Isolation and Characterization of Antimicrobial Peptides from the Leukocytes of the American Alligator ( Alligator mississippiensis )

Saltwater Crocodiles (Crocodylus porosus) are considered one of the least tolerant of conspecifics of all crocodilians. Yet they begin their life living in groups (hatchling crèches) for around two months, suggesting ontogenetic changes in social behaviour may underpin the growing intolerance with increasing age and, or size. In this study, detailed observations on groups of captive C. porosus hatchlings, particularly in the first 6 weeks of life, demonstrated they exist with high levels of close contact and little aggression (tolerance). Yet this quiescent existence is interspersed with sporadic periods of agonistic events (signalling intolerance), with highly distinctive behaviours (N= 12), particularly in the morning (0600-0800 h) and evening (1700-2000 h). Of these behaviours, 5 were postures involving no movement, with 2 non-contact movements, and five contact movements that were considered either discrete (stereotypic; N= 4) or graded (not stereotypic; N= 8), based on whether the form or intensity of the display varied. Ontogenetic shifts in agonistic behaviour were quantified by examining 18 groups of hatchlings, 6 groups each at 1, 13 and 40 weeks of age. Agonistic events between hatchlings at 1 week of age varied in intensity (low, medium, high) and involved one (dominant) or both (combat) individuals. Almost all encounters involved actual contact, with a high number resulting in the instigator losing. At 13 and 40 weeks, a more formalized, hierarchal dominance relationship had established, based primarily on aggression-submission interactions. Conflict was high intensity and more frequent, with the subordinate individual fleeing in response to an approach by a dominant animal that often did not make contact. Social hierarchies among hatchling C. porosus may well underpin the high variability reported in individual growth rates, while the similarity of agonistic behaviours displayed by hatchlings and adults suggests a ‘juvenile structured’ pattern of behavioural ontogeny for this species. Isolation and Characterization of Antimicrobial Peptides from the Leukocytes of the American Alligator (Alligator mississippiensis) Mark Merchant1, Lancia Darville1 and Kermit Murray2 1Department of Chemistry, McNeese State University, Lake Charles, Louisiana, USA 2Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana, USA Abstract We have isolated a 4746 Da peptide (39 amino acids), with antimicrobial activities, from the leukocytes of the American Alligator. The peptide was isolated by acid ultracentrifugation, reverse phase high performance liquid chromatography, and ion mobility chromatography. The mass was determined using matrix-assisted laser desorption ionization. The peptide has a net positive charge (+8), an isoelectric point of 9.5, an arginine and lysine content of 36%, and is extremely amphipathic. Another peptide of 4.9 kDa (43 amino acids) was isolated, and had a net charge of +13 with an arginine and lysine content of 32%. Both of these peptides have several cysteine residues, and show sequence homologies to mammalian b-defensins.