infection with an amphibian pathogenic fungus: is there an altitudinal trend? zool-502 ubc november...
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Infection with an amphibian pathogenic fungus:
is there an altitudinal trend?
ZOOL-502 UBCNovember 2010.
Angie Nicolás
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1980's: decline in amphibian populations
122 spp gone extinct in the past 30 years
1/3 of amphibian populations are threatened (Stuart et al 2004)
Causes involved:
Habitat lossPollutionIncreased UV radiationDisease
In Central and South America 37% of the 113 spp of Atelopus have declined in the past 20 years (La Marca et al, 2005)
Amphibian population declines
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Batrachochytrium dendrobatidis
Phylum Chytridiomycota,
Class Chytridiomycetes,
Order Chytridiales
(Longcore y col., 1999)
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(Marantelli et al 2004)
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Optimum growth 17-25°C50% cultures dies after 48h at 30°C (Longcore et al, 1999)
Experimentally infected frogs exposed to high temperatures are able to eliminate the pathogen (Woodhams et al, 2003)
Interspecific variation in the response to the pathogen (Blaustein et al, 2005; Woodhams et al, 2006)
Lowland frogs are infected less frequently than highland frogs
Prevalence increases in cool months (Berger et al, 2004)
Outbreaks are associated with hot and dry years (Pounds, 1999)
B. dendrobatidis and temperature
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What happens if we consider only one species?
Will prevalence increase with altitude?
Can variations in temperature explain the tendency?
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Hypothesis:
Prevalence with Bd infection will be higher in populations of Mannophryne herminae outside
of B. dendrobatidis optimum thermic range .
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Study area: Henri Pittier National Park. Estado Aragua, Venezuela
Map credit: Dinora Sánchez
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Cata 90 m
La Trilla 115 m
Hidrocentro 375 m
El Salto 600 m
Riítos de Pittier 840 m
Virgen 950 m
Rancho Grande 1158 m
Guacamaya 890 m
Guamita 762 m
Profauna 552 m
Altitudinal distribution of sampling sites
Southern Slope
Northern Slope
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1- Manually collected toads in each site (n=21±4)
2- Sexed and measured (SVL)
3-Toe clipped and stored tissue samples in 70%ethanol.
Recorded air temperature (every hour) for 9 weeks
In the field
In the lab
1-DNA extraction and amplification (qPCR) following Boyle et al 2004.
-Ran samples (duplicates)-0.1, 1, 10 and 100 zoosp. eq. Standards-Positive and negative controls
2-Zoosp.eq. >0.1 = Positive sample
3- Calculate parasitic load
Methodology
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R2 = 0,8543
R2 = 0,5758
10
12
14
16
18
20
22
24
26
28
0 200 400 600 800 1000 1200
Altitud (m)
Tem
p.m
edia
(ºC
)
Norte Sur Lineal (Norte) Lineal (Sur)
ANCOVA Temperature in both slopes
RESULTS
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Mean temperature analysis
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Maximum temperatures analysis
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R2 = 0,842
R2 = 0,57050
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500 600 700 800 900 1000
Altitud (m)
Ho
ras
co
n T
>2
9°C
Nº hs.temp≥29ºC Nºhs.temp >25ºC Tendencia 25º Tendencia 29º
Linear regressions of N° hours with Temp> 25°C and 29°C
790 m910 m
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0
10
20
30
40
50
115 375 552 600 762 840 900 950 1158
Altitud (m)
Pre
vale
nci
a (%
)Prevalences per sampling site
Atelopus
Mean prevalence= 13 ± 5%
27/209 frogs infected
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Variable CV gl Prob, χ2 Mes 7.926 4 0,09432
Altitud 14.301 1 0,00016
SVL 15.185 1 0,0001
Media 0,613 1 0,43357
Máx, 2.036 1 0,15362
Prom>25 5.392 1 0,02023
Prom>=29 3.804 1 0,05112
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VARIABLE LIKELIHOOD RATIO LOWER CI HIGHER CI
ALTITUDE 1,001 0,999 1,002
SVL 0,17 0,065 0,443
Logistic regression analysis
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QUESTIONS
Acknowledgments
Fundación La Salle de Ciencias NaturalesEstación Biológica Rancho Grande
Margarita LampoDinora SánchezFrancisco NavaJavier ValeraCésar HerreraJuan José Cruz