Infection with an amphibian pathogenic fungus:

is there an altitudinal trend?

ZOOL-502 UBCNovember 2010.

Angie Nicolás

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

Batrachochytrium dendrobatidis

Phylum Chytridiomycota,

Class Chytridiomycetes,

Order Chytridiales

(Longcore y col., 1999)

(Marantelli et al 2004)

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

What happens if we consider only one species?

Will prevalence increase with altitude?

Can variations in temperature explain the tendency?

Hypothesis:

Prevalence with Bd infection will be higher in populations of Mannophryne herminae outside

of B. dendrobatidis optimum thermic range .

Study area: Henri Pittier National Park. Estado Aragua, Venezuela

Map credit: Dinora Sánchez

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

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

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

Mean temperature analysis

Maximum temperatures analysis

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

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

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

VARIABLE LIKELIHOOD RATIO LOWER CI HIGHER CI

ALTITUDE 1,001 0,999 1,002

SVL 0,17 0,065 0,443

Logistic regression analysis

QUESTIONS

Acknowledgments

Fundación La Salle de Ciencias NaturalesEstación Biológica Rancho Grande

Margarita LampoDinora SánchezFrancisco NavaJavier ValeraCésar HerreraJuan José Cruz