What is the Difference Between Homospory and Heterospory

The main difference between homospory and heterospory is that the homospory is the production of a single type of spores with the same size whereas the heterospory is the production of two types of spores, megaspores and microspores, with different sizes. Furthermore, most seedless vascular plants and bryophytes are homosporous while all seed plants and some pteridophytes are heterosporous.

Homospory and heterospory are two conditions of spore production. Heterospory is one of the adaptations of plants that ensure their success to the land.

Key Areas Covered

1. What is Homospory
     – Definition, Spores, Life Cycle
2. What is Heterospory
     – Definition, Spore, Life Cycle
3. What are the Similarities Between Homospory and Heterospory
     – Outline of Common Features
4. What is the Difference Between Homospory and Heterospory
     – Comparison of Key Differences

Key Terms

Fertilization, Gametophyte, Heterospory, Homospory, Seeds, Sporophyte

What is Homospory

Homospory or isospory is the production of a single type of spores. These spores are similar in size and sex. The germination of these spores results in a bisexual gametophyte, which develops both male and female gametangia within the same gametophyte. Here, archegonia are the female gametangia that produce egg cells. On the other hand, antheridia are the male gametangia that produce sperm cells. Since both male and female reproductive structures occur in the same gametophyte, these plants tend to undergo intergametophytic self-fertilization. As a result, the following sporophytic generation becomes homozygous completely.

Figure 1: Homosporous Life Cycle

Homospory occurs in lower vascular plants including ferns, club mosses, and horsetails as well as in bryophytes.

What is Heterospory

Heterospory or anisospory is the production of two distinct types of spores: megaspores and microspores. These spores vary both in size and sex. The megaspores are large in size and produce the female gametophyte upon germination. In contrast, microspores are small in size and produce the male gametophyte upon germination. Here, the production of these two types of spores occurs in two types of sporangia known as megasporangia and microsporangia, respectively. Also, plants that produce both types of sporangia in the same sporophyte are called monoecious. Besides, plants that produce each type of sporangia in separate sporophytes are called dioecious.

Figure 2: Heterosporous Life Cycle

Then, the germinated female gametophyte produces archegonia to produce egg cells. Most importantly, the microspore is carried to the female gametophyte either through the wind, water currents or by means of animals. Microspores germinate on the female gametophyte to produce sperm cells. Moreover, fertilization of the male and female gametes occurs on the female gametophyte. Furthermore, heterospory facilitates cross-fertilization. Nevertheless, heterospory mainly occurs in angiosperms and gymnosperms that produce seeds.

Similarities Between Homospory and Heterospory

• Homospory and heterospory are two conditions of spore production.
• Generally, the sporophyte produces spores.
• The germination of spores produces the gametophyte.

Difference Between Homospory and Heterospory

Definition

Homospory refers to the production of a single kind of spore, neither microspore nor megaspore, while heterospory refers to the production of two types of spores differing in size and sex, the male microspore and the female megaspore. Thus, this is the main difference between homospory and heterospory.

Occurrence

Furthermore, another important difference between homospory and heterospory is that the homospory occurs in seedless, vascular plants and bryophytes while heterospory occurs in seed plants and some pteridophytes.

Sex Differentiation

The sex differentiation occurs at the gametophytic stage in homosporous plants while the sex differentiation occurs at the sporophytic stage in heterosporous plants. Hence, this is also a difference between homospory and heterospory.

Gametophyte Formation

The germination of the homospore produces a single type of gametophyte, which is bisexual, while the germination of the megaspore produces female gametophyte and the germination of the microspore produces the male gametophyte. Therefore, we can take this as another difference between homospory and heterospory.

Gametophyte Dependence

Moreover, the gametophyte of the homosporous plants does not depend on the sporophyte. Therefore, it has to depend on the external environment. But, the gametophyte of the heterosporous plants are attached to the sporophyte; hence, it does not depend on the external environment.

Fertilization

Also, self-fertilization is prominent in homosporous plants while cross-fertilization is prominent in heterosporous plants.

Seed

 One other difference between homospory and heterospory is that the homosporous plants do not produce seeds while the heterosporous plants generally produce seeds.

Embryo

Furthermore, the embryo of homosporous plants obtains nutrients from the green prothallus while the embryo of heterosporous plants obtains nutrients from the endosperm in angiosperms and from the female gametophyte in gymnosperms.

Evolutionary Implications

Besides, another difference between homospory and heterospory is that the homospory occurs in primitive plants while the heterospory occurs in more complex plants.

Conclusion

Homospory is the production of a single type of spores. It occurs in seedless, vascular plants. The homospore germinates to produce a bisexual gametophyte. On the other hand, heterospory is the production of two types of spores different in size as well as in sex. They are megaspores, which germinates to produce the female gametophyte and the microspores, which germinates to produce the male gametophyte. Heterospory mainly occurs in seed plants. However, the main difference between homospory and heterospory is the size and the sex of the spores produced by plants.

References:

1. Petersen, Kurt B., and Martin Burd. “Why Did Heterospory Evolve?” Biological Reviews, vol. 92, no. 3, Nov. 2016, pp. 1739–1754., doi:10.1111/brv.12304.

Image Courtesy:

1. ” Sporic meiosis” By Sporic meiosis.png: Original uploader was Menchi at en.wikipedia.Derivative work: Hazmat2 (talk) – This file was derived from: Sporic meiosis.png: (CC BY-SA 3.0) via Commons Wikimedia    
2. “Alternation of generations complex” By Peter coxhead – Own work (Public Domain) via Commons Wikimedia