Attachment may be a basis for specialization in oak aphids

ABSTRACT.

• 1 The potential role of tarsal attachment in host selection was studied in the specialist aphids Tuberculoides annulatus Hartig and Myzocallis schreiberi Hille Ris Lambers and Stroyan.
• 2 M.schreiberi could walk freely on its host, Quercus ilex and on Q.robur, whereas T.annulatus could walk freely on its host, Q.robur but had difficulty on Q. ilex.
• 3 Attachment to the rough-textured leaves of Q.robur was achieved by means of the pretarsal claws, and to the smooth upper surface of individual trichomes on the lower surface of Q.ilex using flexible pretarsal empodia.
• 4 Both behavioural and allometric differences can account for the inability of T.annulatus to grip onto Q.ilex.
• 5 The role of attachment by phytophagous insects in host plant resistance and selection is discussed.

     

Dispersion and Distribution of Pratylenchus scribneri and Hoplolaimus galeatus in Soybean Fields

Examination of dispersional characteristics of Pratylenchus scribneri and Hoplolaimus galeatus indicated that there were patches within soybean fields in which both survival and reproduction wexe enhanced in spite of apparent homogeneity of soil type and topography. Treatment with carbofuran reduced the patchiness (or increased the dispersion) for H. galeatus while it had the opposite effect for P. scribneri. P. scribneri was less highly dispersed in conventional tillage plots than in the zero tillage plots. Populations from quadrats contained entirely within the patches could be described by the normal distribution (in the case of P. scribneri) or by the Poisson distribution (in the case of H. galeatus), while populations from quadrats contained entirely outside the patches could be described by the Poisson distribution for both nematodes. None of the distributions tested (Poisson, normal, negative binomial, Neyman''s) gave an adequate fit when populations from both inside and outside the patches were considered together. In all instances, log₁₀ and ln transformations reduced the goodness of fit of the data to all of the distributions tested. Even with logarithmic transformations, parametric statistics were not appropriate for analysis of data in most instances.     

Segregation products of male mice doubly heterozygous for the RB(6.16) and RB(16.17) translocations: Influence of sperm karyotype on fertilizing competence under varying mating frequencies

The meiotic segregants of male mice heterozygous for Rb(6.16)24Lub and Rb(16.17)7Bnr were viewed, for the first time, at first cleavage metaphase. Chromosomes were analyzed after G-banding, C-banding, and karyotyping. To study sperm aging effects, chromosomes of 202 one-cell zygotes derived from males mating at intervals of approximately 3,14, and 21 days were examined. At least 89.6% of sperm-derived complements were products of 2:2 segregation; at most, a possible 6.4% were 3:1 segregants. The six expected types of 2:2 segregants, both balanced and unbalanced, were equifrequent in the total zygote population derived from sperm of all ages. When the data were analyzed according to mating frequency, the 3-day sperm population considered most likely to be fresh showed a deficiency of the segregant nullisomic for chromosome 6 and disomic for chromosome 17, when compared with the reciprocal segregant (P < 0.025) as well as to all other 2:2 segregants (P < 0.05). However, these sperm fertilized in greater numbers (P < 0.01) than their reciprocal segregant (disomic for 6 and nullisomic for 17) in the 14-day sperm population. While sperm with chromosomal abnormalities are capable of fertilization, the competence of segregants nullisomic for 6 and disomic for 17 apparently depends on the prior storage period in the male. Further, the results suggest that the effect of aneuploidy on sperm function is dependent on the specific chromosome(s) involved.     

Suspending disbelief—of Wynne-Edwards and his reception

Critique of Wynne-Edwards' views on population regulation and sociality suppose a population of discrete, mutually exclusive groups essential to his thought. Yet both his past and present work focus on continually distributed, philopatric populations; his critics have argued the untenability of a position never his own. Wynne-Edwardsian ‘group selection’ focuses on local population productivity under philopatry. A ‘group’ is a local confluence of genotypes which need not be reified, and group selection consists of the differential replication (hence heritability) of the local social environment in which a genotype is embedded. Differential productivity contingent on social environment can eliminate some relational structures on genotypes in favor of others, creating an expanding wave of population productivity as in Wright's shifting balance metaphor. Such a process is inherent in the evolution of reciprocity, where cooperators must cluster to successfully invade a population of defectors. Regulation of resource exploitation in continuously distributed populations may be modeled as overlapping n-person Prisoner's Dilemmas, where each individual participates in several distinct commons and defection represents local over-exploitation of resources.     

Temperature-related divergence in experimental populations of Drosophila melanogaster. II. Correlation between fitness and body dimensions

From a laboratory stock of Drosophila melanogaster (Oregon), reared for more than 20 years at 18° C, a new population was derived and maintained at 28° C for 8 years. The chromosomal and cytoplasmic contribution to genetic divergence between the two populations was estimated. Six body traits and reproductive fitness were taken into account. The third chromosome is responsible for the adaptive difference for temperature between the two lines. Temperature-selected genes which control body size are located on the second and third chromosomes, although the contribution of each chromosome depends on the environment in which the flies develop. The correlation between the chromosomal and cytoplasmic contributions to different traits and fitness, changes with temperature. At 28° C the correlation between fitness and each body trait is proportional to the response to selection exhibited by each of them, but this is not true at 18° C. Body size has, therefore, an adaptive significance in relation to temperature, which is expressed only in the environment where selection occurs. Cytoplasmic genes affect almost all characters to an extent similar to that of chromosomal genes. Inter-chromosomal and nucleo-cytoplasmic interactions are present and also change with temperature. In general, genes selected in a given environment produce greater phenotypic changes in that environment than in another. The population that experienced both temperatures is fitter in both environments, suggesting that the capacity to adapt to warm temperatures depends on genes other than those which are involved in the adaptation to cold.     

The effects of truncating long-range forces on protein dynamics

This paper considers the effects of truncating long-range forces on protein dynamics. Six methods of truncation that we investigate as a function of cutoff criterion of the long-range potentials are (1) a shifted potential; (2) a switching function; (3) simple atom-atom truncation based on distance; (4) simple atom-atom truncation based on a list which is updated periodically (every 25 steps); (5) simple group-group truncation based on distance; and (6) simple group-group truncation based on a list which is updated periodically (every 25 steps). Based on 70 calculations of carboxymyoglobin we show that the method and distance of long range cutoff have a dramatic effect on overall protein behavior. Evaluation of the different methods is based on comparison of a simulation's rms fluctuation about the average coordinates, the rms deviation from the average coordinates of a no cutoff simulation and from the X-ray structure of the protein. The simulations in which long-range forces are truncated by a shifted potential shows large rms deviations for cutoff criteria less than 14 A, and reasonable deviations and fluctuations at this cutoff distance or larger. Simulations using a switching function are investigated by varying the range over which electrostatic interactions are switched off. Results using a short switching function that switches off the potential over a short range of distances are poor for all cutoff distances. A switching function over a 5-9 A range gives reasonable results for a distance-dependent dielectric, but not using a constant dielectric. Both the atom-atom and group-group truncation methods based on distance shows large rms deviation and fluctuation for short cutoff distances, while for cutoff distances of 11 A or greater, reasonable results are achieved. Although comparison of these to distance-based truncation methods show surprisingly larger rms deviations for the group-group truncation, contrary to simulation studies of aqueous ionic solutions. The results of atom-atom or group-group list-based simulations generally appear to be less stable than the distance-based simulations, and require more frequent velocity scaling or stronger coupling to a heat bath.     

Pheromone-mediated sexual selection in the mothUtetheisa ornatrix: Olfactory receptor neurons responsive to a male-produced pheromone

Male Utetheisa ornatrixhave a pair of eversible glandular brushes (coremata) which are displayed during precopulatory interactions with the female. Earlier studies have shown that a pheromone associated with the coremata, hydroxydanaidal (HD), is derived by the males from pyrrolizidine alkaloids (PAs) that they sequester as larvae from their foodplants (Crotalariaspp.) The PAs impart a distastefulness upon Utetheisathat protects both larvae and adults against predation. The receptor neurons specialized for detection of HD are housed in sensilla whose morphological features, as revealed by scanning electron microscopy, classify them as sensilla basiconica. The sensitivity and dynamic range of these receptor neurons were largely unaffected by whether the females were raised on an alkaloid-free diet or on a diet supplemented with Crotalariaseeds. Acetylation of the hydroxyl group of HD substantially reduced the activity of the molecule. None of the antennal sensilla examined contained receptor neurons sensitive to a PA (monocrotaline) or its N-oxide.     

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.     

A maximum likelihood approach to the detection of selection from a phylogeny

Summary A large amount of information is contained within the phylogentic relationships between species. In addition to their branching patterns it is also possible to examine other aspects of the biology of the species. The influence that deleterious selection might have is determined here. The likelihood of different phylogenies in the presence of selection is explored to determine the properties of such a likelihood surface. The calculation of likelihoods for a phylogeny in the presence and absence of selection, permits the application of a likelihood ratio test to search for selection. It is shown that even a single selected site can have a strong effect on the likelihood. The method is illustrated with an example fromDrosophila melanogaster and suggests that delerious selection may be acting on transposable elements.