Saturday, 31 August 2013

Human Pregnancy: Gestation Period Variation Compared with Nanny Goats

One of the stories running during this year’s ‘silly season’, when news media are desperately trying to fill newspapers, radio, television and websites, was one highlighting research1 which showed, in the words of the BBC News website, Pregnancy length “varies naturally by up to five weeks”.

Great surprise was expressed about this range of variation (14% of the mean ovulation to delivery period of 268 days). In practical terms the sheer stupidity of giving expectant mothers a ‘due date’ (with the implication that being ‘overdue’ is abnormal) was highlighted. In these days where education in biological systems has declined to the extent that the public expect certainty in all things biological and medical, the reports helped to highlight that variation and uncertainty are to be expected.

Reading of the extent of the variation, I tried to remember the variation I had found in the goat. In 1978 I collected all the data from the then goat herd at what is now the Babraham Institute that had been recorded between 1954 and 1977, a total of 374 cases2. The mean time between mating and delivery was 150 days (as also found by Sydney Arthur Asdell in 1929). Although 90% of births occurred between 146 and 154 days, the full range was 135-159 days (24 days). The percentage variation (24/150) of 16 is very similar to the latest human data.

So, if we have 14% variation for the human gestation period and 16% for the caprine, what about other mammals? A quick look through a UFAW Handbook and elsewhere suggests a similar level of variation (cat 14%, dog 13%, rabbit 22%, guinea pig 11%, rat 14%). Somebody must have noted this before somewhere but if they have I cannot remember it nor can find reference to it.

Is the variation in the length of pregnancy the simple result in differences in the rate of development of the fetus? Or adaptive in that the time of parturition can be controlled? Or both?

As work on the initiation of parturition by activation of the fetal adrenal developed during the 1970s, the talk in the coffee room was that fetal control of the onset could not be the whole story since some herd animals clearly synchronised parturition in addition to synchronising oestrus. Wildebeest were the prime example. The extent of the control is illustrated by Berger’s studies on American Bison3. Gestation was shorter by approximately 6 days in those females that mated after the seasonal peak, thereby ensuring that births were synchronised with the females that had mated at the peak. There was a difference in whether or not the females were in good body condition. Gestation was earlier in those in good condition but not in those in poor condition. Clearly though there is an advantage in ensuring that births are synchronised since delivering early came with a cost. The tradeoff was that the offspring of those females that delivered early were approximately 20 kg lighter when 6 months old. Achieving synchrony, presumably to lessen the chances of predation, is clearly an important reproductive tactic. But are we any the wiser now as to the physiological mechanism of this control than we were in the mid-1970s?

Finally, is there any evidence of adaptive control of the onset of parturition in human mothers? I know of no evidence, only of all sorts of attempts to get things moving. I have seen the exertion of ascending the Peak in Hong Kong along Hatton Road as one try; the eating of a very large roast-beef dinner as another. Did they work? Well, the babies appeared eventually.

1 Jukic, A.M., Baird, D.D., Weinberg, C.R., McConnhaughey, D.R. & Wilcox, A.J. 2013. Length of human pregnancy and contributors to its natural variation. Human Reproduction doi:10.1093/humrep/det297
2 Peaker, M. 1978. Gestation period and litter size in the goat. British Veterinary Journal 134, 379-383.
3 Berger, J. 1992. Facilitation of Reproductive Synchrony by Gestation Adjustment in Gregarious Mammals: A New Hypothesis. Ecology 73, 323-329.

Monday, 12 August 2013

The Eponym Dictionary of Amphibians: Where’s Conrau?

Starting in 2003 with Whose Bird?, the Eponym Dictionary series (mammals following birds, then reptiles and, this year amphibians) has provided interest and amusement in epi-zoology. As the series has gone on, information from earlier volumes is often repeated, as a necessity since collectors, benefactors and museum workers often have birds, mammals, reptiles and amphibians named after them. There is particular overlap with reptiles and amphibians and I was often miffed to find I had already read an entry in one of the other volumes. I took three double pages at random and found that a third of entries were repeats from earlier volumes.

I found a few omissions. The most remarkable I noted was the absence of Gustav Conrau who collected in the Cameroons in the closing years of the 19th century. He does appear in the volume on reptiles for the gecko, Lygodactylus conraui. Conrau should appear in the volume on amphibians for the genus Conraua, now comprising six species including that famous amphibian, the Goliath Frog, Conraua goliath. The genus was erected by Fritz Nieden in 1908 for G. robusta (Die Amphibienfauna von Kamerun. Mitteilungen des zoologischen Museums Berlin 3, 489-518) and the Goliath Frog, described by Boulenger in 1906 as Rana goliath, was moved into it by Nieden.

The story of Conrau, a German trader and labour recruiter in Cameroon is told in the Eponym Dictionary of Reptiles. He had recruited labour from the Bangwa people for a plantation to the south. When he returned, the Bangwa thought their labourers must have died since they were not with him. The Bangwa held him hostage against their men’s return. He was wounded while trying to escape. He probably killed himself to avoid being captured although he may have been shot by his pursuers. The Germans sent two punitive expeditions as a consequence.

Fritz Nieden (1883-1942), incidentally, does appear – for the caecilian Boulengerula niedeni described in 2005.

The Eponym Dictionary of Amphibians. 2013. Beolens, B., Watkins, M., Grayson, M. Exeter: Pelagic Publishing

Friday, 2 August 2013

Donors of Reptiles to London Zoo 1914/15: 9. C.R. Walker and Mons. de Southoff

I reach the end of this series of posts with failure. I have been unable to find any more information on two donors. This is what Clin Keeling wrote in A Short History of British Reptile Keeping:

First there was one C.R. Walker, F.Z.S., of The Vivarium, West Bromwich, near Birmingham, who during the early days of the war sent, and received on an exchange basis, quite a lot of material to Regent's Park; for example one consignment of his consisted of twenty-five assorted Skinks, Geckos (including the New Zealand species) and Tree Frogs, while during research in another direction I made the fascinating discovery that on 15th October 1913 London's first Soft-shelled Turtles (Trionyx) came from him. As far as we're concerned just who and/or what he was must, pro tem, remain a mystery, although it sounds very much to me as though The Vivarium was a shop that specialised in animals of this kind – in which case it must have been one of the very first in the country and possibly indicative that even at that period there was more demand for them than wenow realise  – or it could even have been some kind of reptile display, or both. As things stand, though, we must leave it there in the shadowy land of speculation.

The only thing I do know is that C.R. Walker was not a Fellow of the Zoological Society in 1910 or 1913. There is a speculative geographical connexion with Herbert Tomlin Pollitt (23 June 1013 post) but that is all I have been able to find. This one needs more work in the Zoo Library because it would be very interesting to shed more light, for the reasons Clin explained, on just who Walker was and what The Vivarium did.

Finally, I have also been unable to find anything about the Mons. de Southoff who donated European salamanders and snakes.