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Biomedical subjects

L Partridge

Publications and source records attributed to L Partridge.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1993

No reduction in the cost of mating for Drosophila melanogaster females mating with spermless males.

Drosophila melanogaster females can incur a cost of mating, manifested as a decrease in longevity and lifetime reproductive success. We investigated whether the cost of mating was a cost of storing and/or receiving sperm by using two types of males that do not transfer sperm (transformer pseudomales and the male offspring of homozygous tudor mothers). Females that were intermittently exposed to males that did and did not transfer sperm did not differ in lifespan, in the absence of any differences in other costly aspects of reproduction, showing that there was no cost to receiving sperm. There was a cost of mating with spermless males; this suggested a potential cost of receiving accessory fluid. However, it was not possible to distinguish this possibility from other explanations, e.g. female injury at mating and the transfer of parasites. The reasons why females continuously exposed to males remated more than was in their reproductive interests is discussed.

Animals↗
PubMed1993

Optimality, mutation and the evolution of ageing.

Evolutionary explanations of ageing fall into two classes. Organisms might have evolved the optimal life history, in which survival and fertility late in life are sacrificed for the sake of early reproduction and survival. Alternatively, the life history might be depressed below this optimal compromise by deleterious mutations: because selection against late-acting mutations is weaker, these will impose a greater load on late life. Evidence for the importance of both is emerging, and unravelling their relative importance presents experimentalists with a major challenge.

Adult↗
PubMed1993

Evolution of aging: testing the theory using Drosophila.

Evolutionary explanations of aging (or senescence) fall into two classes. First, organisms might have evolved the optimal life history, in which survival and fertility late in life are sacrificed for the sake of early reproduction or high pre-adult survival. Second, the life history might be depressed below this optimal compromise by the influx of deleterious mutations; since selection against late-acting mutations is weaker, deleterious mutations will impose a greater load on late life. We discuss ways in which these theories might be investigated and distinguished, with reference to experimental work with Drosophila. While genetic correlations between life history traits determine the immediate response to selection, they are hard to measure, and may not reflect the fundamental constraints on life history. Long term selection experiments are more likely to be informative. The third approach of using experimental manipulations suffers from some of the same problems as measures of genetic correlations; however, these two approaches may be fruitful when used together. The experimental results so far suggest that aging in Drosophila has evolved in part as a consequence of selection for an optimal life history, and in part as a result of accumulation of predominantly late-acting deleterious mutations. Quantification of these effects presents a major challenge for the future.

Aging↗
PubMed1992

On the use of tester stocks to predict the competitive ability of genotypes.

It has been recently claimed that the outcome of competition between two phenotypically indistinguishable strains cannot be predicted from comparisons of their respective performances against a mutant tester stock. Our aim in the present paper is to disprove this claim and to show the potential pitfalls of deriving conclusions from a statistical analysis of experimental designs commonly employed for the study of competitive interactions in genetically homogeneous and heterogeneous mixtures. Using our own data, we conclude that evaluating the competitive interactions of phenotypically indistinguishable wild-type strains by competing them against mutant marked stocks still remains a valuable method.

Analysis of Variance↗