Sains Malaysiana 48(10)(2019): 2103–2111

http://dx.doi.org/10.17576/jsm-2019-4810-05

Morphometric Analysis of Craniodental Characters of the House Rat, Rattus rattus (Rodentia: Muridae) in Peninsular Malaysia

(Analisis Morfometri Ciri Kraniodental Tikus Rumah Rattus rattus (Rodentia: Muridae) di Semenanjung Malaysia)

NURUL HUDA MOHAMAD IKBAL¹, DHARINI PATHMANATHAN³, SUBHA BHASSU¹, KHANOM SIMARANI¹ & HASMAHZAITI OMAR^1,2*

¹Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

²Museum of Zoology, Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

³Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

Diserahkan: 19 April 2019/Diterima: 11 September 2019

ABSTRACT

Rattus rattus which is believed to be native to India is easily found in all continents of the world. With the absence of R. rattus from lineage I and the presence of lineage IV in Southeast Asia, little is known about how rodent morphology varies biogeographically. We evaluate the skull morphometrics in the population of R. rattus in Peninsular Malaysia and examine the intraspecific variation of the skull by assessing 20 craniodental characters of 130 R. rattus specimens. After observing the correlation matrix, highly correlated characters were removed and the remaining 14 craniodental characters were analysed using the conventional morphometrics method via univariate and multivariate statistics. We assessed the impact of age, sex and geographical factors (latitude, longitude and precipitation) on craniodental size. Male and female specimens were analysed separately since statistically significant sexual dimorphism was present. Males showed greater craniodental measurements compared to females. Three distinct age groups (C2, C3 and C4) were visible in the principal component analysis (PCA) and canonical variate analysis (CVA) plots for male and female specimens. Ages C2 and C3 shared similarities in craniodental measurements while C4 showed variability compared to C2 and C3. None of the geographical factors studied showed statistical significance for both male and female R. rattus. The results obtained from this study could potentially be a yardstick to observe if similar variations in craniodental traits are present in R. rattus from other countries in the Southeast Asian region.

Keywords: Conventional morphometrics; craniodental; geographic variation; ontogenetic; sexual dimorphism

ABSTRAK

Rattus rattus yang dipercayai berasal dari India mudah ditemui di setiap benua di dunia. Dengan ketiadaan R. rattus daripada ‘lineage I’ serta kehadiran R. rattus daripada ‘lineage IV’ di Asia Tenggara, sedikit diketahui mengenai bagaimana morfologi tikus berbeza secara biogeografi. Kami menilai morfometri tengkorak populasi R. rattus di Semenanjung Malaysia dan mengkaji variasi intraspesies bagi tengkorak dengan menilai 20 ciri-ciri kraniodental bagi 130 spesimen R. rattus. Setelah memantau matriks korelasi, ciri-ciri berkorelasi tinggi dikeluarkan dan baki 14 daripada ciri-ciri telah dipilih dan analisis dijalankan berdasarkan kaedah morfometri konvensional menggunakan statistik univariat dan multivariat. Kami mengkaji pengaruh umur, jantina dan faktor-faktor geografi (latitud, longitud dan pemendakan) terhadap saiz kraniodental. Dimorfisme seks yang signifikan secara statistik wujud, maka spesimen jantan dan betina dianalisis secara berasingan. Tikus jantan menunjukkan ukuran kraniodental yang lebih besar berbanding tikus betina. Tiga kumpulan umur yang jelas (C2, C3 dan C4) kelihatan pada plot analisis komponen prinsipal (PCA) dan plot analisis variat kanonikal (CVA) bagi kedua-dua spesimen jantan dan betina. Kumpulan umur C2 dan C3 mempunyai persamaan daripada segi ukuran kraniodental manakala C4 menunjukkan perbezaan yang ketara berbanding C2 dan C3. Kesemua faktor geografi yang dikaji tidak menunjukkan keertiaan berstatistik bagi R. rattus jantan dan betina. Hasil yang diperoleh daripada kajian ini berpotensi menjadi panduan untuk dicerap sekiranya variasi yang sama wujud pada ciri-ciri kraniodental dalam R. rattus dari negara-negara lain di rantau Asia Tenggara.

Kata kunci: Dimorfomisme seks; kraniodental; morfometri konvensional; ontogenetik; variasi geografi

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*Pengarang untuk surat-menyurat; email: zaiti_1978@um.edu.my