Community Genetic and Environmental Effects in Extremely Plastic Aquatic and Terrestrial Arthropods

UoM administered thesis: Master of Philosophy

  • Authors:
  • Samuel Purkiss

Abstract

Half of my MPhil used a parasitoid-host system (Pea aphid & A. ervi) to understand the complex interactions, created by community genetic (CG) effects and other ecological factors, that drive evolutionary dynamics. We designed an experiment that sought to understand how intraguild predation (IGP) and indirect ecological effects (IEEs) (aphid symbiosis with protective symbiont) affect the outcome of an established indirect genetic effect (IGE). We established a quantitative genetic half sibling design in the parasitoid wasp Aphidius ervi to understand the genotype specific effects on the phenotype of the pea aphid (Acyrthosiphon pisum) in the presence and absence of an intraguild predator (Chrysoperla carnea). This work aims to improve the integration of CGs into biological pest and disease control schemes in agro-ecosystems, where pest species are becoming resistant to the conventional chemical control methods and an improved understanding of the wider environmental impacts of chemical controls render them increasingly unsuitable The experiment utilised two clonal populations of pea aphid, the established lab clone N116 and a local isolate named the 'Quad' clone, that we established from a female we sampled from our university quad. We did this to try and understand the effect of their different secondary symbionts, identified using 16s rRNA sequencing, on the outcome of the interaction between the parasitoid and host. Moreover, we wanted to try and understand the differences in wasp virulence that we found in our aphid clones. Our analysis showed that the main predictor of wasp virulence was the immunity factor in our aphid clones and that aphid behaviour was significantly influenced by a sire effect and an interspecific IGE (IIGE) effect depending on the context of the interaction. We also identified several secondary symbionts in our aphid clones, most notably the presence of three known defensive symbionts, Hamiltonella defensa, Fukatsuia symbiotica and Serratia symbiotica, in the N116 clone and the presence of Serratia symbiotica in the Quad aphid clone. The other half of my work, with Daphnia magna, sought to explain how changes to the abiotic factors of aquatic environments effect the various behavioural and developmental plastic responses of this keystone species; an understudied area considering the scale of natural and anthropogenic changes faced by ecosystems all around the globe. The types of stress faced by aquatic organisms are multifaceted, the salinization, acidification, light and chemical pollution and increases in temperature now represent real threats to biodiversity across the globe. Moreover, whilst we have a good understanding of the consequences of these when they occur in isolation, we do not yet fully understand the ramifications of the more complex and realistic scenario of these stressors occurring together. The ability of Daphnia to survive and reproduce, long term, in environments exposed to increases in salinity and acidity was tested in conjunction with exposure to constant light (e.g. light pollution) and constant darkness (e.g. eutrophic environments with low light incidence). A laboratory raised clonal population of Daphnia magna was exposed to various combinations of these stressors over 30 days to investigate the impact they had on the life history traits of our populations. After 10 days under 24-hour light, and combinations of other stressors, and despite tangible increases in population size of some treatment groups, the normal reproduction of our daphnia populations was severely disrupted when compared to the controls. Moreover, after 30 days and across all treatments the reproductive success of the daphnia populations (in 24-hour light) dramatically increased, suggesting a plastic response in daphnia tolerance to the treatment conditions. However, in the absence of any light, high mortality occurred across all treatments indicating that it had a much greater negative impact than constant exposure to light. The age structure of the populations, across all combinations of stress and in the absence of a light cycle, varied significantly suggesting that the life history responses of the populations were context specific. Our findings further our understanding of the ecology of a keystone aquatic crustacean under complex abiotic environmental stress and the ability of aquatic organisms to adapt to the novel environments created by anthropogenic effects.

Details

Original languageEnglish
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Award date1 Aug 2019