Mammary Glands and Solenodon

One of the more interesting aspects of Solenodons is the location of their teats, which are located near the buttocks.
Generally, mammary glands are located in several regions. They can be located anteriorly (as in primates, elephants, sea cows and bats), posteriorly (as in horses, cows, sheep, and whales) or serially (as in litter bearing species such as dogs and cats). Anterior mammary glands are located in the thoracic region, whereas posterior mammary glands are located in the inguinal region.
In addition to supplying young Solenodon with nourishment, the teats provide a secondary function. Namely, they aid in the transport of solenodon young. From an interesting article on Solenodons:

We observed a unique mode of maternal-young contact which we have referred to as ‘teat transport’. This phenomenon is well known among some rodents (2), but unreported in insectivores. At seven weeks of age the youngster will accompany its mother on her foraging activities by clinging to one of the two inguinal teats. At this time the teats are very elongated, up to 2 cm in length, enabling the youngster to cling to a teat as it is dragged along close behind. As the infant grows it is able to assert its own locomotion and simply seize the teat and follow, moving when the mother moves, stopping when she stops. The 21/2 month old infant may still show this response and even scratch itself while standing behind the mother holding on to a teat. It would seem that if the solenodon has to change burrows from time to time, then such a teat-transport mechanism enables the female to move with still very dependent young, pulling them along behind her on her teats, rather than attempting to carry them in her mouth. Mouth transport, of course, is a wide-spread phenomenon in small insectivores; however, the solenodon’s teat-transport mechanism is probably quite efficient since the young remain dependent for a long time. During this dependency period, the female can forage and be accompanied by the young.

This is similar to the function of inguinal teats in marsupials – the one difference being that in marsupials the teats used for transport do not produce milk. I could find no information on the actual anatomy of the Solenodon mammary gland so I can’t compare it to, say, marsupials, cows, sheep, or humans. Although, since Solenodon are pretty ancient (as a species – dating back to the time of the dinosaurs) I would expect there to be some similarities with marsupials.
I also wonder if the teat transport might not explain why there are so few venomous mammals – most mammals transport their young by carrying them with their teeth. I have no data on the subject so this is pure speculation. One of the reasons Solenodon was free to evolve venom is that they used teat transport to move their young and wouldn’t run the risk of accidentally poisoning their young (incidentally, nursing is one way mammals build up immunity so a possible test of this might be to examine young Solenodon’s immunity to their own poison). Other mammals, then would have been precluded from developing venom because an alternative transport mechanism was not available for co-option. If I understand Gould correctly, this would be a case of exaption.

An interesting link Comparative Mammary Gland Anatomy

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6 Responses

  1. Thanks for checking on this. Interesting question about teat transportation and venomous mammals. What a surprisingly weird little critter. Glad you made me aware of it. I had no idea!

  2. I had no idea either! They are weird -seem to be half opossum and half mammal. Unfortunately, I have not been able to track down any info on how the venomous shrews transport their young (although weaning takes place after three weeks so transporting them may not be an issue). It would be suggestive if shrews transported their young the same way Solenodon did. Maybe I should try to get a grant to study the issue!

  3. I was thinking the same thing! Maybe you could do your dissertation on this topic. What were you planning on doing your research in, anyway? I know you are interested in sharks.

  4. I was being a little silly about the grant since I’m not in school at the moment. I’m waiting for my wife to finish her education – since I already have a B.A. I will be going back at some point but I haven’t decided if I will continue with anthropology (I do have a MA thesis picked out – would need to take some math classes to do it though) or go into evolutionary biology. Or both (unlike Bush I have plenty of educational ambition, also unlike Bush I lacking the funds to actually have the luxury of being a full time student – I would have to keep working and go to school in the evenings).

  5. I remembered that you were not in school right now, but were planning on going back. You do seem so interested in evolutionary biology. It does seem like the right fit. Did I tell you that I was (in my working past) a student adviser? I seem to have an innate talent for such things! So, I’m always thinking about people and what their interests are, and how jazzed they are about it. I worked through college too, but I didn’t have children, and I didn’t work full time. Working full time (or even part-time) and going to graduate school at night is tough, but it is do-able.
    What is your wife studying?

  6. She’s studying Organizational Development.

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