Journal of
Threatened Taxa | www.threatenedtaxa.org | 26 December 2018 | 10(15):
13024–13028
A report on the possible interbreeding between Grizzled Giant Squirrel Ratufa macroura and Indian Giant Squirrel Ratufa indica from Chinnar
Wildlife Sanctuary in the southern Western Ghats, India
Kiran Thomas
1, D.K. Vinodkumar 2, Jomals Mathews John 3, M. Shaji
4 & P.O. Nameer 5
1,4,5 Centre for Wildlife Studies,
College of Forestry, Kerala Agricultural University, Thrissur
680656, Kerala, India
2 UNESCO C2C for Asia & Pacific
Region, Wildlife Institute of India, Chandrabani,
Dehradun, Uttarakhand 248001, India
3 GIS Analyst, Lincoln GIS District
Office, 105 W Texas Ave, Ruston, Louisiana, 71270 USA
1 kiranzthomas@gmail.com, 2 dkvinod@gmail.com,
3 jomalsjohn@gmail.com, 4 shaji.mohan@kau.in, 5
nameer.po@kau.in (corresponding author)
doi: https://doi.org/10.11609/jott.3995.10.15.13024-13028 | ZooBank:
urn:lsid:zoobank.org:pub:DB10328E-C069-481A-A4C3-71B2AE049517
Editor: Justus Joshua, Green Future Foundation, Trichy, India. Date
of publication: 26 December 2018 (online & print)
Manuscript details: Ms
# 3995 | Received 03 January 2018 | Final received 10 September 2018 | Finally
accepted 20 November 2018
Citation: Thomas, K., D.K. Vinodkumar, J.M. John, M. Shaji & P.O. Nameer (2018). A report on the possible interbreeding
between Grizzled Giant Squirrel Ratufa macroura and Indian Giant Squirrel Ratufa
indica from Chinnar
Wildlife Sanctuary in the southern Western Ghats, India. Journal
of Threatened Taxa 10(15): 13024–13028; https://doi.org/10.11609/jott.3995.10.15.13024-13028
Copyright: © Thomas et al. 2018. Creative Commons
Attribution 4.0 International License. JoTT
allows unrestricted use of this article in any medium, reproduction and
distribution by providing adequate credit to the authors and the source of
publication.
Funding: Kerala Agricultural University (KAU).
Competing interests: The authors declare no competing interests.
Acknowledgements: The authors would like to thank the Chief Wildlife Warden, Kerala State
Forest Department, for the study permit (WL10-947/2013). We also thank the Kerala Agricultural
University (KAU) for the financial support for the conduct of the
research. The Dean, College of Forestry,
KAU, is also thanked for the encouragement and support.
Natural hybridisation
events are recorded in many mammalian orders across the world. Schwartz (1980) reported more than 400
hybrids in mammals and many of them were fertile. Natural hybridisation
among mammals, however, is less understood than that in other vertebrates. The possible evolutionary consequences of hybridisation between sympatric species are scarcely
studied as such hybridisation was thought to be
extremely rare until recently (Ermakov et al.
2002). The role of hybridisation
and introgression in determining plant diversity was widely studied but little
information is available on the effects of these on animal diversification
(Dowling & Secor 1997).
Hybrid animal taxa are rarely
reported worldwide. Careful testing of
the reported hybrid should be done to understand its population viability. According to Dowling & Secor (1997), hybridisation leads
to instantaneous creation of several unique complexes of polyploid
and unisexual animals.
Two
species of the giant squirrels are seen in the Western Ghats, Ratufa indica and R.
macroura.
The former is more widespread in distribution (Borges 2015) while the
latter is confined only to a few sites (Joshua 1992; Babu
& Kalaimani 2014). Though the distribution of these two giant
squirrels mostly does not overlap, they do occur in close proximity at a few
places. One such place is the Palani Hills in Tamil Nadu where they occur at different
elevations (Moore & Tate 1965; Agarwal & Chakraborty 1979).
Morphology of the two species of giant
squirrels in the Western Ghats
Indian
Giant Squirrel Ratufa indica:
The Indian or the Malabar Giant Squirrel is a squirrel of varying pelages whose back is a mixture of maroon and
black with cream or buff underparts. Two subspecies occur in the Kerala part of
the Western Ghats, namely R. i. indica seen north of the Palakkad Gap and R. i. maxima (Image 1) that is seen south of the Palakkad
Gap. Ratufa
indica indica is
completely maroon on its back and ears, with a pale cream venter and pale face
and tail tip. Ratufa
indica maxima is similar to R. i. indica except for its
black saddle across its shoulders, darker maroon on its dorsal side, and uniformily black and brown tail with no pale tip (Menon 2014; Borges 2015).
Grizzled Giant Squirrel Ratufa macroura:
Also known as the Sri Lankan Giant Squirrel, this species is brownish-grey in colour. Its pale
hair tips give it a grizzled look. The
underside is dirty white and the ears, crown, and dorsal midline
are dark brown or black (Image 2).
It has three subspecies of which R. m. dandolena,
the one that occurs in the Western Ghats, is the smallest of the giant
squirrels in India. The ears are short
and brown and the tail has long pale hairs making it look greyish compared to
the tails of the other subspecies (Menon 2014). The cheeks are buff with small dark areas
corresponding to the blackish cheek patches in the other two Indian Ratufa species.
It has prominent black to grey or dark brown patches on the forehead and
shoulders. The nose is pinkish and the
ears are devoid of tufts of hair as in R. indica
(Joshua & Johnsingh 2015).
We present here two instances of
possible hybridisation between R. indica and R. macroura,
observed in 2007 and 2014 from the Anjanad Valley in
the Kerala part of the Western Ghats.
The Anjanad Valley forms part of the Anamalai Hills of the Western Ghats and is one of the three
locations in Kerala where the eastern slopes of the ghats
fall within the Kerala State. It has a
rain shadow effect, as some of the highest reaches and the broadest stretches
of the Western Ghats lie immediately to its west (Nair 1992).
Along the eastern edge of the Anjanad Valley lies the Chinnar
Wildlife Sanctuary. It is located 18km
north of Marayur in the Idukki
District of Kerala State. It is located
between 10.25–10.35 0N & 77.08–77.26 0E and has a total area of 90.44km² (Fig. 1). The Munnar-Udumalpet
Road, SH 17, passes through the sanctuary for 16km and bisects it into almost
equal portions. It is contiguous with Eravikulam National Park to its south and Indira Gandhi
Wildlife Sanctuary to its north. It
forms an integral part of the 1,187km2 block of protected forests
straddling the Kerala-Tamil Nadu border in the Anamalai
Hills.
The terrain is undulating with hills
and hillocks of varying heights. The
altitude ranges from 400m at Chinnar to 2,372m at Nandamalai. The
major peaks in the sanctuary are Varayattumalai
(1,845m), Thengamalai (1,422m), Vellakkalmalai
(1,883m), Jambumalai (1,395m), Aralipana (1,494m).
The area is drained by two perennial rivers passing
through the sanctuary, namely Chinnar and Pambar. During
the northeastern monsoon that brings the major rains in the Anjanad
Valley, a few ephemeral water sources take origin from the higher mountains and
drain the area. The entire valley
remains dry for the rest of the season.
The vegetation varies from sub-temperate
sholas on the mountains to dry scrub in the arid plains. The vegetation of the sanctuary can be
broadly classified into the following types according to Champion & Seth
(1968): southern tropical thorn forest (scrub jungle), southern dry mixed deciduous
forest (dry deciduous forest), southern moist mixed deciduous forest (moist
deciduous forest), tropical riparian fringing forest (riparian forest),
southern montane wet temperate forest (hill shola
forest), and southern montane wet grassland (grassland). The dominant vegetation is dry deciduous
forest followed by scrub forest.
Together they constitute about 50% of the total forest area, which is
located in the low altitude areas. The
riparian fringing forests are linearly distributed along the hill folds and
occupy a small area. Shola forests
occupy a tiny fraction of the total area.
First instance: On 13 May 2007, we
came across an interesting interaction between R. indica
and R. macroura near the forest office of Marayur Forest Division.
In this area, R. i.
maxima has been seen beside a dried stream in a dry deciduous forest
patch adjacent to the Chinnar WS. Interestingly, Marayur
Reserve Forest is a place where R. macroura is
only occasionally seen.
Two male R. indica
were found combating for a female R. macroura. During the course of the combat, one of the
individuals of the R. indica fell to the
ground from a height of about 5m. The
other R. indica then followed the R. macroura and was observed mounting her after a
while. This event happened on a Terminalia bellirica
tree at a height of about 10m. The
copulation lasted only for a few seconds and when separated, they stared at
each other for some time (Image 3). The R.
indica male then continued following the R. macroura, presumably for another attempt to mount. The subsequent attempts, however, were
unsuccessful as the R. macroura resisted the
attempts and chased the R. indica away. Later, both chased each other and were seen
running around for about 21/2 hours, almost non-stop
(Image 4).
Second instance: During our studies
on R. macroura at Chinnar
WS in 2013–14, we came across at least three to four different individuals with
aberrant coat colour, which appeared to be the
hybrids between R. indica and R. macroura (Images 5–7), which is about 17% of the total
population of Grizzled Giant Squirrel
(Thomas & Nameer 2018). There were five instances between August 2013
and April 2014 (Table 1) when we encountered the suspected hybrid individuals
at the sanctuary, the locations of which were mapped (Fig. 2). The general structure of the pelage colour of these hybrids was a mixture of both R. indica and R. macroura. We could, however, observe three different
pelage patterns among the hybrid individuals.
In one case, the pelage looked similar to that of R. indica, excepting the creamy white underparts
and the cheeks, which were brown to chocolate brown in colour
and the tail has chestnut tinge (Image 5).
The second type of pelage looked similar to that of R. macroura, excepting that the grizzled upper part of the
individual appeared brown to black in color (Image 6). The third type of pelage encountered was
similar to that of the darker form of R. indica
but the tail, instead of being completely black, had a pale tip (Image 7), a
character similar to that of R. i. indica.
There was a previous instance of
interbreeding between R. indica and R. macroura where seven hybrid individuals were reported
at Srivilliputhur Grizzled Giant Squirrel Sanctuary
in Tamil Nadu, southern India (Joshua 1992).
Joshua (1996) opined that the R. macroura
was pushed towards the foothills of the Ayyanarkoil
Valley in Grizzled Giant Squirrel Sanctuary, where R. indica
exists. He further noted that the
habitat shift in R. macroura was due to
habitat degradation.
Ratufa indica was historically unknown in the Chinnar
WS. The nearest known distribution of R.
indica is in the Marayur
RF, located towards the southwestern part of the Chinnar
WS. Similarly, R. macroura
was also not known from any habitat outside the riverine forests of Chinnar and Pambar rivers and
their tributaries in Kerala. Over the
last one decade or so, however, there were occasional
sightings of R. macroura from the Marayur RF. These
sightings became more frequent and regular since then. These range expansions of R. macroura to hitherto unknown sites could be due to the
disturbances in its riverine habitats at Chinnar WS
(Thomas & Nameer 2018). The expansion of the range of R. macroura into that of R. indica
enable them to interact closely, thus leading to interbreeding.
It would be interesting to know
whether these hybrids are fertile or not.
Detailed investigation on the status of the hybrid individuals, exact
reasons for hybridisation, and a study on the
genetics of the R. macroura need to be
undertaken at the Chinnar WS to find out the genetic
purity of this species. The mixup and hybridisation between R.
macroura and R. indica
should be monitored to find out its effect on the long-term survival of the R.
macroura, which has a restricted distribution and
a Near Threatened species (Joshua et al. 2008).
The interbreeding could be a challenge to the long-term conservation of R.
macroura at Chinnar
WS. At this juncture, it is noteworthy
to recall the local extinction of the native Red Squirrel Sciurus
vulgaris by the introduced Grey Squirrel Sciurus
carolinensis in southern and northern
England (Lloyd 1983; Reynolds 1985).
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Table 1. The details on the encounter of the suspected hybrids
of Ratufa indica and
R. macroura at Chinnar
Wildlife Sanctuary in the southern Western Ghats
|
Date of
observation |
Location |
1 |
10.viii.2013 |
Chinnar checkpost |
2 |
9.xi.2013 |
Churulipetti |
3 |
23.i.2014 |
Along the stretch of Chinnar to Churulipetti streams |
4 |
14.iii.2014 |
Koottar |
5 |
1.iv.2014 |
Churulipetti |
6 |
13.v.2007 |
Near the District Forest Office of
Marayur Forest Department |