Placentation in the plains zebra (Equus quagga).

The research studied the placental development and fetal gonad functions in pregnant plains zebras and found notable similarities with donkeys rather than horses. It also explored the role of specific hormones and enzymes in the process, highlighting an unusual yet unchanged production mechanism throughout evolution within the Equus genus.

Research Context

In this research, the scientists examined the placental and fetal gonad functions of 12 pregnant plains zebras (Equus quagga). The gestational period of these zebras, estimated to be between 81 and 239 days, provided insights into different stages of pregnancy. This study helped to better understand the reproductive biology of zebras and how it compares to other members of the Equus genus.

Findings and Comparisons

• The zebra placenta was observed to be developmentally 3-4 weeks slower than that of a horse. This delayed development and the presence of long-lived endometrial cups and low zebra chorionic gonadotrophin in maternal serum make zebra pregnancy more comparable to donkey instead of horse pregnancy.
• The presence of few accessory corpora lutea, a type of temporary endocrine structure in mammals, in the ovaries during the first half of gestation also point towards a similarity with donkeys.

Fetal Gonads and Hormonal Activities

• The research identified that zebra fetal gonads start enlargement after 80 days of gestation. These gonads demonstrated positive staining for 3β hydroxysteroid dehydrogenase and 17,20 lyase steroid enzymes.
• Similarly as in horses and donkeys, it’s confirmed that zebra fetal gonads can synthesize C19 androgens, which are then converted by the placenta to C18 estrogens.

Evolutionary Significance

• What the study found remarkable is the persistence of the particular mechanisms of gonadotrophic and steroid hormone production within the genus Equus, against a backdrop of significant physical adaptations and considerable loss of chromosomes throughout its evolutionary journey. Despite the many changes, this feto-placental production process has remained unchanged.