Energy allocation trade-offs in a changing world

Abstract

Life-history trade-offs occur because of finite resources and often are the consequence of organisms attempting to cope with environmental stressors during important life-history events such as growth and reproduction. nthropogenic activity has increased global temperatures and the leaching of endocrine-disrupting chemicals (EDCs) into aquatic habitats, both of which can affect energetics of animals. Movement includes a significant proportion of organisms’ energy budgets and is likely to produce trade-offs with other fitness-related traits. Individuals of the same species can differ substantially in the efficiency with which they move (cost of transport; COT), and these differences may contribute to different strengths of trade-offs between individuals. Here, we show that energy allocation trade-offs between movement and reproduction in female zebrafish (Danio rerio) are partly driven by differences in COT. Increases in temperature, water flow, and exposure to the chemical pollutant bisphenol S (BPS) increase COT. BPS exposure also reduced the maximal movement capacities of adults, and fertilisation rate of eggs. High temperature and water flow caused less efficient individuals to move faster but remain more cohesive when traveling as a group. Additionally, increased temperature and water flow reduced reproductive output, and offspring survival was reduced at high temperatures. We found that thyroid hormones (THs) determined observed differences in COT and most likely facilitated the effects of increased temperatures and BPS. Together, the data show that combinations of environmental stressors may operate simultaneously on different components of movement and reproductive physiology and cause trade- offs that compromise the fitness of aquatic ectotherms. The influence of BPS on movement and reproduction suggests that predicted increases in bisphenol pollution are likely to change population dynamics in fish, which would be exacerbated at higher temperatures.