Lots of you did some research and discovered that naked mole rats are the only eusocial mammal. Here is what some of your classmates had to report about naked mole rats:
Naked Mole Rats are arguably the only eusocial mamal. Eusociality involves reproductive division of labor, overlap of generations, and cooperative care of young.
The language here is a bit complicated, but Max’s definition of eusociality is exactly right. Reproductive division of labor means that one 1 or a few individuals reproduce, while the others have different jobs, such as gathering food, maintaining the tunnels, or caring for young.
The naked mole rat is the first eusocial mammal. One female in the entire community of 80 naked mole rats does all the breeding. It took ten years for scientists to truly consider the naked me rats as eusocial animals because they don’t have the permanent, physical trait that distinguish different levels of the colony. Then scientists found this physical difference. The queen naked mole rat’s spinal bone lengthens during it’s pregnancy so it can hold more babies and still fit into the tunnels of the home.
Wow Rebecca, I thought I was an expert on naked more rats, but I did not know about the longer spine bone in the queens. That is really neat! I watch the naked more rats often at the zoo (you can see them at the Philadelphia zoo or the National Zoo in Washington D.C.) and it is very hard to see any difference – sometimes the queen looks a bit bigger than the others, but it is not a big difference. Thanks for the information!
Naked mole Rats are a mammal with a eusocial system. they live in large colonies with only one female that breeds. The majority of the colony are workers. these can be both males and females and they spend their whole lives working for the colony. The normal colony size is about 80 but there have been colonies with a population up to 295 observed.
Inbreeding is very common in these animals which results in a lot of similar genetic make up.
Great job Annie! You bring up a very important point. In insects like ants and bees, eusociality works because of their very unusual haplo-diploid genetics. It results in female workers being more closely related to their sisters than they would be to their own offspring. As a result, they actually benefit more in terms of fitness (a fancy evolutionary term meaning how many of your own genes get passed down) from raising siblings than they would from raising their own children. Naked mole rats are diploid animals like us, so for them it ought to be a real disadvantage to raise siblings instead of their own offspring. BUT, because they are so inbred, siblings share a lot of the same DNA, so it isn’t a real disadvantage.
Normally, in diploid animals like humans, an individual shares exactly 50% of its genes with its offspring and an average of 50% of its genes with a full sibling. Naked mole rats share more than 80% of their genes with siblings, and so can enjoy high reproductive success through kin selection- that is, contributing to the survival and reproduction of relatives rather than producing their own offspring.
I think that this also sort of answers Akki’s question below:
ANTS have always made me curious since I was a baby. We had an ANT colony in our classroom when I was in 4th grade. We fed them and took notes and observed the colony the entire year. It was very interesting to see the ants organization. Though it seems good that they work so hard and take care of their families, some ants sacrifice seems not good to me. It definitely sounds very unfair to intelligent creatures like us where everyone should be given equal rights. I always wondered why it is like that with ANTS? Probably because their species could survive under any circumstances.
Akki also sent some good links to information on mole rats, and I have included some of my own as well:
and this one is a zoo cam so you can watch the naked mole rats:
Thanks to everyone who participated in this fun research!
Here is a TOUGH question for you all to think about. Normally, organisms act to maximize their reproductive success- that is, to ensure their own survival and reproduction and that of their descendants. We’ve learned that eusocial insects (haplo-diploid) refrain from breeding in order to raise siblings because they actually share more genes with siblings that with their own offspring. We’ve learned that naked mole rats are so inbred that once again, individuals can pass on a large proportion of their own genes by ensuring the survival of siblings. But for normal, non-inbred diploid mammals, could it ever pay off to refrain from breeding in order to assist in the survival and reproduction of relatives? Think about this question, and explain what this quote from the famous evolutionary biologist J.B.S. Haldane means:
“I’d give my life for two brothers or eight first cousins!”– J.B.S. Haldane