Differences in the skin peptides of the male and female Australian tree frog Litoria splendida - The discovery of the aquatic male sex pheromone splendipherin, together with Phe8 caerulein and a new antibiotic peptide caerin1.10

The skin secretions of female and male Litoria splendida have been monitore d monthly over a three-year period using HPLC and electrospray mass spectro metry. Two minor peptides are present only in the skin secretion of the mal e. The first of these is the female-attracting aquatic male sex pheromone t hat we have named splendipherin, a 25 amino acid peptide (GLVSSIGKALGGLLADV VKSKGQPA-OH). This pheromone constitutes about 1% of the total skin peptide s during the breeding season (January to March), dropping to about 0.1% dur ing the period June to November. Splendipherin attracts the female in water at a concentration of 10(-11)-10(-9) m, and is species specific. The secon d peptide is a wide-spectrum antibiotic of the caerin 1 group, a 25 residue peptide (GLLSVLGSVAKHVLPHVVPVIAEKL-NH2) named caerin 1.10. The neuropeptid es of L. splendida are also seasonally variable, the change identical for b oth the female and male. During the period October to March, the sole neuro peptide present in skin secretions is caerulein [pEQDY(SO3)TGWMDF-NH2]; thi s is active on smooth muscle and is also an analgaesic. During the southern winter (June to September), more than half of the caerulein is hydrolysed to [pEQDYTGWMDF-NH2], a peptide that shows no smooth muscle activity. In pl ace of caerulein, a new peptide, Phe8 caerulein [pEQDY(SO3)TGWFDF-NH2], bec omes a major component of the skin secretion. Perhaps this seasonal change is involved in thermoregulation, that is, with the initiation and maintenan ce of the inactive (hibernation) phase of the animal.