Journal of Threatened Taxa | www.threatenedtaxa.org | 26
December 2019 | 11(15): 15004–15014
Amphibian abnormalities and threats in pristine ecosystems in Sri Lanka
G.K.V.P.T. Silva 1,
W.A.D. Mahaulpatha 2 & Anslem
de Silva 3
1, 2 Department of Zoology, Faculty
of Applied Sciences, University of Sri Jayewardenepura Gangodawila,
Nugegoda,
Sri Lanka.
315/1, Dolosbage
Road, Gampola (Central Province), Sri Lanka.
1 gkvpraneethsilva1@gmail.com, 2
mahaulpatha@sjp.ac.lk (corresponding author), 3 kalds@sltnet.lk
(corresponding author)
doi: https://doi.org/10.11609/jott.5394.11.15.15004-15014
Editor: Neelesh Dahanukar, Indian
Institutes of Science Education and Research (IISER), Pune, India. Date
of publication: 26 December 2019 (online & print)
Manuscript details: #5394 | Received 08 January 2019
| Final received 06 November 2019 | Finally accepted 07 December 2019
Citation: Silva, G.K.V.P.T., W.A.D. Mahaulpatha & A. de Silva (2019). Amphibian abnormalities and threats in pristine
ecosystems in Sri Lanka. Journal of Threatened Taxa 11(15): 15004–15014. https://doi.org/10.11609/jott.5394.11.15.15004-15014
Copyright: © Silva et al. 2019. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by adequate credit to the author(s)
and the source of publication.
Funding: University of Sri Jayewardenepura.
Competing interests: The authors declare no competing
interests.
Author details: G.K.V.P.T Silva is a
graduate student from the University of Sri Jayewardenepura with BSc (Special)
in Zoology and presently working as the department research assistant on
wildlife management and conservation engaged with the “Wildlife Circle”,
Department of Zoology, University of Sri Jayewardenepura. Prof. W.A.D. Mahaulpatha is a researcher and a professor
of zoology at the University of Sri Jayewardenepura. She has undertaken many
pieces of research in wildlife conservation and management including
ornithology, herpetology and mammalogy, and she has more than a hundred
publications. As result she received the Presidential Award in 2018. Anslem de Silva MSc. DSc. has
contributed approximately 425 papers. This includes about 50 books and the
latest book was “Naturalist Guide to Reptiles of Sri Lanka’ (2017) published in
the United Kingdom. He has received the Presidential Award for scientific
publication four times. He is currently working as regional chairman of the
Crocodile Specialist Group IUCN for South Asia and Iran.
Author contribution: All authors contributed equally. GKVPTS was the main researcher on this research
project, field sampling, data collection, data analysis and preparation of the
paper. WADM was the supervisor of this piece of research and provided immense
guidance and support from the initiation of the project until the completion,
with her valuable experience and knowledge. AdS
provided some important relevant literature and valuable suggestions with his
expertise in field studies, which contributed a lot to improve parts in the
methodology section and to prepare the manuscript.
Acknowledgements:
I would like to thank the
Department of Wildlife Conservation for providing me the permission to conduct
this research within and outside the Horton Plains National Park (WL/3/2/28/17)
and staff of Horton Plains National Park for the received immense support. I
would like to extend my gratitude to Prof. (Mr.) M. Lannoo, Prof. (Mrs.) R. Rajakaruna and Dr. (Mr.) K. Ukuwela for their comments and valuable suggestions. I
greatly appreciate the support that I received from all the members of wildlife
circle of the University of Sri Jayewardenepura, Department of Zoology.
Abstract: Amphibian abnormalities are caused by numerous etiologies prevailing in the environment. Since amphibians are good bio indicators of
the environment, amphibian abnormalities are popularly known as a veritable
ecological screening tool to assess ecosystem health. The present study was carried out
encompassing within and outside the Horton Plains National Park areas, from
January to November 2017. Distribution
of amphibian morphological abnormalities were assessed in and around the five
lentic water bodies through gross visual encounter. Six quadrates of 1m×2m were randomly placed
in each sampling site. Frequency and
composition of amphibian abnormalities were assessed in a total of 694
amphibians, belonging to four families and 11 species. Thereby, 4.5% and 80.87% abnormality indexes
were accounted for respectively within and outside the park, comprehended
surficial abnormalities, ectromelia and femoral projection abnormality
types. Surficial abnormalities were the
most predominant in both localities, generally occurring at the hind limb
region of pre-mature stages of Taruga eques. Two lentic water bodies were identified as
“abnormality hotspots” within and outside the Horton Plains National park;
however, a multiplicity of possible combinations of potential causes of
abnormalities were present in the environment.
Hence, finding the exact causes of amphibian abnormalities are an extremely
difficult exercise in the field.
Keywords:
Abnormality, Horton Plains National Park, morphological, Taruga
eques.
Abbreviations: DWC—Department
of Wildlife Conservation | GPS—Global Positioning System | HPNP—Horton Plains
National Park | IUCN—International Union for Conservation of Nature |
OHPNP—Outside the Horton Plains National Park | RH—Relative Humidity | T amb—Ambient temperature | Tw—Water temperature.
Introduction
“Abnormality” refers to “any
deviation from normal morphology, independent of whether its origin was
developmental or acquired after proper development” (Lunde & Johnson
2012). Both amphibian malformations and
deformities are included in amphibian abnormalities (Reeves et al. 2008). Amphibian abnormalities can be classified
mainly as surficial abnormalities (infectious diseases/cysts and wounds),
skeletal abnormalities and eye abnormalities (Linder 2003; Reeves et al.
2008). Amphibian abnormalities have
interconnected with many factors including, chemical contaminants (Bridges et
al. 2004; Lunde & Johnson 2012), trematode, cestode, and nematode parasites
(Ankley et al. 2004; Imasuen
& Ozemoka 2012), predators (Johnson et al. 2006;
Johnson & Bowerman 2010) and UV (Ultraviolet) radiation (Blaustein & Johnson 2003; Lannoo
2008).
Anthropogenic activities have
been recognized as a main element for the modification of aquatic habitats
(Johnson & Chase 2004). Especially
nutrient loading in freshwater ecosystems (particularly ponds) directs to the
acceleration of eutrophication that result in shifting the community
composition. This results in various
amphibian abnormalities.
Helminth infections are
considered as a major governing factor for existing amphibian abnormalities and
linked with numerous factors. Most of
the trematode infections in amphibians are recorded from the habitats
associated with agriculture and cattle farms.
Trematodes in the genus Ribeiroria
occur in lentic aquatic water bodies (Johnson et al. 2004). Aquatic snails in lentic aquatic water bodies
serve as intermediate host for Ribeiroria
parasite. When high nutrient levels are
present the snail densities increase exponentially. Free swimming cercariae emerge from infected
snails then penetrate and encyst as metacercariae in
the second intermediate host (Jayawardena et al. 2010b) often around the
developing limb buds of amphibian larvae, leading to improper limb development
(Blaustein & Johnson 2003). In addition to that frequent exposure of amphibians
to chemical contaminants accumulated in lentic water bodies leads to a
reduction of immunity strength. As a
result of that amphibians become highly susceptible to parasitic infections (Kiesecker 2002; Budischak &
Belden 2009; Lunde & Johnson 2012).
Cestodes are one of the major parasite groups which infect the
amphibians. Cestodes commonly occur
within the musculature of the body and in the hind limbs of adult and juvenile
frogs (Gillilland & Muzzall
2002) and a number of metacercariae of helminthes has been recorded in the leg musculature of
deformed amphibians (Gillilland & Muzzall 1999).
There is a considerable effect
on anuran abnormalities from predators existing in natural environments
(Johnson & Bowerman 2010). Most of
these amphibian abnormalities are caused by aquatic predators such as dragonfly
larvae (Bowerman & Johnson 2010; Johnson & Bowerman 2010), small
fishes, crabs, crayfishes (Johnson et al. 2001a, 2006), diving beetles,
predatory odonate nymphs and water scorpions (Ballengee & Sessions 2009). Smaller aquatic predators (insect larvae,
small fishes) attack the exposed portions of larval and metamorphosis stages of
anurans such as the tail or limbs (Bowerman & Johnson 2010). A traumatic loss of an entire limb (Lannoo 2008), however, and wounds of amphibians can be seen
after the metamorphosis which are produced by the attack of large vertebrate
predators (Bowerman & Johnson 2010).
Leech attack causes some of the
abnormalities of amphibians and many abnormality studies have proved that leech
attacks cause a high prevalence of missing limbs (ectromelia) or parts of the
limbs (Johnson et al. 2001a, 2002, 2006; Ballengee
& Sessions 2009; Bowerman & Johnson 2010).
Considering worldwide
abnormality studies it can be seen that most of them have been carried out as
laboratory studies, related with chemical inductions (Burkhart et al. 1998; Lajmanovich et al. 2003) and parasitic inductions (Johnson
et al. 2001a; Stopper et al. 2002) to frog embryos and tadpoles in various limb
bud stages. Only a few studies, however,
have been conducted to investigate abnormalities of amphibians in the field
(Johnson et al. 2001b; Peltzer et al.
2011). As regards the fact that Sri
Lanka is a biodiversity hotspot, only four studies have been mentioned (Rajakaruna & Samarawickrama
2007; de Silva 2009, 2011; Meegaskumbura et al.
2011). Though, abnormality surveys were
based on selected regions of the country, it’s more valuable to extract data
from pristine ecosystems with the purpose of identifying the actual threats of
amphibian’s survival. Therefore, the
present research was undertaken to assess the amphibian abnormalities and their
possible predators which cause amphibian abnormalities encircling the area in
and around the lentic water bodies within and outside the World Heritage Horton
Plains National Park as a comparison of threats and abnormality types possessed
by amphibians against two different localities to ultimately fulfill the knowledge gap of field studies pertinent to
amphibian abnormalities.
Materials and Methods
a) Study
site
The study was conducted within
and outside the Horton Plains National Park (HPNP) from January to November
2017. HPNP is located between 6.802
northern latitudes and 80.807 eastern longitudes (Green 1990) which occupies an
area of 3,160ha and is contiguous with the Peak Wilderness Sanctuary to the
west. It is in the eastern extremity of
the Nuwara Eliya District in Sri Lanka within the
range of 2,100-2,300 m elevation (DWC 2007). Tropical montane cloud forests and
wet pathana grasslands are the two distinct habitats
in the park (Gunatilleke & Gunatilleke
1990) with a narrow ecotone belt of shrubs and herbs between the two.
Most of the lentic water bodies
are surrounded by three main grass types (Chrysopogon
nodulibarbis, Andropogon polyptychos, and Garnotia
exaristata) and one bamboo species (Arundinaria densifolia)
in the grassland habitat (DWC 2007). The
sampling was conducted in selected five lentic water bodies on four days per
month, providing equal effort to each sampling site. Three lentic water bodies (A, B and C) were
selected within the HPNP and two (D and E) were selected outside the HPNP based
on the availability of amphibians (Figure 1A).
Sampling sites, outside the HPNP were located within a range of 1,170.9–1,864.7
m elevation and mainly associated with forested area. GPS (Global positioning system) points of
these sampling sites were recorded using Garmin etrex
Euro hand held GPS receiver.
Six quadrates each 1 x 2 m were
placed within each sampling site for the sampling of amphibians. Three quadrates were randomly placed in the
area 1m from the pond bank outside the pond and three quadrates were randomly
placed inside the pond in the area of 1m from the pond bank (Faruk et al.
2013). Anuran species (larvae, metamorphs, juveniles, and adults) and leeches in these
quadrates were surveyed from morning to after noon (08.00–16.00 h) and during
the night (18.00–20.00 h). Moreover,
vegetation within each plot was searched even when slight movement was detected. Head lamps and torches were used for
nocturnal searches. Larval amphibians
were captured using active sweeps (Dodd 2010), metamorphic anurans were
captured with a dip net or by hand (Ouellet et al. 1997) and adult amphibians
were captured with a dip net or by hand (Wheeler & Whelsh
2008; Urbina & Jenny 2009). A small
amount of water was added to the container to prevent overheating and
desiccation (Wheeler & Whelsh 2008). Overcrowding based on the container size and Tamb was avoided (Lunde & Johnson 2012). At the end of the survey they were released
back to their habitat after removing the ectoparasites from the attached skin
surface of the amphibians. Amphibian
species and their stages were identified using the amphibian guides of Dutta
& Manamendra-Arachchi (1996), Manamendra-Arachchi
& Pethiyagoda (2006), and de Silva (2007). When an amphibian was captured, (a) it was
identified to species level, (b) life stage noted, (c) presence or absence of
the abnormalities assessed (in larvae, metamorphs, juvenile
and adult stages) (If abnormalities were present, they were recorded with the
count, according to the abnormality classifications of guides) and recorded.
b) Identification of amphibian
abnormalities
Amphibian
physical abnormalities (assessed the abnormalities which appeared externally)
were associated with the loss of body parts or organs. External abnormalities were identified
through gross visual inspections (both dorsal and ventral sides of the amphibian
body) and classified based on Meteyer (2000), Johnson
et al. (2001b), Johnson et al. (2002), Lannoo (2008),
Rajakaruna et al. (2008), Reeves et al. (2008),
Johnson & Hartson (2009), and Peltzer
et al. (2011) guides. Surficial
abnormalities (cysts) were identified by careful examination of the external
body surface (dorsal side, ventral side, around the fore limbs and hind limbs)
and using the external morphological features of the infection. Cysts of infected amphibians are found as
clear or brownish colour (Johnson et al. 2004), round, swelling nodules of the
musculature (Ostler 2004). Moreover,
Johnson et al. (2004), Ostler (2004), de Silva (2007, 2009), and Jayawardena et
al. (2010a, b) were referred to for the identification of cysts. Based on the number of cysts (surficial),
severity of amphibian infections were classified as mild and moderate. Mild infectious amphibians possess 1–3
nodules and moderate infectious amphibians possess 4–6 nodules (de Silva 2009).
c)
Identification and sampling of possible predators of amphibians
Leeches were identified by
careful examination of the external body surface of the anuran larvae, metamorphs, juveniles, adults and also the grasses and
shrubs which were adjacent to the bank of the water body. Possible aquatic invertebrate predators of
the amphibian life stages (larvae, metamorphs,
juveniles and adult) were sampled by using the 0.36 × 0.22 m dip net,
performing 2m sweeps at 11 evenly spaced points around each pond’s perimeter
(Bowerman & Johnson 2010). Captured
aquatic predatory varieties were identified, counted, recorded and released to
the same lentic water body. Amphibian
invertebrate predators in the ponds were classified as either abundant (<100
individuals trap per day) or rare (<10 individuals trap per day) based on
density capture per day according to Bowerman & Johnson (2010). Possible large vertebrate predators (aquatic
birds) of amphibians were assessed based on observations in and around the
lentic water bodies.
Aquatic invertebrate predators
of amphibians were identified based on the morphological characteristics
(nature of the abdomen, presence of exoskeleton and arrangement of gills) with
the help of Curtis (2011) and Quek et al. (2014). Possible large vertebrate predators (aquatic
birds) of amphibians were identified (colouration of feathers and beak
and foot type) using Harrison (2011), a bird guide. All types of abnormalities, aquatic
invertebrates and large vertebrate predators as possible threats of amphibians
(which cause amphibian abnormalities) were photographed using a digital camera.
d)
Determination of the environmental variables
Environmental variables of
lentic water bodies were measured to find out the habitat suitability for
amphibians (Hamer & Lane 2002; Urbina & Jenny 2009; Dodd 2010; Sparling
2010). The atmospheric data temperature
(ºC) and relative humidity (RH) were assessed.
Ambient temperature (Tamb) was recorded 2m
above the water surface / ground (using Kestrel 4000 weather meter, USA) and
relative humidity (RH) data were recorded 2m above the ground. In addition to that soil pH values were
obtained using Kelwey soil tester, under the soil
chemical data. Furthermore, dissolved
oxygen (DO) (YSΙ 550A Dissolved Oxygen Instrument), water temperature (Tw), pH
(YSΙ Eco Sense pH 100A meter), and conductivity (YSΙ Eco Sense EC300A
Conductivity meter) were measured using analysis of water physiochemical
data. Soil chemical data and water
physiochemical data were recorded once a month in each plot (as mentioned
above) using a standardized data sheet.
e) Data analysis
The Minitab version 17.0
statistical software was used to calculate the mean and standard deviation (SD)
values of environmental variables and possible predators of amphibians in each
sampling site. Graphical representations
were created using Microsoft Excel 2013 software. Abnormality index (AI) was calculated using
the equation,
AI = (Total number of abnormal amphibians /
Total number of amphibians inspected) × 100%
Results
a) Abundance
of amphibian species
A total of 694 amphibians
belonging to four families and 11 species were recorded during the study in the
five lentic water bodies studied.
Five-hundred-and-eleven individuals were examined inside the HPNP and
183 individuals were examined outside the HPNP (Table 1).
b) Amphibian
abnormalities
Out of the 511 amphibians
examined inside the HPNP, only 23 (4.50%) had abnormalities; however, 80.87% of
amphibians outside the HPNP, possessed abnormalities. Taruga
eques had the most number of abnormalities in both localities—22 inside the
HPNP and 147 outside the HPNP. This was
99.30% of AI outside the HPNP and 95.70% of AI inside the HPNP with respect to
T. eques. Surficial abnormalities
(Image 1) were more dominant than ectromelia and femoral projection abnormality
types in both localities, thereby mild infections (60.00%) (Image 1A and 2B)
and moderate infections (77.55%) (Image 1C) were predominant
respectively within and outside the HPNP (Figure 2A). Cysts were recorded only in T. eques,
accounted for 5.76% within the HPNP and 100.00% outside the HPNP (Figure
2B). Ectromelia was recorded in both T.
eques (Image 2A) (0.58%) and M. greenii
(Image 2B) (0.74%) species. Femoral
projection was found only in F. cf. limnocharis
(Image 2C) which accounted for 5.56% frequency of the
abnormalities. Comparing the abnormality
index with amphibian life stages (Figure 2C), no abnormal larvae were found in
both localities. Abnormal metamorphs were found only inside the HPNP which
accounted for 4.35% of the abnormalities.
A high AI, however, was observed in the juvenile stage than in adults in
both localities—56.52% and 77.70% within and outside the HPNP. Moreover, most of the abnormalities were
found at the hind limb region of amphibians (Figure 2D). When comparing the AI of amphibians in each
sampling site, no abnormal amphibians were recorded in pond C. Amphibians with ectromelia were only recorded
within the HPNP in sampling site B; however, 1.16%, 14.39%, 100%, and 2.78%
abnormality percentages were recorded in A, B, D, and E ponds, respectively
(Table 2). With reference to national
conservation states (determined by IUCN), 94.71% of the amphibians found in the
HPNP were endangered, thereby 4.55% had abnormalities, whereas in contrast 100%
of the amphibians were abnormal outside the HPNP.
c) Comparison of amphibian
predatory density in each sampling site
Damselfly larvae Elattoneura leucostigma
were the most abundant possible predatory type of the amphibians. Damselfly larvae (Image 3A) were recorded in
A, B and C sampling sites within the HPNP.
Water scorpions (Image 3C), dragonfly larvae Orthetrum
glaucum (Image 3B), Pond Herons Ardeola grayii
(Image 3E) were recorded only in pond A.
Leeches (Image 3D) were recorded in A and B sampling sites. Crabs Perbrinckia
glabra (Image 3D) were only found in sampling
site C. No possible predators of
amphibians were recorded in pond E.
Aquatic beetles were only recorded in pond D (Table 3).
d)
Environmental variables of sampling sites
Highest conductivity was
recorded in sampling site E. It may due
to the fact that the water was contaminated with agro-chemicals. Moreover, D lentic water body recorded the
least water pH value which indicates acidic conditions and that more
anthropogenic stressors are present in the water body (Table 4).
Discussion
Both amphibian malformations and
deformities are included in amphibian abnormalities (Reeves et al. 2008). Some of the abnormalities are external
physical abnormalities and others are internal (Blaustein
& Johnson 2003; Spolyarich et al. 2011). The present study did not find any
abnormalities in the family Bufonidae coinciding with
the studies of Lannoo (2008) who observed that the Bufonidae family is less susceptible to abnormalities.
Previous studies have indicated
that less than 5% abnormality prevalence of the population in a particular area
or site is normal (Johnson et al. 2002; Kiesecker et
al. 2004; Piha & Pekkonen
2006; Lunde & Johnson 2012). The
abnormality prevalence within the HPNP was 4.50%, which is within the accepted
range; however, abnormality prevalence outside the HPNP was 86.55% and should
be considered as abnormally high (Piha & Pekkonen 2006). Lentic body wise, pond B inside the HPNP
had 14.5% abnormality prevalence and pond D had abnormality prevalence of
100%. These high abnormality prevalent
sites were classified as ‘‘hotspots’’ with respect to abnormalities (Johnson
& Bowerman 2010). B lentic water
body was located within the pristine ecosystem of HPNP. Moreover, all the water quality parameters
were also within the standard levels for amphibian survival. Therefore, further experiments must be
carried out to find out the exact cause for abnormalities in B water body. In contrast, D lentic water body was located
on the way to HPNP and most visitors use it as a garbage dumping site (which
may be the reason for reporting less DO and soil pH values). As a result of that, this high nutrient
content of the water body provides a better environment to increase the
parasitic density. It might be the major
reason for recording 100% of surficial abnormalities in D lentic water
body. Since, observed abnormality
prevalence of B and D lentic water bodies were greater than the expected
baseline range, further investigations are warranted to find out the locality
specific causes (Lunde & Johnson 2012).
Highest number of amphibian
abnormalities were reported in pre-matured stages of amphibians which may for
the reason that either adult populations of amphibians are less susceptible for
abnormalities against different environmental stressors or they have reduced
survivorship. The survival of abnormal
amphibians declines due to a high predation pressure and inability to capture
its prey (Lunde & Johnson 2012).
Since abnormal adult amphibians are unable to survive long periods of
time in the environment, frequently a smaller number of adult amphibian
populations are discovered with abnormalities (Goodman & Johnson 2011;
Lunde & Johnson, 2012). Previous
abnormality studies have also observed that most of the amphibian abnormalities
are associated with hind limbs (Ouellet et al. 1997; Johnson et al. 2002; Piha & Pekkonen 2006), which
may be resulted by the attack of natural pradators
when they try to avoid the escape of amphibians. Results of the present study also tallies
with these findings as most of the abnormalities found as cysts arise within
the musculature found in the hind limbs.
Surficial abnormalities (cysts)
were the predominant abnormality type recorded in this study. Even the HPNP comprises optimal conditions
for growth of Batrachochytrium dendrobatidis, in the most observed cysts may be caused
by parasitic helminths infected after limb bud stages of amphibians since they
were located within musculature, mostly around limb structures and were easily
visible to the naked eye as swelling round nodules; in contrast pathogenic
cysts are microscopic and confined only to the epidermis (Lunde & Johnson
2012). Lunde & Johnson (2012) also recorded
that the high number of amphibians inhabiting lentic water bodies are commonly
infected with many trematode species that form cysts under the skin within
musculature.
Amphibian abnormalities due to
trematode infections depend on the stage of limb development at which
infections occurred (Schotthoefer et al. 2003). Therefore, timing of the infection is a
critical determinant in forming abnormalities (Jayawardena et al. 2010b). Infection coincides at pre-limb bud
developmental stage of the tadpoles which results in high mortality rate with
axial abnormalities. Trematode
infections acquired at limb bud stage also produces high abnormality rate
including ectromelia (Schotthoefer et al. 2003;
Jayawardena et al. 2010b). Further more, there is no any effect to limb development
and survival of tadpoles when they are infected at the paddle stage (Schothoefer et al. 2003; Jayawardena et al. 2010b). However
after the infection at the paddle stage of amphibians, encysted parasites are
able to remain viable even at the adult stage of amphibians (Imasuen & Ozemoka 2012). This was also observed in the amphibians in
the present study. Existence of
amphibian predators in ponds generally increase the trematode infection of
amphibians (Thiemann & Wassersug 2000; Lunde
& Johnson, 2012). Trematodes
commonly occur in the lentic water bodies with dragonfly larvae (Bowerman &
Johnson 2010; Lunde & Johnson, 2012).
These two factors may have contributed to amphibian abnormalities in the
lentic water bodies that were studied.
All the amphibian abnormalities
cannot be explained away as parasitic infections. Lannoo (2008) and
Lunde & Johnson (2012) observed that high level of ectromelia are present
in frogs even when parasites are absent.
In addition to parasites, amphibian predators (vertebrates and
invertebrates) play a major role in limb abnormalities in amphibians (Bowerman
& Johnson 2010). Larval amphibians
are attacked by small predators including aquatic invertebrates; however, traumatic
loss and injuries in limbs of amphibians (after metamorphosis) are mostly caused
as a result of failed predatory attempts by large vertebrate predators
(Bowerman & Johnson 2010). Bowerman
& Johnson (2010) observed a direct relationship between the leech density
and the abnormality level in field studies and laboratory induction of
leeches. Leeches act as predators at
amphibian larval stages and act as parasites of both larval and adult stages
(Schalk & Forbes 2002; McCallum et al. 2011). Damselfly larvae was the abundant possible
predators recorded in site B and all the ectromelia were observed in the same
pond. Therefore, there is a high
possibility of these predators causing the ectromelia observed in site B.
Water quality values of all
sampling sites were included to the estimated optimum ranges (Sparling 2010)
for amphibian growth and development; however, with respect to soil pH values,
even moderate acidic condition is identical to HPNP (Chandrajith
et al. 2009), strongly acidic conditions can’t be expected within the
sampling sites outside the HPNP, which indicate that both sampling sites
outside the HPNP may have exposed to some anthropogenic activities.
Multiplicity of possible
combinations of potential causes of abnormalities are present in the
environment. Hence, finding the exact
causes of amphibian abnormalities are an extremely difficult exercise in the
field. The fact that abnormalities are
linked with ecology, epidemiology, and developmental biology further increases
the complexity of this problem.
Conclusions
Taruga eques was the most susceptible
amphibian species to abnormalities irrespective of the locality type, indicated
that amphibians may have been exposed to some stress conditions linked with
multiple factors. Present research
findings revealed that toads are less susceptible to amphibian
abnormalities. Since, B and D lentic
water bodies were discovered as abnormality hotspots, further experiments are
crucial at those particular lentic water bodies, for determining the site-specific
cause for amphibian abnormalities. The
present study clearly discloses further that Sri Lankan tree frogs are in a
critical state. Since Taruga eques is confined only to the central
hill regions of the country with declining population and all the amphibians
which belong to endangered conservation state had abnormalities outside the
HPNP, it is clear that mandating urgent measures to carryout extensive
research-based conservation work before including it to critically endangered
state is needed.
The present research data
reveals that potential predators of amphibians are provided with excellent
environmental conditions for their existence within the HPNP as a protected
area in contrast to areas outside the HPNP.
The present research, however, suggests that exigency of extensive
research-based studies for the identification of complex causes for
abnormalities in amphibians integrated with many disciplines, including
ecology, toxicology, parasitology, and developmental biology. These studies will be important not only as
ecological or evolutionary influences, but as significant implications for
conservation and contemporary concerns over widespread amphibian population
losses.
Table 1. Amphibian abundance in and around the lentic
water bodies within and outside the Horton Plains National Park.
Locality
type |
Family
& Species |
Abundance |
Abnormality
Index (%) |
HPNP |
Dicroglossidae Minervarya greenii |
135 |
0.74 |
Microhylidae Microhyla zeylanica |
11 |
00 |
|
Microhylidae Uperodon palmatus |
03 |
00 |
|
Rhacophoridae Pseudophilautus
alto Pseudophilautus frankenbergi Pseudophilautus microtypanum Taruga
eques |
02 01 12 347 |
00 00 00 6.34 |
|
OHPNP |
Bufonidae Duttaphrynus melanostictus |
06 |
00 |
Dicroglossidae Euphlyctis cyanophlyctis Minervarya kirtisinghei Fejervarya
cf. limnocharis |
04 08 18 |
00 00 5.55 |
|
|
Rhacophoridae Taruga
eques |
147 |
100 |
Table 2.
Different abnormality types and abnormality indices recorded in each
sampling site.
Locality type |
Sampling site |
Ectromelia |
Infections |
Femoral projections |
Abnormality index (%) |
HPNP |
A B C |
- 3 - |
4 16 - |
- -
- |
01.16 14.39 00.00 |
OHPNP |
D E |
- - |
147 - |
- 1 |
100.00 02.78 |
Table 3. Comparison of density of amphibian possible
predators in each sampling site number of predators trapped/observed per day.
Locality
type |
|||||
|
HPNP |
OHPNP |
|||
Predator |
A |
B |
C |
D |
E |
Aquatic
beetles |
1.89 ±0.93 |
- |
- |
- |
- |
Crustaceans |
- |
1.44±1.01 |
- |
- |
- |
Damselfly
larvae |
1 .78±1.92 |
104.33±31.89 |
1.22±1.09 |
- |
- |
Dragonfly
larvae |
11.56±6.73 |
- |
- |
- |
- |
Leeches |
01.56±2.01 |
5.44±2.74 |
|
|
|
Pond herons |
02±0.87 |
- |
- |
- |
- |
Water
scorpions |
1 .56±1.01 |
- |
- |
- |
- |
|
|
|
|
|
|
Aquatic
beetles |
- |
- |
- |
01±1.12 |
- |
Table 4.
Environmental variables in and around the lentic water bodies in each
sampling site.
Site |
Environmental
variables (Mean ± SD) |
||||||
Tamb
(˚C) |
RH |
Soil
pH |
DO (mg/L) |
Tw
(˚C) |
Water
pH |
Conductivity (µS/cm) |
|
A |
16.29 ±
0.30 |
94.11±2.57 |
5.90±0.38 |
4.67±0.19 |
15.73±0.53 |
8.14±0.68 |
18.56±5.68 |
B |
16.15±0.58 |
95.05±2.06 |
5.91±0.50 |
4.55±0.26 |
15.75±0.45 |
7.93±0.62 |
17.07±5.79 |
C |
15.88±0.32 |
94.50±2.77 |
5.88±0.45 |
4.65±0.23 |
16.01±0.66 |
8.30±0.66 |
20.95±7.13 |
D |
16.80±0.67 |
95.03±2.66 |
4.49±0.18 |
4.52±0.16 |
16.21±0.77 |
6.89±0.90 |
18.94±4.03 |
E |
15.41±0.89 |
91.95±8.14 |
5.15±0.45 |
4.66±0.19 |
16.99±0.38 |
6.95±0.93 |
25.65±4.50 |
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