Collaborative Research: RUI: Measuring reciprocal natural selection in a contact zone in an obligate pollination mutualism

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This project addresses a fundamental question in evolutionary ecology; how does coevolution between plants and their insect pollinators create biodiversity. Joshua trees (Yucca brevifolia) are spiny, tree-like desert plants that are an iconic species of the American West. The trees are remarkable not only for their bizarre appearance, but also for their highly specialized and unusual means of pollination. They are pollinated exclusively by two species of Yucca moth in the genus Tegeticula; the moths, in turn, reproduce solely by laying their eggs in the flowers. This relationship between the Joshua tree and its pollinators is one of extreme interdependence; both the moth and the plant are entirely reliant upon one another for reproduction. The two species of Yucca moth that pollinate the Joshua tree differ in key features of their anatomy, particularly the size and shape of the female moth ovipositor, the organ used to inject their eggs into the Joshua tree flower. Recent work has shown that the particular trees on which these two moth species lay their eggs differ in features of their floral anatomy; the path through which the moth must insert her ovipositor is longer in trees that are pollinated by moths with a larger ovipositor, and shorter in flowers pollinated by moths with a shorter ovipositor. This anatomical match between the moths and the plants they pollinate likely reflects a history of coevolution, but this hypothesis has never been tested. This project will provide proof of concept that the hypothesis can be tested using reciprocal transplant experiments to quantify natural selection acting on the insects and the plants. In addition, the project will assess the feasibility of using molecular genetic techniques to reconstruct family relationships in the pollinators. The Joshua tree is a keystone species of the Mojave Desert ecosystem of the southwest USA, and is threatened by climate change with extinction over much of its range. Results from this project will inform local and federal conservation efforts to save Joshua trees through expansion of their range. This project will engage a number of undergraduates from a predominately undergraduate institution with research training in molecular genetics and evolutionary ecology.