Congratulations Hiroaki Soma

Professor Hiroaki Soma (at left) recipient of the 2018
IFPA Senior Award

It is a pleasure to record that my good friend and colleague Hiroaki Soma received the Senior Award of the International Federation of Placenta Associations at their recent meeting in Tokyo.

In his address, Professor Soma looked back over 60 years of research including important clinical work on gestational trophoblastic disease in Japan and placental lesions associated with pregnancy at high altitude in Nepal.

In addition, he gave valuable insights about comparative placentation. The range of mammals included chinchilla, giant panda. Japanese serow, sloth, chimpanzee, elephant, manatee and hyrax. As if this were not enough, Professor Soma also presented his research on pregnancy in sharks and rays conducted at the Churaumi Aquarium in Okinawa. 

A placenta pioneer from Philadelphia

Newborn and afterbirth of six-banded armadillo
(Euphractus sexcinctus) from Chapman 1901

Some of the earliest studies of placenta in the United States were those of Henry C. Chapman published in Proceedings of the Academy of Natural Sciences of Philadelphia (available on JStor). His observations on the placenta of a six-banded armadillo (Euphractus sexcinctus) were published in 1901 and went unsurpassed for over a century. Importantly, Chapman noted that polyembryony, known from the more widely studied nine-banded armadillo (Dasypus novemcinctus), did not occur in Euphractus.

Fetal membranes of a kangaroo (Macropus giganteus).
Note the small allantois. From Chapman 1881

Chapman is notable for an early study of the fetal membranes of the Eastern grey kangaroo (Macropus giganteus). He noted that there was a large yolk sac but a relatively small allantois that did not form a placenta.

Zonary placenta of an African elephant (Loxodonta africana)
From Chapman c. 1880

Chapman got his armadillo and kangaroo specimens from the Philadelphia Zoo, but his African bush elephant (Loxodonta africana) placenta was from Cooper and Bailey’s London Circus. His was one of several early descriptions of elephant placentation, including a paper by Assheton (here), but there was then a hiatus until the classical work by Amoroso and Perry in 1964 (here). Based on the records of the elephant keeper, Chapman was able to estimate gestation to 650-655 days.

Henry Cadwalader Chapman (1845-1910)

Chapman came from a prominent Philadelphia family. His grandmother was a Biddle and her sister had married a Cadwalader, which may explain his middle name. He studied medicine then spent three years in Europe under Richard Owen in London and Alphonse Milne-Edwards in Paris.

Chapman’s work has been cited by Mossman, Amoroso, Wislocki and Enders (here), but is in danger of being forgotten. When the next paper on Euphractus appeared in 2012 (here), Chapman’s earlier contribution was not acknowledged.

Steller's sea cow

Reconstruction of Steller's sea cow (Hydrodamalis gigas)
By Emőke Dénes (Natural History Museum in London) (CC BY-SA 2.5)

When first described by Steller in 1741, the range of this sirenian was already restricted. Intensification of hunting led to extinction of the species within another 27 years.

A recent paper with a "stellar" cast of authors (here) uses molecular data to firmly establish the position of Steller's sea cow within crown Afrotheria; with additional morphological data it also shows shows how the species fits into the fossil record.

Steller's sea cow (Hydrodamalis gigas) belongs with the dugong (Dugong dugon) in Family Dugongidae whereas the three species of manatee belong to Trichechidae. Together they make up the Order Sirenia, which is sister to the elephant Order Proboscidea.

Endotheliochorial placenta of the Amazonian manatee

Fetal (fc) and maternal (mc) capillaries are present

Elephants have an endotheliochorial placenta. Therefore it perplexed us that Wislocki had described the placenta of the West Indian manatee (Trichechus manatus) as haemochorial. Therefore we reopened the matter by studying placentas from the Amazonian manatee (T. inunguis). We were able to demonstrate two sets of capillaries (shown above) and conclude this placenta to be endotheliochorial (here).

The allantoic sac of elephants and manatees has four chambers and we have shown this to be a shared, derived character of the superorder Afrotheria (here).

An aquatic past for elephants

Endotheliochorial placenta of the Amazonian manatee

Fetal (fc) and maternal (mc) capillaries are present

The closest relatives to elephants are the dugong and manatees. Placentation in the African elephant Loxodonta africana has been well studied (reviewed here). We were able to show strong resemblances in the placenta and fetal membranes between the elephant and the Amazonian manatee Trichecus inunguis (here).

This hoax photo of the Loch Ness monster

is thought to be an elephant swimming

It has long been suspected that the ancestor of proboscideans was aquatic or semi-aquatic (here). Clues include the presence of nephrostomes in the mesonephros of the fetus (here). Now support comes from an unexpected quarter: myoglobin.

Diving mammals such as whales and seals have high amounts of myoglobin in their muscles to act as a source of oxygen during prolonged submersion. A new study (here) shows that in such species there is an increase in surface charge of the molecule to prevent dimerization occurring at high concentrations of myoglobin. This molecular signature was also found in sirenians and proboscideans. The analysis included two extinct species: the woolly mammoth (previous post) and Steller's sea cow. A phylogenetic analysis suggested that substitutions contributing to increased surface charge on myoglobin occurred in the common ancestor of sea cows, elephants and hyraxes (paenungulates). The conclusion drawn is that this ancestor may have been semiaquatic.