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

Abstract

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.

Variation in cranial morphology of bottlenose dolphins (genus Tursiops) off South Africa

“…Furthermore, significant differences in the crania involving the posterior‐most region and most muscle and ligament attachments may also be due to varying foraging strategies, behavior, and vocalization (Conry et al . ).…”

“…, Frandsen and Galatius , Conry et al . ), geographical variations (Sanvicente‐Anorve et al . , Murphy and Rogan ), allometry (del Castillo et al .…”

Long‐finned pilot whale (Globicephala melas, Traill 1809) subspecies in the Atlantic Ocean: Are there differences in their skulls?

“…), Stenella coeruleoalba (Conry et al . ), and in species of the Phocoenidae family (Galatius et al . ).…”

Variación morfométrica en cráneos del delfín manchado del Atlántico (Stenella frontalis) de Venezuela

“…Las variaciones craneales de tipo morfológicas en cetáceos odontocetos se han reportado en varias especies de delfínidos de los géneros Cephalorhynchus, Delphinus, Lagenodelphis, Stenella y Tursiops (Baker et al, 2002;Loy et al, 2010;Perrin, 1975Perrin, , 1984Perrin, , 2009Perrin et al, 2003Perrin et al, , 2011Pinela et al, 2011;Schnell et al, 1985Schnell et al, , 1986Westgate, 2007). Sobre todo, en los caracteres que se asocian con la alimentación, como son el número y el tamaño de los dientes, la longitud y anchura del rostro, y en el tamaño de la fosa temporal, lo que indica que la variación estaría relacionada con la disponibilidad de presas, a las estrategias de alimentación y a las vocalizaciones (Conry et al, 2016;Perrin, 2009). El género Stenella, con 5 especies de delfines S. frontalis, S. attenuata, S. clymene, S. coeruleoalba y S. longirostris (Wilson y Reeder, 2005) y 6 subespecies (S. a. attenuata, S. a. grafmanni, S. l. centroamericana, S. l. longirostris, S. l. orientalis, S. l. roseiventris), es quizá uno de los que presentan tal número de semejanzas y variaciones intra e interespecíficas respecto de su morfología craneana, que pueden ser fácilmente confundidos entre sí, dificultando su correcta identificación.…”