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L Partridge

Publications and source records attributed to L Partridge.

At least 19 recordsLinked to original sources
PubMed2006

The margin of safety of a left double-lumen tracheobronchial tube depends on the length of the bronchial cuff and tip.

The left tracheobronchial double-lumen tube is the commonest device to separate the left and right lungs for differential ventilation. With the appropriate tube, the left bronchial cuff is positioned in the bronchus so that the cuff is beyond the carina but the tip of the tube does not occlude the aperture of the left upper lobe bronchus. The difference between the length of the left main bronchus and the length of the cuff and tip of the bronchial segment of the tube has been termed "the margin of safety" by Benumof. If the length of the cuff plus the tip exceeds that of the left main bronchus, there will be occlusion of the left upper lobe bronchus. The bronchial cuff and bronchial tip lengths were measured on two hundred and twenty left tracheobronchial (double-lumen) tubes from four manufacturers. The largest cuff-tip length was 40 mm with a Portex 41Fr tube but some 41Fr tubes from all manufacturers had cuff-tip lengths of 33 mm or greater which exceed the length of the shortest left main bronchus measured by Benumof. There was also a marked variation in cuff-tip lengths of the same size tube from the same manufacturer. The largest variation was 18 mm for the Portex 41 but substantial variation of 8 mm or more was found in at least one French size of all manufacturers. Users must be aware that significant cuff-tip length variation occurs and match the selected tube to the patient to ensure an adequate margin of safety.

Bronchi↗
PubMed2003

Influence of female reproductive anatomy on the outcome of sperm competition in Drosophila melanogaster.

Females as well as males can influence the outcome of sperm competition, and may do so through the anatomy of their reproductive tracts. Female Drosophila melanogaster store sperm in two morphologically distinct organs: a single seminal receptacle and, normally, two spermathecae. These organs have different temporal roles in sperm storage. To examine the association between sperm storage organ morphology and sperm competition, we used a mutant type of female with three spermathecae. Although the common measure of sperm competition, P(2), did not differ between females with two and three spermathecae, the pattern of sperm use over time indicated that female morphology did affect male reproductive success. The rate of offspring production by females with three spermathecae rose and fell more rapidly than by females with two spermathecae. If females remate or die before using up second male sperm, then second male reproductive success will be higher when they mate with females with three spermathecae. The results indicate that temporal patterns of sperm use as well as P(2) should be taken into account when measuring the outcome of sperm competition.

Animals↗
PubMed2003

Overwintering in Drosophila melanogaster: outdoor field cage experiments on clinal and laboratory selected populations help to elucidate traits under selection.

Insects can adapt to temperate environments by increasing levels of resistance to cold conditions over winter and/or altering reproductive patterns to focus reproduction in favourable conditions. In temperate areas, Drosophila melanogaster persists over winter at the adult stage. A previous experiment, conducted with flies kept in outdoor population cages in the temperate winter, indicated that temperate populations produced more eggs than did tropical populations following an abrupt increase in reproduction in late winter. In contrast, the tropical populations produced more eggs prior to the increase. Both patterns resulted in a higher net number of surviving offspring for temperate populations. Here we again examine the clinal pattern in reproduction using outdoor cages, this time held under tropical winter conditions. In this environment, surprisingly, egg production was higher and on average earlier in populations originating from temperate areas. However, mortality rates also increased with latitude of origin, and the relationship of lifetime egg production to latitude should therefore be measured. To test the role of altered pattern of egg production per se in the reproductive advantage of temperate populations in the temperate winter, we tested the performance of laboratory lines selected for altered reproductive patterns, under temperate winter conditions. Lines selected for high early fecundity exhibited this characteristic in the field cages and lines selected for late reproduction exhibited a relatively high fecundity in spring. The timing of the abrupt increase in egg production was identical in these sets of lines and occurred at the same time in recently collected populations, suggesting evolutionary conservation of the switch. These findings suggest that changes in early and late reproduction per se determine adaptation to temperate winter conditions, and illustrate how laboratory selection lines can be used to understand traits underlying adaptive shifts in field performance.

Adaptation, Physiological↗
PubMed2002

Temperature modulates epidermal cell size in Drosophila melanogaster.

Most ectotherms show increased body size at maturity when reared under colder temperatures. In principle, temperature could produce this outcome by influencing growth, proliferation and/or death of epidermal cells. Here we investigated the effects of rearing temperature on the cell size and cell number in the wing blade, the basitarsus of the leg and the cornea of the eye of Drosophila melanogaster from two populations at opposite ends of a South American latitudinal cline. We found that, in both strains of D. melanogaster and in both sexes, a decrease in rearing temperature increases the size of the wings, legs and eyes through an effect on epidermal cell size, with no significant change in cell number. Our results indicate that temperature has a consistent effect on cell size in the Drosophila epidermis and this may also apply to other cell types. In contrast, the evolutionary effects of temperature on the different organs are not consistent. We discuss our findings in the context of growth control in Drosophila.

Journal Article↗
PubMed2002

Quantitative genetic analysis of natural variation in body size in Drosophila melanogaster.

Latitudinal, genetic variation in body size is a commonly observed phenomenon in many invertebrate species and is shaped by natural selection. In this study, we use a chromosome substitution and a quantitative trait locus (QTL) mapping approach to identify chromosomes and genomic regions associated with adaptive variation in body size in natural populations of Drosophila melanogaster from the extreme ends of clines in South America and Australia. Chromosome substitution revealed the largest effects on chromosome three in both continents, and minor effects on the X and second chromosome. Similarly, QTL analysis of the Australian cline identified QTL with largest effects on the third chromosome, with smaller effects on the second. However, no QTL were found on the X chromosome. We also compared the coincidence of locations of QTL with the locations of five microsatellite loci previously shown to vary clinally in Australia. Permutation tests using both the sum of the LOD scores and the sum distance to nearest QTL peak revealed there were no significant associations between locations of clinal markers and QTL's. The lack of significance may, in part, be due to broad QTL peaks identified in this study. Future studies using higher resolution QTL maps should reveal whether the degree of clinality in microsatellite allele frequencies can be used to identify QTL in traits that vary along an environmental gradient.

Animals↗
PubMed2001

The Acp26Aa seminal fluid protein is a modulator of early egg hatchability in Drosophila melanogaster.

Drosophila melanogaster male accessory gland proteins (Acps) that are transferred in the ejaculate with sperm mediate post-mating competition for fertilizations between males. The actions of Acps include effects on oviposition and ovulation, receptivity and sperm storage. Two Acps that modulate egg production are Acp26Aa (ovulin) and Acp70A (the sex peptide). Acp26Aa acts specifically on the process of ovulation (the release of mature eggs from the ovaries), which is initiated 1.5 h after mating. In contrast, sperm storage can take as long as 6-9 h to complete. Initial ovulations after matings by virgin females will therefore occur before all sperm are fully stored and the extra eggs initially laid as a result of Acp26Aa transfer are expected to be inefficiently fertilized. Acp26Aa-mediated release of existing eggs should not cause a significant energetic cost or lead to a decrease in female lifespan assuming, as seems likely, that the energetic cost of egg laying comes from de novo egg synthesis (oogenesis) rather than from ovulation. We tested these predictions using Acp26Aa(1) mutant males that lack Acp26Aa but are normal for other Acps and Acp26Aa(2) males that transfer a truncated but fully functional Acp26Aa protein. Females mating with Acp26Aa(2) (truncation) males that received functional Acp26Aa produced significantly more eggs following their first matings than did mates of Acp26Aa(1) (null) males. However, as predicted above, these extra eggs, which were laid as a result of Acp26Aa transfer to virgin females, showed significantly lower egg hatchability. Control experiments indicated that this lower hatchability was due to lower rates of fertilization at early post-mating times. There was no drop in egg hatchability in subsequent non-virgin matings. In addition, as predicted above, females that did or did not receive Acp26Aa did not differ in survival, lifetime fecundity or lifetime progeny, indicating that Acp26Aa transfer does not represent a significant energetic cost for females and does not contribute to the survival cost of mating. Acp26Aa appears to remove a block to oogenesis by causing the clearing out of existing mature eggs and, thus, indirectly allowing oogenesis to be initiated immediately after mating. The results show that subtle processes coordinate the stimulation of egg production and sperm storage in mating pairs.

Animals↗
PubMed2001

Extension of life-span by loss of CHICO, a Drosophila insulin receptor substrate protein.

The Drosophila melanogaster gene chico encodes an insulin receptor substrate that functions in an insulin/insulin-like growth factor (IGF) signaling pathway. In the nematode Caenorhabditis elegans, insulin/IGF signaling regulates adult longevity. We found that mutation of chico extends fruit fly median life-span by up to 48% in homozygotes and 36% in heterozygotes. Extension of life-span was not a result of impaired oogenesis in chico females, nor was it consistently correlated with increased stress resistance. The dwarf phenotype of chico homozygotes was also unnecessary for extension of life-span. The role of insulin/IGF signaling in regulating animal aging is therefore evolutionarily conserved.

Aging↗
PubMed2001

Evolutionary theories of ageing applied to long-lived organisms.

Ageing can evolve by mutation accumulation and pleiotropy (trade-offs). The relative prevalence of these two mechanisms is important for determining the likelihood that mechanisms of ageing are homologous in distantly related organisms, and hence the relevance of long-lived organisms to general mechanisms of ageing. Experimental work with Drosophila, examining the properties of standing genetic variation and mutations that accumulate in real time, has provided little evidence in favour of a role for mutation accumulation, but considerable support for the importance of trade-offs, particularly between early fertility and the rate of ageing. Evidence for the roles of these two processes in the evolution of long-livedness can be derived from the response to selection, comparative studies of life history traits and testing for potential trade-offs at the mechanistic level.

Aging↗
PubMed2001

Insulin/IGF signalling and ageing: seeing the bigger picture.

Although the underlying mechanisms of ageing are not understood, it is known that the longevity of the nematode Caenorhabditis elegans is modulated by an insulin/IGF-signalling pathway. The focus now is on how this pathway is regulated, how it controls nematode ageing, and how this relates to the ageing process in higher animals.

Aging↗
PubMed2001

The contrasting genetic architecture of wing size and shape in Drosophila melanogaster.

Surprisingly little is known about the genetic architecture of body size in natural populations of Drosophila melanogaster. Using both generation means and triple-test-cross analyses, we investigated the genetic architecture of wing size (an indicator of body size) and wing shape in a naturally occurring body size cline. For wing size, we found significant epistatic genetic variance and evidence of past directional selection for increased body size. While wing shape also exhibits significant epistatic genetic variance, there was no indication of directional selection, suggesting instead a history of optimizing selection. Our results support the idea that epistatic variance may be more common in natural populations than was once suspected. Also, our results suggest substantial directional selection on wing size but not shape.

Animals↗
PubMed2001

The genetic bases of divergence in desiccation and starvation resistance among tropical and temperate populations of Drosophila melanogaster.

Desiccation and starvation resistance are two stress-related traits which vary geographically with climate in Drosophila melanogaster. To investigate the contribution of epistasis to population divergence for these traits, we crossed tropical and temperate populations from two different geographical regions to produce F1, F2 and first backcross generations. Line-cross analysis of generation means revealed that genetic bases of divergence for both traits were complex and remarkably similar in a number of respects. Strong additive and dominance effects were present in most of the models, whereas epistatic and maternal effects were less common. The presence of epistatic effects in approximately half of the models presented in this study is consistent with line-cross studies of diverged traits in other animals, and does not support the view that epistasis is the predominant means by which populations diverge. In addition, evidence of maternal effects in both traits adds to a growing body of recent evidence that suggests maternal contributions to population differentiation are more widespread than previously thought. This finding undermines the accuracy of studies inferring epistasis directly from the magnitude of F2 breakdown. More line-cross analysis studies of naturally diverged populations that take into account maternal effects will shed further light on the true incidence of epistasis and its importance in the evolutionary process.

Adaptation, Physiological↗
PubMed2001

Nonclinality of molecular variation implicates selection in maintaining a morphological cline of Drosophila melanogaster.

One general approach for assessing whether phenotypic variation is due to selection is to test its correlation with presumably neutral molecular variation. Neutral variation is determined by population history, the most likely alternative explanation of spatial genetic structure, whereas phenotypic variation may be influenced by the spatial pattern of selection pressure. Several methods for comparing the spatial apportionment of molecular and morphological variation have been used. Here, we present an analysis of variance framework that compares the magnitudes of latitudinal effects for molecular and morphological variation along a body size cline in Australian Drosophila populations. Explicit incorporation of the relevant environmental gradient can result in a simple and powerful test of selection. For the Australian cline, our analysis provides strong internal evidence that the cline is due to selection.

Animals↗
PubMed2001

Female sensitivity to diet and irradiation treatments underlies sex-mortality differentials in the Mediterranean fruit fly.

Large-scale experiments on medflies that were subjected to sterilizing doses of ionizing radiation (plus intact controls) and maintained on either sugar-only or full, protein-enriched diets revealed that, whereas the mortality trajectories of both intact and irradiated male cohorts maintained on both diets are similar, the mortality patterns of females are highly variable. Mean mortality rates at 35 days in male cohorts ranged from 0.2 to 0.3 but in female cohorts ranged from 0.09 to 0.35, depending on treatment. The study reports three main influences: (a) qualitative differences exist in the sex-mortality response of medflies subjected to dietary manipulations and irradiation; (b) the female mortality response is linked to increased vulnerability due to the nutritional demands of reproduction; and (c) female sensitivity to environmental changes underlies the dynamics of the sex-mortality differential.

Animals↗
PubMed2001

Genetic variation for preadult viability in Drosophila melanogaster.

The extent of genetic variation in fitness and its components and genetic variation's dependence on environmental conditions remain key issues in evolutionary biology. We present measurements of genetic variation in preadult viability in a laboratory-adapted population of Drosophila melanogaster, made at four different densities. By crossing flies heterozygous for a wild-type chromosome and one of two different balancers (TM1, TM2), we measure both heterozygous (TM1/+, TM2/+) and homozygous (+/+) viability relative to a standard genotype (TM1/TM2). Forty wild-type chromosomes were tested, of which 10 were chosen to be homozygous viable. The mean numbers produced varied significantly between chromosome lines, with an estimated between-line variance in log(e) numbers of 0.013. Relative viabilities also varied significantly across chromosome lines, with a variance in log(e) homozygous viability of 1.76 and of log(e) heterozygous viability of 0.165. The between-line variance for numbers emerging increased with density, from 0.009 at lowest density to 0.079 at highest. The genetic variance in relative viability increases with density, but not significantly. Overall, the effects of different chromosomes on relative viability were remarkably consistent across densities and across the two heterozygous genotypes (TM1, TM2). The 10 lines that carried homozygous viable wild-type chromosomes produced significantly more adults than the 30 lethal lines at low density and significantly fewer adults at the highest density. Similarly, there was a positive correlation between heterozygous viability and mean numbers at low density, but a negative correlation at high density.

Animals↗
PubMed2001

Rapid loss of stress resistance in Drosophila melanogaster under adaptation to laboratory culture.

We investigate changes in resistance to desiccation and starvation during adaptation of Drosophila melanogaster to laboratory culture. We test the hypothesis that resistance to environmental stresses is lost under laboratory adaptation. For both traits, there was a rapid loss of resistance over a three-year period. The rapidity of the response suggested that mutation accumulation could not account for it. Rather, resistance to environmental stresses appeared to be lost as a correlated response to selection on another trait, such as early fertility, with which stress resistance is negatively genetically correlated. These results suggest that caution is needed when extrapolating from evolution of stress resistance in long-established laboratory stocks to patterns of responses and correlated responses in natural populations.

Adaptation, Physiological↗
PubMed2000

The role of male accessory gland protein Acp36DE in sperm competition in Drosophila melanogaster.

A crucial factor determining sperm fertilization success in multiply mated Drosophila melanogaster females is the efficiency with which sperm are stored. This process is modulated by the accessory gland protein Acp36DE. In this study, we show that the effect of Acp36DE on sperm storage itself alters the outcome of sperm competition. As second-mating males, Acp36DE1 (null) males had significantly lower P2-values than Acp36DE2 (truncation) or Acp36DE+ (control) males, as might be expected as the null males' sperm are poorly stored. We used spermless males, which are null for Acp36DE, to show that, in the absence of sperm co-transfer, Acp36DE itself could not displace first-male sperm. The results therefore suggest that males null for Acp36DE suffer in sperm displacement because fewer sperm are stored or retained, not because Acp36DE itself displaces sperm. Acp36DE1 (null) males also gained significantly fewer fertilizations than controls when they were the first males to mate. Using spermless males, we also showed that significantly more second-male offspring were produced following the transfer of Acp36DE by spermless first-mating males. This implies that the transfer of Acp36DE itself by the first male facilitated the storage or use of the second male's sperm and that co-transfer with sperm is not necessary for Acp36DE effects on second-male sperm storage. Acp36DE may persist in the reproductive tract and aid the storage of any sperm including those of later-mating males or prime the female for future efficient sperm storage. Our results indicate that mutations in genes that affect sperm storage can drastically affect the outcome of sperm competition.

Animals↗
PubMed2000

Limits to natural selection.

We review the various factors that limit adaptation by natural selection. Recent discussion of constraints on selection and, conversely, of the factors that enhance "evolvability", have concentrated on the kinds of variation that can be produced. Here, we emphasise that adaptation depends on how the various evolutionary processes shape variation in populations. We survey the limits that population genetics places on adaptive evolution, and discuss the relationship between disparate literatures.

Animals↗