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1.  Evolutionary rescue and adaptation to abrupt environmental change depends upon the history of stress 
Whether evolution will be rapid enough to rescue declining populations will depend upon population size, the supply of genetic variation, the degree of maladaptation and the historical direction of selection. We examined whether the level of environmental stress experienced by a population prior to abrupt environmental change affects the probability of evolutionary rescue (ER). Hundreds of populations of two species of yeast, Saccharomyces cerevisiae and Saccharomyces paradoxus were exposed to a range of sublethal concentrations of salt for approximately a hundred generations before transfer to a concentration of salt lethal to the ancestor (150 g l–1 NaCl). The fitness of surviving populations of both species was a quadratic function of yield: fitness was greatest for large populations that had been selected on low salt concentrations (less than 20 g l−1 NaCl) and small populations that had adapted to high salt (more than 80 g l−1 NaCl). However, differences occurred between species in the probability of ER. The frequency of ER was positively correlated with salt concentration for S. cerevisiae, but negatively correlated with salt concentration in S. paradoxus. These results not only demonstrate that past environmental conditions can determine the probability of ER after abrupt environmental change, but also suggest that there may even be differences between closely related species that are worth further exploration.
PMCID: PMC3538446  PMID: 23209161
adaptation; rapid evolution; Saccharomyces cerevisiae; Saccharomyces paradoxus; population; environmental change
2.  Evolutionary rescue: an emerging focus at the intersection between ecology and evolution 
There is concern that the rate of environmental change is now exceeding the capacity of many populations to adapt. Mitigation of biodiversity loss requires science that integrates both ecological and evolutionary responses of populations and communities to rapid environmental change, and can identify the conditions that allow the recovery of declining populations. This special issue focuses on evolutionary rescue (ER), the idea that evolution might occur sufficiently fast to arrest population decline and allow population recovery before extinction ensues. ER emphasizes a shift to a perspective on evolutionary dynamics that focuses on short time-scales, genetic variants of large effects and absolute rather than relative fitness. The contributions in this issue reflect the state of field; the articles address the latest conceptual developments, and report novel theoretical and experimental results. The examples in this issue demonstrate that this burgeoning area of research can inform problems of direct practical concern, such as the conservation of biodiversity, adaptation to climate change and the emergence of infectious disease. The continued development of research on ER will be necessary if we are to understand the extent to which anthropogenic global change will reduce the Earth's biodiversity.
PMCID: PMC3538460  PMID: 23209175
extinction; rapid evolution; population; environmental change; genetics; experimental evolution
3.  In-Training Practice Patterns of Combined Emergency Medicine/Internal Medicine Residents, 2003–2007 
This study seeks to evaluate the practice patterns of current combined emergency medicine/internal medicine (EM/IM) residents during their training and compare them to the typical practice patterns of EM/IM graduates. We further seek to characterize how these current residents perceive the EM/IM physician's niche.
This is a multi-institution, cross-sectional, survey-based cohort study. Between June 2008 and July 2008, all 112 residents of the 11 EM/IM programs listed by the Accreditation Council for Graduate Medical Education were contacted and asked to complete a survey concerning plans for certification, fellowship, and practice setting.
The adjusted response rate was 71%. All respondents anticipated certifying in both specialties, with 47% intending to pursue fellowships. Most residents (97%) allotted time to both EM and IM, with a median time of 70% and 30%, respectively. Concerning academic medicine, 81% indicated intent to practice academic medicine, and 96% planned to allocate at least 10% of their future time to a university/academic setting. In evaluating satisfaction, 94% were (1) satisfied with their residency choice, (2) believed that a combined residency will advance their career, and (3) would repeat a combined residency if given the opportunity.
Current EM/IM residents were very content with their training and the overwhelming majority of residents plan to devote time to the practice of academic medicine. Relative to the practice patterns previously observed in EM/IM graduates, the current residents are more inclined toward pursuing fellowships and practicing both specialties.
PMCID: PMC3236164  PMID: 22224155
4.  Extinction Debt in Source-Sink Metacommunities 
PLoS ONE  2011;6(3):e17567.
In an increasingly modified world, understanding and predicting the consequences of landscape alteration on biodiversity is a challenge for ecologists. To this end, metacommunity theory has developed to better understand the complexity of local and regional interactions that occur across larger landscapes. While metacommunity ecology has now provided several alternative models of species coexistence at different spatial scales, predictions regarding the consequences of landscape alteration have been done exclusively for the competition-colonization trade off model (CC). In this paper we investigate the effects of landscape perturbation on source-sink metacommunities. We show that habitat destruction perturbs the equilibria among species competitive effects within the metacommunity, driving both direct extinctions and an indirect extinction debt. As in CC models, we found a time lag for extinction following habitat destruction that varied in length depending upon the relative importance of direct and indirect effects. However, in contrast to CC models, we found that the less competitive species are more affected by habitat destruction. The best competitors can sometimes even be positively affected by habitat destruction, which corresponds well with the results of field studies. Our results are complementary to those results found in CC models of metacommunity dynamics. From a conservation perspective, our results illustrate that landscape alteration jeopardizes species coexistence in patchy landscapes through complex indirect effects and delayed extinctions patterns.
PMCID: PMC3050922  PMID: 21408133
5.  Source–sink dynamics shape the evolution of antibiotic resistance and its pleiotropic fitness cost 
Understanding the conditions that favour the evolution and maintenance of antibiotic resistance is the central goal of epidemiology. A crucial feature explaining the adaptation to harsh, or ‘sink’, environments is the supply of beneficial mutations via migration from a ‘source’ population. Given that antibiotic resistance is frequently associated with antagonistic pleiotropic fitness costs, increased migration rate is predicted not only to increase the rate of resistance evolution but also to increase the probability of fixation of resistance mutations with minimal fitness costs. Here we report in vitro experiments using the nosocomial pathogenic bacterium Pseudomonas aeruginosa that support these predictions: increasing rate of migration into environments containing antibiotics increased the rate of resistance evolution and decreased the associated costs of resistance. Consistent with previous theoretical work, we found that resistance evolution arose more rapidly in the presence of a single antibiotic than two. Evolution of resistance was also more rapid when bacteria were subjected to sequential exposure with two antibiotics (cycling therapy) compared with simultaneous exposure (bi-therapy). Furthermore, pleiotropic fitness costs of resistance to two antibiotics were higher than for one antibiotic, and were also higher under bi-therapy than cycling therapy, although the cost of resistance depended on the order of the antibiotics through time. These results may be relevant to the clinical setting where immigration is known to be important between chemotherapeutically treated patients, and demonstrate the importance of ecological and evolutionary dynamics in the control of antibiotic resistance.
PMCID: PMC2288555  PMID: 17650474
evolutionary ecology; microbiology; infectious disease; antimicrobial resistance
6.  Economic Inequality Predicts Biodiversity Loss 
PLoS ONE  2007;2(5):e444.
Human activity is causing high rates of biodiversity loss. Yet, surprisingly little is known about the extent to which socioeconomic factors exacerbate or ameliorate our impacts on biological diversity. One such factor, economic inequality, has been shown to affect public health, and has been linked to environmental problems in general. We tested how strongly economic inequality is related to biodiversity loss in particular. We found that among countries, and among US states, the number of species that are threatened or declining increases substantially with the Gini ratio of income inequality. At both levels of analysis, the connection between income inequality and biodiversity loss persists after controlling for biophysical conditions, human population size, and per capita GDP or income. Future research should explore potential mechanisms behind this equality-biodiversity relationship. Our results suggest that economic reforms would go hand in hand with, if not serving as a prerequisite for, effective conservation.
PMCID: PMC1864998  PMID: 17505535

Results 1-6 (6)