Relationship between plasma leptin-like protein levels, begging and provisioning in nestling thin-billed prions Pachyptila belcheri.

While there have been many studies in various species examining the physiological role of leptin, there are so far no data in free-living seabirds. In the present study, we assess whether leptin is expressed in thin-billed prions (Pachyptila belcheri) and we investigate its relationship with feeding-related parameters including body condition, begging intensities and provisioning rates. We showed by Western Blot analysis using leptin-specific antibody that leptin-like protein (14-16kDa) is expressed in adipose tissue and liver of nestling thin-billed prions. Plasma leptin-like protein levels, determined by RIA, were in the same range (1-3ng/ml) as in other avian species and increased with age. In two breeding seasons, the plasma leptin-like protein levels were negatively correlated with provisioning rates (R=-0.67 and -0.35 in 2003 and 2004, respectively, P<0.05) indicating that endogenous leptin may be an anorexigenic hormone in wild birds. Plasma leptin-like protein levels were positively correlated with begging intensities (R=0.43 and 0.37 in 2003 and 2004, respectively, P<0.05), and this may be because hungry nestling seabird chicks with low body conditions increased their begging intensities. Plasma leptin-like protein levels did not correlate either with plasma triglyceride or glucose levels in thin-billed prions. Overall, these findings show the presence of leptin-like protein in free-living seabirds and provide new insights into its function and its possible role in feeding-associated behaviours.