Global change implications of adaptation to climatic variability [electronic resource]
Keywords: Biological Sciences

In this thesis I have examined ecology and evolution in a globally changing environment to address how climate change is likely to differentially affect tropical and temperate populations. I have approached the problem theoretically by applying an evolutionary model to global climate data and I have tested specific hypotheses arising from the model and associated theories using checkerspot butterfly populations throughout North and Central America. The study of climatic variability and adaptation has a long history going back to Alexander von Humboldt. I briefly review this history in chapter 1. In chapter 2 I applied an evolutionary model based on the "jack-of-all-trades is a master of none'' principle to global temperature and precipitation data to derive theoretical tolerance curves throughout the globe. Primarily, this model predicts lower thermal tolerance breadths for tropical organisms because over a given year they experience far less thermal variation than temperate populations. The pattern is more complicated when considering precipitation effects. Using IPCC projections of climate change for 2100 I then examined what the relative fitness effects would be across the globe and found that other than the Mediterranean region, areas of the tropics (e.g. Southeast Asia, Central America and Equatorial Africa) would be among the most heavily impacted regions in the world (Bonebrake and Mastrandrea 2010). In chapters 3 and 4 I built on work within temperate checkerspot butterfly systems to examine climatic heterogeneity impacts on ecological and evolutionary process. The heavily studied Euphydryas editha population of Jasper Ridge at Stanford University went extinct in 1998 partly due to increases in precipitation variability in recent decades and its effects on host plant dynamics. To evaluate the potential of habitat creation to buffer the impacts of climatic changes, I participated in a multidisciplinary effort to experimentally alter soil conditions to mimic the unique properties of serpentine grasslands. Our efforts showed some success in lowering the invasibility (invasive species being another threat to E. editha) of experimental sites but also showed that the results were highly contingent on the amount of rainfall in each year (Bonebrake et al. in review). I also studied the evolutionary relationship between oviposition behavior and offspring performance in closely related Euphydryas gillettii. This study showed large effects of inter-annual variation in temperature in a montane E. gillettii Colorado population and that, for example, warm years and oviposition preference can significantly accelerate larval development time (Bonebrake et al. 2010). Finally, in chapter 5 I examined the biophysical, morphological and physiological properties of adaptation to temperate and tropical climates using populations of the widely distributed butterfly Chlosyne lacinia. First, the biophysical model demonstrated that variation in air temperature poorly predicted variation in butterfly body temperature (Tb) and that diurnal variation in Tb was lower for butterflies in El Salvador than Tb variation in Arizona. Second, as for morphological characteristics relevant to butterfly thermoregulation, thorax size was consistently smaller in tropical populations while variation in other characters (fur length, body length and wing absorptivity) was not consistent across latitude. Third, physiological studies showed that C. lacinia in Arizona began flying at colder temperatures (Tb=24 degrees C) than C. lacinia in El Salvador (Tb=27 degrees C). As consequence of these factors combined, the model predicts increased effects of climate change for tropical C. lacinia in the form of greater increases in flight activity time and more prolonged exposure to lethal temperatures (Tb> 45 degrees C) relative to temperate butterflies (Bonebrake et al. in prep).