They use external fertilization, and are mostly hermaphroditic, although some are male or protogynous ( female and then male ) . " Z . sociatus " was found to reproduce seasonally in Panama, and synchronizes the release of gametes with extremely low tides.
32.
In species with external fertilization and male parental care, females are able to distribute her clutch amongst different males and by doing so the female increases the likelihood that at least some of her offspring will receive indirect genetic benefits and / or extensive parental care from a quality provider.
33.
Both gamete competition and gamete limitation assume that anisogamy originated through disruptive selection acting on an ancestral isogamous population with external fertilization, due to a trade-off between larger gamete number and gamete size ( which in turn affects zygote survival ), because the total resource one individual can invest in reproduction is assumed to be fixed.
34.
Dawkins and Carlisle further expanded on this by suggesting that uniparental female care is dominant during internal fertilization because the male has time to desert, and uniparental male care is dominant during external fertilization because the male first waits for the female to deposit the eggs and only then does he fertilize them with his sperm, which gives the female time to escape.
35.
Since the discovery of sperm attraction to the female gametes in ferns over a century ago, sperm guidance in the form of sperm chemotaxis has been established in a large variety of species Although sperm chemotaxis is prevalent throughout the Metazoa kingdom, from marine species with external fertilization such as sea urchins and corals, to humans, much of the current information on sperm chemotaxis is derived from studies of marine invertebrates, primarily sea urchin and starfish.
