Geographical Variation of Skull Morphology and Its Functional Significances in the Red-Cheeked Squirrel

Endo, Hideki; Kimura, Junko; Oshida, Tatsuo; Stafford, Brian J.; Rerkamnuaychoke, Worawut; Nishida, Takao; Sasaki, Motoki; Hayashida, Akiko; Hayashi, Yoshihiro

doi:10.1292/jvms.65.1179

Cited by 13 publications

(12 citation statements)

References 5 publications

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“…However, we could not consider the differences as a result of functional-morphological adaptation in these cases. Although we demonstrated in the proportion analysis [6] that the feeding pattern and locomotion tendencies were diverged among Malaysian and northern Indochinese populations of red-cheeked squirrel, we did not observe differences of adaptational strategy among populations of the black giant squirrel. We suggest that the Ratufa bicolor has highly adapted to arboreal and herbivorous life in its evolutionary process [1,2,10], and that unlike Dremomys species [6] the higher specialization had been totally completed within the single species and has covered the micro-adaptational strategy among the many populations of Ratufa bicolor used in this study.…”

Section: Discussioncontrasting

confidence: 88%

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Geographical Variation of Skull Size and Shape in Various Populations in the Black Giant Squirrel

Endo

Kimura

Oshida

et al. 2004

The Journal of Veterinary Medical Science

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ABSTRACT. We osteometrically examined the skulls of the black giant squirrel (Ratufa bicolor) from three mainland populations (M. Malayan Peninsula, V. South Vietnam, and B. Burma, India and North Thailand) and from two island populations (T. Tioman, and S. Sumatra Islands). The skull in the Malayan peninsula population was significantly smaller than that of the two other mainland populations. It is consistent with Bergmann's rule as shown in the gray-bellied squirrel. The two island populations did not show obvious differences in comparison with the Malayan population in many measurements. In the proportion analysis eliminating the size factor, the differences among populations were not easily confirmed and we concluded that the osteological characters peculiar to each population could not be shown in this species. The first and second principal component scores of M, S, and T populations were intermingled, whereas the V and B populations of V and B were not separated in the chart. We pointed out that the morphological differences were demonstrated between northern and southern groups of the Isthmus of Kra in the mainland populations, and that the two island populations did not show the island-isolation effect in comparison with the M population. The adaptational variation related to feeding and locomotion could not be confirmed among populations of the black giant squirrel as shown in the proportion analysis.

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Section: Discussioncontrasting

confidence: 88%

“…We have pointed out that the northern population of the red-cheeked squirrel is larger than the southern population [6] and that the northern population of the gray-bellied squirrel is smaller than the southern population [7]. The present results on the black giant squirrel are consistent with those of the gray-bellied squirrel.…”

Section: Discussionsupporting

confidence: 85%

Geographical Variation of Skull Size and Shape in Various Populations in the Black Giant Squirrel

Endo

Kimura

Oshida

et al. 2004

The Journal of Veterinary Medical Science

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“…Dietary differences between species or between populations have been suggested as an essential factor driving the cranial diversity within the family (Ball & Roth, 1995;Thorington & Darrow, 1996;Endo et al, 2003). The numerous examples of sympatry between closely related squirrel species have also received attention from researchers (e.g.…”

Section: Introductionmentioning

confidence: 99%

Craniodental mechanics and the feeding ecology of two sympatric callosciurine squirrels in Vietnam

et al. 2009

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This study explores the relationship between feeding habit and craniodental morphology in two closely related sympatric callosciurine squirrels in south-east Asia: Callosciurus erythraeus and Dremomys rufigenis. Both C. erythraeus and D. rufigenis prefer fruits and insects, as generally seen in other tree squirrels. However, C. erythraeus also feeds extensively on hard seeds and tough tree bark, which are rarely included in the diet of D. rufigenis. We tested the hypothesis that C. erythraeus shows structural features in craniodental morphology that provide an advantage for feeding on hard seeds and tough tree bark. Results show that C. erythraeus possesses a greater mechanical advantage of the masseter and temporalis muscles for chewing, and a more robust zygomatic arch, compared with D. rufigenis. Callosciurus erythraeus is capable of generating a greater bite force at a given muscle force at the cheek teeth and its zygomatic arch is more resistant against the stresses generated by the masseter muscle, suggesting adaptation for feeding on hard seeds. Callosciurus erythraeus also exhibits greater leverage of the masseter and temporalis for incision and has a wider skull at the interorbital region, suggesting the capability for efficiently generating a greater bite force and a greater mechanical resistance to increased loads when biting into wood with its anterior dentition. Our findings indicate that the craniodental divergence between C. erythraeus and D. rufigenis may be linked functionally to the differences in their diets. We suggest that their morphological divergence may correlate with their dietary differences and contribute to the sympatric distribution of these closely related squirrels.

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“…C. caniceps has the same range as C. erythraeus and Callosciurus finlaysonii in the lowlands of Thailand, however, it has also been seen in high latitudes up to 4,700 ft in Malaysia [14,17,18,26]. We have already published papers using data of skull measurements of D. rufigenis, C. caniceps and R. bicolor [8][9][10], in this study we used more numerous specimens of the C. caniceps and compared them among many localities in Thailand and Malaysia using statistical analysis to clarify the geographical variation of C. caniceps in Southeast Asia.…”

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Geographical Variation in Skull Morphology of Gray-Bellied Squirrel Callosciurus caniceps

Hayashida

Endo

Sasaki

et al. 2007

The Journal of Veterinary Medical Science

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ABSTRACT. The geographical variation of the gray-bellied squirrel (Callosciurus caniceps) was examined using osteometry of skull in Southeast Asia. From the principal component analysis (PCA), the plots of the northern localities from Nan to Kanchanaburi and those of the southern localities from Narathiwat to Kuala Lumpur in male were completely separated. In female, the plots of the locality from Uttradit to Kanchanaburi and those of the locality from Pattani to Negri Sembilan were completely separated. We called these northern localities and southern localities which are distinguished by the PCA as N group and S group. The size and shape of the skulls of these squirrels indicated the differences between N group and S group from t-test and U-test. These results may be influenced by the two transitions of the phytogeography around the southernmost locality in N group and the northernmost locality in S group in the peninsular Thailand and Malay Peninsula. Localities which are located between N and S groups were called the Middle (M) group. From the PCA among N, S groups and each locality of M group, the plots of localities such as Prachuap Khiri Khan, Chumphon, Krabi, Nakhon Si Thammarat and Trang in both sexes of M group could not be separated from those of N and S groups. We suggest that the sympatric distribution of N and S groups and the hybrid of N and S populations may be seen in these localities of M group.

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Geographical Variation of Skull Morphology and Its Functional Significances in the Red-Cheeked Squirrel

Cited by 13 publications

References 5 publications

Geographical Variation of Skull Size and Shape in Various Populations in the Black Giant Squirrel

Geographical Variation of Skull Size and Shape in Various Populations in the Black Giant Squirrel

Craniodental mechanics and the feeding ecology of two sympatric callosciurine squirrels in Vietnam

Geographical Variation in Skull Morphology of Gray-Bellied Squirrel Callosciurus caniceps

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