Landscape population genetics and the role of organic farming

This project aims at understanding the effect of different farming systems on the genetic diversity of common agricultural species. It is well known that organic farming generally improves the biodiversity and abundance of species in the agricultural landscape (Hole et al., 2005). A reduction in species number and abundance has been shown as a result of the intensification of farming suggesting a relationship between farming intensity and species abundance (e.g. Stoate et al., 2001). Anyway, none of the studies that investigated the effects of pesticides presence and farming intensity has investigated the effect on the genetic diversity and isolation of the populations. It has been shown that, despite the theoretical expectations, also very abundant species like Abax parallelepipedus can be divided in isolated and genetically distinct populations within very few years in response to human activity (e.g. construction of streets: Keller et al., 2004). Therefore, we chose two common agricultural species (field vole, Microtus agrestis, and a non-pest ground beetle, Bembidion lampros) belonging to different taxa and with different dispersal abilities, to investigate the effect of pesticide use and intensiveness of farming on their genetic structuring and diversity

Chromosomal and Cytoplasmic Analysis of Heat Shock Resistance in Natural Populations of Drosophila Melanogaster

We evaluated genetic differences between two populations of Drosophila melanogaster that differed in thermal tolerance. Adults of one tropical population (Mali) survived heat shock (39.5°C for 30 min.) at 84%. By contrast, those from a strain collected in Denmark survived at a rate of only 53%. The greatest effect on variation was differences in cytoplasms, but variation in chromosomes 2 and 1 also played a role on tolerance. Heat shock proteins, however, reside on chromosome 3 and, therefore, variation at these sites is low or differences had little effect on results obtained from the methods employed

On the brink between extinction and persistence

The nature of size fluctuations is crucial in forecasting future population persistence, independently of whether the variability stems from external forces or from the dynamics of the population renewal process. The risk of intercepting zero is highly dependent on the way the variance of the population size relates to its mean. The minimum population size required for a population not to go extinct can be determined by a scaling equation relating the variance to the arithmetic mean. By the use of a derived expression for the harmonic mean defined by the parameters of the scaling equation we show how it is possible to separate the domains of persistence from those of extinction and to facilitate the identification of populations on the brink of extinction

A major QTL affects temperature sensitive adult lethality and inbreeding depression in life span in Drosophila melanogaster

<p>Abstract</p> <p>Background</p> <p>The study of inbreeding depression has major relevance for many disciplines, including conservation genetics and evolutionary biology. Still, the molecular genetic basis of this phenomenon remains poorly characterised, as knowledge on the mechanistic causes of inbreeding depression and the molecular properties of genes that give rise to or modulate its deleterious effects is lacking. These questions warrant the detailed study of genetic loci giving rise to inbreeding depression. However, the complex and polygenic nature of general inbreeding depression makes this a daunting task. Study of inbreeding effects in specific traits, such as age-specific mortality and life span, provide a good starting point, as a limited set of genes is expected to be involved.</p> <p>Results</p> <p>Here we report on a QTL mapping study on inbreeding related and temperature sensitive lethality in male <it>Drosophila melanogaster</it>. The inbreeding effect was expressed at moderately high temperature, and manifested itself as severe premature mortality in males, but not in females. We used a North Carolina crossing design 3 to estimate average dominance ratio and heritability. We found the genetic basis of the lethal effect to be relatively simple, being due mainly to a single recessive QTL on the left arm of chromosome 2. This locus colocalised with a QTL that conditioned variation in female life span, acting as an overdominant locus for this trait. Male life span was additionally affected by variation at the X-chromosome.</p> <p>Conclusion</p> <p>This demonstrates that analysis of large conditional lethal effects is a viable strategy for delineating genes which are sensitive to inbreeding depression.</p

Wildlife friendly agriculture: which factors do really matter? A genetic study on field vole

The distribution of genetic differentiation and the directions of gene flow were determined mainly by landscape factors: thus the expectation that organic fields act as genetic reservoir was not met. The fact that agricultural area presented more sub-populations than the undisturbed one, together with the importance of connectivity and habitat size in shaping gene flow and genetic differentiation, shows that switching to organic farming might not be enough to ensure the conservation of species in the agricultural environment. These results emphasise the need to include landscape structure in management policies

The Effect of Fluctuating Temperatures During Development on Fitness-Related Traits of Scatophaga stercoraria (Diptera: Scathophagidae)

Development of ectotherms is highly temperature dependent. Studies using variable thermal environments can improve ecological relevance of data because organisms naturally face day-to-day stochastic temperature fluctuations as well as seasonal changes in the amplitude of such daily fluctuations. The objective of this study was to investigate if, and to what extent, the use of constant temperatures is justified in studies of the model species, yellow dung fly, Scatophaga stercoraria (L.). We examined the effect of temperature fluctuation on the expression of several life history traits and the effect on subsequent adult longevity. We used two fluctuating temperature treatments with the same mean but different amplitudes (15/21°C, 12/24°C; 12/12 h), and three constant temperature treatments spanning the wide temperature range faced in the wild (12, 18, and 24°C). Large temperature fluctuation was mostly detrimental (lower juvenile survival, slower growth, smaller body size, and longer development), whereas moderate temperature fluctuation usually gave responses similar to the constant regime. When developing in fluctuating temperatures, adult longevity (no effect), body size (lower), and wing shape (narrower wings) deviated from the expectations based on the constant temperature reaction norms, presumably because of acclimation responses. Contrary to some studies no obvious beneficial effects of moderate temperature fluctuation were observed. Instead, yellow dung flies seem to canalize development in the face of temperature fluctuation up to a point when detrimental effects become unavoidable. The relatively greater effects of extreme constant developmental temperatures question their biological relevance in experiment

Detecting purging of inbreeding depression by a slow rate of inbreeding for various traits:the impact of environmental and experimental conditions

Inbreeding depression (ID) has since long been recognized as a significant factor in evolutionary biology. It is mainly the consequence of (partially) recessive deleterious mutations maintained by mutation-selection balance in large random mating populations. When population size is reduced, recessive alleles are increasingly found in homozygous condition due to drift and inbreeding and become more prone to selection. Particularly at slow rates of drift and inbreeding, selection will be more effective in purging such alleles, thereby reducing the amount of ID. Here we test assumptions of the efficiency of purging in relation to the inbreeding rate and the experimental conditions for four traits in D. melanogaster. We investigated the magnitude of ID for lines that were inbred to a similar level, F ≈ 0.50, reached either by three generations of full-sib mating (fast inbreeding), or by 12 consecutive generations with a small population size (slow inbreeding). This was done on two different food media. We observed significant ID for egg-to-adult viability and heat shock mortality, but only for egg-to-adult viability a significant part of the expressed inbreeding depression was effectively purged under slow inbreeding. For other traits like developmental time and starvation resistance, however, adaptation to the experimental and environmental conditions during inbreeding might affect the likelihood of purging to occur or being detected. We discuss factors that can affect the efficiency of purging and why empirical evidence for purging may be ambiguous.</p

Heat-Shock Resistance in Drosophila Populations: Analysis of Variation in Reciprocal Cross Progeny

Genetic variation for resistance to high temperature stress was studied in populations of D. melanogaster and D. buzzatii from different geographic regions. Drosophila melanogaster individuals were presented with either a direct short exposure to a high temperature or exposure to high temperature after receiving a pretreatment, which increased resistance. Heat-stress resistance varied among populations, with one much more resistant than all others under both treatments. Another possessed low stress resistance when exposed without the heat pretreatment; but with pretreatment, resistance increased relative to the other populations. Evidence from reciprocal crosses suggests that the X chromosome of the more resistant population carries alleles that greatly increase resistance, and that one or more factors on the autosomes also affect resistance. Non-additive interaction effects among the three less resistant populations, were suggestive that all differ for various elements that contribute to stress resistance, and that some clearly change inducible resistance more than basal levels. In D. buzzatii, the two least resistant populations were genetically very similar. Crosses to the more resistant population gave results suggesting that the low resistance to heat is dominant. A small X-chromosome effect that increased resistance, and a dominant enhancer of male resistance also may have contributed to variation in resistance