed in both kidney regions or whether the low and high affinity transporter are parts of the same glucose transport moleculc.     

Evolutionary explanations of emotions

Emotions can be explained as specialized states, shaped by natural selection, that increase fitness in specific situations. The physiological, psychological, and behavioral characteristics of a specific emotion can be analyzed as possible design features that increase the ability to cope with the threats and opportunities present in the corresponding situation. This approach to understanding the evolutionary functions of emotions is illustrated by the correspondence between (a) the subtypes of fear and the different kinds of threat; (b) the attributes of happiness and sadness and the changes that would be advantageous in propitious and unpropitious situations; and (c) the social emotions and the adaptive challenges of reciprocity relationships. In addition to addressing a core theoretical problem shared by evolutionary and cognitive psychology, explicit formulations of the evolutionary functions of specific emotions are of practical importance for understanding and treating emotional disorders.     

Introgression of the avian naked neck gene assisted by DNA fingerprints

Theoretical predictions suggest that DNA markers can be useful tools for genomic selection in gene introgression programmes. An experiment was carried out to evaluate the efficiency of using multi-locus DNA markers in an introgression programme designed to transfer the naked neck gene from a donor to a recipient chicken line. The donor line was a commercial egg layer chicken stock heterozygous at the naked neck locus (Na/na⁺), while the recipients were from a Cornish broiler line. These two lines differ markedly in their average body weight, a quantitative trait that can also represent the comprehensive differences between the genomes of the two lines involved. Three groups of naked neck BC₁ individuals were selected according to the following criteria: (i) low band-sharing with their donor grandsires evaluated by multi-locus DNA markers, (ii) high body weight at six weeks of age, and (iii) selection at random as a control group. Birds from each of these groups were mated at random to individuals from the heavier Cornish line to produce three groups of BC₂ individuals whose body weights were recorded weekly from three to seven weeks of age. Results indicated that BC₂ birds obtained from BC₁ parents selected for band-sharing levels and those selected for body weight, performed equally well at 4–7 weeks of age; both were 3.1–3.9% heavier than birds from the randomly selected group. The additional genome recovery of the heavier broiler line, obtained by DNA markers, was found to be in agreement with theoretically predicted values.     

Springtail postmolt vulnerability to pseudoscorpion predation: Mechanisms and implications

Arthropod prey are expected to be more vulnerable to their predators immediately following molt. The effects of springtail (Isotoma carpenteri) postmolt vulnerability on interactions with a pseudoscorpion predator were examined in the laboratory. Springtails exposed to vials pretreated with pseudoscorpions (Apochthonius minimus) delayed molting compared to those prey that were exposed to vials pretreated only with springtails. Although their escape ability (measured as distance jumped) was unaffected by molt condition, postmolt springtails were more profitable in terms of reduced predator handling time following capture. Despite this,A. minimus did not distinguish between postmolt and intermolt prey presented at either end of a T-maze.     

THE QUANTITATIVE GENETICS OF SEXUAL DIMORPHISM IN SILENE LATIFOLIA (CARYOPHYLLACEAE). II. RESPONSE TO SEX-SPECIFIC SELECTION

A well-established theoretical relationship exists between genetic correlations between the sexes and the dynamics of response to sex-specific selection. The present study investigates the response to sex-specific selection for two sexually dimorphic traits that have been documented to be genetically variable, calyx diameter and flower number, in Silene latifolia. Following the establishment of a base generation with a known genetic background, selection lines were established and two generations of sex-specific selection were imposed. Calyx diameter responded directly to sex-specific selection, and the positive genetic correlation between the sexes was reflected in correlated responses in the sex that was not the basis for selection within a particular line. Flower number showed a more erratic response to sex-specific selection in that selection in some lines was initially in the wrong direction, that is, selection for a decrease in flower number resulted in an increase. These erratic responses were attributable to genotype-environment interaction as reflected in significant heteroscedasticity in variance among families. Correlated responses to selection in the sex that was not the immediate basis for selection indicated the possible existence of a negative genetic correlation between the sexes for this trait. These results test for the first time the impact of genetic correlations between the sexes on the evolutionary dynamics of sexually dimorphic traits in a plant species.     

Estimating selection by comparing synonymous and substitutional changes

A higher ratio of substitutional to synonymous changes in between-species than in within-species comparisons has been taken as evidence for positive selection changing amino acids. A model is presented in which a difference of this kind arises as a result of purely neutral mutations, provided that the species compared are sufficiently different to approach a steady state between forward and backward mutation. In Neissseria, substitutions are twice as frequent, relative to synonymous changes, in between-species comparisons: it is shown that the data are consistent with the neutral model. The argument does not invalidate evidence for positive selection, for example in Drosophila, when the species compared are fairly similar.     

Cell-substrate adhesion and metastatic potential of cultured mesothelioma cells induced by asbestos

Cell-substrate adhesion was quantified for two cultured mesothelioma cell lines (epitheliomatus and sarcomatous) on glass, fibronectin and laminin substrates. Interference reflection microscopy (IRM) was used to image the adhesion patterns of cells and a grey level analysis was employed to quantify adhesion. Sarcomatous cells demonstrated marked adhesion to glass and fibronectin-coated substrates but not to laminin-coated substrate, with the greatest adhesion occurring on the fibronectin-coated surface. This adhesion was accompanied by cytoplasmic spreading. By contrast, epitheliomatous cells showed little tendency to adhere to any of the substrates and only showed significant spreading when in contact with the laminin substrate (P < 0.01). A bioassay was used to determine the metastatic potential of each of the cell lines. Via the intravenous route, the sarcomatous cells killed the host rats in 24.7 ± 1.5 (S.D.) days compared to 27.3 ± 0.9 (S.D.) days for the epitheliomatous cells (P < 0.01). After subcutaneous inoculation of tumour cells, the sarcomatous cells killed the host rats in 54.7 ± 0.7 (S.D.) days compared to 48.5 ± 0.5 (S.D.) days for the epitheliomatous cells (P < 0.01). We conclude that the results of the metastasis bioassays were consistent with the predicted behavior of these cell lines based on their ability to adhere to substrates in the in vitro adhesion assays.     

The potential for rust infection to cause natural selection in apomictic Arabis holboellii (Brassicaceae)

Few studies have examined the potential for pathogens with complex life cycles to cause selection on their required alternate (=intermediate) hosts. Here we examine the effects of two fungal pathogens on an herbaceous mustard, Arabis holboellii. One pathogen species uses A. holboellii as a primary host, the other uses it as an alternate host. This plant-pathogen system is especially interesting because the host, A. holboellii, is apomictic; thus individuals reproduce exact copies of themselves. Despite this mode of reproduction, A. holboellii populations are surprisingly genetically diverse. Could frequency dependent selection by pathogens be maintaining clonal diversity? This study assesses the potential for selection by pathogens. In a controlled greehouse experiment we show that there is heritable variation in A. holboellii's resistance to the rust, Puccinia monoica, and that host fitness is severely reduced by P. monoica infection in both the greenhouse and under natural conditions. Field observations indicate that host clones are also differentially susceptible to the short-cycled rust, P. thlaspeos, and that host fitness is reduced by infection to this pathogen as well. Although the preconditions for pathogen-mediated selection are present, frequency-dependent selection by pathogens is unlikely to be important in structuring populations of Arabis holboellii because multiple host genotypes are susceptible to the same inoculum and the pathogen has a long generation time.