Meeting Abstract
Weddell seals (Leptonychotes weddellii) give birth from October to November and ovulate at the end of lactation (5-6 weeks later). Pinnipeds characteristically experience an embryonic diapause that lasts 1-4 months before proceeding with active gestation; however, our work challenges this notion in Weddell seals. From 2014-2017, we used transrectal ultrasonography to assess the reproductive phenology of prime-age adult Weddell seals at the time of ovulation (n=21; mid-November/mid-December) and when embryo implantation was thought to occur (n=82; mid-January/mid-February). Post-partum females, and seals that did not give birth that year (i.e., “no-birth”) were handled at both time points. By late November no-birth females had ovulated, defined by a well-perfused corpus luteum, while 40 days post-partum females were still pre-ovulatory, with large antral follicles. By mid-January/mid-February, 80% of post-partum and 85% of “no-birth” seals were detectably pregnant. Based on anatomical features such as crown-rump-length, fetal heart rate, placentation, and organogenesis, pregnancies were estimated to be between ~7-75 days gestational age. Embryo growth curves were constructed and used to calculate when embryo implantation occurred, placing the start of active gestation coincident with ovulation in Weddell seals. Thus, the period for embryonic diapause appears to be dramatically shortened, or lost altogether. The absence of any significant diapause causes Weddell seals to have the longest (>10 month) active gestation of any phocid. This would reduce the daily energetic costs of pregnancy, but also extends the time that the developing fetus may be vulnerable to environmental perturbations.
