Parasitic
associations of a threatened Sri Lankan rainforest rodent, Mus mayori pococki (Rodentia: Muridae)
Pamoda B. Ratnaweera1,
Mayuri R. Wijesinghe2 & Preethi V.
Udagama-Randeniya3
1,2,3 Department
of Zoology, University of Colombo, Cumaratunga Munidasa Mawatha, Colombo 03,
Sri Lanka.
1(Current affiliation: Science and
Technology Degree Programme, Uva Wellassa University, Badulla, Sri Lanka)
Email: 1 pamoda_b2@yahoo.com; 2 mayrui@zoology.cmb.ac.lk;3 dappvr@yahoo.com (corresponding author)
Date
of publication (online): 26 June 2010
Date
of publication (print): 26 June 2010
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor:Anjum N. Rizvi
Manuscript
details:
Ms # o2194
Received 04 May 2009
Final revised received 28 May 2010
Finally accepted 29 May 2010
Citation: Ratnaweera,
P.B. M.R. Wijesinghe & P.V. Udagama-Randeniya(2010). Parasitic associations of a
threatened Sri Lankan rainforest rodent, Mus mayori pococki (Rodentia: Muridae). Journal of Threatened Taxa2(6): 901-907.
Copyright: ©Pamoda B. Ratnaweera, Mayuri R. Wijesinghe &
Preethi V. Udagama-Randeniya 2010. Creative Commons Attribution 3.0
Unported License. JoTT allows unrestricted use of this article in any medium
for non-profit purposes, reproduction and distribution by providing adequate
credit to the authors and the source of publication.
Author Details: Pamoda B. Ratnaweera, as
a Zoology major student carried out this study as an off shoot of her final
year undergraduate research project at the University of Colombo, Sri Lanka under the guidance of Drs.
Wijesinghe and Udagama
Randeniya. Pamoda has several
research communications presented at national and international forums.
Dr. Mayuri R. Wijesingheis a Senior Lecturer at the Department of Zoology, University of Colombo. Her field of interest is conservation
biology. Her research focuses on the ecology and behaviour of small mammals
(including population dynamics, feeding, space utilization) and amphibians, two
important components of Sri Lanka’s biodiversity and endemism.
Dr. Preethi V. Udagama-Randeniyais a Professor at the Department of Zoology, University of Colombo. Although
she is an Immuno-parasitologist, she has recorded parasites of Sri Lankan
murids, bats, elephants, poultry, pigs, reptiles, amphibians, bovids and
aquarium fishes. She is the recipient of several local research awards.
Author
Contribution: PBR
carried out the field work
(captured animals and collected ectoparasites and faecal matter),
preserved, prepared and
microscopically examined parasite specimens, and prepared the manuscript. MRW
guided the field study, obtained funds for the project and helped with the
writing of the paper. PVU-R guided the identification of the ecto and
intestinal parasites as well as the writing up of the manuscript, corresponded
with international experts to
authenticate the identity of parasites and is the corresponding author.
Acknowledgements:The following institutions are
gratefully acknowledged: the National Science Foundation, Sri Lanka (grant
number: RG/ 2004/ B2) and the University of Colombo for funding this project;
the Forest Department and the Department of Wildlife Conservation for granting
permission to carry out studies on small mammals in the forest reserves of Sri
Lanka. The help of Dr. Mark Harvey, Senior Curator and Head, Department of
Terrestrial Zoology, Western Australian Museum in the identification of the
pseudoscorpion genus is also acknowledged.
Abstract: Parasitic
investigations of the subspecies Mus
mayori pococki were carried out in four rainforests that
included two man and biosphere reserves and two forest reserves of Sri Lanka
from October 2006 to August 2007. Rodents were live-trapped using Shermans
traps. Of the 117 individuals of M.
m. pococki captured 73% were infested with four types of
ectoparasites mites of the genus Echinolaelaps,
a louse Polyplax serrata,
a larval stage of hard tick Ixodesand pseudoscorpions of the genus Megachernes.
Mites were the most abundant ectoparasite of this rodent host. Faecal
examination revealed the presence of a nematode larva of the Order Strongylida
and five types of parasitic ova; three nematode ova types i.e. strongyle, strongyloides,
ascarid types, and cestode and mite ova. In comparison to the non-infested
hosts, those infested did not show a significant difference in body weight and
size. Both sexes had an equal probability of being exposed to ectoparasites.
The present study on the parasitic investigations of M. m. pococki reports
four new host-ectoparasite and six new endoparasitic records for the Sri Lankan
rodent host.
Keywords: Ectoparasites,
intestinal parasites, Mus
mayori pococki, rainforests, Sri Lanka.
For Image & Tables – click here
INTRODUCTION
Wild
animals harbour parasites that in addition to having direct deleterious effects
on their hosts also transmit pathogens (Bechara et al. 1998; Pietzsch et al.
2005). Both parasites and
pathogens affect host physiology, often leading to disease conditions that
could result in host mortality (Bolen & Robinson 1999). Parasitic
infections may also increase vulnerability to predation through alteration of
host behaviour (Mech 1966; Moore 1983). Thus, parasitic infections can directly and indirectly lead to
disruptions in ecological relationships within communities and contribute to
population decline of endangered species (Durrer & Schmid-Hempel 1995;
Krasnov et al. 2005). It follows
that research and knowledge of wildlife diseases are important for wildlife
conservation and management (Bolen & Robinson 1999).
Ecologically,
murids have a significant beneficial impact on the environment as seed
predators and dispersers, as insectivores and as important prey species of
reptiles, birds and mammals (Kern 1981). In the face of rapid deforestation, they face threats of extinction due
to habitat loss. Mus mayori is an
endemic rodent restricted to the southwestern rainforests of Sri Lanka. It
belongs to the subgenus Coelomysand is represented by two subspecies: M. mayori mayori confined to the montane zone
and M. mayori pocockithe low country wet zone (Phillips 1980). M. mayorihas been currently listed as a Vulnerable species (Goonatilake et al.
2008). Parasitic associations of M. mayori have been
poorly investigated. Previous
records of Turk (1950), Phillips (1980) and Crusz (1984) reported the presence
of only two ectoparasites, a mite, Laelaps
atypicus and a flea, Stivalius phoberus, and two intestinal
parasites, a digenean trematode, Brachylaemus
advena and a cestode of the genus Hymenolepis, associated with this rodent
species.
The
objective of this study was to extensively investigate the parasites of M. mayori. The present study reports ectoparasites
and intestinal parasites of M.
m. pococki mainly from two man and biosphere reserves,
Kanneliya and Sinharaja, and two other forest reserves, Yagirala and Walankanda
in the wet zone of Sri Lanka. Concurrently, the incidence of ectoparasite infestations, sex ratios of
infected and non infected individuals, and the effect of body dimensions on
parasitic infestations are also discussed. Such studies may also provide baseline data on parasitic
associations of threatened endemic rodents that would be useful in conserving
this species in the wild.
MATERIALS AND METHODS
Study sites
The
four sites selected for the present study are located in the southwest wet zone
of Sri Lanka and constitute the typical wet evergreen forest type (de Rosayro
1959). The two forests Kanneliya
and Sinharaja which were surveyed extensively are two of the largest and
relatively undisturbed rainforests remaining in the island. The other two forests Yagirala and
Walankanda were sparsely surveyed. Although similar in vegetation, these two forests are much smaller in
extent and are relatively disturbed ecosystems.
The
Kanneliya Forest Reserve (6009’-6018’N & 80019’-80027’E)
is an integral component of a forest complex located in the southwest low
country of Sri Lanka. The average
annual rainfall exceeds 4000mm, which is mainly from the southwest monsoon. The relatively drier periods are from
January to March and the mean monthly temperature is around 270C. Kanneliya, which has an area of 6143 ha
and an elevation of about 300m, is ranked among the most important natural
forests in the Southern Province for the protection of head waters of river
systems (IUCN & Forest Department 1996). Based on the rich faunal and floral diversity the country’s
rainforests are considered as a biodiversity hotspot (Myers et al. 2000). Its
protection was strengthened after this forest was declared a Man and Biosphere
Reserve in 2004 (UNESCO 2008).
The
Sinharaja forest is also located in the wet zone in South-West Sri Lanka (6021’-6026’N
& 80021’-80034’E). This forest covers an area of 11000ha and has an elevation
of about 640m. The annual rainfall
ranges from 3750-5000 mm and the mean monthly temperature ranges from 18-270C. Much of the
precipitation comes during the periods of the southwest monsoon and the
northeast monsoon. It is of
special interest as it represents a biome that dates back in its evolutionary
history to Gondwanaland and is rich in biodiversity and endemism. The forest was designated a Biosphere
Reserve under UNESCO’s Global Network of Biosphere Reserves. Subsequently, UNESCO declared it a
Natural World Heritage Site (Wijesinghe & Brooke 2005).
The
Yagirala (6021’-6026’N & 80006’-80011’E)
Forest Reserve is a rainforest patch much smaller in size covering an area of
about 2000ha. The forest has an elevation of about 134m and receives a
rainfall of 4000mm per year. The
temperature ranges from 27-28.5 0C. The forest is exposed to human
disturbance as its located in close proximity to the main road and human
settlements. The Walankanda Forest
Reserve (6029’N & 80028’E) is a very small patch of
rainforest with an area of about 940ha and an elevation of about 560m. Unlike Kanneliya and Sinharaja, both
these forests are exposed to human disturbance.
Host
M. m. pocockiis a medium-sized mouse with a body length (snout end to anus) of around
90mm. Its tail is slender, scaly
and about the same length as the head and body. Feet are comparatively large; ears are moderately large,
rounded and naked. The general
colour of the upper part of the body is fulvous brown. This species is easily recognized by
its flattened spiny fur of the dorsal area and the pure white under parts
(Phillips 1980).
Trapping procedure
The
live trapping survey of M.
m. pococki was conducted in Kanneliya from October 2006 to
February 2007, and from June to August 2007 in Sinharaja, Yagirala, and
Walankanda forests. Animals were
captured using Shermans traps, baited with mildly roasted coconut kernel. Traps were laid in the evening and
checked the next morning. The
captured animals were removed into handling bags, weighed, measured sexed and
released after the parasitic survey.
A
total of 117 individuals of M.
m. pococki captured from the four different forest reserves
(Kanneliya [N = 99], Sinharaja [N = 11], Yagirala [N = 4] and Walankanda [N =
3]) were screened for ectoparasites. Faecal samples of 12 animals from Kanneliya and three from Walankanda
were examined for intestinal parasites.
Ectoparasites
Body, paws and ears of each
captured individual of M. m.
pococki were examined for the presence of Ectoparasites
(Whitaker 1988). Fur was combed
with a fine brush to collect the ectoparasites. The parasites were picked using fine forceps, fixed in 70%
alcohol, and mounted using a modification of the procedures described by
Whitaker (1988). Mounted specimens
were observed under light microscopy (Nikon, Japan). Parasite load were categorized and ranked as (i) Low if less
than five were detected after a fine search, (ii) Moderate if 5-15 parasites
were observed when combing the fur, (iii) High if more than 15 parasites were
observed during combing.
Ectoparasites were provisionally
identified based on several descriptions and available keys. Keys by Strandtmann & Mitchell
(1963) were used for the identification of the mite, which was confirmed by Dr.
Ashley Dowling, Emeritus Professor of Biology, University of Kentucky,
USA. Identification of the louse
(Ignoffo 1959) was authenticated by Dr. Lance Durden, Assistant Professor of
Biology, University of Southern Georgia, USA. Ticks were identified using available keys (Seneviratna
1965). Pseudoscorpions were
identified by Dr. Mark Harvey, Senior Curator and Head, Department of
Terrestrial Zoology, Western Australian Museum, Australia.
Incidence of parasitized hosts i.e. the percentage of
hosts infected with ectoparasites (Gannon & Willing 1995) was also
determined.
Intestinal
parasites
To examine intestinal parasites,
fresh faecal samples collected from handling bags and those ejected while
handling animals were collected into glass vials containing 10% formalin. A thin faecal smear was prepared on a
drop of saline and iodine separately and was observed under light microscopy
(Kilingenberg 1993). The prepared
smears were screened for parasitic ova and larvae, which were identified using
the WHO (1994) Bench Aids.
Statistical analysis
EpiInfo
Version 6 (USA & World Health Organization, Switzerland) computer software
package was used for analysis of data. Chi squared test was used to compare the incidence of parasitized hosts
in different forest reserves as well as to compare the gender of hosts with ectoparasite
infestations. To investigate the
effects of parasites on the weight reduction and size retardation of infested
hosts, a pairwise t-test was performed using mean body lengths and weights of
infected and non-infected individuals in each forest. The p value was set at 0.05.
RESULTS
Ectoparasites
Four
types of ectoparasites were found to be associated with M. m. pococki: mites,
a louse, a larval stage of a tick and pseudoscorpions. Mites were identified to the generic level
only and found to belong to the genus Echinolaelaps. The louse species was identified as Polyplax serrata. The ticks found on M. mayori from
Kanneliya and Sinharaja were identified as larval stages of the hard tick, Ixodes. A number of pseudoscorpions were found
to belong to the genus Megachernes(Pseudoscorpiones: Chernetidae).
All
four parasites were recorded from Kanneliya. Mites and the tick were recorded from Sinharaja, while only
the mites were found from the other two forest patches. All ectoparasites encountered in this
study were first time records for M.
m. pococki in Sri Lanka.
Intestinal parasites
Examination
of faecal matter revealed the presence of three nematode egg types (Strongyle
type, Strongyloides type, Ascarid type), cestode eggs, mite eggs and a nematode
larva of order Strongylida from M.
m. pococki (Image 1). All egg types and nematode larvae were recorded from Kanneliya while the
hosts collected from Walankanda appeared to be free of intestinal
parasites. All these intestinal
parasitic associations are novel records for endemic M. m. pococki in Sri
Lanka.
Host-parasite parameters
73%
of individuals examined were infested with ectoparasites (N = 117). The incidence of parasitized hosts was
76%, 64%, 50% and 33% from Kanneliya (N = 75), Sinharaja (7), Yagirala (2) and
Walankanda (1), respectively. No
significant difference in incidence was observed collectively in the two man
and biosphere reserves compared to that of the two forest patches (χ2 = 0.07, p > 0.05).
The
mite, Echinolaelaps species, predominated the
ectoparasites where 100% incidence was observed from Kanneliya (Table 1). About four lice were found from three
individuals of hosts from Kanneliya. Two larvae of Ixodesticks were found one each from Kanneliya and Sinharaja. Approximately ten
psuedoscorpions including juveniles and adults were found predating on one
individual of M. m. pocockifrom Kanneliya. Mites were the
only ectoparasites found on M.
m. pococki from Yagirala and Walankanda, while both mites and
ticks were found on those from Sinharaja (Table 1).
Of
the infected animals captured from Kanneliya, 24% (N = 18) showed a High
infestation load, while 24% (N = 18) had a Medium load and 52% (N = 39) showed
Low infestations (Table 1). Three
infected hosts each from Sinharaja carried Low and High parasite loads while
one manifesteded Medium parasite load. Although the number of hosts captured from Yagirala and Walankanda
forest reserves was Low, those that were infested with ectoparasites carried High
parasite loads (Table 1).
Mites
were found on the dorsal and ventral parts of the body, close to the skin of M. m. pococki as well
as freely moving over the fur, while lice were firmly attached to the skin of
the dorsal surface of the animals. Ticks were found attached to the inner surface of the ear lobe, while
the pseudoscorpions were on the dorsal side of the hosts.
The
ectoparasite infestations did not significantly affect either the body weight
or the length of the hosts (Paired T-Test : Weight T = -0.94, p > 0.05; Body
length T = 0.17, p > 0.05) (Table 2). A similar proportion of males and females (50.6% males, 49.4% females)
were infected with ectoparasites (χ2 = 0.02, p > 0.05).
DISCUSSION
Information
on parasitic associations of wild rodents, particularly those inhabiting
rainforests, is scarce. In Sri
Lanka apart from three preliminary studies (Turk 1950; Phillips 1980; Crusz
1984), the last conducted approximately 25 years ago, no recent investigations
are reported on M. mayori. Crusz (1984) specified his finding to
the subspecies M. m. mayori,
and Turk (1950) and Phillips (1980) to the species M. mayori. Thus both the ectoparasites and intestinal parasites reported
in the present study form the first records for endemic threatened M. m. pococki of Sri
Lanka. Although there seems to be
no adverse effects from these parasites on M. m. pococki in Sri Lanka, it has been reported
that sucking lice are responsible for transmitting louse borne typhus in Japan
(Shinozaki et al. 2004) and may be intramurid vectors of murine typhus and
other zoonoses (Durden & Page 2008).
All
mites found during the present study are of the genus Echinolaelaps. They are common all over the world and
are also reported found from southeast Asia (Strandtmann & Mitchell
1963). This mite genus was
previously recorded from the Spiny Rat M. mayori, Common House Rat Rattus rattus kandianusand Long-tailed Tree Mouse Vandeleuriaspp. in Sri Lanka (Turk 1950). Several species of Echinolaelaps were recorded from New Guinea,
Borneo, Thailand, Vietnam and Indonesia (Strandtmann & Mitchell 1963;
Durden & Page 2008) from Rattus spp. and several other murids. Echinolaelaps is
reported to be a vector of Hepatozoonspp., the protozoan blood parasites which infect rats, and
also suspected to be a vector of murine typhus because of its abundance on the
reservoir host (Jakeman 1961).
The
two Ixodesticks found on M. m. pocockiduring the current investigation could not be further identified, as both
specimens were larval stages. Genus Ixodesis uncommon in Sri Lanka and is represented by only two species, I. petauristae,
recorded from Petaurista
philippensis lanka (The Grey Flying Squirrel) and I. ceylonensisrecorded from both R. r.
kandianus (Common House Rat) and from Herpestes lanka (Grey
or Silvery Mongoose) (Seneviratna 1965). The
ticks recorded in the present study form a new host-parasite record from Sri
Lanka. Although Ixodes ticks in Sri
Lanka have low medical and veterinary significance, Ixodes species in other countries are
responsible for transmission of Lyme disease and other zoonotic diseases
(Spielman et al. 1985; Cotte et al.2008). I. granulaus from Malaya transmit a virus
causing Russian Spring Summer Encephalitis (Seneviratna 1965). Kurtenbach et al. (1995) reported
that infestation of rodents with larval I. ricinus is an important factor in the
transmission cycle of Borrelia
burgdorferi in German woodlands. As suggested by Seneviratna (1965), it may be plausible that
this Ixodestick species was introduced to Sri Lanka from other countries through migrant
birds, as the island is a destination for a huge number of migrant bird species
from all over the world. Ixodus ticks are
known to occur in areas where there is high rainfall and dense vegetation (Gray
2001) which conforms to the two rainforests of the present study.
Eight
species of pseudoscorpions of the family Chernetidae are recorded from Sri
Lanka (Harvey 2008). The
pseudoscorpions of genus Megachernesdetected in the current study form a new record for Sri Lanka. Pseudoscorpions are known to feed on
insects and mites (Verma 2002), making it likely that the pseudoscorpions found
in the present study were preying upon the mites found on M. m. pococki. Most M. m. pocockiindividuals harboured the mite of the genus Echinolaelaps (100% incidence from all infested
hosts). Thus, it may be inferred
that the environmental conditions of the forest offers optimal conditions for
the survival of mites.
The
low species diversity and inflated densities spontaneously lead to the concept
of ‘density compensation” (MacArthur et al. 1972). Species of ectoparasites are likely to compete for
resources. In the absence of some
competitors the remaining species may respond by increased densities, or a
change in the use of space (Bengtson et al. 1986). This may be a plausible reason for a fewer number of M. m. pococki caught
from the forest patches at Yagirala and Walankanda, to harbour high parasitic
infestations. Although no disease conditions
were detected in them, it would be important to ascertain if the low abundance
of M. m. pocockiin those forests is linked to high parasite loads. Since these two forests are small and isolated forest
patches in contrast to Kanneliya and Sinharaja, it would be interesting to
examine if the higher parasite loads are a result of the greater anthropogenic
disturbances.
Pathogens
transmitted by ectoparasites cause diseases that alter the physiology and
behaviour of the host. These can
be manifested through their feeding and mobility, resulting in weight loss and
reduced growth (Jog & Watve 2005). Heavier animals are infected more significantly by parasites than
lighter ones (Waweru & Odanga 2004). However, in the present study individuals with high load of infestation
were similar in body weight and size to the non-infected individuals and both
sexes have an equal probability to be infested by ectoparasites. Only 27 % of hosts were found to
be free of ectoparasites in this study. The reason could be that the parasites
were not colonized by chance (Krasnov et al. 2006).
Helminths
are cosmopolitan and play a significant role in the morbidity and mortality of
people and animals in many parts of the world. Most prevalent are the intestinal helminths and these
infections are often diagnosed by observing ova and/or juvenile nematodes
faecal samples. Helminths also
have the potential to regulate the abundance of the host populations (Scott
& Lewis 2008). It is not
possible to identify parasite ova to the species level unless adult parasites
are observed. Such an examination
within the context of the present study will necessitate the sacrificing of
wild rodents which is not desirable for endangered populations which are
currently facing threat.
Although
the present study was only an off-shoot of an ecological investigation of
rodents, it is the first study that reveals levels of parasitic infestations in
wild rodents in Sri Lanka. It is
unfortunate that some of the parasites were not identified to the species level
because some distinguishing structures were not clear in the processed
specimens. The present survey
records high ectoparasite infestations in Kanneliya. Fewer numbers of ectoparasites from Sinharaja, Yagirala and
Walankanda may be ascribed to small numbers of host specimens
investigated. This study is
significant as it revealed parasitic associations of the wild dwelling
threatened endemic murid rodent M.
m. pococki. Small
populations that are prone to parasitic infections can easily be wiped out from
their habitats; hence parasite surveys are important for the conservation of
wildlife populations. Wild animals
harbouring parasites can also spread diseases to humans. Despite the limitations encountered,
investigations of this nature, providing information on parasitic associations
of native rodents are vital in order to assess the magnitude of the impact of
these parasites on wildlife populations as well as to ascertain the potential
health risks to humans. ‘Conservation Medicine’ conceptualizes that future disasters with
regards to parasitic infestations may be averted by integrating our knowledge
of parasites, pathogens and host physiology with that of ecology and society so
as to begin to evolve towards a more mature relationship with living nature
(Soule 2002).
This
is the first parasitic investigation conducted on wild murids, and more
importantly on a threatened endemic rodent, in rainforests in Sri Lanka. Such studies will provide baseline data that would be useful in conserving
these species in the wild.
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