Master’s student Alby Dang successfully defended his thesis research, an examination of cooperative dynamics in the Joshua tree/yucca moth mutualism, in a public presentation and meeting with his thesis committee this morning. Alby was the first graduate student to join the Yoder Lab, interviewing for a position in summer 2017 and enrolling the next fall, and he is now the first Master’s graduate from the lab.
In his thesis research, Alby examined the widely held understanding that the evolution of the yucca-yucca moth mutualism has been driven primarily by conflicting interests in the two partner species. Yucca moths lay eggs in yucca flowers before actively pollinating them. The flowers produce no nectar or other rewards, but yucca moth larvae eat the seeds inside fertilized flowers as they develop into fruits. Yuccas have no other pollinators, and the moth larvae eat a small portion of the total seed crop produced by pollination, so the interaction is beneficial — but it may also set up a conflict, in which moths would benefit from laying as many eggs as possible in each pollinated flower, and their host plants would benefit from receiving pollination without sacrificing any seeds to feed moth larvae. Yuccas have been shown to kill off flowers that receive too many pollinator eggs, and it is generally understood that this “sanction” keeps the moths from getting too greedy.
Alby instead considered a way in which yuccas and moths might have an interest in common: a moth that provides better pollination services might produce more seeds in a single fruit, which might support more of her larvae. To test this idea, Alby collected mature fruits from populations of Joshua tree, Yucca brevifolia and Y. jaegeriana, caught pollinator larvae as they exited, and counted the seeds in each fruit. He used genetic marker data to identify larvae whose mothers had visited multiple trees, potentially carrying higher quality “outcross” pollen rather than simply transferring pollen between different flowers on the same tree — and tested the hypothesis that these “mobile moms” helped to produce bigger seed crops that supported more larvae. Look for a formal publication reporting his results in the near future!