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Posted by pbio on 07 May 2009 at 22:27 GMT

Author: Margarita Lampo
Position: Researcher
Institution: Centro de Ecología. Instituto Venezolano de Investigaciones Científicas.
Additional Authors: D. Sánchez, F. Nava-González, C.Z. García and A. Acevedo.
Submitted Date: November 24, 2008
Published Date: December 1, 2008
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

Lips et al. (1) recently proposed that the spread of Batrachochytrium dendrobatidis (Bd) is sufficient to explain the spatiotemporal patterns of amphibian declines in Central and South America. They suggested independent introductions followed by waves of spread. For Venezuela, the authors suggest that Bd was introduced in the Cordillera de la Costa from which it spread westward into the Cordillera de Los Andes towards Colombia. This hypothesis rests on two premises, each of which we examine in light of the available evidence.
Bd was introduced into the Cordillera de la Costa in 1977 where it produced declines in naïve populations of Atelopus cruciger. The earliest Bd report at the Cordillera de la Costa in Venezuela dates to 1986 (2). Lips et al. propose 1977 as the probable date of Bd introduction to Venezuela on the assertion that the first amphibian declines for Atelopus cruciger occurred during this year, and thus Bd must have arrived then and produced these declines. In addition to the circularity of this argument, already pointed out (3), the premise that there were population declines during 1977 at the Cordillera de la Costa can be contested based on the information available from museum collections. Lips et al.´s conclusion is based on a previous study showing the number of specimens of A. cruciger deposited in 12 museum collections since1920 (2), which later expanded (4). The number of specimens deposited in these collections varied with time, with high and low years scattered along the time series. Except for the latter period covering nearly two decades, all others lasted a few years and were followed by high years. For example, 65 specimens were deposited in these collections in 1980, three years after the date proposed by Lips et al. for the decline. If the disease had been introduced in 1977 and produce the dramatic declines that have been documented elsewhere (5), the species should have been locally extinct long before these specimens were collected.
Declines occurred in a wavelike pattern at the Cordillera de Mérida between 1988 and 1995. Lips et al. claim that population declines are the result of Bd epidemic outbreaks and, thus, they indicate the timing of these events. While the documented arrival of Bd to an amphibian community at el Cope, Panama, indicates that this can be true -declines occurred within months of the first detection of the pathogen- years of declines (DODs in Lips et al. 2008) proposed for some Venezuelan species have long time lags with respect to the year when Bd was first reported in the locality. For example, infection was detected in A. carbonerensis, A. sorianoi and A. mucubajiensis collected during 1988 (6), but DODs proposed for A. carbonerensis at the same locality and for A. mucubajiensis at a nearby locality (˜ 9km) are 1993 and 1995, five and seven years after the pathogen was detected. For A. sorianoi, in contrast, the proposed DOD coincides with the year when infection was first detected. If there can be a lag time of seven years between pathogen arrival and host decline in some populations while others crash upon the arrival of the pathogen, declines must not be indicative of Bd arrival and/or DODs (thus the dates of Bd arrival) proposed for some Venezuelan species by Lips et al. (2008) are not correct.
In conclusion, we have demonstrated that some assumptions of the invasive wave model proposed by Lips et al. 2008 to explain the patterns of declines in Venezuela show inconsistencies with existing data.
1. K. R. Lips, J. Diffendorfen, J. R. Mendelson III, M. W. Sears, PLOSBiology 6, 441-454 (2008).
2. E. Bonaccorso, J. M. Guayasamin, D. Méndez, R. Speare, Herpetol. Rev.34, 331-334 (2003).
3. J. A. Pounds, L. A. Coloma, Nature Rep.2, 57-59 (2008).
4. J. Manzanilla, E. La Marca, Mem.Fund. La Salle Cienc. Nat.157, 5-30 (2004).
5. K. R. Lips et al., Proc.Nat.Acad.Scien.USA 103, 3165-3170 (2006).
6. M. Lampo, A. Rodríguez, E. La Marca, P. Daszak, Herpetol.J.16, 395-402 (2006).

No competing interests declared.