Hermaphrodite hook up site
I don't have a reference, but I was thinking all multicellular life and I'd have to imagine that when you factor in plants, that external fertilization is relatively the norm (as is hermaphrodism (dioecy) for the plants).As to earthworms, I disagree about your description of them.
Most species lay a pile of eggs that a male squirts sperm on or squirt eggs while the male squirt sperm and then they hope for the best.So it seems logical that the hermaphrodite way of reproduction is more successful than the "normal" way. The group of fish known as hamlets en.wikipedia.org/wiki/Hamlet_(fish) are simultaneous haermaphrodites, like snails.But it is not, as far as I know all higher developed species are using the standard way of reproduction (male and female). Many other fish are sequential hermaphrodites, but that is probably outside the scope of your brief - its quality not quantity.I honestly don't have any clue as to how daunting (or simple) that is, but I'd imagine that the sophistication of the systems would play a pretty key role.Makes me wonder how much this has been researched in true hermaprhodites.Earthworms are small slow creatures living in soil, I don't imagine they have high rates of encounter, and therefore low rates of encountering the opposite sex, therefore hermaphroditism would be favoured as discussed above.
Further, you say most species are external fertilisers (do you have a reference for this?
sort of like asking 'why do we bother getting married and buying houses when we could just hook up at a bar every weekend?
' hermaphrodites can reproduce more easily, but other organisms invest more in their offspring and also often have a harder time getting around to mating. It is perhaps easiest to address the question by countering it and asking why dioecy (2 sex systems/2 gonochoric types e.g. As you have pointed out there are obvious advantages to being a hermaphroditic species such as more chance of mating - more likely to provide an advantage at very low population densities where interactions are infrequent.
If a hermaphrodite animal (like slug, snail, etc) finds a partner they can mate immediately.
If another animal with "normal" reproduction (lets say a mouse) finds a partner they can only mate if they have the opposite gender.
I suppose the main thing I keep coming back to is the overwhelming disadvantage gender has in terms of potential to create offspring. ) species essentially act as little more than sperm donors, thus half the individuals have effectively zero fitness.