Variation in Growth Drives the Duration of Parental Care: A Test of Ydenberg's Model

Altered Oxidative Status as a Cost of Reproduction in a Seabird with High Reproductive Costs

AbstractLife history theory posits that reproduction is constrained by a cost of reproduction such that any increase in breeding effort should reduce subsequent survival. Oxidative stress refers to an imbalance between the prooxidant reactive oxygen species (ROS) and antioxidant defense. If not thwarted, ROS can cause damage to DNA, lipids, and proteins, potentially increasing the rate of senescence and decreasing cellular function. Reproduction is often associated with higher metabolic rates, which could increase production of ROS and lead to oxidative damage if the animal does not increase antioxidant protection. Thus, oxidative stress could be one mechanism creating a cost of reproduction. In this study we explored how reproduction may affect oxidative status differently between male and female thick-billed murres during early and late breeding seasons over three consecutive years. We manipulated breeding efforts by removing an egg from the nest of some individuals, which forced females to relay, and by handicapping other individuals by clipping wings. We measured total antioxidant capacity (TAC), uric acid (UA) concentration, and malondialdehyde (MDA; an index of lipid oxidative damage) concentration in blood plasma as well as activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) in red blood cells. Oxidative status was highly variable across years, and year was consistently the most important factor determining oxidative status; inconsistent results in previous field studies may be because reproductive oxidative stress occurs only in some years. Females had lower SOD and GPx and higher MDA and TAC than males immediately after egg laying, suggesting that the cost of egg laying required investment in cheaper nonenzymatic antioxidant defenses that had lower capacity for defending against lipid peroxidation. Delayed birds had lower UA and lower SOD, GPx, and CAT activity compared with control birds. In conclusion, when reproductive costs increase via higher energy costs or longer breeding seasons, the oxidative status of both male and female murres deteriorated as a result of reduced antioxidant defenses.

A critical evaluation of the index of patch quality

The inverse optimality approach can allow us to learn about an animal's environment by assuming their behaviour is optimal. This approach has been applied to animals diving underwater for food to produce the index of patch quality (IPQ), which aims to provide a proxy for prey abundance or quality in a foraging patch based on the animal's diving behaviour. The IPQ has been used in several empirical studies but has never been evaluated theoretically. Here, we discuss the strengths and weaknesses of the IPQ approach from a theoretical angle and review the empirical evidence supporting its use. We highlight several potential issues, in particular with the gain function-the function describing the energetic gain of an animal during a dive-used to calculate the IPQ. We investigate an alternative gain function which is appropriate in some cases, provide a new model based on this function, and discuss differences between the IPQ model and ours. We also find that there is little supporting empirical evidence justifying the general use of the IPQ and suggest future empirical validation methods which could help strengthen the case for the IPQ. Our findings have implications for the field of diving ecology and habitat assessment.

Preparing biomedical students for the unknown: Some unusual challenges for students to help them understand the fundamentals of empirical research

Make teaching challenging again: a pedagogic approach to educate students on how to do science rather than learn about it.