Comparative analysis reveals loss of the appetite-regulating peptide hormone ghrelin in falcons

- Compared GHRL, which encodes the appetite regulator ghrelin, of 31 bird species.
- No canonical GHRL start-codon in peregrine and saker falcons.
- Retrotransposon inserted in intron 0 of falcon GHRL.
- Ghrelin is anorexigenic in birds and loss could be a predatory adaptation in falcons.

Ghrelin and leptin are key peripherally secreted appetite-regulating hormones in vertebrates. Here we consider the ghrelin gene (GHRL) of birds (class Aves), where it has been reported that ghrelin inhibits rather than augments feeding. Thirty-one bird species were compared, revealing that most species harbour a functional copy of GHRL and the coding region for its derived peptides ghrelin and obestatin. We provide evidence for loss of GHRL in saker and peregrine falcons, and this is likely to result from the insertion of an ERVK retrotransposon in intron 0. We hypothesise that the loss of anorexigenic ghrelin is a predatory adaptation that results in increased food-seeking behaviour and feeding in falcons.