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Other Reproductive Strategies


Other Reproductive Strategies
u Another reproductive strategy is to produce fewer young that are more capable of surviving to adulthood.

u Some invertebrates and vertebrates have a spermatophore, or sperm capsule, that helps a male deliver sperm directly to a female in one way or another. The advantage of a spermatophore is that a male only needs to mate with a female once, and there is a relatively high chance that he is the father of that female’s embryos.
Other Reproductive Strategies

u An advance beyond the spermatophore is internal fertilization, in which the male needs to be in contact with the female. All reptiles have internal fertilization.
u But even among reptiles there are a few species that give birth to live offspring, called viviparous reproduction, which is common in environments that may be too cold, or where the warm season is too short for optimal development of eggs. North American garter snakes, banded water snakes, and timber rattlesnakes that live in seasonally cold environments all give birth to live young that are ready to eat and act like miniature adults.
u This also occurs in the ocean. Skates and rays internally fertilize eggs during sex, as do their relatives the sharks. Internal fertilization is efficient, and it increases the likelihood of fertilization by reducing sperm wastage in the open water.
u It also protects the young, allows them to arrive in the world as miniature versions of their parents, and even allows the mother to select a new environment that is optimal for her offspring and allows her to move there prior to giving birth. Internal development of offspring ensures that the energy-rich eggs produced by females are not eaten by predators and that most of the energy spent by females on reproduction is passed to the embryos.
u While animals that give birth to live young are called viviparous, rays represent a third variation: They are ovoviviparous, which means that their embryos rely on substantial yolk within the egg during initial stages of development. After the yolk nutrients stored in the egg have been absorbed by the embryo, it ingests or absorbs an organically rich uterine milk called histotroph, which is produced by the mother and secreted into her uterus.
u By comparison, many other bony fish lay eggs. The infant fish go through metamorphosis as they develop from embryo to larva, or fry, and then onto the juvenile stage while the tiny creatures absorb the yolk sac. After the yolk sac is absorbed, the individual fish needs to be able to feed on its own.