Assessment of the status of threatened herpetofauna following fire in sub alpine habitat at Lake Mountain and Mount Bullfight, near Marysville, north-east Victoria



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3.3 Amphibian Chytrid Fungus


One hundred and fifty-seven swabs were collected from Lake Mountain, consisting of 156 swabs from Common Froglets and one swab from a Litoria ewingii-complex frog. Forty-seven swabs were collected from frogs at Mount Bullfight NCR; 17 of these were from Common Froglets,
30 from Alpine Tree Frogs.

Fungal prevalence at Lake Mountain was high, with seven of eight sites returning positive readings for the fungus (Table 3). Site L13, which returned an equivocal result, had only one swab tested. Equivocal results represent either one or two of the three test assays returning a positive result. This could be evidence of contamination of the sample or may represent a very low number of fungal spores in the sample (Hyatt et al. 2007). Equivocal swabs are considered neither negative nor positive for the fungus. The Southern Brown Tree Frog captured at site L1 tested negative for the fungus.

At Mount Bullfight NCR, 42 of the 45 swabs (93%) returned negative results for the fungus (Table 3). The remaining three swabs returned equivocal results.

Table 3. Results from tests for the Amphibian Chytrid Fungus at Lake Mountain and Mount Bullfight Nature Conservation Reserve.



Site

Location

Total swabs

Positive

Negative

Equivocal

Lake Mountain
















L1

Echo Flat

1

0

1

0

L4

Echo Flat

70

24

19

27

L5

Echo Flat

5

5

0

0

L6

Echo Flat

10

9

0

1

L7

Jubilee Track

27

25

1

1

L9

Royston

20

19

0

1

L10

Royston

19

15

0

4

L12

Echo Flat

4

4

0

0

L13

Home Trail

1

0

0

1




Subtotal

157

101

21

35

Mount Bullfight NCR
















B2

Lower main bog

45

0

42

3

UB5

Upper Bullfight bog 5

2

0

2

0




Subtotal

47

0

44

3



3.4 Comparison of 2010/2011 Amphibian Chytrid Fungus results to the 2009/2010 results

3.4.1 Lake Mountain Amphibian Chytrid Fungus results


Although swabs were taken from fewer sites at Lake Mountain this season, more frogs were swabbed in total, with an additional 120 animals tested (Table 4). The focus this year was on swabbing a larger number of frogs from fewer sites, instead of fewer frogs from a greater number of sites, to increase confidence in the results. In 2009/2010, 12 sites were tested for the fungus, and 11 sites had five or fewer swabs obtained. This year, nine sites were tested for the fungus and four sites had five swabs or less tested, with an average of 17 swabs tested.

A high prevalence of Amphibian Chytrid Fungus was detected this year at Lake Mountain, with seven of the nine sites returning positive results. Only three sites (L3, L8 and L13) have not returned positive readings for the fungus over the two seasons sampled. This is due to the low numbers of swabs obtained at these sites. Due to the prevalence of the fungus throughout the plateau, it is unlikely that these sites are fungus-free.



Table 4. Comparison of Amphibian Chytrid Fungus results from the 2009/2010 and 2010/2011 survey seasons at Lake Mountain.

Site

Location

2009/2010

2010/2011

Total swabs

No. of positives

Chytrid detected

Total swabs

No. of positives

Chytrid detected

L1

Echo Flat

4

3

Detected

1

0

Not detected

L2

Echo Flat

7

6

Detected

NA

NA

Not tested

L3

Echo Flat

4

0

Not detected

NA

NA

Not tested

L4

Echo Flat

5

5

Detected

70

24

Detected

L5

Echo Flat

1

1

Detected

5

5

Detected

L6

Echo Flat

NA

NA

Not tested

10

9

Detected

L7

Jubilee Trk

2

0

Not detected

28

26

Detected

L8

Jubilee Trk

1

0

Not detected

NA

NA

Not tested

L9

Royston

3

0

Not detected

20

19

Detected

L10

Royston

2

0

Not detected

19

15

Detected

L11

Echo Flat

2

1

Detected

NA

NA

Not tested

L12

Echo Flat

5

2

Detected

4

4

Detected

L13

Home Trail

2

0

Not detected

1

0

Not detected




Total

38

18




158

102




3.3.2 Mount Bullfight NCR Amphibian Chytrid Fungus results


At Mount Bullfight NCR, the collection of swabs for diagnostic testing focused on the main lower bog (site B2) in order to increase certainty of the status of the fungus at this location. A total of 45 swabs were collected this season, an increase of 32 from the 2009/2010 season (Table 5). Similar to the previous year, all swabs from 2010/2011 returned a negative or equivocal result, suggesting that the site is likely to still be free of the fungus.

Table 5. Comparison of the Amphibian Chytrid Fungus results from the 2009/2010 and 2010/2011 survey seasons at Mount Bullfight NCR.









2009/2010

2010/2011

Site

Location

Total swabs

No. of positives

Chytrid detected

Total swabs

No. of positives

Chytrid detected

B1

Small pool near main lower bog

1

0

Not detected

0

0

Not tested

B2

Main lower bog

13

0

Not detected

45

0

Not detected

B5

Road side drain

5

0

Not detected

0

0

Not tested

UB5

Upper bog 5

0

0

Not tested

2

0

Not detected




Total

19

0




47

0





3.3.3 Analysis of the likely prevalence of the Amphibian Chytrid Fungus at Mount Bullfight NCR and Lake Mountain


Based on the diagnostic tests conducted on swabs collected during the 2010/2011 field season, the most likely disease prevalence at Mt Bullfight NCR is 0, with 95% confidence interval (0, 0.084). At Lake Mountain, the most likely disease prevalence is 0.829, with 95% confidence interval (0.751, 0.891) (Figure 19). A binomial test led to rejection of the null hypothesis of equal chytrid prevalence between the two populations (p < 0.0001).

Figure 19. Likely prevalence of Amphibian Chytrid Fungus at Mount Bullfight Nature Conservation Reserve and Lake Mountain, based on diagnostic testing of swabs collected during 2010/2011.

4 Discussion

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