A hypothetical organism alternates between plant and animal stages over its life cycle. The organism exhibits equally extreme sexual dimorphism.

The generations are diplobiontic a la some species of red algae: gametophyte (androphyte and gynophyte), carposporophyte (microcarpophyte and megacarpophyte) and tetrasporophyte (microtetraphyte and megatetraphyte).

The life cycle occurs like so:

  1. the animal-like gynophyte is fertilized by contact with the pollen of the plant-like androphyte
  2. the gynophyte gestates animal-like carposporophytes which consume their mother
  3. many carpophytes are produced by a single gynophyte and their motility allows them cover more distance
  4. the carposporophytes asexually gestate plant-like tetrasporophytes which eventually consume their parent and root in nearby soil
  5. the tetraphytes will asexually clone themselves to cover more ground
  6. the megatetraphyte asexually spawns motile gynophytes which may travel further away
  7. the microtetraphyte grows multiple androphytes which are completely dependent on their parent a la angiosperms

(This organism is based on the "pequeninos" from Speaker for the Dead with some inspiration from the specworld Illion.)

Is such an organism and its reproductive cycle plausible?


2 Answers 2


Plausibility of a reproductive cycle is always hard to prove, but I'd point out the life cycle of the Jellyfish as a suggestion that it might be reasonable.

Jellyfish lifecycle

Adult male jellyfish release sperm into the water, which either combines with an egg released into the water or an egg held in the female. Then:

The fertilized eggs then develop into planulae (singular: planula), which are ciliated free-swimming larvae shaped a bit like a miniature flattened pear. After several days of development, the planulae attach to a firm surface and transform into flower-like polyps. The polyps have a mouth and tentacles that are used to feed on zooplankton.

Polyps reproduce asexually by budding—when a polyp divides roughly in half to produce a new genetically identical polyp—or they can produce or transform into medusae, depending on the type of jellyfish. Hydrozoan polyps bud medusae from their sides; cubozoan polyps each transform into a medusa.

The one thing I would make sure of with your system is that each step produces enough viable offspring. Several of your steps call for consuming the previous generation's body. This is only a viable reproductive mechanism if your individuals are quite confident that enough of their child will survive the full cycle. Make sure the environment rewards this dangerous behavior. There's certainly cycles in nature that involves consuming the parent, but I'm not aware of any which have to do it multiple times in a cycle.

  • $\begingroup$ I would think each step would produce multiple offspring and all of the sessile morphs are capable of self-cloning. Does that solve the problem? $\endgroup$
    – Anonymous
    Commented Feb 8, 2017 at 16:25
  • 1
    $\begingroup$ @Anonymous It definitely would help. It would also be important to make sure that none of the gestation which consume the parent are easy to disrupt. For example, at least one species of octopus (I forget which) has a mother who gives her life for her young. She does it in a tight crack of a rock where it is hard for predators to possibly disrupt the process. That being said, having a lifecycle where at least one part is capable of asexual reproduction would definitely help the odds. It could keep the species alive until conditions are favorable for the rest of the cycle. $\endgroup$
    – Cort Ammon
    Commented Feb 8, 2017 at 16:34

Everything is plausible, but the specialization in the real world has its reasons. At some point if you would introduce another species that specialize in something to the ecosystem they would dominate the thing they specialize. As animals they could eliminate plants; rip them out so that they can actually root to soil, without plants already filling the space. But an another animal that has no restrictions of having to be also a plant could specialize better on being an animal and eliminate them.


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