| Description |
Carotenoids are vibrant red, yellow, and orange pigments that are responsible for many colorful displays seen throughout all domains of life. In animals, carotenoids are essential for vision and play diverse roles ranging from protection against oxidative stress to sexual selection in birds. While most animals cannot produce their own carotenoids, several arthropod species laterally acquired carotenoid biosynthetic genes from fungi. One of those arthropod species is the two-spotted spider mite Tetranychus urticae, a major herbivorous pest of crop plants that feeds on over a thousand different plant species and has shown resistance to more active ingredients in pesticides than all known arthropods except one. T. urticae is also globally distributed and is particularly successful in temperate zones where it goes into diapause to survive cold winters. The two-spotted spider mite is an excellent organism to further the understanding of carotenoid metabolism in animals. Besides general qualities that make it a good model (such as ease of laboratory use and a short life cycle), deficiencies in most steps of the biosynthetic pathway leading from plant precursors to red-orange, oxidized keto-carotenoids produce easily identifiable color mutants. In addition to carotenoid metabolism, the spider mite species' generalist lifestyle and pest status have facilitated genetic mapping of resistance traits. Despite this, little work has been done on understanding carotenoid metabolism and the genetic response to long-term pesticide selection. Factors shaping the mite's genetics in different parts of the world have also not been addressed. iv I have started to answer these and related research questions in my Ph.D. Among our findings, we determined that endogenously produced carotenoids are required for all mite pigmentation as well as overwintering in the diapause state. We also found a single locus that underlies loss of diapause and that appears to be under selection in many parts of the world. We showed that pesticides with the same mode of action can elicit very different selection responses. And in the course of this work, we developed a method that uses data from a genetic cross to condense the 640-scaffold T. urticae genome assembly into three chromosomes. |
