VAN VALKENBURGH, B; SEDLMAYR, JC; Univ. of California, Los Angeles: Cephalic Vasculature in Canidae
Canids are an ubiquitous group of basal carnivorans, yet, outside domestic dogs ,very little is known of canid anatomy or physiology. Canids can provide an important test of the correlation of purported vascular physiological devices with important physiological behaviors that protect against thermal brain damage and extensive water loss. Canids are highly active pursuit predators, often engaging in intensive exercise in warm and arid environments. This lifestyle suggests canids should possess vascular devices associated with selective temperature regulation and as switches for panting to protect against extensive water loss. Laboratory studies have demonstrated selective brain cooling in canids and wild canids are not known to greatly suffer from heat stroke and water loss. Taxa within their sister clade Aeluroidea possess complex carotid retia that have been associated with selective hypothalamic cooling. We studied canid head vasculature to address the dearth of anatomical data and to address the above physiological questions. This study was conducted within a comparative framework to elucidate homologous vascular structures and patterns and to determine stability or evolutionary transformation of form across canid phylogeny. We examined numerous species across the spectrum of canid phylogeny with an emphasis on basal and highly derived taxa. Attention was given to the gray fox (Urocyon), a basal canid, to best reconstruct the ancestral canid cephalic vascular system. A variety of methods were used in the course of this study, including vascular injection, stereoangiography, CT scanning, SEM, and histological sectioning. An important discovery is the apparent lack of specialized vascular physiological devices in extant canids. Cephalic structures and patterns are very similar between both Urocyon and the derived Canis, and neither of these taxa have a carotid rete. A carotid rete is likely absent in the ancestral canid.
