Hybridogenesis, Resistance to Disease, Blood Types, Xenotransplantation . . .

[Flyndaran]

Originally Posted by vicky_molokh

To be a species most definitely doesn't require reproduction to be with anyone else. An overwhelming majority of monocellular species reproduce asexually in the first place. They also sometimes employ horizontal gene transfer between other species and themselves.

I feel extra bad about that mistake, because I was just reading about horizontal gene transfer and transposons in the human genome.
I was mainly thinking about sexually reproducing tetrapods.

[Bruno]

The first thing to note is that "species" is, like kingdom, phylum, class, order, and family, a purely human, organizational concept. It's not an inherent characteristic, and because of that there's no such thing as a simple one sentence description of "what is a species" that doesn't immediately prompt a string of exceptions.

There's multiple "species" in the arctic circle that form an east-to-west gradient with a break in the mid-atlantic area (I think? possibly off the coast of siberia instead). IIRC the technical term is "ring species".
Grab any two specimens in the group from neighboring areas, and they can interbreed no problem. But the animals at the two end-points cannot interbreed, and indeed a sample from one end-point and a sample from half-way around the ring may have great difficulty breeding without something like artificial insemination.

What's the difference between a coyote, a domestic dog, and a grey wolf, anyways?

They're all inter-fertile, but dogs don't even come from this continent. The "red wolf" may even be a population that was initially seeded by coyote-wolf hybrids, but is now entirely stable as a closed population with little to no input from either "parent species" (although it almost certainly does get gene 'leakage' in from both parent groups).

But we accept that coyotes, domestic dogs, and the grey wolf are different species, and we argue about whether the red wolf is or isn't, when it's probably more correct to say that the coyote-red wolf-grey wolf are a "ring" species of sorts.

EDIT: Species is a useful intellectual tool, but it really is a shorthand for "this particular population which we are defining by relatedness". The lines are drawn just as arbitrarily as saying the folks on the west side of the street live in Nepean, and the folks on the east side of the street live in Ottawa. Like political boundaries, species boundaries are a mental trick that's useful for human brains, but the people on either side of the street aren't different. We've just organized them that way.

[Varyon]

Originally Posted by vicky_molokh

S1 females can still 'infect' H0 males with symbiotice gamete-colonies. While the chances are lower than on a direct path, this can nonetheless indirectly result in the gamete-colonies reaching an H0 female.

Does this also happen with S1 males? That is, if an S1 male who has previously been active with an S1 female* mates with an H0 female, is there competition between the male's and female's gametes to actually fertilize the egg?

You also note that exowombs can allow for S1 to mate with S1. Does this mean S1 females actually do produce eggs? If so, are these eggs always H0, or can they be S1? If they can be S1, that indicates an S1-S1 mating could produce a diploid S1 (instead of the normal hybrid) - what would that be like?


*If I'm interpreting things correctly, putting female in quotes might be appropriate here - the individual appears female (by H0 standards), but produces parasitic** spermatophores*** rather than eggs. This is "male with a more complicated method of reproduction."

**A symbiote is beneficial or at least neutral to the host, but this directly reduces the host's ability to successfully reproduce - his sperm have to compete with those of S1.

***Not actually spermatophores, but probably the closest thing to it that I'm aware of.

[vicky_molokh]

Originally Posted by Varyon

Does this also happen with S1 males? That is, if an S1 male who has previously been active with an S1 female* mates with an H0 female, is there competition between the male's and female's gametes to actually fertilize the egg?

Nah, it's not competition. The two colonies will merge and shuffle genes with horizontal transfer. Ultimately, either the colony will become rather homogenous, or it will stay chimeric. The latter is more probable, depending on just how much variation counts as chimeric in your opinion. Then, in the end, the colony will get H0 genes, which it will pass along horizontally. Sooner or later, that colony will 'decide' to turn into an embryo with the appropriate mix.

Originally Posted by Varyon

You also note that exowombs can allow for S1 to mate with S1. Does this mean S1 females actually do produce eggs? If so, are these eggs always H0, or can they be S1? If they can be S1, that indicates an S1-S1 mating could produce a diploid S1 (instead of the normal hybrid) - what would that be like?

The gamete-colony cells are not different between (anatomical) males and females. They just don't 'decide' to turn into an embryo in an S1 environment. They require external conditions to match those of either an H0 or S2 uterus.

Exowomb + certain bioalchemical triggers does in fact produce viable pure S1 embryos, whether parthenogenetic, homogenous-mixed from two or more parents, or chimeric, depending on the specifics. Such purebreed S1's tend to have an unhealthy deficit of skin and hair pigmentation, but otherwise exhibit all the normal S1 traits. (For comparison, S2's tend to have lower melanin than the two main strains of H0 and than K0 and T0, but still within range of what would be considered plausible for a healthy human.)

Originally Posted by Varyon

*If I'm interpreting things correctly, putting female in quotes might be appropriate here - the individual appears female (by H0 standards), but produces parasitic** spermatophores*** rather than eggs. This is "male with a more complicated method of reproduction."

**A symbiote is beneficial or at least neutral to the host, but this directly reduces the host's ability to successfully reproduce - his sperm have to compete with those of S1.

It's not proper to call them all males either, since the gamete-colony from an individual of either anatomical sex can be used to produce a fully viable embryo, even without the involvement of H0 gametes. It just requires a proper environment.

It's symbiotic in the sense that it does provide some benefits for the host. But yeah, the hijacking is kinda scary-looking, which causes a . . . controversial . . . opinion of H0's towards S1's.

[Bruno]

Originally Posted by vicky_molokh

It's not proper to call them all males either, since the gamete-colony from an individual of either anatomical sex can be used to produce a fully viable embryo, even without the involvement of H0 gametes. It just requires a proper environment.

Neither phenotype is "male" or "female" on the classic mammalian system, it sounds like - they use an alternate gender system.

That said, humans have a tendency to insist on using the words "male" and "female" when dealing with reproduction-related phenotypes, even with species with four (or more!), like some species of lizard and bird.

My suspicion is that a biologist might classify both phenotypes of S0 as "parthenogenic females" since they don't have two sets of sex organs and therefore can't be hermaphrodites.

S1s are also obligate parasites with funky lifecycles, which is pretty common for parasites - this is actually kind of tame compared to some of the contortions internal parasites go through. The two phenotypes are distinguished by gross anatomy, and have different reproductive strategies but the same intermediate host species.

I'm not clear on what a "homogenous mixed" embryo is that's distinct from a chimera. Do you mean "chimera who's cellular lineages are blended evenly across the entire body"? That's still a chimera. That's also highly unlikely, even if you put the colonies in a blender.

The fact that in the natural condition both phenotypes parasitize another species to incubate the young doesn't make either of them male any more than a female parasitic wasp is "male" because it implants in another creature, or a female seahorse is "male" because it transfers the eggs to a male who carries them to term internally.

Which is something I sometimes feel like arguing about, but there's really no helping nomenclature.

[Flyndaran]

Originally Posted by Bruno

...
That said, humans have a tendency to insist on using the words "male" and "female" when dealing with reproduction-related phenotypes, even with species with four (or more!), like some species of lizard and bird.
...

Those vertebrates are still only functionally male or female, just variant phenotypes as you say. Insects though with very different non-breeding castes may deserve different words.

[vicky_molokh]

Originally Posted by Bruno

Neither phenotype is "male" or "female" on the classic mammalian system, it sounds like - they use an alternate gender system.

That said, humans have a tendency to insist on using the words "male" and "female" when dealing with reproduction-related phenotypes, even with species with four (or more!), like some species of lizard and bird.

There are birds and lizards with four or more actually distinct XX/XY equivalents? ó_O
I know there are birds with multiple different mating strategies expressed by the same genetic sexes, but that's not the same thing. AFAIK.

Originally Posted by Bruno

My suspicion is that a biologist might classify both phenotypes of S0 as "parthenogenic females" since they don't have two sets of sex organs and therefore can't be hermaphrodites.

I think you mean S1. Though when they inherit the X/Y bit from H0, it doesn't even do anything. Anatomical sex for them is something that isn't set until later months of gestation. In some cases even until after gestation. (And in cases of S2, often roughly until the onset of puberty!)

Originally Posted by Bruno

S1s are also obligate parasites with funky lifecycles, which is pretty common for parasites - this is actually kind of tame compared to some of the contortions internal parasites go through. The two phenotypes are distinguished by gross anatomy, and have different reproductive strategies but the same intermediate host species.

I was thinking it isn't all that tame. It seems to top even that funky was that has host-immune-system-defeating virus DNA integrated in its reproductive system code.

Originally Posted by Bruno

I'm not clear on what a "homogenous mixed" embryo is that's distinct from a chimera. Do you mean "chimera who's cellular lineages are blended evenly across the entire body"? That's still a chimera. That's also highly unlikely, even if you put the colonies in a blender.

Yeah, that's mostly a platonic ideal - a case of the lineages exchanging so much that analysis of the resulting individual wouldn't detect the chimerism.

Originally Posted by Bruno

The fact that in the natural condition both phenotypes parasitize another species to incubate the young doesn't make either of them male any more than a female parasitic wasp is "male" because it implants in another creature, or a female seahorse is "male" because it transfers the eggs to a male who carries them to term internally.

Which is something I sometimes feel like arguing about, but there's really no helping nomenclature.

This is why I insert (anatomical) when describing them.

[Flyndaran]

Originally Posted by Bruno

..

The fact that in the natural condition both phenotypes parasitize another species to incubate the young doesn't make either of them male any more than a female parasitic wasp is "male" because it implants in another creature, or a female seahorse is "male" because it transfers the eggs to a male who carries them to term internally.

Which is something I sometimes feel like arguing about, but there's really no helping nomenclature.

The one that produces numerous cheap gametes is the male, and the one that produces few expensive large gametes is the female. Everything else is just life form lineage "habit".
The fact that earth life seems to prefer the female keep hold of the fertilized gametes, all her eggs in one basket so to speak, is one of those generally good ideas that we tend to give more importance to that it really deserves.

[Flyndaran]

Originally Posted by vicky_molokh

There are birds and lizards with four or more actually distinct XX/XY equivalents? ó_O
I know there are birds with multiple different mating strategies expressed by the same genetic sexes, but that's not the same thing. AFAIK.
...

Look at the monstrosity that is monotreme sex determination. Platypuses have 10 sex chromosomes.
As far as I know, even the oceanic life that has variant sexes, they still fall into male or female, just with varying "chirality" where some types of males can only mate with some types of females.

[Bruno]

Originally Posted by vicky_molokh

There are birds and lizards with four or more actually distinct XX/XY equivalents? ó_O
I know there are birds with multiple different mating strategies expressed by the same genetic sexes, but that's not the same thing. AFAIK.

Neither birds nor reptiles are on the XX/XY system, to my knowledge. Many reptiles don't use genes to determine sex at all - crocodiles use the temperature the eggs incubate at.

Boa constrictors have ZZ ("male"), ZW ("female"), and WW ("female", thanks science). WW boas are produced by parthenogenesis, it's not clear if they then mate with ZZ boas to produce "normal" ZW boas, or if they just then reproduce via more parthenogenesis.

There's a bird family that I'm totally blanking on the name of that biologists end up distinguishing the two types of males and the two types of females by the color of the cheek patches. Male 1 and Male 2 are different sizes as well as different colors, Female 1 and Female 2 differ in producing a few large eggs, or more, smaller eggs. This is expressed in their Z and W genes - it's really more like Z0 and Z1, W0 and W1. All four combinations produce viable offspring, each combination is better for different environmental conditions. They're adapted for a changing environment.

EDIT: I'm blanking on the fun lizards with complex sex determination but it's similar - they're classified as having sub-types of "standard" sex chromosomes. They all produce color and behavioral differences, and potentially size and other differences (like the egg size and clutch size in the birds). They come with different mating strategies, because there's really no point in having something that complicated unless it offers an adaptive bonus - and being able to pull another mating strategy out of your hat is flexible in a dynamic environment.

Nobody knows wtf is up with platypus sex determination - they have 10 "sex chromosomes" but no SRY gene, so they're not using the alleged sex chromosomes for sex determination. They're possibly doing something temperature dependent like crocs.