Ranavirus could speed up extinction
for the endangered frog, Rana sevosa
Julia E. Earl, Matthew J. Gray and William B. Sut...
The Big Unknowns:
Can Ranavirus affect population dynamics?
Can Ranavirus cause local or global extinction?
Evidence so fa...
Population Models
• Great tool to examine how changes in survival
might affect populations
• Start with species most likel...
Dusky Gopher Frog- Rana sevosa
• One of the most
endangered frogs in the
USA- listed in 2001
• Only one regular, viable
po...
Model
Juveniles Adults
• Very simple stage-structured matrix model of
females
• Parameterized using data from 1995-2001
mo...
Calibrating the Model
• Examined correlations between model
generated data and actual data (r = 0.6-0.8)
• Sensitivity ana...
Simulations
• Ran model with 3 hydroperiods: 148 (Glen’s
pond average), 200 (slightly wetter
period), and functionally per...
Adult Exposure to Ranavirus
Quick Extinction with No Intervention
7
8
9
10
11
12
13
14
15
16
17
148 (Glen's Pond Avg.) 200
TimetoExtinction(years)
Ave...
Intervention: Hydroperiod
• Experimental water addition in 2001 (Seigel et al.
2006)
• Examined a non- limiting hydroperio...
Permanent Hydroperiod
40
45
50
55
60
65
70
75
80
85
No
disease
Every 50 every 25 every 10 every 5 every 2
TimetoExtinction...
Supplemental Rearing
• Water addition not feasible- too expensive
• Rearing all the eggs in cattle tanks beside the
pond i...
• Previous scenarios- all populations went
extinct within 1000 years
– Not true with this scenario
0
0.05
0.1
0.15
0.2
0.2...
Conclusions
• Exposure to ranavirus could speed up extinction and
increase extinction probabilities, depends on exposure
i...
Future Directions
• Data to come on other life stages of the Dusky
Gopher Frog- larvae, metamorphs
• Wood frog model- comp...
Acknowledgements
• Help with Gopher Frog trials: Becky
Hardman, Dr. Becky Wilkes, Dr. Debra Miller
• Funding:
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Ranavirus could speed up extinction for the endangered Mississippi gopher frog

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2013 International Symposium on Ranaviruses
by Julia Earl

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Ranavirus could speed up extinction for the endangered Mississippi gopher frog

  1. 1. Ranavirus could speed up extinction for the endangered frog, Rana sevosa Julia E. Earl, Matthew J. Gray and William B. Sutton
  2. 2. The Big Unknowns: Can Ranavirus affect population dynamics? Can Ranavirus cause local or global extinction? Evidence so far: – About 40-60% of USA amphibian die-offs (1996- 2005) attributable to ranavirus (Green et al. 2002, Muths et al. 2006) – Common Frogs- adult populations decline ~80% in ponds with ranavirus (Teacher et al. 2010)
  3. 3. Population Models • Great tool to examine how changes in survival might affect populations • Start with species most likely to be vulnerable to extinction – closed populations of an endangered species – examine effects of ranavirus exposure in one life stage at a time – different intervals of exposure
  4. 4. Dusky Gopher Frog- Rana sevosa • One of the most endangered frogs in the USA- listed in 2001 • Only one regular, viable population- Glen’s Pond (MS) • Pond breeder- eggs in Dec. • Metamorphs emerge in June when the pond dries • Adults in long leaf pine often associated with Gopher Tortoise Burrows IUCN
  5. 5. Model Juveniles Adults • Very simple stage-structured matrix model of females • Parameterized using data from 1995-2001 monitoring Glen’s pond (Richter et al. 2001, 2003) • Built in stochasticity in the model- drew random values for parameters from a normal distribution each year • Hydroperiod threshold for metamorph production- 190 days
  6. 6. Calibrating the Model • Examined correlations between model generated data and actual data (r = 0.6-0.8) • Sensitivity analysis- which parameter values change the model the most? – Sensitive to survival from eggs to juveniles • Further- data from 2000s suggests population decline of 10% each year (Pechmann, unpubl. data) – Our model output is consistent with this
  7. 7. Simulations • Ran model with 3 hydroperiods: 148 (Glen’s pond average), 200 (slightly wetter period), and functionally permanent • Ranavirus- challenge trials complete on adults, showed 100% mortality in water bath – See Bill Sutton’s Poster! – Die-off concentrations of virus (103 pfu/mL) – Assuming only adults are exposed – Examined different exposure intervals
  8. 8. Adult Exposure to Ranavirus
  9. 9. Quick Extinction with No Intervention 7 8 9 10 11 12 13 14 15 16 17 148 (Glen's Pond Avg.) 200 TimetoExtinction(years) Average Hydroperiod (days) No Disease Adult Ranavirus Yr. 1 Adult Ranavirus Yr. 5 Adult Ranavirus Yrs. 1 & 10 Adult Ranavirus Yrs. 1 & 5
  10. 10. Intervention: Hydroperiod • Experimental water addition in 2001 (Seigel et al. 2006) • Examined a non- limiting hydroperiod – Assumes water added to the pond every year
  11. 11. Permanent Hydroperiod 40 45 50 55 60 65 70 75 80 85 No disease Every 50 every 25 every 10 every 5 every 2 TimetoExtinction(yrs) Disease Interval (years) **Realistic intervals
  12. 12. Supplemental Rearing • Water addition not feasible- too expensive • Rearing all the eggs in cattle tanks beside the pond is the current strategy – Producing 200-900 juveniles each year – Population now at a 10% increase each year (Joe Pechmann, personal communication) • Examined this scenario (still adult mortality only)
  13. 13. • Previous scenarios- all populations went extinct within 1000 years – Not true with this scenario 0 0.05 0.1 0.15 0.2 0.25 No disease Every 50 Every 25 Every 10 Every 5 Every 2 Every 1 ExtinctionProbability Disease Interval (years)
  14. 14. Conclusions • Exposure to ranavirus could speed up extinction and increase extinction probabilities, depends on exposure interval and intervention strategy • Unlikely to have a large effect for Dusky Gopher Frogs if the current intervention is maintained – The population dynamics are not actually very sensitive to adult mortality – Future data on other life stages will be really important • However, interactions with other stressors could make this worse • Results will need to be reassessed if other populations become viable creating a metapopulation
  15. 15. Future Directions • Data to come on other life stages of the Dusky Gopher Frog- larvae, metamorphs • Wood frog model- comparing exposure in different life stages- WDA Thurs. – Even this common species can go extinct • Add a transmission component and using meta-population models
  16. 16. Acknowledgements • Help with Gopher Frog trials: Becky Hardman, Dr. Becky Wilkes, Dr. Debra Miller • Funding:

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