Morphological Indicators of Olfactory Capability in Wobbegong Sharks (Orectolobidae, Elasmobranchii)

Abstract

Elasmobranchs are thought to possess an acute sense of smell, but the relationship between the anatomy of their olfactory organs and their sensory ecology is poorly understood. Moreover, the ecological diversity of elasmobranchs as a group indicates that there might be considerable interspecific variation in the importance of the olfactory sense. Wobbegong sharks, with their sedentary lifestyle and ambush predatory technique, probably utilize their senses differently than other shark species, making it difficult to generalize about their olfactory capabilities and olfaction-dependent behaviors. In this study, the number of olfactory lamellae and the surface area of the olfactory epithelium were measured as a means of assessing relative olfactory sensitivity in four species of wobbegong shark (the Western wobbegong, Orectolobus hutchinsi; the spotted wobbegong, O. maculatus; the ornate wobbegong, O. ornatus; and the dwarf spotted wobbegong, O. parvimaculatus). We also present a phylogenetic comparative analysis between wobbegongs and other elasmobranchs for which published data on olfactory morphology are available. There is a significant difference in the total number of olfactory lamellae between most species, but not between O. hutchinsi and O. maculatus, although the olfactory sensory surface area is comparable between these two species and O. ornatus. Orectolobus parvimaculatus has a significantly larger olfactory sensory surface area than the other three species, and there is a positive relationship between total body length and olfactory sensory surface area for all four species. Assuming that these morphological measures are true indications of olfactory capability, the olfactory abilities of wobbegongs are as good as, or better than, other benthic elasmobranchs. Interspecific differences in olfactory ability within this group of benthic ambush predators could indicate relative differences in prey detection, intraspecific recognition and mate detection.