Some vertically inherited symbionts spread within host populations by manipulating the reproduction of their host to enhance their own transmission. Our current knowledge of these reproductive parasites is very weak, save a single well-characterized bacterium Wolbachia. In this proposal, we seek to fill this void for one bacterium, Arsenophonus.
In the wasp Nasonia vitripennis (a parasitoid of various fly species), Arsenophonus nasoniae distorts the sex ratio of wasp progeny, increasing the proportion of daughters up to 90% by killing sons. Whilst Arsenophonus is a maternally inherited bacterium, it can also be horizontally transmitted at high frequency among wasps developing within a fly host. Arsenophonus is inoculated into the fly host and then ingested by the developing wasp offspring.
This peroral transmission of the bacterium to the next generation of wasp is unique, in contrast to the cytoplasmic mode of transmission typical of other micro-organisms distorting sex ratio, and makes this an important comparator. Our project will therefore focus on Arsenophonus-arthropod symbioses, and develop a global view of the range and nature of these interactions.
We will score the incidence of Arsenophonus across a large panel of arthropod species, test for sex bias in prevalence that would indicate a sex ratio distorting phenotype, and use DNA sequence to identify the major Arsenophonus lineages. We will also test the hypothesis that genome plasticity is an important contributor to adaptability of inherited bacteria, transfer of DNA via phage increasing the ability to colonize new hosts and develop a variety of infective phenotypes.
In addition, we will investigate the effect of natural selection acting on genes likely to be involved in host-parasite interactions. In the course of this project, we will use an integrative approach to identify the common and specific mechanisms in which natural selection acts in this symbiosis.
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