The evolution of food hoarding: from environmental pressures to brain mechanisms #HOARDEVOL
The emergence of novel behaviours not only provides insight into the selective pressures
which cause behaviours to evolve, but also provides an opportunity to understand how existing physiological and neurological mechanisms can be modified to control them. Some species have evolved to store rather than consume food while availability is high, for consumption when food is scarce. This behaviour is called food hoarding and is present in multiple taxa. Key physiological and neurological mechanisms have been shown to underpin an animal’s motivation to hoard food, including the stress hormone corticosterone (cort) and consumption regulating neuropeptides, neuropeptide Y (NPY) and agouti-related protein (AgRP). However, whether variation in cort, NPY and AgRP, or an interaction between them regulates hoarding behaviour is yet to be examined. This project will experimentally address these knowledge gaps using two closely related bird species that live in social groups during winter when hoarding motivation is high: the food hoarding coal tit, Periparus ater, and the non-hoarding great tit, Parus major. This project will identify the hypothalamic regions activated during high hoarding motivation between a hoarding and non-hoarding species, and examine whether cort, NPY and AgRP receptor density, and NPY/AgRP expression within these regions is linked to hoarding behaviour.
Is inter-individual variation in corticosterone linked to environmental conditions?
The environmental conditions experienced during breeding influence the energetic demands of both parents and their developing offspring. Elevated baseline corticosterone (CORT) is associated with increased foraging and food intake, and can enable animals to meet the demands of reproduction under harsh conditions. Using the blue tit, Cyanistes caeruleus as a model species, I investigated whether the foraging conditions experienced during breeding namely, asynchrony with the peak in caterpillar abundance, weather variables and territory scale oak-density influenced baseline CORT in adults and nestlings.
Do glucocorticoids predict fitness?
Harsh environmental conditions are often associated with reduced reproductive success and elevated glucocorticoids in a variety of vertebrates. This has lead to the assumption that elevated glucocorticoids, such as CORT should be associated with reduced reproductive success, and thus fitness. I tested this hypothesis using free-living blue tits, over multiple years, by measuring the foraging conditions experienced during brood rearing, and investigating whether they were associated with baseline CORT in adults and nestlings, and if they affected reproductive success. Then I related parental CORT concentrations to fitness proxies, i.e. reproductive success.
Stress hormones and sexually-selected traits
In blue tits both sexes exhibit bright blue UV-reflectant crown feathers, which have previously been shown to be attractive to the opposite sex. In males there is evidence that UV reflectance of the crown feathers is an honest signal of quality. To examine whether this is the case for female blue tits’ I measured maternal feather colouration (UV signal) during brood rearing and related it to indices of reproductive success. Also as there is growing evidence that circulating CORT concentrations influence both the color (Mougeot et al., 2010; Roulin et al., 2008) and growth (Romero et al., 2005) of feathers, CORT may mechanistically link an individual’s state with the expression of plumage coloration. We found that mothers with more UV reflectant crown feathers did not lay more eggs, but did fledge more offspring than duller females. Also they experienced relatively lower levels of stress hormones during arduous periods of chick rearing. This work provided novel evidence that maternal baseline CORT is associated with UV plumage signal in free-living birds, and may be an important mechanistic link between an individual’s ornamentation, state and reproductive performance.
Song production and the social environment
Song production is costly; therefore, males should modulate its production according to its probable benefits. For example, males may increase song production when receptive females are near by. To explore this I investigated the influence of female availability and attentiveness upon song investment in male house finches, Carpodacus mexicanus. House finches are highly social and non-territorial. Yet the influence of other males within a social group upon male song production is unknown.
Therefore, I manipulated male attractiveness by changing plumage colouration through carotenoid supplementation, and investigated whether male attractiveness or the relative attractiveness of the male social group influenced investment in song.
What factors determine nest placement in the Marsh Tit, Poecile palustris?
In the marsh tit, nest placement is determined by the female. Therefore placement of the nest could be manipulated by a female preference to facilitate extra-pair copulations (Mennil et al. 2004). Using a four year study of a population of Marsh Tits in Monks Wood, Cambridgeshire, GIS was employed to investigate whether proximity of conspecifics or structure of the woodland habitat within the breeding territory influenced nest location. (Collaborators: Richard K Broughton and Dr Shelley A Hinsley, Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE28 2LS, UK)
Can network theory contribute to our understanding of disease spread and the creation of control methods?
The maintenance and spread of disease is dependent upon the pattern of contacts between individuals within a population. Wildlife populations act as a host for disease, which can pose a risk to both human health and economically important species. Therefore, an investigation into contact structures within populations would provide an understanding of the risk of disease spread and inform the design of management strategies. However, previous research has focused on employing network theory to investigate how theoretical network topologies affect the persistence and spread of disease. There is a lack of knowledge about naturally occurring contact patterns and their stability under different environmental conditions in specific host-disease systems. This study employed a spatial stochastic simulation model of a badger population infected with bovine TB to derive transmission contact patterns, and investigate the impact of epidemiological parameters and control strategies upon network structure. (Collaborators: Dr Piran White and Dr Mark Bulling, University of York, Environment Department, Heslington, York, YO10 5DD, UK)