Meeting Abstract
Increased investment in current reproduction can have a negative influence on survival to, or future fecundity of, a subsequent breeding attempt. Life-history theory predicts that current and ‘residual’ reproductive value should be balanced at each time point to maximise fitness. Thus, experimental manipulations of current reproductive investment (e.g. brood size manipulation) are required to demonstrate ‘costs of reproduction’. Although cost of reproduction (and other trade-offs) must have a physiological basis, few experimental studies include comprehensive physiological analysis, and the physiological basis of reproductive costs remains poorly understood. We handicapped female European starlings (Sturnus vulgaris) using wing-clipping, and compared foraging behaviour, breeding productivity and physiology with control females. We obtained repeated measurements of biomechanical traits (mass, wing length, wing area) and 13 physiological traits during incubation and chick–rearing of 1st and 2nd broods; this included measures of oxidative stress, muscle damage, metabolic regulators, immune function, aerobic capacity, and intermediary metabolism. We used behavioural observations and radio-telemetry to obtain information on foraging behaviour of the same individuals (nest-visit rate rate, flight distances). Wing-clipped females continued to “work hard” with similar provisioning rates compared with control females, but had lower current breeding productivity and lower survival, i.e. they appeared to show a clear cost of (increased) reproductive effort. We will use our physiological data to test hypotheses about the mechanistic basis of individual variation in a) workload ability (e.g. provisioning rate, flight distance, breeding productivity), and b) costs of workload (breeding failure, return rate, future fecundity).
