Biochemical measures of age in the Blue Crab

The critical need for better information on age structure of crustacean populations like the blue crab has lead to alternative, biochemical approaches for age determination.   Scientists are now studying the accumulation of a mixture of compounds called lipofuscin, in an attempt to determine the age of crustaceans more accurately.

 The scientific basis behind the possibility of using these compounds is their formation and where they might accumulate in animal tissues.

 All Organisms that breathe oxygen generate free radicals(a chemical species that possess an unpaired electron in the outer electron shell of the molecule) as a by-product of metabolism.  The free radicals extra valence electron make them highly reactive and capable of reacting with and interfering with the function of other molecules in cells, especially DNA.  If these molecules are damaged they could eventually cause problems with proper functioning of the cell. 

 To reduce possible damage from free radicals, cells have evolved to use a series of reactions that appear to link these reactive oxidants with lipids, and proteins to form the mixtures of products termed lipofuscins.  Lipofuscins also known as “age pigments” are highly stable compounds that accumulate in cells over the life of the organism.  Since the formation of lipofuscin is dependent upon metabolism, it should increase in concentration as long as the cell is alive.  Studying this concentration in animals under controlled conditions, scientists can estimate chronological age.

 Where the lipofuscins accumulate is also important.  Although they are likely to form in all cells, most cells turnover at different rates, which is difficult to follow over the lifespan of an organism.  Nervous tissues are special, however, because they divide and are replaced very slowly in all organisms.  In these tissues the lipofuscin has the chance to accumulate for long periods of time and its concentration can be used as a method of measuring age.

 Free radicals have been implicated in the cause of several diseases including rheumatoid arthritis, Alzheimer's disease, hypertension, liver cell injury and cancer.  That’s why you should eat your fruits and vegetables.  Fruits and vegetables contain antioxidants, which bind with the free radicals, so that they don’t interfere with other molecules within the cell. 

Lipofuscin data

     The bright yellow spots in this picture are lipofuscin deposits.

Experimental data gathered by rearing crabs in a controlled setting has demonstrated the following age correlations.

Procedure: 

1. Click here:  lipofuscin   , then cut and paste the lipofuscin data into an excel spreadsheet.
2. Create a histogram of  Lipofuscin concentration vs. frequency. 

3. Below, calculate the distribution of crabs according to age. 

4. Compare LF data with previous carapace data to answer the following questions.

 Questions:

1. How do the histograms for LF and carapace width compare, What are the differences if there are any?

2. What environmental factors could effect Lipofuscin accumulation, and how?

3. Why is lipofuscin extracted from the eye stalk of blue crabs?

4.   If  lipofuscin concentration is an accurate measurement of age, what happens to the population distribution?

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