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Causes of Amphibian Declines

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Title: Causes of Amphibian Declines


1
Causes of Amphibian Declines
  • Julie Robertson
  • Biol 402
  • November 18, 2008

Pacific treefrog
2
(No Transcript)
3
  • One-third to one-half of the worlds 6000 known
    amphibian species could vanish in our lifetime,
    resulting in the single largest mass extinction
    since the disappearance of the dinosaurs.
  • -Vancouver Aquarium Marine Science Center

4
Overview
  • Trends in Amphibian Populations
  • Global Status
  • Threats to Amphibians
  • Complex Causes of Amphibian Declines
  • The Effect of Trematode Infection on Amphibian
    Limb Development and Survivorship
  • Conclusions
  • 2008 Year of the Frog
  • Questions

5
Trends in Amphibian Populations
  • Declining throughout North America and Europe

Houlahan (2000)
6
IUCN Red List Assessment for all 5,918 Known
Amphibian Species
EX Extinct EW Extinct in the wild CR
Critically endangered EN Endangered VU
Vulnerable NT Near threatened LC Least
concern DD insufficient information
7
Threats to populations
IUCN 2008
8
Broad Causes of Declines
  • Embryo Mortality with S. ferax
  • Complex causes of amphibian population declines.
  • (Kiesecker et al 2001)
  • Reduced Fitness with Ribeiroia
  • The effect of trematode infection on amphibian
    limb development and survivorship.
  • (Johnson et al 1999)

9
Background
  • Knew that S. ferax outbreaks, in connection with
    UV-B radiation, were correlated with high
    amphibian embryo mortality.
  • Disease outbreaks on several species occurring
    simultaneously
  • Believed that ozone depletion was causing
    increased UV-B radiation, leading to increases in
    mortality.
  • Wanted to know if it was Climate change that was
    increasing UV-B radiation, rather than ozone
    depletion.

10
Methods
  • Oregon Cascade Mountains between 1990 and 1999
  • Measured 3 variables
  • Number of embryos deposited
  • Percent of S. ferax related mortalities
  • Depth at which embryos developed
  • Conducted field experiment
  • Manipulated depth at which embryos were raised
  • Embryos were subjected to either full UV-B
    exposure, or completey shielded.
  • Collected summer S.O.I. data and winter
    precipitation data

11
Southern Oscillation Index
  • Air pressure difference between Tahiti and Darwin
    is recorded
  • The monthly fluctuations in this air pressure
    difference is used to calculate the Southern
    Oscillation Index (S.O.I)
  • Sustained negative values of S.O.I. are
    associated with El Nino events

12
Southern Oscillation Index
13
Climate Change Affects Depth
  • Knew that El Nino events are increasing in
    frequency and intensity due to climate change
  • As S.O.I. increases, precipitation in the North
    Cascades increases

14
Climate Change Affects Depth
  • Showed that depth of water column at oviposition
    sites was a function of S.O.I.

15
UV-B Radiation
  • Causes embryo mortality
  • Attenuates with depth

White Shielded from UV-B Grey Exposed to UV-B
16
Saprolegnia ferax
  • Infected eggs easily detected
  • Infected eggs do not hatch

17
Saprolegnia ferax
  • Acts synergistically with UV-B radiation
  • Increases embryonic mortality
  • Complex transfer from infected fish through soil

Black UV Blocking filter
18
Saprolegnia ferax
  • More than 50 of embryos that developed in
    shallow water became infected
  • Less than 19 of embryos that developed in deep
    water became infected
  • No UV-B influence on S. ferax related mortality
    in deep waters

19
CLIMATE CHANGE
REDUCED POOLS
UVB EXPOSURE
PATHOGEN OUTBREAKS
EMBRYO MORTALITY
20
Broad Causes of Declines
  • Embryo Mortality
  • Complex causes of amphibian population declines.
  • (Kiesecker et al 2001)
  • Reduced Fitness
  • The effect of trematode infection on amphibian
    limb development and survivorship.
  • (Johnson et al 1999)

21
Reduced Fitness
  • Number of reported deformed amphibians increasing
    since early 1990s
  • Causes thought to include
  • UV-B radiation
  • Biocide contamination
  • Parisite infection
  • retinoids

22
Methods
  • Surveyed 35 ponds in Santa Clara County,
    California
  • Focused on Pacific tree frogs (Hyla Regilla)
  • Egg masses were collected from Eel River
  • Six treatments
  • Control
  • Light
  • Intermediate
  • Heavy
  • Alaria mustelae
  • Alaria mustelae and Ribeiroia

23
Results
  • 85 of tadpoles exposed to Ribeiroia developed
    severly abnormal limbs
  • Tadpole survival declined with increasing
    parasite density
  • High survival rates in control group
  • High rates of abnormalities in Heavy treatment
    group
  • Alaria infected tadpoles, but had no effect

24
Ribeiroi spp.
  • Survivorship frequency decreases with increasing
    Ribeiroia density
  • Abnormality frequency increases with increases
    Ribeiroia density
  • Survivorship and abnormality frequencies
    unaffected by Alaria infection
  • Survivorship frequency significantly lower after
    Ribeiroia treatment
  • Abnormality frequency significantly higher after
    Ribeiroia treatment

25
Infection to Death
  • Direct mortality
  • Indirect mortality
  • Few abnormal adults found in the field

26
Recent Increases
  • Limb abnormalities shown to be caused by
    Ribeiroia
  • Recent increases could be caused by
  • Host species
  • Accelerated eutrophication
  • Removal of predators
  • Further research needed

27
Conclusions
  • Amphibian populations declining drastically
  • Complex interactions between abiotic and biotic
    factors, on global and local scales
  • Climate change, depleting ozone layer (and other
    factors?) leaving amphibians more vulnerable to
    disease outbreaks

28
2008 Year of the Frog Campaign
  • http//www.youtube.com/watch?v2hBdHydtF1I
  • http//www.amphibianark.org/online-petition.php

29
Questions?
30
Literature Cited
  • Houlahan J.E. (2000). Quantitative evidence for
    global amphibian population declines. Nature 404
    752-755.
  • Johnson P.T.J., Lunde K.B., Ritchie E.G. Launer
    A.E. (1999). The effect of trematode infection on
    amphibian limb development and survivorship.
    Science 284 802-804.
  • Kiesecker J.M. Blaustein A.R. (1995). Synergism
    between UV-B radiation and a pathogen magnifies
    amphibian embryo mortality in nature. Proceedings
    of the National Academy of Sciences of USA
    92(24) 11049-11052.
  • Kiesecker J.M., Blaustein A.R. Belden L.K.
    (2001). Complex causes of amphibian population
    declines. Science 410 681-684.
  • Kiesecker J.M., Blaustein A.R. Miller C.L.
    (2001). Transfer of a pathogen from fish to
    amphibians. Conservation Biology 15(4)
    1064-1070.
  • Pounds A.J. (2001). Climate and amphibian
    declines. Nature 410 639-640.
  • Vanaqua.org
  • Wikipedia.org
  • Youtube.come
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