Difference Between Metagenesis and Metamorphosis

Main Difference – Metagenesis vs Metamorphosis

Metagenesis and metamorphosis are two phenomena that describe the growth and development processes of organisms. The main difference between metagenesis and metamorphosis is that metagenesis is the alteration of generations between sexual and asexual phases whereas metamorphosis is the existence of distinct stages of the life cycle. Metamorphosis mainly occurs in plants. The sexual generation is called the gametophyte while the asexual generation is called the sporophyte in plants. The basic stages of the metamorphosis are egg, larva, pupa, and adult. The two types of metamorphosis are complete metamorphosis and incomplete metamorphosis. Metamorphosis mainly occurs in insects.

Key Areas Covered

1. What is Metagenesis
     – Definition, Stages, Examples
2. What is Metamorphosis
     – Definition, Stages, Examples
3. What are the Similarities Between Metagenesis and Metamorphosis
     – Outline of Common Features
4. What is the Difference Between Metagenesis and Metamorphosis
     – Comparison of Key Differences

Key Terms: Adult Stage, Complete Metamorphosis, Egg, Gametophyte, Incomplete Metamorphosis, Larva, Metagenesis, Metamorphosis, Nymph, Pupa, Sporophyte

What is Metagenesis

Metagenesis refers to the alteration of generations between sexual and asexual reproduction. It is commonly called the alteration generations. The sexual generation is called the gametophyte, and the asexual generation is called the sporophyte. The gametophyte is haploid while the sporophyte is diploid. The haploid spores germinate to produce the haploid gametophyte. The gametophytes produce haploid gametes by mitosis at their maturity. The fusion of gametes produces the diploid sporophyte. Ultimately, the gametophyte produces haploid spores by meiosis. The alteration of generations in plants is shown in figure 1.

Figure 1: Alteration of Generations

Metagenesis mainly occurs in plants. It also occurs in algae, Rhizaria, fungi, slime molds, and animals. The features of the two generations may vary depending on the type of organism. In algae, both gametophyte and sporophyte are separate and independent organisms. In bryophytes such as mosses, liverworts, and hornworts, the gametophyte is dominant over the sporophyte. In vascular plants, the sporophyte is dominant over the gametophyte. In flowering plants, the gametophyte is reduced to few cells inside the sporophyte.

What is Metamorphosis

Metamorphosis refers to the process of transformation from an immature form to an adult form in distinct stages. Both body form and the habitat may change during metamorphosis. Based on the stages of each life cycle, two types of metamorphosis can be identified.

Complete Metamorphosis

Complete metamorphosis includes egg, larva, pupal, and adult stages, which differ greatly in morphology. The lifecycle of butterflies, ants, fleas, bees, beetles, moths, and wasps are examples of the complete metamorphosis. The complete metamorphosis starts with the laying of eggs by the female insect. The larva, which is the second stage of the complete metamorphosis, are hatched from the eggs. The larval stage can completely differ from the adult stage in morphology, behavior, and/or habitat. The larval body is soft and worm-like. The characteristic feature of the larva is their ravenous feeding. Due to this great appetite for food, the larval stage shows very fast growth. During their growth, larva molts their skin several times. The pupal stage begins with the formation of cocoons around the larvae. The larva is inactive and does not feed when they are inside the cocoons. Their bodies develop more segments, internal organs, legs, and wings. The pupal stage may exist from 4 days to several months. The break out of the cocoon frees a fully developed larva. Different stages of complete and incomplete metamorphosis are shown in figure 2.

Figure 2: Complete and Incomplete Metamorphosis

Incomplete Metamorphosis

Incomplete metamorphosis refers to a type of insect development in which gradual changes occur in the insect during the development from the egg to the adult. The three stages of the incomplete metamorphosis are egg, nymph, and adult. The eggs are laid by the female insect. In most cases, the eggs are covered by an egg case, which protects and hold the eggs together. The eggs hatch into younger nymphs. The nymph resembles the adult without wings. The nymph is also smaller than the adult. The nymph eats the same food as the adult. It develops into the adult through a series of molts. It shed its exoskeleton 4-8 times. When it becomes an adult, the molting does not occur. The incomplete metamorphosis occurs in termites, lice, true bugs, grasshoppers, praying mantis, crickets, and cockroaches.

Similarities Between Metagenesis and Metamorphosis

• Metagenesis and metamorphosis are two types of growth and development of organisms.
• Both metagenesis and metamorphosis occur in multicellular organisms.
• Both metagenesis and metamorphosis produce morphologically distinct phases in the life cycle of organisms.

Difference Between Metagenesis and Metamorphosis

Definition

Metagenesis: Metagenesis refers to the alteration of generations between sexual and asexual reproduction.

Metamorphosis: Metamorphosis refers to the process of transformation from an immature form to an adult form in distinct stages.

Significance

Metagenesis: Metagenesis is the formation of alternative, sexual and asexual generations.

Metamorphosis: Metamorphosis is the formation of distinct morphological stages in the life cycle.

Stages

Metagenesis: Metagenesis produces gametophyte and sporophyte alternatively.

Metamorphosis: Metamorphosis produces egg, larva, pupa, and adult.

Ploidy

Metagenesis: The ploidy of the organism alternates between the generations in metagenesis.

Metamorphosis: The ploidy of the organism is not changed during metamorphosis.

Types

Metagenesis: Metagenesis possesses two phases: haploid phase and diploid phase.

Metamorphosis: The two types of metamorphosis are complete metamorphosis and incomplete metamorphosis.

Occurrence

Metagenesis: Metagenesis mainly occurs in plants. It also occurs in Rhizaria, fungi, slime molds, and animals.

Metamorphosis: Metamorphosis mainly occurs in insects. It also occurs in fishes, amphibians, mollusks, tunicates, crustaceans, cnidarians, and echinoderms.

Conclusion

Metagenesis and metamorphosis are two types of growth and developmental processes of organisms. Metagenesis is the alteration of generations between sexual and asexual phases. Metamorphosis produces distinct stages during the life cycle; egg, larva, pupa, and adult. The main difference between metagenesis and metamorphosis is the distinct stages in each type of growth process.

Reference:

1. “What is Metagenesis?” Biology-Today.com, 26 Aug. 2012, Available here.
2. “Alternation of generations.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 13 Oct. 2017, Available here.
3. “Metamorphosis.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 26 Aug. 2016, Available here.

Image Courtesy:

1. “Alternation of generations simpler” By APeter coxheadderivative work: Peter coxhead (talk) – This file was derived from  Alternation of generations.svg (Public Domain) via Commons Wikimedia
2. “Holometabolous vs. Hemimetabolous” By Username1927 – Own work (CC BY-SA 4.0) via Commons Wikimedia