An integrated investigation of the population genetics, physiological stress, and movement patterns in the American pika

The objective of this dissertation was to examine how ecological and micro-evolutionary factors may influence the response of alpine mammals to reductions in habitat quality projected under climate change using the American pika (Ochotona princeps) as a model system. I begin with an overview of anthropogenic impacts on global ecology and ecosystem functioning with an emphasis on the vulnerability of mountain systems to environmental change. I then introduce the American pika and discuss contemporary population loss across the species’ range particularly at the southern end of its distribution in the Great Basin and northeastern California where the regional effects of climate change are expected to increase the co-occurrence of warm and dry conditions over the next few decades. In Chapter 1, I explore the effects of site, season, territory quality (microclimate temperature data) on patterns of physiological stress (via corticosterone stress hormones) in two high-elevation sites in the eastern Sierra Nevada. In Chapter 2, I examine the effects of habitat fragmentation on patterns of long-term pika occupancy as measured by 40 years of census data, and its association with habitat quality (patch perimeter and size), physiological stress, and climate variables calculated from local weather station data for a pika population located at the southern end of the species’ range. In Chapter 3, I track changes in the structure and distribution of genetic variation, effective population size, and movement patterns over the last 65 years within this same vulnerable pika population through the use of historical and contemporary genetic datasets. In Chapter 1, I found that patterns of stress differed significantly among pikas at two sites despite close geographic proximity and that the effects of site, year, territory, and individual diversity on patterns of pika stress were substantial compared to the relatively minor effects of microclimate predictors. In Chapter 2, I discovered significant associations among pika occupancy, temperature patterns, and stress hormone concentrations that suggest a role of individual physiologic response in demographic stability. Finally, in Chapter 3, I provide evidence of genetic erosion and its putative relationship with local climate for a genetically unique pika population at risk of extirpation

Human IGF-I propeptide A promotes articular chondrocyte biosynthesis and employs glycosylation-dependent heparin binding

Background Insulin-like growth factor I (IGF-I) is a key regulator of chondrogenesis, but its therapeutic application to articular cartilage damage is limited by rapid elimination from the repair site. The human IGF-I gene gives rise to three IGF-I propeptides (proIGF-IA, proIGF-IB and proIGF-IC) that are cleaved to create mature IGF-I. In this study, we elucidate the processing of IGF-I precursors by articular chondrocytes, and test the hypotheses that proIGF-I isoforms bind to heparin and regulate articular chondrocyte biosynthesis. Methods Human IGF-I propeptides and mutants were overexpressed in bovine articular chondrocytes. IGF-I products were characterized by ELISA, western blot and FPLC using a heparin column. The biosynthetic activity of IGF-I products on articular chondrocytes was assayed for DNA and glycosaminoglycan that the cells produced. Results Secreted IGF-I propeptides stimulated articular chondrocyte biosynthetic activity to the same degree as mature IGF-I. Of the three IGF-I propeptides, only one, proIGF-IA, strongly bound to heparin. Interestingly, heparin binding of proIGF-IA depended on N-glycosylation at Asn92 in the EA peptide. To our knowledge, this is the first demonstration that N-glycosylation determines the binding of a heparin-binding protein to heparin. Conclusion The biosynthetic and heparin binding abilities of proIGF-IA, coupled with its generation of IGF-I, suggest that proIGF-IA may have therapeutic value for articular cartilage repair. General significance These data identify human pro-insulin-like growth factor IA as a bifunctional protein. Its combined ability to bind heparin and augment chondrocyte biosynthesis makes it a promising therapeutic agent for cartilage damage due to trauma and osteoarthritis

Life on the edge—a changing genetic landscape within an iconic American pika metapopulation over the last half century

Declines and extirpations of American pika (Ochotona princeps) populations at historically occupied sites started being documented in the literature during the early 2000s. Commensurate with global climate change, many of these losses at peripheral and lower elevation sites have been associated with changes in ambient air temperature and precipitation regimes. Here, we report on a decline in available genetic resources for an iconic American pika metapopulation, located at the southwestern edge of the species distribution in the Bodie Hills of eastern California, USA. Composed of highly fragmented habitat created by hard rock mining, the ore dumps at this site were likely colonized by pikas around the end of the 19th century from nearby natural talus outcrops. Genetic data extracted from both contemporary samples and archived natural history collections allowed us to track population and patch-level genetic diversity for Bodie pikas across three distinct sampling points during the last half- century (1948–1949, 1988–1991, 2013–2015). Reductions in within-population allelic diversity and expected heterozygosity were observed across the full time period. More extensive sampling of extant patches during the 1988–1991 and 2013–2015 periods revealed an increase in population structure and a reduction in effective population size. Furthermore, census records from the last 51 years as well as archived museum samples collected in 1947 from a nearby pika population in the Wassuk range (Nevada, USA) provide further support of the increasing isolation and genetic coalescence occurring in this region. This study highlights the importance of museum samples and long-term monitoring in contextualizing our understanding of population viability