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H C J Godfray

Publications and source records attributed to H C J Godfray.

13 recordsLinked to original sources
PubMed2006

Phylogenetic analysis of trophic associations.

Ecologists frequently collect data on the patterns of association between adjacent trophic levels in the form of binary or quantitative food webs. Here, we develop statistical methods to estimate the roles of consumer and resource phylogenies in explaining patterns of consumer-resource association. We use these methods to ask whether closely related consumer species are more likely to attack the same resource species and whether closely related resource species are more likely to be attacked by the same consumer species. We then show how to use estimates of phylogenetic signals to predict novel consumer-resource associations solely from the phylogenetic position of species for which no other (or only partial) data are available. Finally, we show how to combine phylogenetic information with information about species' ecological characteristics and life-history traits to estimate the effects of species traits on consumer-resource associations while accounting for phylogenies. We illustrate these techniques using a food web comprising species of parasitoids, leaf-mining moths, and their host plants.

Animals↗
PubMed2006

Fossil-calibrated molecular phylogenies reveal that leaf-mining moths radiated millions of years after their host plants.

Coevolution has been hypothesized as the main driving force for the remarkable diversity of insect-plant associations. Dating of insect and plant phylogenies allows us to test coevolutionary hypotheses and distinguish between the contemporaneous radiation of interacting lineages vs. insect 'host tracking' of previously diversified plants. Here, we used nuclear DNA to reconstruct a molecular phylogeny for 100 species of Phyllonorycter leaf-mining moths and 36 outgroup taxa. Ages for nodes in the moth phylogeny were estimated using a combination of a penalized likelihood method and a Bayesian approach, which takes into account phylogenetic uncertainty. To convert the relative ages of the moths into dates, we used an absolute calibration point from the fossil record. The age estimates of (a selection of) moth clades were then compared with fossil-based age estimates of their host plants. Our results show that the principal radiation of Phyllonorycter leaf-mining moths occurred well after the main radiation of their host plants and may represent the dominant associational mode in the fossil record.

Animals↗
PubMed2005

Aphid protected from pathogen by endosymbiont.

Aphids are associated with several facultative bacterial endosymbionts that may influence their interactions with other organisms. We show here that one of the three most common facultative symbionts of pea aphid (Acyrthosiphon pisum), the bacterium Regiella insecticola, has a major effect on host resistance to a fungal pathogen. Experimental establishment of the bacterium in uninfected aphid clones led to higher survival after fungal attack. The bacteria also increased the aphid's inclusive fitness, because the presence of the symbiont reduced the probability of fungal sporulation on aphid cadavers, hence lowering the rate of transmission of the disease to nearby related aphids.

Animals↗
PubMed2005

Fitness effects and transmission routes of a microsporidian parasite infecting Drosophila and its parasitoids.

A microsporidian infection was discovered in laboratory cultures of Drosophila species. Ultrastructural examination suggested it belonged to the poorly characterized species Tubulinosema kingi, and morphological and sequence data are presented. We explored how T. kingi affected the fitness of Drosophila melanogaster and D. subobscura, as well as the fitness of 2 of their parasitoids, Asobara tabida and Pachycrepoideus vindemiae. In Drosophila, infections caused changes in most of the traits we looked at that were associated with fitness, in particular causing a 34-55% reduction in early-life fecundity. Parasitoid fitness was affected more severely by infection than that of their hosts, with pupal mortality in particular increasing by 75-89%. We investigated the most important routes of transmission for T. kingi in a laboratory setting. Letting Drosophila larvae feed on medium contaminated with spores from infected dead flies resulted in 100% infection. Low levels of transmission (<10%) were found between larvae, and vertically between mothers and their offspring. Parasitoids developing in infected hosts all became infected, but infected adults were neither able to transmit the pathogen to their offspring nor to their offspring's Drosophila host, either directly, or via contamination of the ovipositor or other body parts. A field survey of Drosophila and their parasitoids in southern England revealed no natural infections. We discuss the potential importance of Microsporidia in parasitoid-host interactions, and for those working with Drosophila in the laboratory.

Animals↗
PubMed2005

Body sizes of hosts and parasitoids in individual feeding relationships.

In a natural community of 49 species (12 species of aphids and 37 species of their parasitoids), body lengths of 2,151 parasitoid individuals were, to an excellent approximation, related to the body lengths of their individual aphid hosts by a power law with an exponent close to 3/4. Two alternative models predict this exponent. One is based on surface area to volume relationships. The other is based on recent developments in metabolic ecology. Both models require a changing ratio (in both host and parasitoid) of length to diameter with increasing body length. These changing ratios are manifested differently in the two models and result in testably different predictions for the scaling of body form with increasing size. The estimated exponent of 3/4 for the relationship between individual host body size and individual parasitoid body size degrades to an exponent of nearly 1/2, and the scatter in the relationship between aphid and parasitoid body length is substantially increased, if the average length of a parasitoid species is examined as a function of the average length of its aphid host species instead of using measurements of individuals.

Animals↗
PubMed2005

The evolution of host use and unusual reproductive strategies in Achrysocharoides parasitoid wasps.

We studied host selection and exploitation, two crucial aspects of parasite ecology, in Achrysocharoides parasitoid wasps, which show remarkable host specificity and unusual offspring sex allocation. We estimated a molecular phylogeny of 15 Achrysocharoides species and compared this with host (plant and insect) phylogenies. This tri-trophic phylogenetic comparison provides no evidence for cospeciation, but parasitoids do show phylogenetic conservation of the use of plant genera. Patterns of sequence divergence also suggest that the parasitoids radiated more recently (or evolved much faster) than their insect hosts. Three main categories of brood production occur in parasitoids: (1) solitary offspring, (2) mixed sex broods and (3) separate (split) sex broods. Split sex broods are very rare and virtually restricted to Achrysocharoides, while the other types occur very widely. Our phylogeny suggests that split sex broods have evolved twice and provides evidence for a transition from solitary to mixed sex broods, via split sex broods, as predicted by theory.

Animals↗
PubMed2003

Population dynamics and gene transfer in genetically modified bacteria in a model microcosm.

The horizontal transfer and effects on host fitness of a neutral gene cassette inserted into three different genomic loci of a plant-colonizing pseudomonad was assessed in a model ecosystem. The KX reporter cassette (kanamycin resistance, aph, and catechol 2, 3, dioxygenase, xylE) was introduced on the disarmed transposon mini-Tn5 into: (I) the chromosome of a spontaneous rifampicin resistant mutant Pseudomonas fluorescens SBW25R; (II) the chromosome of SBW25R in the presence of a naturally occurring lysogenic-phage (phage Phi101); and (III) a naturally occurring plasmid pQBR11 (330 kbp, tra+, Hgr) introduced into SBW25R. These bacteria were applied to Stellaria media (chickweed) plants as seed dressings [c. 5 x 104 colony-forming units (cfu)/seed] and the seedlings planted in 16 microcosm chambers containing model plant and animal communities. Gene transfer to pseudomonads in the phyllosphere and rhizosphere was found only in the plasmid treatment (III). Bacteria in the phage treatment (II) initially declined in density and free phage was detected, but populations partly recovered as the plants matured. Surprisingly, bacteria in the chromosome insertion treatment (I) consistently achieved higher population densities than the unmanipulated control and other treatments. Plasmids were acquired from indigenous bacterial populations in the control and chromosome insertion treatments. Plasmid acquisition, plasmid transfer from inocula and selection for plasmid carrying inocula coincided with plant maturation.

Bacteriophages↗
PubMed2003

Diversity of bacteria associated with natural aphid populations.

The bacterial communities of aphids were investigated by terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments generated by PCR with general eubacterial primers. By both methods, the gamma-proteobacterium Buchnera was detected in laboratory cultures of six parthenogenetic lines of the pea aphid Acyrthosiphon pisum and one line of the black bean aphid Aphis fabae, and one or more of four previously described bacterial taxa were also detected in all aphid lines except one of A. pisum. These latter bacteria, collectively known as secondary symbionts or accessory bacteria, comprised three taxa of gamma-proteobacteria (R-type [PASS], T-type [PABS], and U-type [PAUS]) and a rickettsia (S-type [PAR]). Complementary analysis of aphids from natural populations of four aphid species (A. pisum [n = 74], Amphorophora rubi [n = 109], Aphis sarothamni [n = 42], and Microlophium carnosum [n = 101]) from a single geographical location revealed Buchnera and up to three taxa of accessory bacteria, but no other bacterial taxa, in each aphid. The prevalence of accessory bacterial taxa varied significantly among aphid species but not with the sampling month (between June and August 2000). These results indicate that the accessory bacterial taxa are distributed across multiple aphid species, although with variable prevalence, and that laboratory culture does not generally result in a shift in the bacterial community in aphids. Both the transmission patterns of the accessory bacteria between individual aphids and their impact on aphid fitness are suggested to influence the prevalence of accessory bacterial taxa in natural aphid populations.

Animals↗
PubMed2003

A few-polyhedra mutant and wild-type nucleopolyhedrovirus remain as a stable polymorphism during serial coinfection in Trichoplusia ni.

Few-polyhedra (FP) mutants of nucleopolyhedroviruses (NPVs) are a well-known phenomenon during serial passage of virus in cell culture. Under these circumstances such mutants produce low yields of occlusion bodies (OBs) and poorly occlude virions, but they are selected for through advantageous rates of budded virus replication. Spontaneous insertion of transposable elements originating from host cell DNA into the viral fp25 gene has been shown to be a common cause of the phenotype. A model of NPV population genetics predicts that mutants with these characteristics might persist within stable polymorphisms in viral populations during serial passage of virus in vivo. However, this hypothesis was previously untested, and FP mutants have not been recovered from field isolates of NPVs. We isolated and characterized an FP mutant that arose during routine passage of Autographa californica multinucleocapsid NPV (AcMNPV) in cell culture and identified a transposable element within the fp25 gene. We tracked the fates of coinfecting wild-type and FP mutant AcMNPV strains through serial passage in fifth-instar Trichoplusia ni larvae. The levels of both strains remained stable during successive rounds of infection. We applied the data obtained to a model of NPV population genetics in order to derive the frequency distribution of the multiplicity of cell infection in infected insects and estimated that 4.3 baculovirus genomes per OB-producing cell would account for this equilibrium.

Animals↗
PubMed2002

Costs of resistance in insect-parasite and insect-parasitoid interactions.

Most, if not all, organisms face attack by natural enemies and will be selected to evolve some form of defence. Resistance may have costs as well as its obvious benefits. These costs may be associated with actual defence or with the maintenance of the defensive machinery irrespective of whether a challenge occurs. In this paper, the evidence for costs of resistance in insect-parasite and insect-parasitoid systems is reviewed, with emphasis on two host-parasitoid systems, based on Drosophila melanogaster and pea aphids as hosts. Data from true insect-parasite systems mainly concern the costs of actual defence; evidence for the costs of standing defences is mostly circumstantial. In pea aphids, the costs of standing defences have so far proved elusive. Resistance amongst clones is not correlated with life-time fecundity, whether measured on good or poor quality plants. Successful defence by a D. melanogaster larva results in a reduction in adult size and fecundity and an increased susceptibility to pupal parasitoids. Costs of standing defences are a reduction in larval competitive ability though these costs only become important when food is limited. It is concluded that costs of resistance can play a pivotal role in the evolutionary and population dynamic interactions between hosts and their parasites.

Animals↗
PubMed2002

Maternal-offspring conflict leads to the evolution of dominant zygotic sex determination.

Sex determination in many species involves interactions among maternally expressed genes (eg, mRNA's and proteins placed into the egg) and zygotically expressed genes. Recent studies have proposed that conflicting selective pressures can occur between maternally and zygotically expressed sex determining loci and that these may play a role in shaping the evolution of sex determining systems. Here we show that such genetic conflict occurs under very general circumstances. Whenever sex ratio among progeny in a family affects the fitness of either progeny in that family or maternal fitness, then maternal-zygotic genetic conflict occurs. Furthermore, we show that this conflict typically results in a "positive feedback loop" that leads to the evolution of a dominant zygotic sex determining locus. When males more negatively effect fitness within the family, a male heterogametic (XY male) sex determining system evolves, whereas when females more negatively effect fitness in the family, a female heterogametic (ZW female) system evolves. Individuals with the dominant sex allele are one sex, and the opposite sex is determined by maternally-expressed genes in individuals without the dominant sex allele. Results therefore suggest that maternal-zygotic conflict could play a role in the early evolution of chromosomal sex determining systems. Predictions are made concerning the patterns of expression of maternal and zygotic sex determining genes expected to result from conflict over sex determination.

Animals↗