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

Abstract

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.

Zoo elephant research: contributions to conservation of captive and free‐ranging species

“…Calves nurse for up to 5 years, so females can be pregnant and lactating at the same time. There are no additional CLs produced during gestation (Lueders et al ., ). Rather, acCLs and the ovCL begin to regress c .…”

Use of Ultrasonography in Wildlife Species

“…41 Today, the leading application for ultrasonography is still in the area of reproduction in wildlife mammalian (and other) species (see Figure 76-3, C through F). 11,12,16,25,44,66 Beyond reproductive assessment and monitoring, ultrasonography is highly useful when it comes to the application of assisted reproductive technologies, many of which are performed under the guidance of ultrasound. 11,12,16,25,44,66 Beyond reproductive assessment and monitoring, ultrasonography is highly useful when it comes to the application of assisted reproductive technologies, many of which are performed under the guidance of ultrasound.…”

Physiologically Persistent Corpora lutea in Eurasian Lynx (Lynx lynx) – Longitudinal Ultrasound and Endocrine Examinations Intra-Vitam

“…Thus, 3D ultrasound is being used more often for pregnancy diagnostics in wildlife medicine [13] and to study ovarian topography and function in various species [12], [14], [15]. Topographic maps of each ovary can be generated to demonstrate the exact position of individual CLs over time.…”