Bio lecture: Sexy Legs: how frogs amplex their way to success

On a lark we decided to head down to the Biology Department at the College of Charleston.  On Mondays they have a noon lecture.  The W’s were in; so the whole gang went.  The kids were disappointed that the cushy chairs were not in this lecture hall.  It’s the little things, you know.

The best part of the lecture was the understanding the process that scientists go through when undertaking a project.  She showed how she went through each step.

Dr. Susan Peters from the University of NC at Charlotte was the lecturer.  Her speciality is morphology.  She has studied frogs for 15 years.  As a morphologist, she asks these types of questions:

  1. How do structures function in animals?
  2. Does that function affect fitness?
  3. Which properties may be most important to enhance function and fitness?
  4. Where does the structure arise from?  Is it a positive grand mutation or is it modification that is replicated?
She stressed the need to observe and document Nature Function – get out into the wild (or the least artificial environment as possible) and take pictures, write observations, measure angles from your pictures.

From National Geographic.

She also stressed that a model organism must be easily accessible. (You will need a lot of the organism.) You also want a creature who has application across the order.
She chose the North American bullfrog.  In the past 15 years, she has worked to understand three aspects of their morphology:
  1. Hopping and swimming behavior – kinematics
  2. Structure and function – fiber/muscle types
  3. Forelimb dimorphia – which muscles are different in males and females and why?
THIS IS STEP ONE IN SCIENCE:  MAKE AN OBSERVATION ABOUT THE WORLD AND WONDER WHY.
She observed that males and females have different sized forelimbs.  This is exciting for several reasons – one is that you are looking at the same species and comparing granny smith apples to granny smith apples not to golden delicious apples.

Two male green frogs sparing - from FWG's blog.

A bit of country wisdom:  Bullfrogs are territorial creatures and during mating season they defend their territory in a sort of sumo wrestling way.  They also call for females in the evenings and nights during mating season.  Most country kids who live near a pond can tell you that frogs have no idea what they are hopping on in the dark. You can get a frog to jump on your hand thinking that your hand is a female.  They can hold that position for several hours.  But why would you let them?  It is just funny to gross out your mom.

American toads in amplexus. From The Sojourns in Nature Photo Blog.

A bit of science thought:  The mounting of male (usually smaller) frogs onto female frogs is called amplexus (Latin for embrace). All fertilization of eggs is external.  It can take anywhere from two hours to two weeks. (Yes! That is correct.)  The female sheds gametes into the water and the male fertilizes them.   The male has to maintain the embraces for quite sometime with a partner who is not necessarily agreeable.    Dimorphic is a term for physiological differences between males and females of the same species.
So that said, what do frogs use their forelimbs for?
  1. territorial defense (grappling)
  2. swimming
  3. propping themselves up
  4. minor use in hopping
  5. amplexus
STEP TWO:  SEE IF SOMEONE ELSE HAS WONDERED WHAT YOU ARE WONDERING AND DID EXPERIMENTS ON IT.
She and her team researched frog forelegs and previous studies. What research had been previously done?  
All previous studies had been aimed at the Flexor carpi radialus (FCR).  If you were going to eat frog forelegs, this is the muscle you would go for.  It is the larger of the four main muscles in the arm. What about males v. females?
  1. Proportionately larger (really bigger)
  2. Conflicting data on the type of muscle fiber making up the  FCR.  This is very important because there are three main types of muscle and certain ones “oxidize” quicker and thus the muscle won’t fatigue as easily.
  3. Larger glycogen stores
  4. More mitochondria
  5. More fat
All of this suggests that the muscle can handle larger force with less fatigue.
STEP THREE: POSE YOUR QESTIONS AND GATHER PRELIMINARY DATA.
She and her team dissected forelimbs to look at all the muscles and compare them. Took lots of nature and lab pictures to look at behavior and realistic angles for the muscles to work. Basically they figured out what each muscle did.
QUESTION 1: Are all the muscles in the forelimb different dimorphicaly?  No – just three.
  1. Muscle 1 bring in the elbow and wrist into the embrace
  2. Muscle 2 also works in tandem with muscle 1
  3. Helps rotate the wrist to aid in control of the female body.
QUESTION 2:  What is the isometric force (contraction to relaxation time) of these individual muscles and the one main muscle that is not dimorphic?
QUESTION 3:  Does testosterone surges during mating season affect muscle growth, strength, and fatiguability?  This question is what her lab is working on now.
STEP FOUR: FIGURE OUT HOW YOU WILL FIND OUT THE ANSWERS TO YOUR MAIN QUESTIONS.
She and her team worked to create a lab experiment using an oscilloscope.
To answer Q2, they pealed back the skin on the forearm and attached electrodes and sensors to the four muscles and provided electrical pulses to the muscle and then measured the responses after  1, 2,  and 4 minutes.
What they found was that the Ca2 levels increased?  Basically the cells, which could absorb the calcium being used back into themselves easily, were not absorbing it all back into the cytoplasm.  Hmmm.  They also discovered that as the time went on, the absorption rate was less until it plateaued in the 3 to 4 minute range.  Higher calcium means less fatigue in the muscles and saving energy.  Thus the frog can hold on for longer and with more force.
To answer Q3, they have just recently castrated a number of frogs and have inserted a testosterone pill in half.  Their research is preliminarily showing that, yes, it does.
STEP FIVE:  POSTULATE OTHER QUESTIONS FOR YOU OR OTHERS TO DISCOVER THE ANSWERS TWO.
At the end she listed a whole bunch of new questions that her research has led her to want to know the answers to.
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Filed under AV, Biology, BW, Going outs (Field Trips), JV, MMcC, Science

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