Research Interests

 

My research focuses on the processes driving evolutionary diversity across spatial and temporal scales.  At the local scale, novel pathogens exert strong selection on naive hosts.  The pathogen causing avian malaria (Plasmodium relictum) was introduced to Hawaii and subsequently caused the rapid decline of native honeycreeper species.  In recent years, some individuals of Hawaii amakihi (Hemignathus virens) have demonstrated the ability to survive malaria infection.  We are investigating the genomic underpinnings of this rapid adaptation.

 

Susceptibility to pathogens influences population structure in black-tailed prairie dogs (Cynomys ludovicianus). Prairie dogs suffer 95-100% mortality during plague outbreaks. In Boulder County, re-colonization replenished genetic diversity in some, but not all, colonies.  Interestingly, colonists have higher heterozygosity than animals present before extirpation.


At the macroevolutionary scale, habitat constraints influencing predator abundance, burrowing ability and plant availability may act as selective agents.  Gunnison’s prairie dogs (C. gunnisoni) are split into two geographically disparate subspecies that occupy distinct habitats and are genetically differentiated.  Using complementary approaches that include population genomics, coalescence theory and ecological niche modeling, I examine the contributions of different selection pressures to genetic diversity across scales.


Ongoing Projects:


Recolonization of prairie dogs following plague epizootics

Black-tailed prairie dogs (Cynomys ludovicianus) inhabit a fragmented landscape in the Front Range of Colorado, with populations interspersed with urban development.  Periodically, populations are extirpated by a highly virulent bacterial pathogen, Yersinia pestis, which causes sylvatic plague.  Plague causes 95-100% mortality of prairie dog colonies, followed by recolonization from nearby populations.  After extirpation/ recolonization, genetic diversity of the metapopulation as a whole does not change.  However, individual colonies vary in their degree of genetic diversity depending, in part, on the landscape matrix (see below).  Founders of new colonies have higher neutral heterozygosity than pre-plague residents; additionally, the few plague survivors have unusually high heterozygosity.  (See More)


Genomic basis of resistance to avian malaria in Hawaii amakihi:

Hawaiian honeycreepers are a classic example of adaptive radiations, but recently many species have declined to the brink of extinction due to the introduction of avian malaria.  Although the disease is highly virulent, one species-- the Hawaii amakihi-- has evolved some resistance to malaria.  We are working to understand whether resistance is conferred by few or many loci, what type of selection favored the evolution of resistance, and whether patterns are similar among islands and across taxa.  (See More)


Genetic and ecological differentiation in Gunnison’s prairie dogs

The U.S. Fish and Wildlife Service recently designated Gunnison’s prairie dogs (Cynomys gunnisoni) as warranted but precluded from listing in the montane portion of its range, leading to questions of population connectivity and plague susceptibility in  comparison to the prairie portion of its range.  Although formal subspecies are not recognized by consensus, the montane habitat is occupied by C.g. gunnisoni, whereas C.g. zuniensis is found in the prairie habitat.  The two putative subspecies have been proposed to differ in morphology, vocalizations, and genetics, and I will explore whether different ecological conditions are associated with each subspecies.  (See More)


Connectivity in altered landscapes

Connectivity of populations influences the degree to which species maintain genetic diversity and persist despite local extinctions.  Anthropogenic landscape change has fragmented populations of species worldwide, and the front range of Colorado is an example of a landscape influenced by multiple types of habitat change, including urbanization and land conversion to agriculture.   We investigate how these landscape changes influence black-tailed prairie dog dispersal through the landscape matrix.  (See more)