Accepted mutations in a gene family: Evolutionary diversification of duplicated DNA

Summary We report and compare the DNA sequences of 14 silkmoth (Antheraea polyphemus) chorion genes, derived from either cDNA or chromosomal DNA clones. Seven of these genes are members of the A multigene family, and seven are members of the B family. Where available, the previously reported (Jones and Kafatos 1980) intronic and extragenic flanking DNA sequences are also considered. Closely related sequences are compared, revealing the types of spontaneous mutations that were fixed during paralogous evolution. Segmental mutations (i.e. mutations other than substitutions) are nearly always interpretable as small duplications or deletions. related to small direct repeats. Segmental mutations are strongly constrained in the coding regions, although they do occur. Nucleotide substitutions also appear to be under selective constraints: relatively few substitutions leading to amino acid replacements are accepted, silent substitutions leading to some codons (especially purine-terminated ones) are disfavored, and different compositional biases are maintained in different parts of the sequences. Other sequence differences can be interpreted as indicative of neutral drift, including most differences in non-coding regions and most T/C transitions in third-base positions. In the non-coding regions, which are thought to be only loosely constrained by selection, transitions are observed more frequently than might be expected: they account for 52% of all substitutions, and they appear to be favored two to threefold over transversions when allowance is made for the skewed base composition of these regions.     

Orthostasis fails to produce active limb venoconstriction in adolescents.

Orthostasis is characterized by translocation of blood from the upper body and thorax into dependent venous structures. Although active splanchnic venoconstriction is known to occur, active limb venoconstriction remains controversial. Based on prior work, we initially hypothesized that active venoconstriction does occur in the extremities during orthostasis in response to baroreflex activation. We investigated this hypothesis in the arms and legs of 11 healthy volunteers, aged 13-19 yr, using venous occlusion strain gauge plethysmography to obtain the forearm and calf blood flows and to compute the capacitance vessel volume-pressure compliance relation. Subjects were studied supine and at -10, +20, and +35 degrees to load the baroreflexes. With +20 degrees of tilt, blood flow decreased and limb arterial resistance increased significantly (P < 0.05) compared with supine. With +35 degrees of tilt, blood flow decreased, limb arterial resistance increased, and heart rate increased, indicating parasympathetic withdrawal and sympathetic activation with arterial vasoconstriction. The volume-pressure relation was unchanged by orthostatic maneuvers. The results suggest that active venoconstriction in the limbs is not important to mild orthostatic response.     

Pre-release feeding on yeast hydrolysate enhances sexual competitiveness of sterile male Queensland fruit flies in field cages

Recent laboratory studies of mass‐reared flies in small cages have found that periods of just 24‐ or 48‐h access to yeast hydrolysate can substantially enhance mating performance of mass‐reared male Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q‐flies’). Using field cage tests that provide a better approximation of nature, we here investigated whether access to yeast hydrolysate for 48 h after adult emergence improves the ability of male and female mass‐reared, sterile Q‐flies to compete sexually with wild‐type flies that had been provided continuous access to yeast hydrolysate. Mating probability of sterile males was significantly increased by 48‐h access to yeast hydrolysate; sterile males provided 48‐h access to yeast hydrolysate had mating probability similar to that of wild males provided continuous access to yeast hydrolysate, whereas sterile males deprived of access to yeast hydrolysate had much lower mating probability. Unlike males, access to yeast hydrolysate for 48 h did not increase mating probability of sterile female Q‐flies. We instead found that wild females provided continuous access to yeast hydrolysate had higher mating probability than sterile females that did or did not have 48‐h access to yeast hydrolysate. This result raises the possibility that a bisexual Q‐fly strain might operate essentially as a male‐only release when the flies are given access to yeast hydrolysate during a 48‐h pre‐release holding period. Sterile males given access to yeast hydrolysate for 48 h mated significantly earlier in the evening than wild males and, as in other recent studies, this tendency was associated with an increased tendency to mate on the trees rather than the cage walls. There was no evidence of sexual isolation in this study, as wild and sterile mass‐reared flies showed no evidence of preferential mating with their own kind. Further studies are now needed to assess the potential for pre‐release access to yeast hydrolysate to improve sexual performance and longevity of sterile, mass‐reared, Q‐flies in the field.     

Effect of sex,age and morphological traits on tethered flight of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) at different temperatures

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a pest of fruit and vegetable production that has become established in 42 countries in Africa after its first detection in 2003 in Kenya. It is likely that this rapid expansion is partly due to the reported strong capacity for flight by the pest. This study investigated the tethered flight performance of B. dorsalis over a range of constant temperatures in relation to sex and age. Tethered flight of unmated B. dorsalis aged 3, 10 and 21 days was recorded for 1 h using a computerized flight mill at temperatures of 12, 16, 20, 24, 28, 32 and 36 °C. Variations in fly morphology were observed as they aged. Body mass and wing loading increased with age, whereas wing length and wing area reduced as flies aged. Females had slightly larger wings than males but were not significantly heavier. The longest total distance flown by B. dorsalis in 1 h was 1559.58 m. Frequent short, fast flights were recorded at 12 and 36 °C, but long-distance flight was optimal between 20 and 24 °C. Young flies tended to have shorter flight bouts than older flies, which was associated with them flying shorter distances. Heavier flies with greater wing loading flew further than lighter flies. Flight distances recorded on flight mills approximated those recorded in the field, and tethered flight patterns suggest a need to factor temperature into the interpretation of trap captures.     

Thermal biology,population fluctuations and implications of temperature extremes for the management of two globally significant insect pests

The link between environmental temperature, physiological processes and population fluctuations is a significant aspect of insect pest management. Here, we explore how thermal biology affects the population abundance of two globally significant pest fruit fly species, Ceratitis capitata (medfly) and C. rosa (Natal fruit fly), including irradiated individuals and those expressing a temperature sensitive lethal (tsl) mutation that are used in the sterile insect technique. Results show that upper and lower lethal temperatures are seldom encountered at the field sites, while critical minimum temperatures for activity and lower developmental thresholds are crossed more frequently. Estimates of abundance revealed that C. capitata are active year-round, but abundance declines markedly during winter. Temporal autocorrelation of average fortnightly trap captures and of development time, estimated from an integrated model to calculate available degree days, show similar seasonal lags suggesting that population increases in early spring occur after sufficient degree-days have accumulated. By contrast, population collapses coincide tightly with increasing frequency of low temperature events that fall below critical minimum temperatures for activity. Individuals of C. capitata expressing the tsl mutation show greater critical thermal maxima and greater longevity under field conditions than reference individuals. Taken together, this evidence suggests that low temperatures limit populations in the Western Cape, South Africa and likely do so elsewhere. Increasing temperature extremes and warming climates generally may extend the season over which these species are active, and could increase abundance. The sterile insect technique may prove profitable as climates change given that laboratory-reared tsl flies have an advantage under warmer conditions.     

Improved analyses of human mtDNA sequences support a recent African origin for Homo sapiens

New quantitative methods are applied to the 135 human mitochondrial sequences from the Vigilant et al. data set. General problems in analyzing large numbers of short sequences are discussed, and an improved strategy is suggested. A key feature is to focus not on individual trees but on the general "landscape" of trees. Over 1,000 searches were made from random starting trees with only one tree (a local optimum) being retained each time, thereby ensuring optima were found independently. A new tree comparison metric was developed that is unaffected by rearrangements of trees around many very short internal edges. Use of this metric showed that downweighting hypervariable sites revealed more evolutionary structure than studies that weighted all sites equally. Our results are consistent with convergence toward a global optimum. Crucial features are that the best optima show very strong regional differentiation, a common group of 49 African sequences is found in all the best optima, and the best optima contain the 16 !Kung sequences in a separate group of San people. The other 86 sequences form a heterogeneous mixture of Africans, Europeans, Australopapuans, and Asians. Thus all major human lineages occur in Africa, but only a subset occurs in the rest of the world. The existence of these African-only groups strongly contradicts multiregional theories for the origin of Homo sapiens that require widespread migration and interbreeding over the entire range of H. erectus. Only when the multiregional model is rejected is it appropriate to consider the root, based on a single locus, to be the center of origin of a population (otherwise different loci could give alternative geographic positions for the root). For this data, several methods locate the root within the group of 49 African sequences and are thus consistent with the recent African origin of H. sapiens. We demonstrate that the time of the last common ancestor cannot be the time of major expansion in human numbers, and our results are thus also consistent with recent models that differentiate between the last common ancestor, expansion out of Africa, and the major expansion in human populations. Such a two-phase model is consistent with a wide range of molecular and archeological evidence.      

A covariotide model explains apparent phylogenetic structure of oxygenic photosynthetic lineages

The aims of the work were (1) to develop statistical tests to identify whether substitution takes place under a covariotide model in sequences used for phylogenetic inference and (2) to determine the influence of covariotide substitution on phylogenetic trees inferred for photosynthetic and other organisms. (Covariotide and covarion models are ones in which sites that are variable in some parts of the underlying tree are invariable in others and vice versa.) Two tests were developed. The first was a contingency test, and the second was an inequality test comparing the expected number of variable sites in two groups with the observed number. Application of these tests to 16S rDNA and tufA sequences from a range of nonphotosynthetic prokaryotes and oxygenic photosynthetic prokaryotes and eukaryotes suggests the occurrence of a covariotide mechanism. The degree of support for partitioning of taxa in reconstructed trees involving these organisms was determined in the presence or absence of sites showing particular substitution patterns. This analysis showed that the support for splits between (1) photosynthetic eukaryotes and prokaryotes and (2) photosynthetic and nonphotosynthetic organisms could be accounted for by patterns arising from covariotide substitution. We show that the additional problem of compositional bias in sequence data needs to be considered in the context of patterns of covariotide/covarion substitution. We argue that while covariotide or covarion substitution may give rise to phylogenetically informative patterns in sequence data, this may not always be so.      

Effects of Colchicine Application to Preganglionic Axons on Choline Acetyltransferase Activity and Acetylcholine Content and Release in the Superior Cervical Ganglion

Abstract: These experiments investigate the effect of block, by colchicine, of fast axonal transport in the cat's cervical sympathetic trunk (CST) on the superior cervical ganglion's choline acetyltransferase (ChAT) enzyme activity, acetylcholine (ACh) content, and ACh release. Electron microscopy on the segment of the CST exposed to colchicine 1 or 4 days earlier showed disappearance of microtubules and accumulation of vesicles and smooth membrane tubules but no disruption of the axonal cytomatrix. At 4 days following colchicine treatment, the number and size of synaptic boutons per grid square in the ganglion ipsilateral to the colchicine-treated CST were similar to those in the control ganglion. At 2 and 4 days following exposure of the CST to colchicine, ChAT activity in the ipsilateral ganglion was reduced to 76 ± 8 and 54 ± 6% of control values, respectively. ACh stores in the ganglia were also reduced (to 81 ± 6% of control values at 2 days and to 51 ± 5% of control values at 4 days). Ganglionic transmission and its sensitivity to blockade by hexamethonium during 2-Hz CST stimulation were not impaired at day 4 postcolchicine. ACh release evoked by 2-Hz stimulation of colchicine-treated axons was similar to release from untreated axons, despite the decrease in the ganglionic ACh content. In contrast, ACh release evoked by 20-Hz stimulation was depressed. The amount of ACh released during 5-Hz stimulation in the presence of vesamicol by the terminals of colchicine-treated axons was similar to that released by the terminals of untreated axons. These results suggest the following conclusions: (a) Colchicine-sensitive fast axonal transport contributes significantly to maintaining ChAT stores in preganglionic axon terminals. (b) The half-life of ChAT in sympathetic preganglionic terminals is ～4 days. (c) One consequence of colchicine-induced block of axonal transport is a reduced ACh content of preganglionic nerve terminals. (d) This decrease in ACh content appears to be the result of a loss in a reserve transmitter pool, whereas the size of the readily releasable compartment is maintained.     

Transport and processing of the Rous sarcoma virus Gag protein in the endoplasmic reticulum.

The Gag proteins of replication-competent retroviruses direct budding at the plasma membrane and are cleaved by the viral protease (PR) just before or very soon after particle release. In contrast, defective retroviruses that bud into the endoplasmic reticulum (ER) have been found, and morphologically these appear to contain uncleaved Gag proteins. From this, it has been proposed that activation of PR may depend upon a host factor found only at the plasma membrane. However, if Gag proteins were cleaved by PR before the particle could pinch off the ER membrane, then the only particles that would remain visible are those that packaged smaller-than-normal amounts of PR, and these would have an immature morphology. To distinguish between these two hypotheses, we made use of the Rous sarcoma virus (RSV) Gag protein, the PR of RSV IS included on each Gag molecule. To target Gag to the ER, a signal peptide was installed at its amino terminus in place of the plasma membrane-binding domain. An intervening, hydrophobic, transmembrane anchor was included to keep Gag extended into the cytoplasm. We found that PR-mediated processing occurred, although the cleavage products were rapidly degraded. When the anchor was removed, allowing the entire protein to be inserted into the lumen of the ER, Gag processing occurred with a high level of efficiency, and the cleavage products were quite stable. Thus, PR activation does not require targeting of Gag molecules to the plasma membrane. Unexpectedly, molecules lacking the transmembrane anchor were rapidly secreted from the cell in a nonmembrane-enclosed form and in a manner that was very sensitive to brefeldin A and monensin. In contrast, the wild-type RSV and Moloney murine leukemia virus Gag proteins were completely insensitive to these inhibitors, suggesting that the normal mechanism of transport to the plasma membrane does not require interactions with the secretory pathway.