TheAuk 116(4):957-963, 1999 EVOLUTION OF TOXICITY IN PITOHUIS: I. EFFECTS OF HOMOBATRACHOTOXIN ON CHEWING LICE (ORDER PHTHIRAPTERA) JOHN P. DUMBACHER 1 Department of Ecology andEvolution, The University ofChicago, 1101East 57th Street, Chicago, Illinois60637,USA ABSTRACT.--Birds in the genus Pitohui carrythe potent neurotoxin homobatrachotoxin in their skinand feathers. In this study, I tested whether homobatrachotoxin canrepelor kill chewing lice (orderPhthiraptera). Whenindividualfeather licewereoffered a choice of two feathers on which to feed or take shelter, the lice preferred nontoxic feathers to feathers of the mosttoxicpitohui species, Pitohui dichrous. Moreover, the presence of toxicP.dichrous feathers significantly shortened the life spanof captive feather lice.These results suggest thathomobatrachotoxin repels and kills lice and may thusprotect pitohuis against licein- festation. Received 10 April 1998, accepted 8 February 1999. SPECIES IN THEAVIANGENUS PITOHUI carry a potent alkaloid neurotoxin in their skin and feathers (Dumbacher et al. 1992). Pitohui toxin, known as homobatrachotoxin (homoBTX), is a member of a well-known family of steroidal al- kaloids thatdepolarize nerve andmuscle mem- branes by binding and activating voltage-de- pendentsodium channels (Albuquerque et al. 1971). In some cases,concentrations of toxin are suffidently high that merely handling an individual Hooded Pitohui (Pitohui dichrous) can irritate buccal membranes and can cause sneezing and burning,wateryeyes (Salvadori 1881, Majnepand Bulmer 1977, Dumbacher et al. 1992).Anthropological evidence suggests that the toxin defends pitohuisfrom human hunters(Majnepand Bulmer 1977;Kocher- Schmid1991, 1993), and other workers have speculated that it also defends pitohuis against natural predators (Diamond 1992) and arthro- pod ectoparasites (Mouritsen and Madsen 1994, Poulsen 1994). Nevertheless, no studies have directly investigated if theenemies of pi- tohuis are deterred by homoBTXor how homoBTX deters them. Arthropod ectoparasites arenatural enemies ofpitohuis andpotential targets forpitohui de- fensive chemicals. HomoBTX has been shown to affect a wide range of vertebrates andinver- tebrates(Albuquerque et al. 1971, Daly and • Present address: MolecularGenetics Laboratory, National Zoological Park, Smithsonian Institution, 3001 Connecticut Avenue NW, Washington, D.C. 20008, USA. E-mail:jdumbacher@nzp. si.edu Spande 1986, Dwivedy 1988). With the notable exceptions of pitohuisand Phyllobates frogs, nearlyevery animal that contains voltage-de- pendent sodium channels is poisoned by ba- trachotoxins, includingdistantly related ar- thropods. Also, bird licecan influence host fit- ness in several ways. Lice canaffect the ener- geticsand survival of hosts(Clayton 1990, Booth et al. 1993, Brown etal. 1995), reduce egg numbers and hatching rates (Derylo 1974, DeVaney 1976), reduce mating success (Ham- ilton and Zuk 1982, Clayton 1990, Loye and Zuk 1991, Clayton and Tompkins1995), and transmitpathogens (Marshall 1981, Clayton 1990). Therefore, defense against licemight be underselection. Finally, a highproportion of a pitohui's totaltoxin is concentrated in theskin and feathers. Because lice live and feed on feathers, skin, and subdermal blood supplies, pitohui toxins could constitute a formidable barrierto these ectoparasites. HomoBTXs, and toxins in general, couldde- fendbirds against lice through several alter- native mechanisms. Toxins could (1) reduce lousefecundity, (2) reducelousesurvival, (3) reduce the influence of liceonhost fitness (e.g. by delaying maturation, lengthening the lifecy- cle, or suppressing appetite), and (4) favorably effect louse transmission rates by reducing im- migration or inducingemigration. Here, I re- portexperimental studies thatexamine wheth- er feather lice exhibit an active choice against naturallytoxic pitohui feathers and examine whether the presence of natural levels of 957