Question

What is the major take-home point of the study? Why is this

What assumptions do the authors make, based on the blog post? Do the authors deal with these assumptions?

His first winter at the University of Mississippi Field Station, Matt Pintar was wading through some ponds where he noticed a large number of egg masses. Clear jelly surrounded most of these egg masses, but a whitish jelly encased some of them. These egg masses were produced by the spotted salamander, Abystoma maculatum, which immediately made Pintar wonder why these differences exist within this species. Biologists use the term “polymorphism” to describe a situation like this, in which two or more forms (poly = multiple, morph = form) exist within a population.

Could it simply be random chance that there were two egg mass morphs? Or was one morph better than the other in getting fertilized by the appropriate sperm, or in keeping the eggs together? Alternatively, perhaps one morph was better at providing nutrients or protecting against predators. The puzzle is that if one morph was superior to the other, then that morph would be favored by natural selection, should outcompete the other, and ultimately cause the second morph to go extinct. So why did both morphs persist in this population of spotted salamanders?

Pintar and his colleague Willliam Resetarits Jr. thought it most likely that the polymorphism was a chance event that provided no benefit to the salamanders. But they did consider the alternative that one morph might be better in some conditions, while the other morph was better in other conditions. Surveys done about 25 years ago suggested that the polymorphism might be connected to differences in water chemistry, so Pintar and Resetarits decided to explore this possible link with a combination of observations of natural ponds and field experiments on artificial ponds.

Answer 1

• The major take-home point of the study is that the polymorphism can persist in a population without offering any particular advantage or disadvantage over the other trait.

This is because, the polymorphisms in the jelly enclosing the egg masses of the salamander might be due to the different genetic mutations that occured in them, as they co-exist in the same water population. Different water conditions is unlikely a reason for this variation.

This can be simplified by giving an analogy to the polymorphisms of the blood groups in humans; which result due to the different modifications in the antigenic groups without offering any specific advantage. Hence, these promote diversity in the traits.

• Assumptions made by the authors regarding polymorphisms:

1. One morph might have more superiority than the other in terms of providing food or protection from predation.
2. Competition for fertilization by the sperm could be causing variation among the morphs.
3. The superiority of the different morphs might be dependent on the conditions they are exposed to.
4. Difference in water chemistry could be resulting in this polymorphism.

The authors are assuming the different possibilities of the polymorphism and stating their hypothesis but none of them have been addressed with an experimental evidence.