Weddell seal blood: Part two
Back to blood!
If you’re just tuning in, make sure you read the previous post to get the basics on blood. Here, we’ll DIVE DEEPER into the in-the-field research we’re working on now. This gets to the heart of our study!
Before we do that, here’s a brief recap of the difference between Weddell seal blood and human blood:
- Weddell seals have higher levels of hemoglobin and hematocrit than humans do, which increases their oxygen-carrying capacity.
- In addition…Weddell seals have about 10 times more blood (by volume) than humans do. Yes, their bodies are quite a bit bigger, but the difference is not strictly proportional. Blood makes up 7-8% of weight in a human body, compared to 20-22% of weight in a Weddell body. That’s nearly 3 times more blood per pound, if you compared humans to Weddell seals.
In the field
On my first expedition down here, the research team took blood samples on each seal in our study to find out:
- The number and size of red blood cells
- Hematocrit level
- Hemoglobin level
These measurements tell us about the animal’s health and how much oxygen the seal’s body can store. This time, we are using our samples to get all three of those measurements again, but we also want to know one more thing – if the seal is pregnant!
Can you tell that from a blood sample? Yes!
Weddell seal blood and pregnancy
Look how big this mama-to-be is! Photo credit: Vicki Heinrick.
Photo credit: Vicki Heinrick Antarctica.gov.au You may remember that the focus of this research project is on female Weddell seals – those that have pupped recently and those that have skipped a breeding cycle. The team is hoping to find out if there is a relationship between pupping (giving birth) and molting (shedding fur). Why, you ask? Another great question! Those two activities take a LOT of energy and our team is trying to understand how these energy-expensive tasks and the seals’ physical condition relate to one another. So, to test our hypothesis, we need to know which seals are pregnant.
But, how will we do that?
Ultrasound machine
…By using an ultrasound machine. And here’s a brief description of how it works?
Basically, an ultrasound uses sound waves to ‘see’ inside a body (in our case, a seal). It sends sound waves, too high for us to hear, into a body. The sound hits a surface (like tissue, bone, muscle etc.) and bounce back, like an echo in a cave, to produce a picture.
Doctors often use ultrasounds on pregnant women to monitor the growth of a baby; we use it to detect if a seal is pregnant.
Here’s a picture of the ultrasound we use. Photo credit: Michelle Shero.
And here’s the ultrasound image of seal embryo. Photo credit: Michelle Shero.
We used a low-resolution ultrasound during the 2012 expedition to measure blubber thickness. It was a bit persnickety and often difficult to use, and to detect pregnancy, we need to use a much more complex machine. The scientists think a blood test would be a simpler and easier way to see if a seal is pregnant. Why? Because it can be complicated and time-consuming to haul a battery-operated ultrasound machine around on the ice, and a blood test would allow us to test for pregnancy in a larger number of seals
So, how does a blood test detect pregnancy in a seal?
We’re learning that right now! The neat thing about science is that research is never really finished – we can always learn more! In the time leading up to this trip, our research team was hard at work trying to develop a pregnancy test for the seals. Our hypothesis is that certain hormone levels will be higher in the blood of pregnant seals.
What are hormones?
Hormones are chemical substances that act like messenger molecules in all mammals’ bodies. Different hormones play different roles to regulate the activity of cells and organs in the body.
What hormones are we looking for?
Thyroxin (T4) and triiodthronnine (T3) – hormones produced by the thyroid gland that regulate metabolism, or how much energy an animal uses. Animals with higher T4 and T3 may be more likely to become pregnant because they can use more energy to support a growing pup.
Estrogen – the primary sex hormone of females, plays a key role in the reproductive cycle. Estrogen helps prepare a potential mom to breed and begin a pregnancy.
Progesterone – a hormone that plays a key role in the reproductive cycle by stimulating the mother’s uterus (the organ where fetal development and growth occurs) to prepare for pregnancy and keeps the pregnancy healthy once the fetus starts growing
Relaxin – a hormone produced by the placenta in pregnant animals and so can indicate pregnancy. Relaxin helps mothers give birth
Cortisol – a stress hormone that is higher in animals that aren’t getting enough energy. We expect animals that have lower cortisol (aren’t as stressed) will be more likely to become pregnant and have healthy pups.
Growth hormones – these can be examined to see if the mother is getting proper nutrients during pregnancy and is able to use them to support a growing fetus
The Weddell seal team taking blood. Photo credit: Alex Eilers.
How will we know if our hypothesis is right?
We will draw blood samples from many female seals to establish a baseline of what hormones are normally present and what levels are normal. Then, during the season seals could be pregnant (January-February), we will draw more samples to find out if the hormone levels have changed. The seals that have levels consistent with pregnancy will be monitored to see if they pup. We will also see if seals with different hormone levels are molting faster or slower, since hormones that change with pregnancy and condition can also speed up or slow down hair growth.
One hypothesis after another
Like I said before, science is a process, and we’re always learning more! So, by tracking what factors influence a seals pregnancy and how a seals physical condition and energy expenditures might influence these factors, the team is learning more about this highly adaptive marine mammals. These answer will, in turn, allow scientists to create another hypothesis to find out why!