![]() Because of her higher investment, if a female mates with a male of poor genetic quality, and her offspring don’t survive as a result, she has wasted a lot of energy and resources and ended up with nothing. Why do you think this is? Generally females invest more energy, care, and time in the offspring than a male does, and she has a limited number of eggs compared to practically limitless sperm produced by males of most species. “Females are choosy, while males are not” is a gross generalization, but biologically it tends to be true across most species that reproduce sexually, whether they reproduce with internal or external fertilization. Fewer offspring are produced through this method, but their survival rate is higher than that for external fertilization. Internal fertilization also increases the likelihood of fertilization by a specific male. In many instances, the embryo is isolated within the female, which limits predation on the young. ![]() Internal fertilization has the advantage of protecting the fertilized egg from dehydration on land. This occurs in most mammals, some cartilaginous fish, and a few reptiles. The offspring develops in the female and is born alive. Fertilized eggs are retained inside the female, and the embryo receives nourishment from the mother’s blood through a placenta.This occurs in some bony fish, some sharks, some lizards, some snakes, some vipers, and some invertebrate animals. Fertilized eggs are retained inside the female’s body, but the embryo receives nourishment from the egg’s yolk and the young are fully developed when they are hatched.This occurs in most bony fish, many reptiles, some cartilaginous fish, most amphibians, two mammals, and all birds. Fertilized eggs are laid outside the female’s body and develop there, and the embryo receives 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. (credit: “OakleyOriginals”/Flickr) Internal Fertilization In other species, including many amphibians, individual males court individual females to induce the female to release the eggs, at which point the male releases the sperm to fertilize that individual female’s eggs.ĭuring sexual reproduction in toads, the male grasps the female from behind and externally fertilizes the eggs as they are deposited.In this situation, males and females are often not interacting with each other as individuals, but massed together so that all sperm and all eggs are in the same location. In some species, including some fish, crustaceans, mollusks, and other invertebrates, there are environmental (water temperature, length of daylight) or biological (pheromones) cues that cause males and females to release gametes at the same time.Getting the sperm and egg together requires that the gametes be released at the same time and in the same location to increase the likelihood of fertilization (otherwise all those gametes are wasted!) How does that happen? Water protects the eggs from drying out during development. The information below is adapted from OpenStax Biology 43.2Įxternal fertilization occurs in aquatic environments where both eggs and sperm are released into the water, a process called spawning. Fertilization can occur either inside ( internal fertilization) or outside ( external fertilization) the body of the female. Sexual reproduction starts with the combination of a sperm and an egg in a process called fertilization. Describe different ways that males compete for mates. ![]()
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