Effects of bushfire exposure on prenatal and early life development in humans: a life history perspective

Abstract

Taking a life history theory perspective, this dissertation considers the effects of bushfire related stress on a suite of human reproductive outcomes. Life history theory suggests that human reproduction is responsive to environmental pressure and that this responsiveness can be detected via changes to reproductive strategy, such as degree of maternal investment. Using multivariate analysis, this dissertation examines the effects of maternal fire exposure in two populations on gestational age, birth weight, secondary sex ratio, plurality rates, fertility rates, and behavioural indicators. It hypothesises that decreases will be observed in those measures that indicate degree of maternal investment, such as birth weight, gestational age, and plurality, as well as predicting decreases in sex ratio associated with differential loss in early pregnancy. It suggests that behavioural indicators will worsen as sequela of in utero stress. Using a mixed-methods approach, the dissertation also documents the experience of mothers who have lived through bushfires while pregnant, hypothesising that they will have experienced considerable subjective and objective stress. The dissertation finds that reproductive responses vary considerably between the populations studied and potentially in relation to the intensity of fire exposure. Contrary to the hypothesis, it finds that birth weights increased in the population exposed to a smaller fire (the 2003 Canberra fire), while remaining unchanged in the population exposed to a larger fire (Black Saturday fire, Victoria, 2009). However, the reverse was true of secondary sex ratio, which decreased in the population exposed to the Black Saturday fire, while remaining unchanged in the Canberra population. Gestational age was unaffected in both cases. Behavioural indicators and fertility rates were largely unaffected by fire exposure, although they both appeared sensitive to other environmental factors. Mothers in both fires reported feeling stressed, although mothers exposed to the Black Saturday fire reported higher perceived and objective stress. Mothers in both fires reported that public support and information were, at times, insufficient. Taken together, the findings indicate the functioning of finely tuned evolutionary mechanisms that adjust to environmental conditions only where a threshold of severity is met, thereby protecting reproductive strategy from the influence of more transient stressors.