Ecological speciation in Neochlamisus bebbianae leaf beetles: the role of postmating isolation and the genetic basis of host use traits

Abstract

Ecological speciation is defined as the process by which reproductive isolation arises between populations as a result of ecologically based divergent selection between environments. Selection is ecological when individual survival and reproduction are dependent on interactions with its environment. Selection is divergent when it works in contrasting directions on specific traits between populations or individuals. I used populations of the leaf beetle <i>Neochlamisus bebbianae</i> associated with Bebb’s willow (<i>Salix bebbianae</i>) and red maple (<i>Acer rubrum</i>) that are currently undergoing ecologically-driven divergence and speciation to address the role that ecology plays in generating reproductive isolation and speciation. These two ”host forms” offer an excellent study system to answers questions regarding ecological speciation due to their geographic overlap and their divergence in habitat preferences, host-associated fitness, and host-associated assortative mating. This thesis involves two complimentary projects aimed at (a.) understanding the genetic architecture of traits associated with ecological adaptation to different hosts that contribute to reproductive isolation and (b.) examining the unknown nature of postmating isolation that has evolved between these ecologically differentiated populations. To address these projects I have used a single experimental design that employs controlled genetic crosses within and among populations of <i>N. bebbianae</i> adapted to each host plant over multiple geographic localities, multiple years and within one year, over multiple generations. In doing so, I was able to uncover and contrast the genetic basis for host use on each plant and the role of different postmating barriers that arise during the speciation process.