Morphological differentiation of the vertebral column of three Lagenorhynchus species in association with their habitats

MARCHESI, MC; MORA, MS; GONZALEZ JOSÉ, R; GOODALL, RNP

San Francisco

Conferencia; 21st Biennial Conference on the Biology of Marine Mammals; 2015

Society for Marine Mammalogy

For cetacean species, habitat complexity constitutes an important agente of selective pressure relative to the performance of locomotor behaviors. It has been proposed that pelagic fast swimming species would have ostelogical features that promote a more stable vertebral column. The Peale?s dolphin (Lagenorhynchus australis), the dusky dolphin (L. obscurus) and the hourglass dolphin (L. cruciger) are closely related species with distribution restricted to the Southern Hemisphere; inhabiting coastal, platform and pelagic waters, respectively. The objective of this research was to study centrum morphology and column regionalization of the dusky dolphin, relative to the other two southern Lagenorhynchus species. Three measurements were taken on each vertebra, starting with the first thoracic: centrum length (CL), width (CW) and height (CH). The Relative Centrum Length (RCL = [CL/0.5 x (CW + CH)]) was used as an indicator of the area of contact between vertebra. Vertebral columns were divided into functional series and the percentage of the skeleton occupied by each region was calculated and tested for significant differences. All the specimens analyzed have a regionalization of the column into three stable and two flexible areas. The dusky dolphin has an intermediate pattern of centra morphology with some features similar to the hourglass dolphin and some resembling the Peale`s dolphin. The degree of flexibility is intermediate between the other two species but the stability of the mid torso is more similar to that of the hourglass dolphin. Moreover, differences in the proportion of the spine represented by the regions in the anterior part of the columns (cervical, thoracic, and anterior and mid torso) are significant in comparison with the hourglass and the Peale?s dolphin. Interestingly, substantial morphological differences in some attributes can be observed, despite their close phylogenetic relationships. These differences would be related with the ecological niche and the habitat of each species