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L Partridge

Publications and source records attributed to L Partridge.

At least 55 records · Page 3Linked to original sources
PubMed1998

Body size and cell size in Drosophila: the developmental response to temperature.

In Drosophila, like most ectotherms, development at low temperature reduces growth rate but increases final adult size. Cultures were shifted from 25 degrees C to low (16.5 degrees C) or to high (29 degrees C) temperature at regular intervals through larval and pupal stages, and the flies of both sexes showed an increase or decrease, respectively, in the size of thorax, wing and abdominal tergite. Size changes in the wing blade resulted from changes in the size of the epidermal cells (with only a small increase in cell number in males reared at low temperature). The temperature-shifts became less effective as they were made at successively later developmental stages, demonstrating a cumulative effect of temperature on adult size. The thorax and wing develop from the same imaginal disc, with most cell division occurring in larval stages, but they differ in timing of temperature sensitivity, which extends only to pupariation or into the late pupal stage, respectively. Growth of the adult abdomen occurs largely after pupariation but its size is temperature-sensitive through both larval and pupal stages. We discuss growth control in Drosophila and the likely effects of temperature on food assimilation, growth efficiency and allocation of nutrients to the production of different tissues.

Journal Article↗
PubMed1998

Pervasive effects of P element mutagenesis on body size in Drosophila melanogaster.

A set of Drosophila melanogaster was generated, all derived from a common isogenic base stock and each with a single new P element insert on the second or third chromosome. The lines were scored for their body size, measured as thorax length. P inserts were associated with highly significant effects on body size, although the genotypes of the construct and of the control prevented deduction of the direction of mutant effects. In addition to mutant effects on the thorax length of both sexes, there were also highly significant sex-specific effects. Pleiotropic effects of inserts affecting body size on viability and bristle number, as ascertained in a separate study of these lines (Lyman et al., 1996), were weak, Insertional mutagenesis is potentially a powerful tool for investigating the genes involved in size-control in Drosophila, but the technique requires fine tuning for use on polygenic and fitness-related traits.

Animals↗
PubMed1997

Heritability of pre-adult viability differences can explain apparent heritability of sperm displacement ability in Drosophila melanogaster.

Sperm displacement has been the subject of a large number of evolutionary studies because of its effects on relative male reproductive success. To understand better the evolutionary role of variation in sperm displacement ability (SDA), an obvious aim is to measure its heritability. In this paper, we show that a standard method used to measure the heritability of SDA can be misleading. First, we show that using conventional methods (based on counts of adult offspring of multiply mated females), SDA appears to be heritable. However, an examination of potentially confounding variables strongly suggests that this result is misleading, and that the heritable component is more likely to be pre-adult viability. Consequently, it is likely that there is little measurable heritable genetic variation for SDA in D. melanogaster. We conclude that, although conventional methods of measuring sperm displacement will usually be adequate for phenotypic measurements, greater care must be taken when measuring genetic variances.

Animals↗
PubMed1997

Ageing: levelling of the grim reaper.

Recent observations of a levelling of the death rate in extreme old age, in both experimental species and humans, are posing difficult problems for evolutionary biologists, in particular about the evolution of the post-reproductive period.

Aging↗
PubMed1997

Genetic variation for total fitness in Drosophila melanogaster.

We measured the heterozygous effects on net fitness of a sample of 12 wild-type third chromosomes in D. melanogaster. Effects on fitness were assessed by competing the wild-type chromosomes against balancer chromosomes, to prevent the production of recombinants. The measurements were carried out in the population cage environment in which the life history had been evolving, in an undisturbed population with overlapping generations, and replicated measurements were made on each chromosome to control for confounding effects such as mutation accumulation. We found significant variation among the wild type chromosomes in their additive genetic effect on net fitness. The system provides an opportunity to obtain an accurate estimate of the distribution of heterozygous effects on net fitness, the contribution of different fitness components including male mating success, and the role of intra-chromosomal epistasis in fitness variation.

Animals↗
PubMed1997

The effects of reproduction on longevity and fertility in male Drosophila melanogaster.

We examined the effect of reproduction on subsequent survival and fecundity of male Drosophila melanogaster by reversing the reproductive status of individuals part-way through life. Reproduction had a much more marked effect on fertility than survival: males with a history of reproduction showed complete sterility at a time when upwards of 80% of their cohort were still alive. Analyses of survival rates alone gave a misleading measure of the impact of ageing. Sterility appeared to be attributable mainly to a reduction in sperm count. Early reproduction caused permanent, irreversible damage to both survival and fecundity, with risk playing an apparently minor role. Individual differences in frailty appeared to be of little consequence for the interpretation of these reversal experiments, although its possible occurrence made definite detection of risk difficult.

Journal Article↗
PubMed1997

Mating and hormonal triggers regulate accessory gland gene expression in male Drosophila.

Drosophila melanogaster males transfer accessory gland proteins, as part of their seminal fluid, to females during each mating. Since accessory gland proteins are important for male reproductive success, it is important that the male replenish the proteins he transferred during mating. Previous studies had shown that mating induces the resynthesis of accessory gland proteins, but since mating includes a set of stereotyped behavior patterns as well as the act of copulation, it was not known which aspect of the mating process induces accessory gland protein synthesis. By exposing males to females whose ovipositors had been sealed shut, we have shown that resynthesis of accessory gland proteins occurs only when seminal fluid is transferred to females. By applying juvenile hormone or 20-hydroxyecdysone topically to the cuticle of male flies, we showed that these hormones can act in vivo to stimulate the synthesis of accessory gland proteins to levels similar to those observed after mating.

Journal Article↗
PubMed1997

Influence of temperature and activity on the metabolic rate of adult Drosophila melanogaster.

We measured metabolic rates of adult male Drosophila melanogaster allowed to evolve in the laboratory at 18 and 25 degrees C and compared these with measurements of metabolic rates of flies collected along a latitudinal gradient in Australia. Metabolic rates of flies that had evolved in the laboratory at low temperature were 5-7% higher than those of flies allowed to evolve at high temperature. Metabolic rates of field collected increased with latitude when measured at 18 degrees C but not at higher temperature (25 degrees C) and were about 9% greater in high latitude (approximately 41'00) flies than low latitude (16'53) flies. Metabolic rate was strongly influenced by measurement temperature; estimated Q10s ranged from 1.79 to 2.5 for measurements made at 18 and 25 degrees C. Metabolic rate scaled isometrically with body mass; the estimated slope of a ln-ln regression of metabolic rate and body mass was 1.03 +/- 0.1. We used our measures of metabolic rate and activity to estimate the minimum cost of transport (MCOT) while walking. The estimates of MCOT have high standard errors (lab, 34.30 +/- 14.2 ml O2/g/km; and field, 38.0 +/- 17.0 ml O2/g/km); however, they differ by only 3-9% from predicted values based on allometric relationships reported in the literature.

Animals↗
PubMed1997

Joint regulation of cell size and cell number in the wing blade of Drosophila melanogaster.

We used Drosophila melanogaster to test for compensatory control of cell area and cell number in the regulation of total wing area. In two random bred wild-type base stocks collected from different geographic locations we found a negative association between the area and the number of cells in the wing blade. Three replicate lines were selected for increased or decreased wing area, with cell area maintained at the same level as in the three controls. After eight generations of selection, despite a large and highly significant difference in wing area between the large, control and small selection lines, cell area did not differ significantly between them. Rather, the difference in wing area between selection regimes was attributable to differences in cell number. Over the course of selection, the initially significant negative correlation between cell area and cell number in the wing increased, providing evidence for compensatory regulation of cell area and cell number. As a result of the increasingly negative association between the two traits, the variance in wing area declined as selection proceeded. It will be important to discover the mechanisms underlying the compensatory regulation of cell area and cell number.

Animals↗
PubMed1997

Genetic and environmental responses to temperature of Drosophila melanogaster from a latitudinal cline.

Field-collected Drosophila melanogaster from 19 populations in Eastern Australia were measured for body size traits, and the measurements were compared with similar ones on flies from the same populations reared under standard laboratory conditions. Wild caught flies were smaller, and latitudinal trends in size were greater. Reduced size was caused by fewer cells in the wing, and the steeper cline by greater variation in cell area. The reduction in size in field-collected flies may therefore have been caused by reduced nutrition, and the steeper cline may have been caused by an environmental response to latitudinal variation in temperature. No evidence was found for evolution of size traits in response to laboratory culture. The magnitude of phenotypic plasticity in response to temperature of development time, body size, cell size and cell number was examined for six of the populations, to test for latitudinal variation in plasticity. All characters were plastic in response to temperature. Total development time showed no significant latitudinal variation in plasticity, although larval development time showed a marginally significant effect, with most latitudinal variation at intermediate rearing temperatures. Neither thorax length nor wing size and its cellular components showed significant latitudinal variation in plasticity.

Adaptation, Physiological↗
PubMed1996

Female fitness in Drosophila melanogaster: an interaction between the effect of nutrition and of encounter rate with males.

Female Drosophila melanogaster were maintained at five levels of nutrition, with either continuous or intermittent exposure to males. Remaining frequency increased with nutrition and was higher with continuous exposure to males. Age-specific and lifetime egg production increased with increasing nutrition, but lifespan peaked at intermediate nutrition. Females on the three highest nutritional levels showed a cost of mating in reduced survival, but only at the highest food level did this reduced lifespan lead to a significant cost of mating for lifetime egg production. The data suggest that remating frequencies in laboratory cultures may evolve to a low enough level for the cost of mating to be only weakly expressed, if at all. Further data are required to assess the importance of the cost of mating in natural populations, where the evolution of low remating frequencies might be expected to be opposed by other costs.

Animal Nutritional Physiological Phenomena↗
PubMed1995

Thermal evolution of growth efficiency in Drosophila melanogaster.

Drosophila melanogaster shows geographic clines in body size, with genetically larger flies being found further from the equator and at higher altitudes. In the laboratory, evolution at lower temperatures results in genetically larger flies, and development at low temperature increases adult body size. This study demonstrates that when newly hatched larvae from laboratory temperature selection lines were raised on fixed amounts of food (yeast) at the same temperature, larvae from the lines with the cold evolutionary history required less food to produce a given size of adult. Larvae from both high- and low-temperature selection lines required more food, however, to make a given size of adult when grown in the cold than when grown in the hot. The opposite associations between growth efficiency and adult body size seen with evolution or development at low temperature are puzzling, and suggest that different mechanisms may underlie the size changes. Since environmental and evolutionary effects of temperature on body size seem to be widespread among ectotherms, some basic aspects of thermal physiology must be involved.

Analysis of Variance↗
PubMed1995

Cost of mating in Drosophila melanogaster females is mediated by male accessory gland products.

Female Drosophila melanogaster with environmentally or genetically elevated rates of mating die younger than controls. This cost of mating is not attributable to receipt of sperm. We demonstrate here that seminal fluid products from the main cells of the male accessory gland are responsible for the cost of mating in females, and that increasing exposure to these products increases female death rate. Main-cell products are also involved in elevating the rate of female egg-laying, in reducing female receptivity to further matings and in removing or destroying sperm of previous mates. The cost of mating to females may therefore represent a side-effect of evolutionary conflict between males.

Animals↗
PubMed1995

Cellular basis and developmental timing in a size cline of Drosophila melanogaster.

We examined 20 Drosophila melanogaster populations collected from a 2600-km north-south transect in Australia. In laboratory culture at constant temperature and standard larval density, a genetic cline in thorax length and wing area was found, with both traits increasing with latitude. The cline in wing area was based on clines in both cell size and cell number, but was primarily determined by changes in cell number. Body size and larval development time were not associated among populations. We discuss our results in the context of selection processes operating in natural and experimental populations.

Analysis of Variance↗
PubMed1994

Gene-environment interaction for body size and larval density in Drosophila melanogaster: an investigation of effects on development time, thorax length and adult sex ratio.

We measured the effect of larval density on thorax length, development time, sex ratio and a measure of total fitness, using strains of Drosophila melanogaster artificially selected for increased thorax length, control lines otherwise cultured in an identical way, and the base stock from which the lines had been derived. We used the addition experimental design (Mather & Caligari, 1981). No genotype-environment interaction was observed when comparing the reduction in thorax length of 'large' and 'control' lines with increasing larval density for any culture series, i.e. rank ordering of genotypes and additive genetic variances remained the same in all the environments tested. In contrast, the reduction in thorax length for the base stock as density increased was proportionally smaller than that of the 'large' and 'control' lines. Development time increased more rapidly with larval density in the 'large' lines than in the 'controls' or base stock. Sex ratio was unaffected by larval density but thorax length and the development time of females were more affected than those of males by increasing larval density. The estimate of total fitness showed clear evidence of gene-environment interaction for the effect of body size on fitness, with genetically large individuals at an increasing disadvantage with increasing larval density.

Animals↗