Query about pelvic 'fusing' and evolutionary motivations

[kiania]

Hi!

I'm actually over from the african pygmy hedgehog forums, but I'm trying to find out why females suffer from fused (to whatever extent) pelvises, and was told that guinea pigs suffer the same condition.

Obviously, in captivity, it doesn't (in theory, if good breeding practices are followed) matter a jot, but deep down, I'm a nosey scientist, and I was wondering if anyone here knew the evolutionary motivations for such a condition in wild individuals?

Generally speaking, animals live to reproduce. In pygmy hogs, they 'fuse' at about one year old (assuming no mating), and then live to approximately three years old (in captivity). Using captive as an example for wild, which is a little off, I know, but that means that if there is no breeding in the first 1/3 of life, then they cannot breed in the last 2/3rds of life - which seems a little biologically unsound, assuming reproduction (then caring for offspring until they can cope on their own) is the key to most animal's existance. I am sorry to say I have no idea how long a guinea pig lives (I'd guess at ~6 years?), having longed for one as a small child, but never getting one. But I would assume that the problem is similar.

I google searched, and this forum was the only one to cite a journal article on the subject (of whether all guinea pigs 'fuse', I believe), so I figured there might be someone here that knew why this process happens in guineas

Thanks in advance for any suggestions, they will be gratefully received!

 

[MrPiggle]

These usually an evolutionary reason for everything, and I suppose if it dint work it wouldn't happen, knowing that guinea pigs are social it may be considered that its evolved along side this? living in "herds" and early "breeding" age goes hand in hand I suppose, and fusion wouldn't be a "problem". But it should be considered that guinea pigs are domesticated now so it may be worth considering "wild" cousins ?

If that makes any sense?

 

[Wiebke]

Pelvises don't fuse in guinea pigs, but the ligaments that connect the pelvic bones get less elastic and the contractions get weaker after about 8 months old. This can be very dangerous for older first time mums, considering that guinea pig babies are the largest and most developed of all rodents due to their being roamers and not having babies in a nest or set.

Here are the details:
http://www.theguineapigforum.co.uk/showthread.php?t=37379

 

[paulag]

It's sometimes not so much that something evolved for a reason, but that it was an accidental consequence of something else and then wasn't selected out. In the wild cavies live in herds and so would never avoid being pregnant from a very young age. Chances are that their life expectancy is pretty short as well so a lot of then may not even reach the age at which this happens.

Although hedgehogs don't live in herds, evidence from my back garden suggests that in European hedgehogs at least the male hedgehogs are pretty damn persistent when the females come into season. So the chances are no female hedgehog gets through her first tear without a pregnancy either

Paula

 

[kiania]

I know 'fused' isn't the right word for either genus, it was a general phrase to get the point across

And yes, hedgehogs are persistant, but they are usually solitary. I would have thought that mating in solitary animals might be a take-it-when-you-can-get-it thing, but since they fuse/tighten ligaments similar to cavies, it doesn't seem to follow.

I've got to the point where I think it must be coevolved with something else within their anatomy, or perhaps that rather than 'wasting' resources on infants, they can then 'waste' them on this. Essentially saying that it is their static state, and that the pressure of giving nutrients to growing infants prevents the development of tightened ligaments (or fusing, or the right turn of phrase!). Or at least, that is my current theory (no idea how it could be tested for mind you!).

Once again, thank you for your input, it is appreciated.

And, on the upside, I had a looksie around your forum for piggie diets, since we have a small horde of them at work, and I feel guilty just giving bits of carrot, cabbage and apple (better than nothing since I'm part-time, but still, it seems repeative!). I'll try them on tiny bits of chopped up celery, baby tomatoes, little bit of kiwi and cucumber - one connundrum down, and a win for the guineas...might try a tinsy bit of banana as well, I know agouti can only have a tiny lump each per week, so wasn't sure about it for the guineas, but seems they can. Huzzah! Thanks again

 

[Freela]

I love hedgehogs- I kept african pygmy hedgehogs for twelve years!

I'm not sure that there is an evolutionary advantage of any kind to the pelvis fusing and making labour more difficult... I think it likely has more to do with the fact that, in nature, there is no way that a guinea pig would hit a year of age without mating! It just would never happen. Having stretched out the bones and ligaments to give birth the first time, it wouldn't present a problem in the future. It's only because breeding is more managed in captivity that it's even an issue, kwim?