Why do sponges avoid self fertilization

Story Source: Materials provided by University of Zurich. Shimizu, Seiji Takayama. Gene duplication and genetic exchange drive the evolution of S-RNase-based self-incompatibility in Petunia. Nature Plants , ; 1 1 : DOI: ScienceDaily, 8 January University of Zurich. Sophisticated system prevents self-fertilization in petunias. Retrieved November 14, from www. New research These proteins do so by a caspaseindependent mechanism, suggesting Parthenogenesis is a form of asexual reproduction in which an egg develops into an individual without being fertilized.

The resulting offspring can be either haploid or diploid, depending on the process in the species. Parthenogenesis occurs in invertebrates such as water fleas, rotifers, aphids, stick insects, and ants, wasps, and bees.

Ants, bees, and wasps use parthenogenesis to produce haploid males drones. The diploid females workers and queens are the result of a fertilized egg.

Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Parthenogenesis has been observed in species in which the sexes were separated in terrestrial or marine zoos. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males. It is possible that the asexual reproduction observed occurred in response to unusual circumstances and would normally not occur.

Sexual reproduction is the combination of reproductive cells from two individuals to form genetically unique offspring. The nature of the individuals that produce the two kinds of gametes can vary, having for example separate sexes or both sexes in each individual. Sex determination, the mechanism that determines which sex an individual develops into, also can vary.

Hermaphroditism occurs in animals in which one individual has both male and female reproductive systems. Invertebrates such as earthworms, slugs, tapeworms, and snails Figure Hermaphrodites may self-fertilize, but typically they will mate with another of their species, fertilizing each other and both producing offspring.

Self-fertilization is more common in animals that have limited mobility or are not motile, such as barnacles and clams. Many species have specific mechanisms in place to prevent self-fertilization, because it is an extreme form of inbreeding and usually produces less fit offspring. Mammalian sex is determined genetically by the combination of X and Y chromosomes.

In mammals, the presence of a Y chromosome causes the development of male characteristics and its absence results in female characteristics. The XY system is also found in some insects and plants. Bird sex determination is dependent on the combination of Z and W chromosomes. Notice that this system is the opposite of the mammalian system because in birds the female is the sex with the different sex chromosomes.

The W appears to be essential in determining the sex of the individual, similar to the Y chromosome in mammals. Some fish, crustaceans, insects such as butterflies and moths , and reptiles use the ZW system. More complicated chromosomal sex determining systems also exist.

For example, some swordtail fish have three sex chromosomes in a population. A common misconception about hermaphroditic reproduction is that organisms fertilize their own eggs with their own sperm. In fact, most species do not self-fertilize, and many are physically incapable of self-fertilization. They are the most numerous animals on Earth. Most invertebrates are insects.

However, simpler invertebrates evolved before insects. Some, like the sponges you will read about in this concept, have existed virtually unchanged for hundreds of millions of years. Their continued existence is evidence that they are well adapted for their habitats. They also evolved some of the most important traits that are found in almost all animals today. Without the traits that evolved in sponges and other simple invertebrates, you would not exist.

Sponges are aquatic invertebrates that make up the phylum Porifera. The word "porifera" means pore-bearing. The phylum is aptly named. As you can see from Figure below , a sponge has a porous body.

There are at least 5, living species of sponges. Almost all of them inhabit the ocean, living mainly on coral reefs or the ocean floor. Sponge on a Coral Reef. This orange sponge is covered with pores. Can you predict the function of the pores?

Sponges come in a variety of shapes and sizes. For example, they may be shaped like tubes, fans, cones, or just blobs. They range in diameter from about a centimeter 0. Many species live in colonies that may be quite large. Adult sponges are sessile. This means they are unable to move from place to place.