Defensive anointing: extended chemical phenotype and unorthodox ecology

Summary. Many animals acquire substances on their integument from heterospecifics through anointing. In active or self-anointing, animals rub against scent sources or they apply them by appendage or mouth. In passive anointing, animals adsorb emitted chemicals. Most investigators suggest that chemicals appropriated via anointing deter predators, ectoparasites, and/or microbial pathogens. Similarly, nesting birds and brood parasites of social insects acquire chemicals from and reside unmolested near or within insect colonies. The acquisition through anointing of chemicals that deter predators, ectoparasites, microbial pathogens, and other offenders, i.e. defensive anointing, constitutes an extended phenotype: the genetic machinery by which defensive compounds are synthesized does not reside with the anointing organisms, but the sensory mechanisms and/or behavioral tendencies by which chemicals are appropriated from heterospecifics do. The ecological relationships between anointing organisms and chemical donors, and between chemical donors and those responding to chemicals appropriated via anointing, may be unorthodox. Interactions between anointing organisms and chemical donors typically entail abrasive contact with or other damage to the latter. These encounters sometimes are evidenced by telltale marks on chemical donors or by chemicals deposited on the integument of anointing organisms. The organisms furnishing chemicals and those affected by them may not interact, and they may even occupy different habitats, because mobile anointing organisms are the medium by which chemicals are disseminated. Thus, in allelochemical studies where anointing is involved, species can be tested, with ecological legitimacy, using chemicals from organisms they might fail to interact with in nature. Practical implications of anointing stem from its potential importance in conservation and captive management, where consideration is given to the protection that animals derive by accessing topically acquired chemicals from heterospecifics.