The Ovary of Rock Hyrax of the Genus Procavia

Kayanja, F. I. B.; Sale, J. B.

doi:10.1530/jrf.0.0330223

Cited by 7 publications

(3 citation statements)

References 3 publications

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“…Another recognized close relative of the elephant, the hyracoideae, also show a zonary placenta and multiple CL. Hyracoideae may give birth to up to four young [43] and the number of conceptus match the number of CLs [44]. Thus, CLs form from ovulated follicles rather than from LUF.…”

Section: Discussionmentioning

confidence: 99%

Gestating for 22 months: luteal development and pregnancy maintenance in elephants

Niemuller¹,

Rich²,

Gray³

et al. 2012

Proc. R. Soc. B.

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The corpus luteum, a temporally established endocrine gland, formed on the ovary from remaining cells of the ovulated follicle, plays a key role in maintaining the early mammalian pregnancy by secreting progesterone. Despite being a monovular species, 2-12 corpora lutea (CLs) were found on the elephant ovaries during their long pregnancy lasting on average 640 days. However, the function and the formation of the additional CLs and their meaning remain unexplained. Here, we show from the example of the elephant, the close relationship between the maternally determined luteal phase length, the formation of multiple luteal structures and their progestagen secretion, the timespan of early embryonic development until implantation and maternal recognition. Through three-dimensional and Colour Flow ultrasonography of the ovaries and the uterus, we conclude that pregnant elephants maintain active CL throughout gestation that appear as main source of progestagens. Two LH peaks during the follicular phase ensure the development of a set of 5.4 + 2.7 CLs. Accessory CLs (acCLs) form prior to ovulation after the first luteinizing hormone (LH) peak, while the ovulatory CL (ovCL) forms after the second LH peak. After five to six weeks (the normal luteal phase lifespan), all existing CLs begin to regress. However, they resume growing as soon as an embryo becomes ultrasonographically apparent on day 49 + 2. After this time, all pregnancy CLs grow significantly larger than in a non-conceptive luteal phase and are maintained until after parturition. The long luteal phase is congruent with a slow early embryonic development and luteal rescue only starts 'last minute', with presumed implantation of the embryo. Our findings demonstrate a highly successful reproductive solution, different from currently described mammalian models.

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Section: Discussionmentioning

confidence: 99%

Gestating for 22 months: luteal development and pregnancy maintenance in elephants

Niemuller¹,

Rich²,

Gray³

et al. 2012

Proc. R. Soc. B.

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“…Interstitial cells are found in the fetal gonads of many mammalian species including the elephant [14]; human [15], spotted hyena [16], guinea pig [17], rock hyrax [18] and in some—for example the horse [19] and the Common and Grey seals [20]—they cause a significant increase in fetal gonadal volume. In the female fetus in most of these species, the interstitial cells develop independent of follicles within the presumptive ovarian medulla.…”

Section: Introductionmentioning

confidence: 99%

Growth and development of the ovary and small follicle pool from mid fetal life to pre-puberty in the African elephant (Loxodonta africana)

Stansfield

Nöthling

Allen³

2012

BMC Vet Res

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BackgroundFollicle numbers and developing ovarian morphology, particularly with reference to the presence of interstitial tissue, are intimately linked within the ovary of the African elephant during the period spanning mid-gestation to puberty. These have not been previously quantified in any studies. The collection of 7 sets of elephant fetal ovaries between 11.2 and 20.2 months of gestation, and 29 pairs of prepubertal calf ovaries between 2 months and 9 years of age during routine management off-takes of complete family groups in private conservancies in Zimbabwe provided an opportunity for a detailed study of this period.ResultsThe changing morphology of the ovary is described as the presumptive cortex and medulla components of the fetal ovary settled into their adult form. Interstitial tissue dominated the ovary in late fetal life and these cells stained strongly for 3β–hydroxysteroid dehydrogenase. This staining continued postnatally through to 4.5 years of age suggesting continued secretion of progestagens by the ovary during this period. The considerable growth of antral follicles peaked at 28% of ovarian volume at around 16.7 months of fetal age. The numbers of small follicles (primordial, early primary and true primary), counted in the cortex using stereological protocols, revealed fewer small follicles in the ovaries of animals aged 0 to 4.5 years of age than during either late fetal life or prepubertal life.ConclusionsThe small follicle populations of the late-fetal and prepubertal ovaries of the African elephant were described along with the changing morphology of these organs. The changes noted represent a series of events that have been recorded only in the elephant and the giraffe species to date. The expansion of the interstitial tissue of the fetal ovary and its continued presence in early post natal life may well contribute to the control of follicle development in these early years. Further research is required to determine the reasons behind the variation of numbers of small follicles in the ovaries of prepubertal calves.

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“…Based on vaginal smear composition, their cycles are estimated to be of around 14 days (Gombe 1983). Hyracoidea species show remarkably long pregnancies (around seven months) for their small size and have hemochorial placentation (Kayanja 1973). It is unclear whether sources other than the CL provide progesterone for the full length of pregnancy.…”

Section: Afrotheriamentioning

confidence: 99%

The Shifting Role and Regulation of the Corpus Luteum in Vertebrate Reproduction: A Synthetic Review

Basanta,

Pavlicev

2024

Preprint

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A hallmark of eutherian pregnancy is its dependency on elevated progesterone levels for its entire length. This fact substantially affected the evolution of pregnancy and even the life history of eutherians. Progesterone synthesis by the ovarian corpus luteum, however, long predates all origins of vertebrate viviparity, which requires reconsidering the role of the corpus luteum and progesterone before and beyond placental mammals. Pregnancy originated repeatedly by co-opting the ancestral luteal phase of the ovarian cycle. Therefore, it represents a physiological equivalent and “serial homolog” of the nonpregnant luteal phase. Because of this relationship, we argue that understanding the origin and evolution of pregnancy can substantially benefit from examining the evolution and regulation of the corpus luteum during nonpregnancy. In the first part of this paper, we investigate what is known about the evolution of the corpus luteum and its changing regulation and function across vertebrates, covering both pregnant and nonpregnant cycles wherever possible. Studying pregnancy in the context of the nonpregnant cycle reveals the key evolutionary innovation that facilitated the characteristically long eutherian pregnancies: the regulatory decoupling of the pregnant and nonpregnant cycle, that is, the evolution of maternal recognition of pregnancy. Only after the two cycles became separately modifiable, could gestation length increase without deleteriously extending the time to the next fertile phase. In this review, we argue that, assuming selection for body size increase, the origin of MRP led to a punctuated increase of gestation length, which could imply that we overestimate pregnancy length in the eutherian ancestor when using conventional phylogenetic inference methods. Mechanistically, decoupling between cycles means that the progesterone-dominated phase in pregnancy is extended beyond that of nonpregnancy. In eutherians, this is achieved by extending the lifespan of progesterone-producing corpus luteum, providing additional corpora lutea, extraovarian sources of progesterone, or a combination of these. Alternatively, it can also be accomplished by shortening the nonpregnant cycle. The differences in underlying mechanisms for decoupling among the major eutherian lineages suggest that they originated independently, which leads us to conclude that eutherian gestation consists of parts that are not homologous across eutherians. Consequently, eutherian gestation length is not a homologous trait that can be productively compared across species directly. Finally, we find no evidence for an increase in gestational length due to maternal-fetal conflict. Rather, as long appreciated, body size explains a major portion of the variation in gestation length in eutherians. This suggests that the increase in eutherian gestation length was driven by the need to accommodate an increasing body size, a well-documented trend (Cope’s rule), once independent evolution of pregnant and non-pregnant cycles became possible.

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The Ovary of Rock Hyrax of the Genus Procavia

Cited by 7 publications

References 3 publications

Gestating for 22 months: luteal development and pregnancy maintenance in elephants

Gestating for 22 months: luteal development and pregnancy maintenance in elephants

Growth and development of the ovary and small follicle pool from mid fetal life to pre-puberty in the African elephant (Loxodonta africana)

The Shifting Role and Regulation of the Corpus Luteum in Vertebrate Reproduction: A Synthetic Review

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