University of Massachusetts Amherst, Massachusetts
The enormous diversity of plant-feeding insects is often attributed to adaptive radiation: new species arise as populations acquire the ability to attack new hosts. But for some insect groups – especially those that include extremely polyphagous species, able to feed on dozens of plant families – adaptive specialization through host-use trade-offs fails to explain why generalism persists. One alternative hypothesis is the phylogenetic meristem hypothesis. A generalist lineage, with a large population size and wide geographic range, persists through time. Similar to how plant meristem grows, it continually gives rise to new shoots, or small populations that become isolated on the peripheries of its range. These small populations can lose the ability to feed on a fraction of their ancestral host plants through genetic drift, effectively becoming specialized. The large population size of the generalist buffers it against extinction, acting as a kind of phylogenetic meristem from which new species arise. Here we attempt to test some of the predictions of the phylogenetic meristem hypothesis, mainly that generalist lineages have larger population sizes than their close specialist relatives, by conducting a phylogenomic analysis of the Diaspidiotus ancylus species complex (Hemiptera: Diaspididae). We use a newly developed UCE probeset for armored scales to delimit species boundaries and estimate a species tree using both coalescent and concatenation methods.