The recent emergence of amphibian chytridiomycosis has precipitated competing hypotheses regarding the endemic versus novel nature of the causative agent, Batrachochytrium dendrobatidis (Bd ). We conducted a retrospective survey of the California Academy of Sciences' (San Francisco, California, USA) amphibian collection, testing for presence of Bd in 4 amphibian species collected from central California between 1897 and 2005. The earliest detection of Bd was found in 2 Rana catesbeiana in 1961, and the data support the hypothesis that Bd was a novel pathogen introduced into central California prior to 1961 that spread out geographically and taxonomically from at least one central location and is now endemic throughout most of central California. The taxonomic pattern of infection prevalence and the ecological constraints of the 4 species we tested suggest that, although Bd was initially detected in R. catesbeiana, the more efficient and most likely local vector for Bd in central California is actually Pseudacris regilla.KEY WORDS: Chytridiomycosis · Batrachochytrium dendrobatidis · Rana draytonii · Natural history collections · Pseudacris regilla · R. catesbeiana · R. boylii · Co-kriging Resale or republication not permitted without written consent of the publisherDis Aquat Org 83: [1][2][3][4][5][6][7][8][9] 2009 Despite these disadvantages, natural history collections nonetheless present our only opportunity for retrospective surveys when seeking answers to questions within an historical context.Examination of current and archived specimens has documented Bd on all continents that harbor amphibians (Bosch et al. 2001, Weldon 2002, Weldon et al. 2004, Une et al. 2008. Weldon et al. (2004) examined 697 archived amphibians collected in South Africa from 1879 to 1999 and detected the earliest known Bd infection in Xenopus laevis collected in 1938. They found that the pathogen was widespread in Africa and concluded that Bd was a stable endemic infection in southern Africa for the 23 yr period before Bd was first detected on another continent. Their museum survey results formed the basis for the hypothesis that Bd originated in Africa and supported the proposal that X. laevis was most likely the original global vector of the pathogen. X. laevis was globally exported out of Africa beginning in 1935, when it became the test species used for human pregnancy assays (Tinsley & McCoid 1996). Rana catesbeiana has also been postulated as a global vector of Bd (Daszak et al. 2004, Garner et al. 2006, Fisher & Garner 2007, as both R. catesbeiana and X. laevis are relatively asymptomatic when infected (Parker et al. 2002, Daszak et al. 2004) and both species are globally transported for the pet, food and laboratory trades (Tinsley & McCoid 1996, Cunningham et al. 2003, Daszak et al. 2004, Fisher & Garner 2007.The earliest known Bd-positive specimens outside of Africa were 2 Rana clamitans collected in July 1961 in Quebec, Canada, as documented by Ouellet et al. (2005), who surveyed amphibian collections from 2 Can...

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