What would be a plausible mechanism for conception involving an arbitrary number of gametes?

Question

I am attempting to devise a mechanism whereby a species may reproduce in a communal manner. A number of individuals, ranging from two to arbitrarily high, may contribute gametes to a mass spawning and the resulting offspring will be genetically related to all of the parents who contributed. This would potentially allow for predominantly collectivist social structures as with social insects without limiting the population of reproductive individuals or resorting to an r-selection strategy where paternal relations are unknown and family groups could not develop. The intent is for any given community to function as one gigantic biological family.

As far as I am aware, no such reproductive cycle exists on Earth. Earthly life only ever has one or two parents contributing nuclear DNA.

EDIT: The problem I run into is with the cellular machinery. I assume the process would be similar to alternation of generations where the dominant generation has X-ploidy and the subsidiary generation of syncytia divides into X-ploid zygotes. How would the gametes would merge? How would the syncytia sort the chromosomes into viable zygotes? What would be an ideal ploidy under this system?

EDIT: One of the few examples in fiction I can think of are the Than-Thre-Kull from Gene Roddenberry's Andromeda. Even if it is unlikely to evolve, there must be some logical explanation? I read the paper "Genetic algorithms with multi-parent recombination" which convinced me it's possible, but it was concerned with computer science and not biology.

Answer 1

Instead of actually mixing an arbitrary number of gametes, give the organism a microscopic caste or morph capable of reproduction among themselves.

Consider this: The adult organisms all drop their gametes together in a spawning pool, where they combine at random in the normal sexual manner. However, instead of developing into the large, terrestrial adults, the zygotes become microscopic animals that mature very quickly and proceed to breed among themselves, producing more microscopic offspring. This continues for several generations, before an internal or external trigger causes the microscopic morph to instead produce tadpoles that develop into the large, (presumably intelligent?) adults.

By this point, the creatures who crawl out of the spawning pool will technically be several generations removed from their 'parents' and will therefore have an effectively random mix of genes from all the parents who contributed to the original pool.

Answer 2

The main issue with evolution is that it's all about concurrency in reproduction. So it would go in directions that an individual would aim for maximum of offspring and also might care for his offspring to improve their chances. A simple solution would be to construct a society which postulates rules where this is not possible - say to reduce conflicts.

In natural evolution i could imagine some species that only has a single male or female and the rest of the population is the opposite gender. Like the queen in an ants colony. Also naked mole-rats evolved something similar. The reason could be that the individuals barely produce enough sperm or eggs for the "queen" so every single one needs to contribute. As you want communists you could consider the "queen" without brain just like a reproductive tank.

Answer 3

Since DNA is basically genes put together, you might want that every single individual which contributs has a part of this DNA in the "pool". Splitting and recombining this DNA might be the answer of your problem. Then your child will have an entire new DNA, which includes 10% parent 1 DNA, 20% parent 2, etc...

Important thing

Using DNA, as someone said before, is bound to a very specific mechanism in the reproduction cycle. It's fragile, and has a tendency to mutate easily. More parents = more mutation.

Answer 4

I don't remember the exact volume it was mentioned, but the Yeerks in Animorphs were a species of slugs that reproduced by having around three of their kind "combine", and then replicate into many offspring. This ultimately meant that to reproduce, three Yeerks died in the process, but it still resulted in quite a few offspring.

How this works on a cellular level isn't really clear though, and it's possible that the Yeerks are just splitting their cells up into multiple organisms, seeing as they can already do something similar with brains.

Ultimately, whatever system you use will need to produce multiple offspring with each copulation.

One idea would be that the species could lay slimy eggs all in one place. The slime around the eggs could also contain gametes that invade other eggs; however each gamete would not require a full set of chromosomes. Each eggs can decide on specific chromosomal variants to accept depending on the environmental conditions, and would ultimately end up adopting multiple gametes, picking and choosing chromosomes from each. Alternatively, there might actually be 3-5 different types of gametes that the eggs accept, which ultimately limits the offspring to just 1 "mother" and 5~ "fathers" each. (Not that the fathers would really be identifiable outside of genetic testing)

It's a complicated system, and it might actually result in a few malformed offspring every few batches, but it would achieve the desired result in the end,

Answer 5

It sounds like you’d have something resembling an orchid. Some plants have polyploid chromosomes as the norm, and orchids can have triploid (3x), tetraploid (4x) and even pentaploid (5x) sets of chromosomes. Polyploidy in plants is not always as fatal as it would be in other organisms like human beings. In plants it just seems to make them more fantastic, so if you have an alien race that enjoys having more petals, more fins, more tentacles, then look toward plants, beta fish, and anemones for inspiration. Perhaps there is still two genders but the genes “stack” when you have group sexy-time going on. For example, an ovum can be pollinated by two or three different individuals and the ovum/egg-cell is totally fine with that.

Or, perhaps there are three genders. Male, female and gene blender. So, the male and female parts do their thing, and the third contributes some kind of RNA factory device that breaks them down and puts them together again in a different order, Frankenstein style. For example, take a group of fertilized eggs, then mix up the DNA, by swapping segments of code between them. Imagine taking bits of Lego from different kits and making each kit a little bit different by exchanging some bricks, as an analogy.

Answer 6

One option would be chimerism. Perhaps reproduction results in numerous zygotes with two parents each (in the case of two parents, all the zygotes would be essentially full siblings, while more than two parents result in zygotes with varied parentage). However, instead of simply growing into a multicellular adult exclusively through mitotic cell division, like human zygotes usually do, these zygotes are designed to seek out other zygotes and bond with them to create a chimera - a multicellular organism with genetically distinct cell lines. This occasionally happens to humans in the case of vanishing twins, where twins form and then one dies and gets absorbed by their sibling in early gestation, but in your species, it's the norm.

Now, what purpose would this serve? Well, chimerism can have immune benefits, since genetically distinct immune cells can protect more effectively against different threats. If one zygote would have been very good at fighting off pathogen A but weak to pathogen B, and the other would have had the reverse pattern, their chimera will be moderately good at fighting both pathogens.

In addition, maybe it forms the basis for cell differentiation. Cells in multicellular organisms decide what role to perform based on chemical signals from nearby cells. Perhaps some form of chemical negotiation leads to each zygote deciding to specialize in a specific cell type. This could result in selecting zygotes who are better suited to forming certain cells - for example, a zygote with a deleterious mutation could be blocked from forming cells that express the mutated gene, such as lung cells if the mutation affects lung mucosa formation (like cystic fibrosis). You would still want all zygotes contributing to immune cell development, however, or else they won't get the immune benefits of chimerism.

Whichever zygotes form the reproductive organs will be the only ones that pass on their genes further, so you would probably see significant inter-zygote competition for that role. One possibility would be to have multiple gamete-producing glands forming in multiple body regions, for example maybe this species would repurpose sweat glands to produce gametes. Alternatively, they may simply have each zygote release proto-gamete cells into the bloodstream at a certain stage of development, and these cells are attracted to and cluster in the developing reproductive glands.

This system could easily result in a sex system, with each zygote being capable of only producing one type of gametes. In two-parent individual, this would result in distinct sex types, analogous to male and female, while multi-parent chimeras would have some individuals who produce both types of gametes (with hermaphrodites being more common the more parents contributed to the offspring).