Since sponges cannot move, each individual can only fertilize its own egg during sexual reproduction3/1/2024 In ovoviparity, fertilized eggs are retained in the female, but the embryo obtains its nourishment from the egg’s yolk and the young are fully developed when they are hatched. Chicken eggs are an example of this second type. Reptiles and insects produce leathery eggs, while birds and turtles produce eggs with high concentrations of calcium carbonate in the shell, making them hard. This occurs in most bony fish, many reptiles, some cartilaginous fish, most amphibians, two mammals, and all birds. In oviparity, fertilized eggs are laid outside the female’s body and develop there, receiving nourishment from the yolk that is a part of the egg. There are three ways that offspring are produced following internal fertilization. Internal fertilization occurs most often in land-based animals, although some aquatic animals also use this method. The survival rate of eggs produced through broadcast spawning is low. Therefore, millions of eggs must be produced by individuals, and the offspring produced through this method must mature rapidly. The presence of the fertilized eggs and developing young in the water provides opportunities for predation resulting in a loss of offspring. For sessile aquatic organisms like sponges, broadcast spawning is the only mechanism for fertilization and colonization of new environments. Broadcast spawning can result in a greater mixture of the genes within a group, leading to higher genetic diversity and a greater chance of species survival in a hostile environment. The trigger for egg and sperm release (spawning) causes the egg and sperm to be placed in a small area, enhancing the possibility of fertilization.Įxternal fertilization in an aquatic environment protects the eggs from drying out. This allows the female to select a particular male. Pairs of fish that are not broadcast spawners may exhibit courtship behavior. (credit a: Dan Bennett credit b: “OakleyOriginals”/Flickr) (b) During sexual reproduction in toads, the male grasps the female from behind and externally fertilizes the eggs as they are deposited. Figure 1. (a) Salmon reproduce through spawning.
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