Abstract

In several animal species the vomeronasal organ (VNO) or accessory olfactory system has been shown to play a significant role in reproductive and social behavior. Access to the VNO is possible from the nasal cavity, the oral cavity or both, depending on the species. Entrance from the oral cavity is by way of the incisive ducts which are located on the rostral portion of the hard palate. An analogous arrangement in some cetaceans appears to be two furrows in the same area called Jacobson's grooves. The presence of these grooves has been reported for baleen whales, including the bowhead. In the bowhead, each groove is situated perpendicular to and on either side of the midline of the rostral hard palate.

Tissues from the rostral area of the hard palate were collected from 12 whales. Each specimen of the hard palate displayed a topographical horseshoe shaped pattern, consisting of grooves, a centrally located papilla and paired "foramina" (incisive pits), similar to the design found in the bovine species.

A sagittal section through the center of each incisive pit showed that each pit ends approximately 5-10 mm beneath the surface. It appears that the pit in the bowhead whale is a vestigial remnant of the incisive duct which may have functioned in a land-based evolutionary predecessor. The paired vomeronasal organ in the early cetaceans, which is located adjacent to the nasal septum and dorsal to the hard palate in other animals, may have migrated to a more caudal position along with the nasal cavity.

Background

The bowhead whale (Balaena mysticetus) is one of ten living species of baleen whales, of Mysticetes. It is the only baleen whale whose range is restricted to the Arctic and is one of the largest of the remaining whales, with recent records of individuals approaching 60 feet in length. It is among the most endangered of living whales. Intensely hunted in the western Arctic during the last century by commercial whalers, its number plummeted drastically; the most recent counts place its numbers at only about 4,000 individuals (9).

For more than 2,000 years the Eskimos of northern Alaska have hunted the bowhead whale. The Eskimos depend on these animals for food, shelter and clothing. Although the whale can only be hunted seasonally as it passes on its annual migration between the Bering and Beaufort Seas, the highly prized skin and blubber (muktuk), muscle, kidney and other portions have traditionally been stored in ice cellars, contributing generously to the subsistence needs of these people throughout the year.

A quota system has been developed by the International Whaling Commission (IWC) that sanctions the annual harvest of a limited number of bowheads by Eskimo hunters. This quota is derived from the most recent population estimates. The Alaska Eskimo Whaling Commission has been formed to consider the position of the IWC and to implement its findings within the framework of Eskimo whaling practice while seeking to preserve the whaling culture so important to native Arctic inhabitants.

Rapid industrial expansion within the Arctic in recent years has placed new pressures on native cultures and on wildlife inhabitants. There is particular concern among the Eskimos that exploitation of offshore petroleum reserves could threaten the bowhead resource should a subsea oil well blow out or an oil spill result in sudden environmental contamination. This concern has stimulated interest in the assembly of baseline data on the biology of the bowhead whale in order to establish an information pool that can serve as a control for any later comparison that might be necessary following an environmental accident.

Structural Studies

Structural studies on the digestive and reproductive systems, as well as Jacobson's grooves, are being conducted in the Department of Veterinary Anatomy at Texas A&M University. Hopefully, these studies will result in a better understanding of anatomical arrangements that will permit more accurate assessments of physiological function within these systems as well as their response if exposed to environmental contaminants.

Information addressing the reproductive process is essential in any attempt to safeguard the existence of a threatened species. The vomeronasal or accessory olfactory system is considered an important sensory apparatus related to reproductive behavior in animals (1,2,5,6,8,10). Thus far, we have investigated the sensory system which bulls use to detect heat; it is an accessory olfactory system located just above the roof of the mouth, known as the vomeronasal (Jacobson's) organ. The gross and microscopic anatomy of the bovine VNO and the two duct systems associated with it have been described in our studies (4). Our studies of plugging the VNO duct suggest that manipulation of the VNO system can have practical effects involving various reproductive behaviors in cattle. There is also the possibility that animals use the VNO as an organ of "taste" for assessing various characteristics of foodstuffs; recent studies in rodents indicate that food and drinking material do gain access to the VNO. We are investigating the possible existence of a VNO in the bowhead whale to gain insights into the possible role of a VNO in the whale's reproductive, social and food "communication system."

Tissue from the rostral area of the hard palate was collected from 12 whales at Eskimo harvest sites along the north Alaskan coast. Each section of hard palate measured approximately 24x14 cm, and displayed a topographical horseshoe shaped pattern accompanied by grooves, a centrally located papilla and paired foramina (incisive pits), that is similar to the pattern found in bovine species.

In other animals access to the VNO is possible from the nasal cavity, the oral cavity or both, depending on the species. Entrance from the oral cavity is by way of the incisive ducts which are located on the rostral portion of the hard palate. An analogous arrangement in some cetaceans appears to be two furrows in the same area called Jacobson's grooves (sometimes referred to as Jacobson's organ). The presence of these grooves has been reported for baleen whales, including the bowhead (7). In the bowhead, each groove is situated perpendicular to and on either side of the midline of the rostral hard palate. A saggital section through the center of each groove showed that and incisive pit ends approximately 5-10 mm beneath the surface. The stratified squamous epithelium of the groove receives papillae from the underlying dermis which contain encapsulated nerve endings similar to those reported in the skin by investigators at Louisiana State University (3). We have not found any evidence of a specialized sensor in the groove. The groove itself shows no communicating duct. It appears that this incisive pit of the bowhead whale is a vestige, a remnant of the incisive canal which may have functioned in a previous stage of the species many years ago while still on land. The paired VNO, which is located adjacent to the nasal septum dorsal to the hard palate in other animals may have migrated to a more caudal position along with the nasal cavity. There is much evidence that supports the evolution of cetaceans from a land dwelling mammal. The aquatic life favored the caudal and dorsal shift of the external nares with the perfection of methods for sealing them from water. An actual VNO has not been confirmed in cetaceans. The significance of Jacobson's grooves in the bowhead whale remains unclear. However, their persistence in the Mysticetes and their relationships to sensory activities in other mammals encourages a consideration of their function in certain cetaceans. Any such environmental sensor could hold much survival value for an endangered species such as the bowhead.

Acknowledgments

We thank the Eskimo whaling captains who permitted the collection of materials used in this report. Special thanks to the North Slope Borough, Barrow, AK for providing the funding.

References

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