Peptide gene expression profiles in response to fasting and re-feeding in hoarding and non-hoarding titmice species

Abstract

The avian appetite regulatory system has been continuously studied over the last decades but it is less well understood than the mammalian system. It has also been studied much more in domestic birds than in wild passerine species. This PhD aims to investigate the role of different neuropeptides as well as gut peptides in controlling and regulating the ingestive behaviours of songbirds. My aim was to pinpoint candidate peptide genes that may differentiate a hoarding from a non-hoarding bird species and I used non-hoarding great tits (Parus major) and blue tits (Cyanistes caeruleus) to make comparisons with a closely-related hoarding species, the coal tit (Periparus ater) In this context, I used molecular techniques combined with video analysis to quantify selected peptide gene mRNAs suspected from the literature to play a major role in controlling both food intake and hoarding behaviour. By identifying candidate peptide genes that respond to an individual’s nutritional state, I was able to make some distinctions between hoarding and non-hoarding species. I also established for the first time in passerines the tissue distribution of gene expression in the gut for cholecystokinin (CCK), proglucagon (GCG), insulin and peptide YY. Overall, this study suggests that proglucagon (GCG) both in the gut and the hindbrain, as well as hypothalamic agouti-related protein (AGRP) and pro-opiomelanocortin (POMC) gene expression could be used as neural signals reporting the nutritional state of titmice. Moreover, hypothalamic AGRP and POMC, and hindbrain GCG and POMC seem to be involved in the regulation of food hoarding in coal tits. These observations support observations from the hamster literature that peptides that are known to control and regulate food intake are also involved in food hoarding.