Issue One: All of the races in this setting are going to be based on real-world animals that have rare and unusual mating and reproductive habits. We're going to have parthogenesis, facaultative gender and extreme sexual dimorphism - because those things actually exist among animals here on earth. If you are offended by discussion such oddities, I do not want your input. If you are offended because I'm likely gonna have different stat lines for different genders among the elephant-seal analogs, I do not want your input. Suggest a better way to model such extreme sexual dimorphism and I'll listen, but if you're here to whine about how that's sexist, then I'm gonna remind you that I am not talking about the real-world nature or ideal of human beings with such a design decision and then I'm gonna put you on ignore. The overall point here is the same as all fantasy roleplaying: to learn more about ourselves by pretending to be others who are very different.
Issue Two: Is going to be how we get to something that can be called a "culture" while keeping the reproductive methods a viable strategy for producing offspring. The human standard of lengthy gestation and risky birth followed by over a decade of parental / bi-parental care is just not going to be applicable to all of these races. As much as I want to make things plausible, crazy stuff like ancestral memory, psychic powers, memetic brain parasites and "dude it's magic" is going to end up being invoked.
Issue Three: This is a D&D world. All that crazy naturalist reproduction is gonna get mapped to creatures that exist in most D&D games. This is gonna mean rewriting chunks of the flavor for many of them. Still I would like to keep such rewrites small enough that the original creature is still recognizable.
Issue Four: This is a D&D world, so there have to be plausible explanation for why certain individuals of each playable species might become adventurers. Now that the very nature of this project is gonna mean that the "rescue and marry the princess" quest is gonna be out the window for several of these races. I can deal with that, but if it's absolutely impossible to have adventure hooks for individuals within a race,then the race cannot be a playable race.
So with those disclaimers out of the way, here's the first draft of candidate critters and their reproductive habits:
- Ants/Bees or other hive insects - where most individuals are sterile Workers or Soldiers and reproduction is carried out by Queens and Drones.
- Aphids - who reproduce clonally for dozens of generations but have a single generation of cripples which reproduces sexually in order to lay eggs which can survive the winter.
- Black Widow or Praying Mantis - something that practices sexual cannibalism.
- Parasitoid Wasps - which incubate their eggs inside another species
- Seahorse - in which the incubation / gestation of fertilized eggs is transferred back from the mother to the father. Alternately, birds that split nesting duties would work here, but the mechanics of the seahorse bit is less familiar to most players and therefore more potentially interesting
- Snails - hermaphrodites who shoot love darts at each other
- Spotted Hyenas - who have a nepotistic matriarchal society
- Elephant Seals - who have extreme sexual dimorphism, due to a winner-takes-all competition among males within limited breeding. Over half of each year's pups are sired by a single bull male.
- Komodo Dragons - these aquatic reptiles reproduce both sexually and asexually. However the way their chromosomes work means that a female who reproduces asexually lays a clutch of eggs that hatches into both males and females. This allows a single female alone to colonize a new island while maintaining the disease and parasite resistance conferred by sexual reproduction. Also, they may be poisonous or just infectious. Also they like to reuse nesting sites of birds.
- Frogs - or something else with Lek-based reproduction, where they have a big rave/orgy each mating season.
- Blood Flukes - when a male and female mate they bond physically and their morphology changes with each taking on new tasks.
- Humans - here both as a reference point for players, and also because the human strategies of extended parental care and menopause are seemingly unique.