The reproductive tract of a pilot whale Globicephalus melas.
Keywords: cetacean, whale, pilot, tractThis reproductive tract was obtained from a dead, beached long finned pilot whale (Globicephalus melas) found in New Brunswick in November 2013. The time of death was unknown but postmortem changes were minimal.
The vagina and vulva were absent but the reproductive tract was otherwise complete. The gross appearance of the reproductive tract showed many similarities between this species and our domestic animals; specifically cattle and horses. The uterus was most like that of a mare, being approximately T-shaped with a long uterine body. There was a small inter-cornual ligament and two long horns. Proportionally, these horns were almost twice as long as those in a mare or cow, presumably to accommodate an elongated calf that weighs approximately 100 kg at birth.
The uterus was suspended by a mesometrium that did not contain a obvious dominant uterine artery such as that seen in mares in cows.
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As mentioned, the vulva and vagina were absent. However, the cervix had been retained and was a source of fascination for this author. This macroscopic image of the cervix shows large numbers of folds and complex folding within folds, giving the mucosa and almost feather-like appearance.
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The reader is encouraged to click on this image to appreciate the nature of those folds. It is tempting to suggest that the structure forms a sperm reservoir in the living animal. Similar folding in other species, together with the cervical mucus has certainly been proposed as reservoirs in other species. The reader is encouraged to click on this image to fully appreciate this anatomy.
The cervix itself was more reminiscent of that of a mare than a cow, having no interlocking transverse ridges but instead, a series of longitudinal folds leading to the uterus. Interestingly, the cervix became narrow in its most cranial portion as shown by the light black arrows in the image below. In both of the images in this amalgam, an accumulation of tenacious mucus can be seen in the cranial portion of the cervix. This has been seen by the author in other marine mammals (the grey seal and a dolphin). It is possible that this cervical mucus play a role in protecting the contents of the uterus under conditions of high water pressure in these deep diving animals.
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The endometrium was very similar in gross appearance to that of the mare with no evidence of multiplex (ruminant-type) placentation. This suggests that the Pilot whale has diffuse placentation like that of the mare. The bifurcation of the uterus occurs about 10 to 12 cm cranial to the internal os of the cervix (see yellow arrows) again, more similar to the uterus of the mare than that of a cow.
On the other hand, the ovaries as seen below, are reminiscent of those of a cow in both scale and function.
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They were approximately 5 x 2.5 cm (left) and 8 x 2.5 cm (right). Although a fairly robust tunica albuginea was present, ovulation appeared to occur through the surface of the ovaries. The crown of a corpus luteum (yellow arrow) with a small depression in its center was seen in the right ovary.
On close examination, there were a total of 7 or 8 corpora albicanti in both ovaries combined. Some of these were very small and presumed to be older than others. The age of marine mammals is sometimes determined by the number of corpora albicanti in the ovaries but several hundred sections of each ovary must be examined to determine the number of corpora albicanti with any accuracy. Also, the incidence twin ovulations, lactational anestrus, break-through ovulation during suckling (see below) and nutritional effects cannot be discounted. Therefore growth rings in the teeth (see below) are usually used to age cetaceans instead.
Literature reviewed in Cetacean Societies: Field Studies of Dolphins and Whales (Ed.Janet Mann ISBN-13: 978-0226503417) suggests that toothed whales (Odontocetes, such as this pilot whale), unlike the baleen whales (Mysticetes) do not generally ovulate or conceive in early lactation. As mentioned, this whale was lactating at the time of his death and one of the whales found together with the female was presumed to be her calf. Because whales may suckle for many years, it is unlikely that this female had ovulated recently; consistent with the absence of a corpus luteum in either ovary.
To one who is used to the appearance of ovarian structures in domestic animals, the dominance of the corpora albicanti is remarkable because corpora albicanti are usually difficult to see in domestic animals except for a period of days or weeks after ovulation. In many marine mammals however, corpora albicanti persist for years, probably because of their remarkable fibrotic structure. Although the term corpora albicanti or corpus albicans is used in our domestic animals, true "white bodies" (as the Latin name suggests) is not nearly as obvious as in marine mammals.
This image shows the remarkable fibrosis present in one of the corpora albicanti from this whale.
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The histologic appearance of the corpora albicanti (CA) are shown at upper and lower left in the composite image below. The degree of fibrosis is obvious. Also of interest in this image are the following:
- The collapsed theca interna of the Graafian follicle adjacent to the CA in the upper left image. The resemblance between these follicles and those of land mammals is striking.
- At upper right there is section of the cortex of the ovary taken from a younger whale that accompanied this one, possibly her calf. There were no corpora albicanti on those ovaries, supporting the contention that this was a juvenile (pre-or peripuberal) animal. However, large numbers of primary, secondary and tertiary follicles are present in this section. Fine detail is absent because of significant autolysis in the specimen but their presence is certain. This is supported by the macroscopic image that follows this one.
- At lower right in the image is a cross section of the uterine wall of the juvenile whale. The resemblance between this section and a uterine biopsy in a mare is remarkable. In this case gland complexity and cross sections were minimal, also suggesting that this uterus had not been under the influence of progesterone in the recent past i.e. the animal had not yet begun to have estrous cycles.
In the image shown below, a cross section of the ovary of the ovary of the mature whale is seen at left and that of the juvenile at right. A corpus albicans can be seen in the mature whale's ovary, just under the cortex, presumably displaced to medullary region by physical constraints. In both ovaries, the delineation between the medulla and the oocyte-rich cortex is amazing to this author. Such a clear delineation in not present in any domestic animal. Also striking is the thickness of the cortex (white bars) in the juvenile compared to that of the older animal. Histologically, the cortex of the adult was sparsely populated with oocytes suggestion that absolute ovarian senescence may occur in this species.
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Aging of the whale and the adolescent were determined by counting the layers of dentine that had been added from the pulp cavity over the course of the animal's life; approximately one each year. This procedure was conducted by Mr Yves Morin Yves.Morin@dfo-mpo.gc.ca courtesy of the Department of Fisheries and Oceans, Canada.
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The age rings in the adult at left in this image show that it was approximately 15 years old when it beached itself. Female Pilot whales may breed for 50 years, making it somewhat surprising that the cortex appeared to be so depleted of oocytes at only 15 years. By comparison, the adolescent was shown to be approximately 14 months of age, Accordingly, the ovarian cortex to be as well populated with oocytes.
An interesting finding in this whale was the structure of the ovarian adnexa. The larger of the two images in this amalgam serves as a key for the following discussion.
A large ovarian bursa was present and in the illustration below, it was filled with the tip of a rubber glove stuffed with paper towel to demonstrate its volume. The black arrow shows the entrance to the bursa.
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The uterine tube (fallopian tube) was a source of amazement. The entrance to the uterine tube (in effect the infundibulum) had, relatively speaking, an enormous opening and unlike fallopian tubes in domestic species, did not narrow rapidly distal to the ovary. This structure was identical on the left and right sides of the tract and showed no evidence of fibrosis or hydropsalpinx suggesting that it may be abnormal. The physiological and anatomical basis for this structure could be the basis for a fascinating discussion!
Notes: http://en.wikipedia.org/wiki/Long-finned_pilot_whale
Gestation lasts approximately 12 to 15 months and calving occurs once every 3 to 5 years. Calves are generally 1.8 m (5 ft 11 in) at birth, and weigh about 102 kg (225 lb). The calf nurses for up to 27 months, with some evidence for longer lactation and extensive mother calf bonds. Most calves are born in the summer, though some calving occurs throughout the year. The males may compete for mates with fights involving butting, biting, and ramming. Mating also involves these activities, and some females carry scars from bites inflicted by males during the breeding season. Females have been observed to have calves as late as 55 years old, and lactate as late as 61. This evidence indicates that females may nurse their last calf until puberty (up to 10 years in males).
