Heritable symbionts in a world of varying temperature

Heritable microbes represent an important component of the biology, ecology and evolution of many plants, animals and fungi, acting as both parasites and partners. In this review, we examine how heritable symbiont–host interactions may alter host thermal tolerance, and how the dynamics of these interactions may more generally be altered by thermal environment. Obligate symbionts, those required by their host, are considered to represent a thermally sensitive weak point for their host, associated with accumulation of deleterious mutations. As such, these symbionts may represent an important determinant of host thermal envelope and spatial distribution. We then examine the varied relationship between thermal environment and the frequency of facultative symbionts that provide ecologically contingent benefits or act as parasites. We note that some facultative symbionts directly alter host thermotolerance. We outline how thermal environment will alter the benefits/costs of infection more widely, and additionally modulate vertical transmission efficiency. Multiple patterns are observed, with symbionts being cold sensitive in some species and heat sensitive in others, with varying and non-coincident thresholds at which phenotype and transmission are ablated. Nevertheless, it is clear that studies aiming to predict ecological and evolutionary dynamics of symbiont–host interactions need to examine the interaction across a range of thermal environments. Finally, we discuss the importance of thermal sensitivity in predicting the success/failure of symbionts to spread into novel species following natural/engineered introduction

Who pays for home care? A study of nationally representative data on disabled older Americans

Background: We examine who pays for services that support disabled older Americans at home. We consider both personal sources (e.g., out-of-pocket payment, family members) and publicly funded programs (e.g., Medicaid) as sources of payment for services. We examine how the funding mix for home care services is related to older people’s economic resources, needs for care, and other socio-demographic characteristics. Methods: Our sample consists of 11,725 person-years from the 1989, 1994, 1999, and 2004 waves of the National Long-Term Care Survey. Two-part regression analyses were performed to model hours of care received from each payer. “Random effects” and “fixed effects” estimation yielded similar results. Results: About six in ten caregivers (63 %) providing home care services are paid by personal sources alone. By contrast, 28 % receive payment from publicly funded programs alone, and 9 % from a combination of personal and public program sources. Older people with family incomes over 75,000 dollars per year receive 8.5 more hours of home care overall than those in the lowest income category (less than 15,000 dollars). While the funding mix for home care services is strongly related to older people’s economic resources, in all income groups at least 65 % of services are provided by caregivers paid in whole or in part from personal sources. In fact, almost all (97 %) home care received by those with family incomes over 75,000 dollars per year are financed by personal sources alone. Conclusions: We outline the implications that heavy reliance on personally financed services and economic disparities in overall services use has for disabled older Americans and their families