Eric Snajdr

Physiological Effects on Demography: A Long‐Term Experimental Study of Testosterone’s Effects on Fitness

Understanding physiological and behavioral mechanisms underlying the diversity of observed life‐history strategies is challenging because of difficulties in obtaining long‐term measures of fitness and in relating fitness to these mechanisms. We evaluated effects of experimentally elevated testosterone on male fitness in a population of dark‐eyed juncos studied over nine breeding seasons using a demographic modeling approach. Elevated levels of testosterone decreased survival rates but increased success of producing extra‐pair offspring. Higher overall fitness for testosterone‐treated males was unexpected and led us to consider indirect effects of testosterone on offspring and females. Nest success was similar for testosterone‐treated and control males, but testosterone‐treated males produced smaller offspring, and smaller offspring had lower postfledging survival. Older, more experienced females preferred to mate with older males and realized higher reproductive success when they did so. Treatment of young males increased their ability to attract older females yet resulted in poor reproductive performance. The higher fitness of testosterone‐treated males in the absence of a comparable natural phenotype suggests that the natural phenotype may be constrained. If this phenotype were to arise, the negative social effects on offspring and mates suggest that these effects might prevent high‐testosterone phenotypes from spreading in the population.

Natural Selection on Testosterone Production in a Wild Songbird Population

Because of their role in mediating life‐history trade‐offs, hormones are expected to be strongly associated with components of fitness; however, few studies have examined how natural selection acts on hormonal variation in the wild. In a songbird, the dark‐eyed junco (Junco hyemalis), field experiments have shown that exogenous testosterone alters individuals’ resolution of the survival‐reproduction trade‐off, enhancing reproduction at the expense of survival. Here we used standardized injections of gonadotropin‐releasing hormone (GnRH) to assay variation in the testosterone production of males. Using measurements of annual survival and reproduction, we found evidence of strong natural selection acting on GnRH‐induced increases in testosterone. Opposite to what would be predicted from the survival‐reproduction trade‐off, patterns of selection via survival and reproduction were remarkably similar. Males with GnRH‐induced testosterone production levels that were slightly above the population mean were more likely to survive and also produced more offspring, leading to strong stabilizing selection. Partitioning reproduction into separate components revealed positive directional selection via within‐pair siring success and stabilizing selection via extrapair mating success. Our data represent the most complete demonstration of natural selection on hormones via multiple fitness components, and they complement previous experiments to illuminate testosterone’s role in the evolution of life‐history trade‐offs.

Predictors of burnout in public library employees

Work stress and professional burnout are recognized as concerns for public library employees, yet little research has been conducted. The purpose of the current study was to better understand burnout and the contributing factors in a state-wide sample of public library employees in Indiana. Using a web-based survey, 171 employees of public libraries reported their level of burnout (emotional exhaustion, cynicism, and professional efficacy; Maslach Burnout Inventory-General Survey) and potential predictors, including levels of autonomy, co-worker support, work pressure, technology attitudes, and recovery experiences. A subset of 70 completed the burnout measures twice, allowing for predictions of change over time. Most predictors were correlated with burnout cross-sectionally, except for technology attitudes. Emotional exhaustion was positively associated with work pressure, and negatively associated with autonomy, role clarity, coworker support, and recovery experiences of relaxation, mastery, and control. Similar patterns were found for cynicism and reduced efficacy. However, over a period of approximately six months, only role clarity predicted decreased burnout (emotional exhaustion) above prior levels of burnout.