Sexual dimorphism of Dall's porpoise and harbor porpoise skulls

Frandsen, Marie Schou; Galatius, Anders

doi:10.1016/j.mambio.2012.04.005

Cited by 13 publications

(14 citation statements)

References 25 publications

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“…Dimorphism in the epaxial muscles has been described for Dall's porpoises, where the males display a thoracic hump between the blowhole and dorsal fin (Jefferson ). These findings are supported by Frandsen and Galatius (), who found caudal displacement of the occipital condyles in male Dall's porpoises. Frandsen and Galatius () also predicted that the dimorphism observed in this area may allow for larger neck muscles and provide stabilization of the head during powerful swimming and physical confrontations.…”

Section: Discussionsupporting

confidence: 80%

“…These findings are supported by Frandsen and Galatius (), who found caudal displacement of the occipital condyles in male Dall's porpoises. Frandsen and Galatius () also predicted that the dimorphism observed in this area may allow for larger neck muscles and provide stabilization of the head during powerful swimming and physical confrontations. However, no literature was found describing differences in fluke thrust during the upstroke between male and female dolphins.…”

Section: Discussionsupporting

confidence: 80%

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Sexual dimorphism in striped dolphin (Stenella coeruleoalba) crania from South Africa

Conry

Pistorius

Plön

et al. 2016

Marine Mammal Science

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This study assessed the extent of sexual dimorphism in striped dolphin (Stenella coeruleoalba) cranial size and shape off the South African coast. Dorsal and ventral features of 60 striped dolphin crania from both the western and eastern coasts of South Africa were analyzed using landmark‐based geometric morphometrics. Although there was no evidence of dimorphism in cranial size, evidence for small, but significant, variation in both dorsal and ventral cranial shape was found between the sexes. The observed dimorphism was partly associated with changes in shape around the temporal fossa, occipital condyle and supraoccipital bone, the nasal bone, and the paraoccipital process and basiocciptal. The temporal fossa serves as an attachment point for the temporal muscle, which functions to close the lower jaw, and the occipital area serves as the anterior insertion of the epaxial muscles, which power the upstroke of the flukes during swimming. Both the paraoccipital process and basiocciptal are associated with the functioning of the hyoid apparatus, which serves as an attachment point for muscles and ligaments involved in feeding and sound production. These findings suggest the possibility of differences in diet, foraging behavior, vocalizations, and locomotion between the sexes of this species.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionsupporting

confidence: 80%

Sexual dimorphism in striped dolphin (Stenella coeruleoalba) crania from South Africa

Conry

Pistorius

Plön

et al. 2016

Marine Mammal Science

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“…We applied a three‐dimensional geometric morphometric approach, which has been demonstrated to be a powerful tool for the study of geometrical shape in biological structures and may provide insights into their evolutionary history and intraspecific variation (Monteiro‐Filho et al, ; Amaral et al, ). Another goal was to test which skull region differ the most in the growth pattern between species, because specific parts of the skull in cetaceans are subject to different functional and evolutionary constraints (e.g., Guidarelli et al, ; Frandsen and Galatius, ). Based on previous studies in cetacean cranial development (e.g., Perrin, ; del Castillo et al, , in press), we hypothesize that the rostrum will be the region that differ the most, both in size and shape during growth.…”

Section: Introductionmentioning

confidence: 99%

Skull ontogeny and modularity in two species of Lagenorhynchus: Morphological and ecological implications

Castillo

Viglino

Flores

et al. 2016

Journal of Morphology

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Comparisons of skull shape between closely related species can provide information on the role that phylogeny and function play in cranial evolution. We used 3D-anatomical landmarks in order to study the skull ontogeny of two closely related species, Lagenorhynchus obscurus and Lagenorhynchus australis, with a total sample of 52 skulls. We found shared trends between species, such as the relative compression of the neurocranium and the enlargement of the rostrum during ontogeny. However, these are common mammalian features, associated with prenatal brain development and sensory capsules. Moreover, we found a posterior displacement of the external nares and infraorbital foramina, and a strong development of the rostrum in an anteroposterior direction. Such trends are associated with the process of telescoping and have been observed in postnatal ontogeny of other odontocetes, suggesting a constraint in the pattern. Interspecific differences related to the deepness of facial region, robustness of the feeding apparatus and rostrum orientation may be related with the specific lifestyles of L. obscurus and L. australis. We also tested the presence of three different modules in the skull (basicranium, neurocranium, rostrum), all of which presented strong integration. Only the rostrum showed a different ontogenetic trajectory between species. Even though we detected directional asymmetry, changes in this feature along ontogeny were not detectable. Because asymmetry may be related to echolocation, our results suggest a functional importance of directional asymmetry from the beginning of postnatal life. J. Morphol. 278:203-214, 2017. © 2016 Wiley Periodicals,Inc.

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“…This latter phenomenon is expressed as either a resource defence polygyny or female (harem) defence polygyny, and it usually results in males being larger than females [ 18 , 19 ]. Therefore, the vast majority of studies of sexual dimorphism in mammals have focused on SSD, while relatively few examined variation in shape [ 20 , 21 , 22 , 23 , 24 , 25 ], especially in Cetaceans [ 26 ]. Odontocetes cetaceans (toothed whales) show different degrees of SSD, from the sperm whale having males 1.6 times larger than females, to the monomorphism of Delphinidae [ 11 , 27 ].…”

Section: Introductionmentioning

confidence: 99%

Intra- and Interspecific Interactions as Proximate Determinants of Sexual Dimorphism and Allometric Trajectories in the Bottlenose Dolphin Tursiops truncatus (Cetacea, Odontoceti, Delphinidae)

Francesco

Loy

2016

PLoS ONE

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Feeding adaptation, social behaviour, and interspecific interactions related to sexual dimorphism and allometric growth are particularly challenging to be investigated in the high sexual monomorphic Delphinidae. We used geometric morphometrics to extensively explore sexual dimorphism and ontogenetic allometry of different projections of the skull and the mandible of the bottlenose dolphin Tursiops truncatus. Two-dimensional landmarks were recorded on the dorsal, ventral, lateral, and occipital views of the skull, and on the lateral view of the left and the right mandible of 104 specimens from the Mediterranean and the North Seas, differing environmental condition and degree of interspecific associations. Landmark configurations were transformed, standardized and superimposed through a Generalized Procrustes Analysis. Size and shape differences between adult males and females were respectively evaluated through ANOVA on centroid size, Procrustes ANOVA on Procrustes distances, and MANOVA on Procrustes coordinates. Ontogenetic allometry was investigated by multivariate regression of shape coordinates on centroid size in the largest homogenous sample from the North Sea. Results evidenced sexual dimorphic asymmetric traits only detected in the adults of the North Sea bottlenose dolphins living in monospecific associations, with females bearing a marked incision of the cavity hosting the left tympanic bulla. These differences were related to a more refined echolocalization system that likely enhances the exploitation of local resources by philopatric females. Distinct shape in immature versus mature stages and asymmetric changes in postnatal allometry of dorsal and occipital traits, suggest that differences between males and females are established early during growth. Allometric growth trajectories differed between males and females for the ventral view of the skull. Allometric trajectories differed among projections of skull and mandible, and were related to dietary shifts experienced by subadults and adults.

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Sexual dimorphism of Dall's porpoise and harbor porpoise skulls

Cited by 13 publications

References 25 publications

Sexual dimorphism in striped dolphin (Stenella coeruleoalba) crania from South Africa

Sexual dimorphism in striped dolphin (Stenella coeruleoalba) crania from South Africa

Skull ontogeny and modularity in two species of Lagenorhynchus: Morphological and ecological implications

Intra- and Interspecific Interactions as Proximate Determinants of Sexual Dimorphism and Allometric Trajectories in the Bottlenose Dolphin Tursiops truncatus (Cetacea, Odontoceti, Delphinidae)

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