Periodic Reporting for period 1 - CortFit (Using reaction norms to identify glucocorticoid phenotypes and their relationship to fitness in individuals of a wild vertebrate.)
Reporting period: 2015-04-01 to 2017-03-31
Objective 1: Determine glucocorticoid flexibility of individuals under standardized conditions
Objective 2: Determine relationships between glucocorticoid flexibility, reproductive performance and fitness in free-living great tits
Study 2: Does individual GC flexibility predict reproductive success in free-roaming great tits? This project addressed objective 2, and aimed to assess individual GC responsiveness and HPA axis functioning in great tits in winter. We expected plasticity in baseline GC, e.g. a stronger response to temperature manipulation, to be positively related to reproductive success. Furthermore, we expected a more responsive HPA axis, e.g. strong stress response and robust negative feedback, to be associated with higher reproductive success. Prior to the breeding season, 24 animals were exposed to a temperature change and an HPA-function test. Great tits roost overnight in nest boxes in winter, providing an opportunity for relatively easy capture. Additionally, temperature inside a nest box can be manipulated relatively easily. Birds were caught at night, and assigned to either a control (10 animals), or a temperature manipulation group (14 animals). Upon capture, each bird was sampled to obtain baseline GCs. Temperature manipulation consisted of placing a heating pad in the bottom of the nest box, which was run off of a car battery. Birds were then returned to the box and left alone for three hours, after which each bird was recaptured and sampled again. Control birds were treated identical, except the heating pad was never turned on. After the second sample, birds were exposed to standardized stressor, containment in a cloth bag. After 30 minutes, a stress-induced sample was taken, immediately followed by a dexamethasone injection to induce negative feedback. A final sample was taken 90 minutes post injection. During the breeding season, 18 birds were found again actively building nests, and could thus be tracked to obtain measures of reproductive performance and success, including laying date, number of eggs, hatching success, feeding rate, and fledging success. This allowed us to investigate how winter GC flexibility is associated with reproductive success. This project is currently undergoing final data analysis and manuscript writing. Preliminary data was presented at the 2016 SICB conference in Portland, Oregon, USA.
Public outreach was an important aspect of this project. During the spring of 2015, a local high school biology class was guided around my experimental forest. This offered a great opportunity to interact with young students about research and to provide hands on experience on what it is like to be a field biologist. Additionally, some of the ideas and work described in this project were presented during seminars at Carleton University in Canada (February 2015), and Linkoping University in Sweden (October of 2015).