Research — The Stone Lab

I.

Speciation & Reproductive isolation

We are broadly interested in how species persist as recognizable units upon secondary contact in the wild. To answer this question we make use of long-standing hybrid zones as "natural laboratories": especially when they form between species with divergent floral characteristics and/or across environmental gradients.

We plan to continue studying hybrid zones, speciation, and the evolution of reproductive isolation in Penstemon to answer specific questions, like:

What is the genetic architecture of reproductive isolation?
Does floral differentiation constitute a reproductive barrier?
Do reproductive characters change in populations experiencing secondary contact (reinforcement)?
Are patterns of genomic divergence and reproductive isolation predictable?

Penstemon davidsonii at Crater Lake.

Hybrids between P. davidsonii and P. rupicola.

Penstemon rupicola at Crater Lake.

A P. davidsonii x P. rupicola hybrid at Crater Lake.

II.

Floral evolution & Pollination biology

Hummingbird pollination has evolved in Penstemon more than twenty independent times. Beyond the propensity to transition to hummingbird pollination, the remarkable diversity of floral shape, size, and color across the genus has led many to speculate that adaptation to different suites floral visitors has contributed to its diversification. We are interested in:

Identifying the genetic basis for floral variation
Connecting variation in floral traits to differences in pollinator assemblages
Understanding how interactions with floral visitors contribute to diversification

More broadly, we are interested in the evolution of floral traits across Penstemon and other plant groups and in using pollination biology as a lens through which to better understand speciation and the repeatability of adaptation.

Figure 3 from Stone et al., 2026. Quantification of floral differentiation between parent species. (A) Profiles of a typical P. newberryi and P. davidsonii flower, to scale. Lines and numbers on the P. davidsonii flower correspond to some of the key traits measured from the profile photographs. (B) PCA of floral trait multivariate space. Points are colored according to their proportion of P. newberryi ancestry, as inferred with Admixture. (C) Ridgeline plots of the top eight most informative traits as identified with the Random Forest (RF) classifier. Plots are ordered from top-to-bottom and left-to-right in order of importance in the RF classifier. Numbers on plots correspond to measurements in panel A.

III.

Phylogeography & Conservation genetics

Penstemon is broadly distributed across the North American continent and has considerable variation in the geographic extent of species' ranges; some species are common and widespread, while others are narrowly endemic and exceedingly rare. This combination of traits makes the genus an excellent system for both studies of population structure over geographic space and studies with an applied conservation focus. We use phylogeographic and population genomic approaches to:

Reconstructing historical species distributions and projecting distributions into the future
Identifying patterns of population structure and linking these to historical biogeographic processes
Characterizing genetic diversity and population structure in rare and narrowly distributed species
Using genome-scale data to inform the conservation of threatened and narrowly endemic taxa

Penstemon caryi, a rare plant endemic to the Bighorn and Pryor Mountains, in bloom.

Fruits of Penstemon dissectus, an endangered plant endemic to Georgia.

Part of Figure 2 from Stone & Wolfe, 2021. Structure plots of Penstemon davidsonii (top) and Penstemon cardwellii (bottom) in the Pacific Northwest.