Sponge Reproduction Advanced Douglas Wilkin, Ph.D. Jennifer Blanchette
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AUTHORS Douglas Wilkin, Ph.D. Jennifer Blanchette
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C HAPTER
Chapter 1. Sponge Reproduction - Advanced
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Sponge Reproduction Advanced
• Explain how sponges reproduce sexually and asexually.
Does this animal reproduce? Of course it does. But how? Recall that all living organisms must reproduce. Is this sea sponge male or female? Or neither? Or both? Reproduction of Sponges
Despite the fact that adult sponges cannot move, they are capable of sexual reproduction. Sexual reproduction is the formation of a new organism by the fusion of gametes - an egg and a sperm cell. The sperm is usually produced by the male parent and the egg is produced by the female parent. However, most species of sponges are hermaphroditic, meaning that each individual can produce both eggs and sperm ( hermaphrodite). Gametes contain half of the genetic information of each parent (half of their chromosomes), and their fusion during fertilization provides a complete set of chromosomes to the offspring. Sponges are also able to reproduce asexually. Asexual reproduction does not involve the formation of gametes. The offspring are often formed by budding from a single parent organism. In this concept, we will discuss how sponges carry out each of these types of reproduction. Sexual Reproduction of Sponges
Most sponges are hermaphrodites, but an individual will usually only make one type of gamete at a time, so they are not able to self-fertilize. The general life cycle of a sponge is depicted in the Figure below. Gametes develop from the differentiation of either choanocytes or amoebocytes, depending on the species. Sperm produced by the “male” sponge (one that is producing sperm at the time of reproduction) is concentrated and released into the aquatic environment through the oscula. The sperm floating in the water reach the “female” sponge (one that is producing eggs at the time of reproduction) by the pumping action of choanocytes. In the same way that food is obtained, the choanocytes trap sperm cells as they flow through the interior of the organism. The sperm are then delivered to the eggs by the amoebocytes. Eggs are stored within the mesohyl, and that is where fertilization takes place to form a zygote. Once the zygote develops into a larva, it is usually released back into the water. A larva is 1
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FIGURE 1.1 The sponge life cycle includes sexual reproduction. Sponges may also reproduce asexually.
a juvenile stage of an organism that is structurally very different from the adult stage. In the case of sponges, this is certainly true since the larvae of many species are able to swim using tiny hair-like projections called cilia that beat repeatedly to move the organism through the water. As the larvae continue to develop in the water, they become structurally more similar to adult sponges and lose their locomotive ability. At this point they settle and attach to a solid support where they complete development to the adult stage. For a video of sponges producing sexually, see http://www.youtube.com/watch?v=mVavqt4Sbyo (1:16)
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Asexual Reproduction of Sponges
Sponges are also capable of asexual reproduction. This is accomplished by one of two mechanisms: external budding or internal budding. External budding is when a portion of the sponge breaks off and then regenerates into a complete organism. Internal budding takes place by the formation of internal buds called gemmules. Gemmules are a small collection of several different types of cells that are enclosed by a protective covering. This is an important survival mechanism in unfavorable conditions where the adult may not survive. The protected gemmule can withstand harsh conditions and can begin to develop into an adult sponge when conditions are more favorable. One fascinating feature of some sponge species has been demonstrated by forcing individual animals through a sieve. 2
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Chapter 1. Sponge Reproduction - Advanced
This causes all of the cells of the animal to separate from each other. If the separated cells are incubated together in an aqueous environment, they begin to move and function somewhat independently. Over time the cells will come together to reform the original animal. This finding has strong implications for how multicellular animals may have arisen from the aggregation of single-celled organisms. Vocabulary
• budding: A form of asexual reproduction in which a new organism develops from an outgrowth, or bud, on another one; the bud may stay attached or break free from the parent. • gemmules: A small collection of several different types of cells that are enclosed by a protective covering. • hermaphrodite: An animal that can produce both eggs and sperm. Summary
• Sponges are able to reproduce both sexually using gametes and asexually by budding. • Even though sponges are hermaphroditic, individuals will only make one type of gamete at a time. • There are two forms of asexual reproduction that sponges can go through: external budding and internal budding. Practice
Use this resource to answer the questions that follow. • Reproduction Sponges at http://www.iaszoology.com/reproduction-sponges/ . 1. How can sponges reproduce through fission and fragmentation? 2. What are reproduction bodies? 3. How are larva different between syconoid sponges and asconoid sponges? Review
1. 2. 3. 4. 5. 6.
What does it mean to be hermaphroditic? Can sponges self-fertilize themselves? What kind of cells do sponge gametes develop from? Name some differences between the larva stage and the adult stage of sponges. What are some advantages of forming gemmules? What fascinating phenomenon of sponges points to how multicellular animals may have arisen?
References 1. LadyofHats for CK-12. CK-12 Foundation . CC-BY-NC-SA 3.0
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