The key difference between progressive and retrogressive metamorphosis is that progressive metamorphosis is a process where an organism increases its complexity and develops more advanced characters over the course of metamorphosis, while retrogressive metamorphosis is a process where an organism’s advanced characters disappear or reduce over the course of metamorphosis.
Metamorphosis is a biological process where an organism physically develops by changing its structure after birth or hatching. This process takes place through cell growth and differentiation. Some insects, fish, amphibians, cnidarians, crustaceans, mollusks, echinoderms, tunicates undergo metamorphosis based on the change in nutrition source or behaviour. An animal can undergo complete metamorphosis (holometabolous), incomplete metamorphosis (hemimetabolous) or no metamorphosis (ametabolous) at all. Progressive and retrogressive metamorphosis are two different types of metamorphosis processes.
CONTENTS
1. Overview and Key Difference
2. What is Progressive Metamorphosis
3. What is Retrogressive Metamorphosis
4. Similarities – Progressive vs Retrogressive Metamorphosis
5. Progressive vs Retrogressive Metamorphosis in Tabular Form
6. Summary
What is Progressive Metamorphosis?
Progressive metamorphosis is a process where an organism increases its complexity and develops more advanced characters over the course of metamorphosis. In this type of metamorphosis, the adult stage is more advanced than the larval stage. The larval stage possesses degenerated characters. On the other hand, the adult stage possesses advanced characters. It is commonly observed in anurans of Amphibians.
There are different progressive morphological changes that appear in the anurans of Amphibians in the metamorphosis. It involves the progressive development of the limbs. Moreover, the forelimbs in frogs develop under cover of the opercular membrane breakthrough to the exterior in metamorphosis. Also, the gill arches of anurans of Amphibians modify into the hyoid apparatus. In these animals, the middle ear develops in connection with the first pharyngeal pouch in metamorphosis. Further, the tympanic membrane that is supported by the circular tympanic cartilage develops over the course of metamorphosis in these animals. In addition, the eyes protrude on the dorsal surface of the head, eyelids develop, and tongue is developed from the floor of the mouth in these animals over the time of metamorphosis.
What is Retrogressive Metamorphosis?
Retrogressive metamorphosis is a process where an organism’s advanced characters disappear or reduce over the course of metamorphosis. In retrogressive metamorphosis, the larva has advanced characters that are lost in development. On the other hand, an adult has degenerated primitive characters. For example, a urochordate adult shows degenerative characters, while a free-swimming tadpole larva shows more advanced chordate characters that are lost during metamorphosis.
A well-known retrogressive metamorphosis is commonly observed in tunicates like Herdmania. The larva of Herdmania is 1-2 mm long, and it has only 3 hours to survive. During this period, it has to swim and search for a suitable substratum for attachment. Therefore, the larva needs advanced features such as a notochord in the tail, dorsal hollow nerve chord, sense organs (ocellus and statocyst). However, all these advanced characters are lost during metamorphosis. Moreover, the Herdmania transforms into a bag like sedentary animals attached to a rock by a foot during metamorphosis.
Similarities Between Progressive and Retrogressive Metamorphosis
- Progressive and retrogressive metamorphosis are two different types of metamorphosis processes.
- Both processes are seen in animals.
- They explain how an organism physically develops by changing its structure after birth or hatching.
- Both processes help organisms to adapt to a changing environment.
Difference Between Progressive and Retrogressive Metamorphosis
Progressive metamorphosis is a process where an organism increases its complexity and develops more advanced characters over the course of metamorphosis, while retrogressive metamorphosis is a process where an organism’s advanced characters disappear or reduce over the course of metamorphosis. So, this is the key difference between progressive and retrogressive metamorphosis. Furthermore, in progressive metamorphosis, the larval stage possesses degenerated characters, and the adult stage possesses advanced characters. On the other hand, in retrogressive metamorphosis larval stage possesses advanced characters, and the adult stage possesses degenerated characters.
The below side by side comparison details the differences between progressive and retrogressive metamorphosis.
Summary – Progressive vs Retrogressive Metamorphosis
Metamorphosis is the striking change of structure in an individual after birth or hatching. Hormones called molting and juvenile hormones regulate this process. Progressive and retrogressive metamorphosis are two different types of metamorphosis processes. Progressive metamorphosis is a process where an organism increases its complexity and develops more advanced characters over the course of metamorphosis. Retrogressive metamorphosis is a process where an organism’s advanced characters disappear or reduce over the course of metamorphosis. Thus, this is the summary of the difference between progressive and retrogressive metamorphosis.
Reference:
1. “Metamorphosis of Amphibians: Phylum Chordata.” Biology Discussion, 22 July 2016.
Image Courtesy:
1. “Frog-water-frog-lily-pads-amphibian-2211972” (CC0) via Pixabay