Anatomical Clues to the Possible Existence of a Vomeronasal Organ in the Bowhead Whale (Balaena mysticetus)
Raymond F. Sis, DVM, PhD; Raymond Tarpley, DVM, PhD; Thomas F. Albert, VMD,
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.
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 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
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.
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.
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