|MadSci Network: Zoology|
Some of the most important adaptations of many organisms involve the timing and energy expenditure involved in reproduction. Different organisms reproduce in very different ways. For example, coral colonies release many millions of eggs once each year during a mass spawning, and only a tiny fraction of these eggs survive. In contrast, primates, like humans reproduce once every several months and only have one (or occasionally more) offspring each time, but expend an awful lot of energy maximising the chance that each offspring survives - not only are the embryos protected by the mother until birth (rather than being born as defenseless eggs), but primate babies are not self sufficient for a considerable time after birth. These are two broad approaches to reproduction, one making as many offspring as possible, the other using the same energy to make sure that each of a small number of offspring has a good chance of surviving.
Octopi generally lay clusters of eggs in rocky areas, and care for the developing embryos by protecting and cleaning them and flushing the egg mass with jets of water. After the eggs hatch, the adults die. Organisms like octopi, squid and cuttlefish, that produce all of their offspring at one time, investing all their energy in one reproductive effort, are referred to as semelparous. The evolutionary logic behind this is fairly obvious - the mother can expend all of her energy on producing a large number of eggs, with good yolk supplies so that they can hatch as mini-adults rather than helpless embryos, and can spend all her time guarding the eggs from predators. Female octopi do not eat whilst caring for/ guarding eggs, but instead live off food reserves stored in the body tissues. It is simply a way of ensuring that as many of the babies survive as possible - the ultimate in parental sacrifice.
Some good sources of information about octopus biology include the Cephalopod Page and About Octopi.
Try the links in the MadSci Library for more information on Zoology.