On August 6th we will celebrate the one-year birthday of our
first naked mole-rat litter since 2007. We’re so excited about this milestone, we’re even making them a
tuber cake. In the past year, eight litters were born to c
ompeting queens, Galinda and Elphaba -a total of 136 pups in 12 months! Twenty-one have survived pup-hood and are growing into healthy adult naked mole-rats. Our colony has doubled in size in just one year!
This milestone started Life Science manager Sarah Moore thinking about the difficulties of mole-rat survival – even in captivity.
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Two seemingly opposing things can be said of naked mole-rats: They are extremely long lived for their size and the first months of life are fraught with danger and a low probability of survival. If a naked mole-rat can survive the first few weeks of life, it has a good chance to go on to live a long and healthy existence. However, the challenges of those first days are often insurmountable. The last three litters born in our colony have had no surviving pups. The difficulties associated with making it through pup-hood have become increasingly apparent.
At birth, a naked mole-rat weighs less than 2 grams. Its eyes and ears are sealed closed and it can only drink milk. But it is not entirely helpless. From birth, mole-rat pups can right themselves if they fall over and wriggle through piles of older animals, working their way to the top of the heap. This is critical for them, as those who are unable to climb, risk being crushed.
It is during these first five days that we notice big problems – such as if the queen has not been providing milk or if the pups are unable to nurse. Pups are so tiny we can see milk in their stomachs if it is present. Without milk, the babies cannot survive.
Rarely do necropsy results from animals at this age point to disease. Indeed, often nothing can be concluded from studying pups that die in their first week. In fact, with large litters it is common for some of the pups to be more fully developed than others and it is rare that all of the litter members survive.
By the fifth day if all is well, the pups have grown significantly and are moving around the enclosure. They still need milk to survive and they are still highly vulnerable. But once they pass the five-day mark, we feel optimistic enough to post a birth announcement on this blog!
Between days five and ten, a second set of concerns begins. It is in this time that pups gain enough autonomy, but it is also during this time that they begin to pick up any viral or bacterial infections that may be present in the colony. We have found that frequent changes of bedding help reduce this risk. Even so, individuals with any inborn health problems may succumb during this week.
At ten days old, a mole-rat pup moves about easily, nurses well, and may be sampling food. Surprisingly, their first bites are often tough root vegetables rather than the soft dough balls we also provide. Baby mole-rats have teeth from the first day of their life. But their eyes remain sealed until their 20th day. This is less of a setback for tunnel dwellers than it would be for animals that evolved above ground.
Over time, naked mole-rat pups reach a third, difficult phase: The transition to a diet of entirely solid food. The cecal pellets passed from other workers are critical to the pups’ ability to navigate this change. Once they are eating solid food, they get to work cleaning chambers and taking on the everyday chores of a regular naked mole-rat. But that doesn’t mean they stop growing. Naked mole-rats usually take about 18 months to reach full size.
So why have some of our litters been successful while recent litters have be totally unsuccessful? There are likely a number of factors and we surely don’t know all of them. Aside from all of the inherent risks and tribulations of early pup-hood, it could be that our colony is reacting differently to new pups. Remember, half our colony has been born in the past year. Perhaps because of their youth and lack of skill in pup-rearing, the young pups are injuring the babies more than other adults would.
Additionally, our colony is the largest its population has ever been. Is there a limit to the number of individuals that can be sustained in a colony? Do the adults respond differently to new litters when the population has reached its limit? These are all questions we are asking now, and we will continue to post updates and new observations as they come. However, one thing is always certain with naked mole-rats: there will always be more questions.
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