Local adaptations to wet climate has contributed to phenotypic variation in

Giant Squirrel of South Asia

Kajanka Mathiaparanam, Madhushika Silva, Ruwansha Galagedara & Sampath Seneviratne

Department of Zoology, Faculty of Science, University of Colombo, Colombo 03, Sri Lanka

Local Adaptations

OrganismSelective

Pressures of the Environment

Mal-adaptive Genes

Adaptive Genes

Shape up Phenotype and Genotype

Local Adaptations

Speciation

Physical BarrierStop Gene Flow

Divergence Speciation

3 Sub Species of Grizzled Giant Squirrel

• Ratufa macroura dandolena

• Ratufa macroura macroura

• Ratufa macroura melanochra

Local Adaptations or Genetic Drift?

•We studied whether phenotypic patterns in the Giant Squirrel in Sri Lanka, was driven by adaptations to local environment or due to genetic drift by isolation from mainland (India), using morphometric characters representing the general shape, size and coat appearance.

Methodology

• 53 study skins from the National Museum, Colombo

Fresh Skin Measurements

(from catalogue)Study Skin

Measurements

Body Length Facial Hair Length

Ear Length Tail Length

Hind Foot Length Tail Hair Length

Methodology

• Score of 1-5 was assigned for the coat colour.

• Correlations between phenotypic characters and climatic factors of the capture locations were studied.

Variation with distance• We measured the distance of each specimen to the

coastline of mainland India; Geographic distance.

• But the climate is heterogeneous.

• We assume that the dispersal is easier “within” a climatic zone than “across”.

• To accommodate this climatic influence on animal distribution, we drew a second line across the island;

biogeographic distance.

• The baseline is curved towards the wet zone in the biogeographic distance axis

• Clinal gradation along the biogeographic distance in;

Coat color, Length of facial hairTail hair

(Lighter and shorter fur near the mainland, darker and longer in the extreme south)

• Clinal distribution along geographic distance axis in; Length of the hind foot

Variation with annual rainfall

• Clinal variation along the rainfall axis in;

Both morphometric and coat-associated characters, except ear length

• Transition of the phenotype has taken place at the areas of intermediate rainfall

• The larger forms are found in the wetter areas. Except ear length (peak at areas of intermediate rainfall)

Variation with elevation• Body measurements – no

correlation with the elevation• Properties of the pelage – a

positive correlation (coat color and fur length increased with the increasing elevation)

Results

• PC1 : highest weightage from

Body length, hind foot & fur length• PC2 : highest weightage from

Ear and tail lengths• The variation of body shape and size

strongly correlated with the coat color

(R2 0.59, F 1,40 57.02 P < 0.001)

PC1

PC2

PC1

Mor

phom

etric

s

Colour classes

As the results show

• higher the humidity the darker and bigger the individual is

• Individuals in the dry zone tend to have a lighter coat

• Individuals in the intermediate zone tend to have intermediary coat color

This leads to the conclusion……………• Distance (genetic drift)

cannot be the sole driving force of divergence of this species……………………

The pattern of distribution of Giant Squirrel ……..

strongly influenced by rainfall

supporting a role in local adaptation to wet southern forests in the

island

The concordance of rainfall and phenotypic differences is most clear in the intermediate zone, where intermediate phenotypes were seen

AcknowledgementsDr. Nirmalie Pallewatta and the staff of the Department of Zoology, University of Colombo

Director and the curator, National Museum, Colombo

Dr. Manori Gunathilake, National Museum, Colombo

Ms. Chamalka Kothalawala ,National Museum, Colombo

Dr. Armando Garaldez of the University of British Columbia

Department of Wildlife Conservation of Sri Lanka

University of Colombo Research Grants (AP/3/2012/CG/30)

All those who contributed towards the specimen collection of Ratufa at the National collection

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Contact info: +94-710-821177 ;sam@sci.cmb.ac.lk