Wednesday, 26 October 2016

Congratulations Camilla Whittington

Camilla Whittington with sea horses University of Sydney
Viviparity and pregnancy has evolved numerous times and Camilla Whittington has set herself the ambitious task to seek similarities in gene expression that support pregnancy in sea horses, viviparous lizards and marsupial mammals. Her paper on the transcriptome of the brood pouch of a male sea horse was highlighted in a previous post.

Now I am delighted to report that Camilla has been awarded a Fondation L'Oréal Women in Science Fellowship. It is good that this award exists and especially encouraging that research in comparative biology of pregnancy has become known to a wider public through the publicity surrounding Camilla's Award.

Sea horses from Camilla's web site
To learn more about Camilla's Work visit her web site. For hard science you can read about the comparative genomics of hormone signalling in the chorioallantoic membrane here.

Monday, 10 October 2016

Did placental oxygen transfer support increased brain metabolism as humans evolved?

Cerebral blood flow in relation to age of fossil skulls
from 12 hominin species.
Reproduced from Seymour et al.  R S Open Science (CC-BY)
There is much interest in how increased brain size impacted on dimensions of the pelvis, birth weight and placentation as humans evolved (here). Increased brain growth in fetal life would seem to demand a greater placental blood flow to ensure an adequate oxygen supply. This may have led to increased invasiveness (discussed here) and indirectly to the risk of preeclampsia (here). 

But what if there was an increase not only in size but in the metabolic rate of the brain?

In a novel approach, Seymour, Bosiocic and Snelling attempted to assess cerebral blood flow in fossil adult hominins as a surrogate for oxygen supply to and consumption by the brain. As their starting point they measured the diameter of the carotid foramen in skulls of fossil hominins ranging from Australopithecus to archaic Homo sapiens (the carotid foramina carry the principal arteries supplying the brain). As can be seen in the figure, their main finding was that during hominin evolution cerebral blood flow increased disproportionately to brain size. The implication was that there was a progressive increase in the metabolic rate of the brain.

Of course this approach required some major assumptions (see below). But if the metabolic rate of the adult brain did increase successively as humans involved, so perhaps did that of the fetal brain. Here more is at play than the rate of blood flow to the brain. In adults the blood becomes fully saturated in the lungs, but that is not the case in fetal life. The oxygen content of the blood reaching the brain is dependent on placental function (reviewed here).

For Neanderthals there is enough data to conclude that brain size at birth did not differ from that of modern humans (here). But if human fetal brain had a higher metabolic rate than Neanderthal fetal brain, it might still have required a more efficient placenta.

Assumptions: The approach adopted by Seymour et al. relied on rearranging an equation for shear stress to isolate one of its determinants, blood flow rate. To accomplish this, shear stress must first be estimated using a scaling model that relates shear stress to body size. This is the weak point in the analysis, but the authors point to a previous study that verified the approach in primates and marsupials

Tuesday, 4 October 2016

Horned armadillos and rafting monkeys

A giant caiman (Purussaurus neivensis) and small
litopterns (Megadolodus molariformis)
Illustration Velizar Simeonovski (C) 2016 by Darin A. Croft
I thoroughly recommend this new book on South American fossil mammals of the Caenozoic Era. Intended for a broad readership, it is a times fanciful. The full caption to the above figure reads, "A giant caiman (Purussaurus neivensis) finally strikes in a fury of mud and water after quietly approaching a group of small litopterns (Megadolodus molariformis) drinking at the river."

Indiana University Press ISBN 978-0-253-02084-0

The book is dedicated "to anyone who has ever wondered what a notoungulate looked like," which makes me the target audience. I read extensively about the fossil fauna when writing about the placentation of the extant species (here). The extinct families that lived side by side with marsupials and earlier xenarthrans were so unfamiliar as to seem wraith-like.

The xenungulate Carodnia vieirai from Itaboraí
Illustration Velizar Simeonovski (C) 2016 by Darin A. Croft
Darin A. Croft has worked closely with Velizar Simeonovski to bring extinct taxa to life. "The xenungulate Carodnia vieirai passes under the shadows of the dense vegetation of Itaboraí at high noon" is another example. This is the same artist who illustrated Extinct Madagascar (previous post).

After some introductory chapters the subject matter is arranged according to 15 fossiliferous localities. Conspicuously absent is Lagoa Santa in Brazil where the Danish palaeontologist P. W. Lund worked in the Nineteenth Century (here). His extensive Collection is housed at the Natural History Museum of Copenhagen University.