Entomology & Insect Sciences GIDP
Wolbachia Conference 2018
June 17-22, 2018
Terrestrial arthropods, including insects, commonly harbor heritable intracellular symbionts. These symbionts cannot survive outside the host and often confer novel beneficial phenotypes to the host to maintain stable vertical transmission. While many heritable symbionts are mutualistic, symbionts can also maintain vertical transmission through direct manipulation of host reproduction to favor infected female progeny via mechanisms like cytoplasmic incompatibility (CI). The efficacy of symbiont-induced effects often varies under changing environmental conditions, potentially leading to destabilization of the symbiosis. For example, increased temperatures reduce the titer of a common reproductive manipulator, Wolbachia, and the strength of its conferred CI. Another manipulative symbiont, Cardinium, infects ~ 6% of Arthropods, including the whitefly parasitoid, Encarsia suzannae; this symbiont also induces CI in its host, however there appears to be little homology between the CI mechanisms of Cardinium and Wolbachia. Currently, little is known concerning the impact of temperature on the Cardinium-E. suzannae association, including whether temperature disrupts the CI phenotype. Furthermore, the mechanism by which Cardinium induces CI is unclear, although several candidate CI genes have been found in the Cardinium genome. Here, we investigated the effect of warm and cool temperatures on bacterial titer and CI strength in the Cardinium-E. suzannae system, and determined the timing of expression for three CI candidate genes throughout E. suzannae development.
Abstract for Lay Audience
Most terrestrial arthropods, including insects, form associations with bacteria. Some of these bacterial partners live inside insect cells, cannot survive outside of their host, and are not contagious but instead are inherited from mother to offspring. Because of this restricted lifecycle, heritable symbionts have evolved numerous evolutionary strategies for maintaining their own transmission, often involving modification of the insect host biology or phenotype. These symbiont-modified phenotypes can have major impacts on host ecology and evolution, such as granting hosts increased resistance to important natural enemies, pathogens, or stress, or expanding host dietary range. A common and extreme strategy consists of the symbiont manipulating the host reproductive system itself in a way that favors survival of offspring carrying the symbiont. This benefit comes at the expense of uninfected host offspring, causing the hosts with symbionts to become relatively more abundant and increasing the likelihood of future symbiont transmission. I am studying a reproductive manipulation called cytoplasmic incompatibility (or “CI”), caused by the bacterium Cardinium. CI is a type of mating incompatibility between male and female hosts with and without the symbiont that results in an increase in progeny with the symbiont. I am particularly interested in how environmental factors like temperature influence symbiont-induced phenotypes and the stability of the insect-bacterium symbiosis. For example, in the case of the parasitic wasp, Nasonia vitripennis, and its manipulative bacterium, Wolbachia, exposure to elevated temperatures reduced the strength of its CI phenotype; this weaker phenotype was correlated with reduced symbiont density within the host. Cardinium is known to cause CI in my study organism, Encarsia suzannae, a parasitic wasp that lays its eggs and develops within sap-sucking whiteflies. However, it is unclear how the players in this symbiosis respond to differing temperatures. Utilizing two regimens consisting of the hot and cold temperature extremes of the wasp habitat, as well as a control regimen, I am testing the effects of temperature on the reproductive phenotype as well as Cardinium persistence within the host. These experiments may provide insight into the mechanism of the CI phenotype, and potentially reveal consequences of a dynamic climate on the stability of this type of heritable symbiosis.