Our lab group has a strong track record of working with a range of insect model organisms and agricultural pests including: Helicoverpa armigera (cotton bollworm); Trialeurodes vaporariorum (glasshouse whitefly); Adalia bipiunctata (2 spot ladybird); Bombus terrestris (buff-tailed bumblebee) and Drosophila melanogaster. The successful candidate could focus on any of these organisms (or a combination) in order to answer different questions during their PhD. Depending on the study species, virulence of infections can be studied by assessing: insect survival, feeding, growth rate, or fecundity. One benefit of studying entomopathogenic fungi is that it is possible to estimate pathogen fitness by studying onward transmission potential at the end of an infection cycle: the pathogen breaks out through the insect cuticle and sporulates on the dead insect, these spores can be counted to assess parasite fitness.
The key aims to be addressed during the PhD can be tailored to suit the interests and skills of the successful candidate. However, suitable project aims would include:
Aim 1. How does the virulence of single infections compare to mixed infections?
Whilst many studies have pitted two pathogens against each other in coinfection trails and compared virulence to single infections, these experiments rarely yield generalisable conclusions. In this PhD the successful candidate will study coinfection effects on hosts for a panel of ~10 different fungal pathogen strains, providing multiple pairwise estimates of coinfection virulence compared to single infections. In nature most instances of coinfection probably result from sequential exposure to several different pathogens. This study will move on to investigate the impact of infection order on the outcome of coinfection by pairs of fungal pathogens.
Aim 2. A proof-of-concept development of novel fitness read-outs using high throughput mid-infrared spectroscopy and artificial intelligence to estimate ageing and infection burden. Working in close collaboration with Glasgow University the project will seek to develop new techniques to assess virulence and pathogenicity using infrared spectroscopy of insect bodies following different infection treatments. This will build on existing Glasgow expertise in determining insect age, species identity and infection status using infrared spectroscopy techniques. Once complete, this work will open up novel opportunities to use these teqchniques later in the PhD.
Aim 3. To what extent is the outcome of coinfection specific to individual host genotypes?
Host populations are usually very genetically variable with respect to infection defence. Resistance genes are often specific in their effects, such that a given genotype may effectively defend against one pathogen strain/species but be susceptible to a second. Host genetic variability has been largely ignored thus far in studies of coinfection biology. This PhD will study different families of insect host (representing different genotypes) and investigate the consistency of coinfection effects across a panel of host genotypes.
Aim 4. How does coinfection alter pathogen virulence evolution?
Coinfection can influence the virulence that an individual host experiences. However, it can also influence the course of pathogen evolution. Within-host competition between pathogen strains/species for transmission opportunities can alter selection pressures on pathogens, potentially selecting for both increased and decreased virulence depending on the infection scenario. This PhD could culminate with an experimental evolution study where pathogen strains are repeatedly passaged through hosts either under coinfection or single infection treatments, before changes in pathogen virulence are assessed.
The PhD will use a combination of laboratory techniques including: insect rearing and infection studies, pathogen culture and preparation, microscopic quantification of pathogen spores, molecular quantification of pathogen loads under coinfection (PCR/qPCR/microsatellites). Furthermore, subject to the interest of the candidate, host immune response activity could be assayed both by phenotypic means (eg phenoloxidase, haemocyte numbers & encapsulation assays) and by assessing immune gene expression profiles by qPCR.