Projects

Photograph of non-pollinating fig waspsAlthough figs (genus Ficus) are a diverse and a common component of tropical and subtropical ecosystems, individual species often occur at extraordinarily low population densities, creating a challenge for successful fig wasp dispersal between hosts and pollination.

Graph showing autocorrelation analysis of fine-scale genetic structureIn early papers (Loiselle et al. 1995; Kalisz et al. 2001), we introduced a measure of inter-individual genetic relatedness that has become the default in the most-widely-used software for the spatial autocorrelation analyses of fine-scale genetic structure (FSGS) within populations.

Satellite image of the Sonoran DesertWe have combined traditional population genetic approaches with coalescent and graphical modeling techniques to gain insight into how deep-time geological and shallow-time climatic changes have influenced species distributions and the spatial organization of genetic variation. Mexico’s Baja California Peninsula is for us a model landscape in which to study large-scale patterns of spatial genetic structure.

Photograph of Laelia rubescens (an orchid)We have used terrestrial and epiphytic orchids as model systems to investigate the processes influencing the evolution of fine-scale, spatial genetic structure within populations and how this structure may be altered by various factors, including human-mediated disturbance.

Graph of Sonoran Desert columnar cactus Pachycereus schottiiIn collaboration with Rodney Dyer (Virginia Commonwealth U.) we have developed population graphs, a novel network-based procedure for quantifying patterns of inter-population gene flow (Dyer & Nason 2004; Dyer et al. 2010). While most population geneticists recognize that gene flow is probably best represented in the form of interacting networks of populations, in boiling down this complexity to one or a few summary statistics (e.g., Fst) most of our analytical procedures fail to capture the spatially-explicit connectivity among populations that we are often most interested in.

Photograph of purple loosestrifeCombining ecological and genetic approaches, we have examined the process of biological invasion in three different plant systems. In multiflora rose (Rosa multiflora) we used genetic markers to quantify the relative contributions of sexual reproduction via seed versus vegetative reproduction via clonal spread to local patterns of invasion (Jesse et al. 2010). In purple loosestrife (Lythrum salicaria) we compared phenotypic plasticity of native European versus invasive North American populations in response to variation in water and nutrient levels (Chun et al. 2007).

Images of Eurosta Solidaginis (goldenrod gall fly) and Solidago altissima (goldenrod)The exceptional diversity of phytophagous insects may be due in part to their propensity for speciation via host-race formation. In our research, we have focused on two closely-related goldenrods (Solidago altissimaand S. gigantea) and their insect herbivores as a model system to study host shifts (and eventual speciation) by multiple evolutionarily independent insect lineages on the same host plant pair.