EF 03: Origin and Evolution of the Bracovirus-Braconid Wasp Symbiosis

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Many parasitoid wasps in the family Braconidae lay their eggs inside the bodies of caterpillars, which ultimately die after serving as food and home for the developing wasp offspring. There is great complexity to the physiological and endocrine interactions between the wasp and its caterpillar host. No aspect of this is more remarkable than the evolutionary incorporation of viruses by the wasps into their toolkits of host manipulation. The bracoviruses are fully integrated into the wasp chromosomal DNA, yet functional genes are still packaged as "proviruses" and "exported" into the caterpillars along with the wasp eggs. These genes are involved in influencing the caterpillars' immune and endocrine systems in ways that enhance survival of the wasp larvae inside. This project explores the incredible evolution of this interaction between wasps and viruses. It is one of the few cases known of a mutually beneficial relationship between a virus and a eukaryotic organism, and in addition is remarkable in that the genomes of wasp are so intertwined that the viruses are no longer an independent entity, but instead act as an endosymbiont, more or less like mitochondria and chloroplasts. The design of this project involves comparing phylogenies ("evolutionary trees") of both wasps and viruses, inferred from comparisons of DNA sequences, to explore how long the wasps and viruses have been coevolving. So far the PI has demonstrated that the wasp and virus phylogenies are essentially identical within a large genus of the wasps, and have also shown that the wasps that carry the viruses form a single evolutionary lineage. Remaining to be determined is whether the wasp and virus phylogenies are identical through the whole wasp group that carries the viruses, and where these viruses may have come from (i. e., which other groups of viruses may be related). With the solution to these last two questions, a more complete picture of how this remarkable association developed will be revealed. The results will be of interest not only to evolutionary biologists, but may well have practical implications in terms of designing sophisticated control strategies against caterpillar pests.