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Tuesday, September 2, 2008

Sea star mating, salmon sniffing, and killer whale body temperature

One of the things I love about being a naturalist is being stumped when someone asks me a question I don't know the answer to. It pushes me to further my understanding of the natural world, because the first thing I always do when I get home is find the answer to the question. Here are a couple of my favorites from so far this year.

How do you tell a male and female sea star apart?
This one was interesting, because I didn't even know if there were male and female sea stars, or if a single organism could produce both eggs and sperm. It turns out, though, that individual sea stars do have a gender. Unfortunately, the only way you can tell them apart is by analyzing their gonads (which are internal, by the way), or - and this is the method I prefer - stand around and wait until they release their gametes! Another interesting tidbit I picked up is that some sea stars can also reproduce asexually - one arm will split off and regenerate into a complete separate organism.

How do salmon know which streams to return to when they spawn?
I knew the answer to this question was by using their sense of smell, but when pressed for further details I realized I didn't know very much. Based on local soil type and vegetation, each stream has its own chemical composition which results in a distinct smell. Baby salmon imprint on this olfactory cue - this means that the smell they are following is neither inherited (they imprint on it soon after hatching), nor is it influenced by other cues from other streams they pick up while migrating to the ocean (the imprinting window is a very short one). When the activation of sex hormones induces the salmon to spawn, they recall this olfactory cue from their long-term memory. When researching this I also learned that "smoltification" is a word, meaning the metamorphosis of a young salmon into a smolt, which includes developing preadaptations for life in salt water.

What is the body temperature of a killer whale?
It's not too often someone stumps me with a killer whale question, but here was one I definitely should have known the answer to and didn't. The answer is between 97.5 and 100.4 degrees F. The motivation for this question was a curiosity as to how killer whales stay warm in the frigid local waters. While I knew their layer of blubber (3-4 inches thick) played a role, it turns out there are other mechanisms that help as well:
  • Since killer whales have decreased limb size, they have less surface area exposed to the external environment compared to their land counterparts. This allows them to contain more of their heat in the core of their body.
  • They also have a higher metabolic rate than land mammals, which generates heat.
  • Breathing is a quick way to lose body heat, and since they breathe less frequently than land mammals they lose less heat that way.
  • The arteries in their external limbs such as flippers, flukes, and fins are surrounded by veins. This allows outgoing blood from the heart to transfer some of their heat to blood on the way back to the heart, rather than lose all its heat to the environment.
  • Finally, when a whale dives, less blood is circulated to the body surface, which conserves heat as well.
It's really amazing how many adaptations contribute to thermoregulation of cetaceans, and I can honestly say this is one area that we have a much greater understanding of due to marine parks where these things can be studied with much more ease in captive animals. This information on orca thermoregulation was all taken from Sea World's website.


juliana said...

I'm definitely trying to teach "smoltification" to the fifth graders!

Monika said...

Haha, awesome! I thought you would appreciate that bit. I'm going to try and incorporate the word whenever I talk about salmon.

The K said...

I thoughificated that you perhaps humorified the term smoltification. But, I made-ellied a mistake. The word is real. Learn something every day.

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