#histotrophy

[uncharismatic-fauna]

Uncharismatic Fact of the Day

Surprisingly enough, mammals aren't the only animals that provide their young with milk! The giant freshwater stingray is one of several species of cartelaginous, live-bearing fish that sustain their young to term through a form of maternal care called histotrophy, in which the mother provides her embryo(s) with nutritional, milk-like secretions known as trophonemata while they're in the uterus.

(Image: A giant freshwater stingray (Urogymnus polylepis) caught and released by Cambodian fishermen, by Chhut Chheana)

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[rxttenfish]

putting these in their own post, old conversation/discussion/lore dumps about merfolk reproduction, with date and also sometimes what prompted it

-

[Overview on what merfolk children are like, Jan 12th 2022]

The first thing to remember is that merfolk are more closely related to amphibians than anything else alive today. 

While they aren’t modern amphibians proper, and belong to an entirely different clade all their own, with themselves and the leviathans being the only extant members remaining, there’s still a lot of similarities among them. Sure, they have more derived features, but that’s just due to them ending up with selective pressures to convergently evolve things like scales and claws. And their specific reproductive strategy is one of the places where this is the most obvious.

You know how amphibians will create many squishy eggs that entirely lack a shell and cannot be taken out of water? Merfolk do the same! However, they also encountered the same issue that other tetrapods also had. Namely, that the eggs could both dry out, but also that they were remarkably delicate. Amniotes solved this issue through the creation of the amniotic sac, hence the name, allowing them to create eggs ( and, later, switch to live birth ).

The clade merfolk belong to took a... different route. As in, they never actually switched to any kind of shelled egg! They looked at their squishy eggs that needed to be laid in water, and instead decided to begin just using themselves as their pool of water.

A given merfolk will release several dozen eggs at the same time, and they’ll still be contained within the body. If these eggs are fertilized, then they’ll begin to develop and go through roughly the equivalent stages of fetal development (or, in this case, the comparison would directly go to things like tadpoles and metamorphosis). Merfolk also have a form of histotrophy, which brings me to exactly what happens during development.

Namely, in that merfolk will begin to cannibalize each other in the womb. This wasn’t universal amongst their clade, some others would simply release the young as effectively-tadpoles and others would already be inclined towards larger numbers of offspring, but among all living members, only one pup will be born at a time. While it certainly does help with things like minimizing immediately-fatal birth defects, largely this is just because of space and resource constraints. Merfolk and leviathans both are K-selected species, and having carnivorous offspring that hatch, begin to kill and eat each other in the womb, and have one remaining at the end is a fairly easy way to do so. 

This is also why twins are so rare — because it requires for two pups to make it that far without killing each other in the womb, and that thinning-out happens rather early on in gestation. There can be problems, if one kills the other far later on than they were supposed to.

Merfolk similarly have long pregnancies for this reason, as well as just how their pups are born. Namely, they also needed their pups to be able to both swim and (somewhat) defend themselves from the moment of birth, plus they are simply large animals, so they need that extra time. 14 months is the universal average amongst merfolk.

The parents will also have a hormonal shift during that time. Merfolk, evolutionarily speaking, had an issue with other merfolk killing and sometimes cannibalizing pups, and for a lot of other marine predators, mer pups make for very easy meals. So, in order to prevent this, soon-to-be mer parents will have a dip in their social needs and will separate off to themselves, to have the pup in a safe, isolated location. Similarly, they will become more irritable and defensive, protective of their new pup and very, very stubborn in not letting anyone else near them. I’ve been waffling back and forth on how intense to exactly make it, whether it be just a more emotional time or if it’s outright more of a fugue state, but regardless, they will refuse to let anyone else close to the location or to the pup, and can be a lot more eager to try and physically deter anything that is not letting them have their space. As in, there are warning signs within the Merkingdom that mean that a couple with a new pup is there, and you should turn back now unless you possibly want to get bit.

You can think about merfolk as new parents in the same way you might consider a mother crocodile. Do not approach, they are territorial and aggressive and immensely protective, and you are not uniquely safe from it.

It fades back to normal after a few weeks or so, when the pup is considered “ready” to be safely brought into the community of other merfolk. In the past, some merfolk have counted the day where it fades enough to come back as the new pup’s birthday, but in the modern era, they will often count the actual day of birth (since new parents can still easily mark that down so long as they have a clock with them and no one else is sending them into a frenzy). The parents will still stick with the pup and care for them basically until their adulthood (around the same time as it is for humans), but they will also begin communally raising the pup with everyone else. Most communities will consider any children within them to be basically everyone’s children, with some special weight given to their blood family, but largely with expectations on everyone to play some part. This is why there’s actually very little pressure for any mer that is not a royal to become a parent, but LOTS of pressure for them to be good around kids. 

It’s also a good explanation for why merfolk compulsively adopt children that they might find, even if they aren’t actually other merfolk. If the Merkingdom didn’t refuse to let anyone past their borders, then merfolk would rather quickly form a reputation for massive mixed-species families, their urge to adopt is that strong.

But all of this comes back to merfolk pups in of themselves:

Pups are born already very developed and independent. They are capable of swimming with decently powerful tails, they have very strong vocal cords for chirping and shrieking, ability to chase after small fish ( and their parents), claws, and a full set of teeth. While adult merfolk have their own dentition, as pups, all merfolk are born with a set of simple, needle-like teeth. They do not have the jaw power of adults yet, but they are perfectly adapted to eat and process soft-bodied prey and meat that has been stripped of bone, and will require being fed like this from the moment they are born. They also have a fairly strong grip — as merfolk will carry their pups a bit like sloths do. Chest-to-chest, both facing forward, with the pup’s hands beneath the adult’s arms, easily within reach to hold onto should something happen. For abyssals, they are born without bioluminescence and their fins cannot yet maintain the consistent shape of the adults’.

And, yes, if they are placed upon land at this early stage, mer pups can even begin walking from the moment of birth.

Taking care of them is, likewise, about as straining as you could imagine a baby that could run around on its own and open cabinets would be. They’re kinda feral.

-

[On merfolk war gods, April 6th 2024]

i mentioned the other day about how a lot of merfolk gods of war and violence are connected to childcare, and i've been meaning to explain it a little more-

merfolk do give live birth, and as amphibians their tadpoles go through a full metamorphosis in the womb, coming out as basically tiny versions of the adults. this is something that their specific lineage of temnospondyls specialized in, since they were actually rather terrestrial and were made to be able to travel long distances over land between wet areas and to adapt to a variety of conditions easier. oviviviparity meant that they weren't reliant on vernal pools at all, with some lineages then depositing the live tadpoles in a water source, some of them going through full metamorphosis before birth, some having more or less tadpoles in general with a variety of r- and k- selection depending on their individual adaptations.

merfolk in particular, then, are descended from a group that began to specialize not only in metamorphosis in the womb, but also in having fewer offspring that they invested greater resources into, making sure that they were as likely to survive the strain as possible. they also already fed their live offspring within the womb by both histotrophy and oophagy, putting extra resources into making sure they were healthy and strong when they were born. which is why when the lineage began to select for reduced offspring, the solution was mostly… just to keep them in longer, and to provide an additional source of nutrition in the form of intrauterine cannibalism. this guaranteed not only was only one offspring born at a time, but also that they were the healthiest among all the tadpoles, minimizing immediately-lethal mutations.

you also have the adults, who at this point in their evolutionary history, had predation by other merfolk being a major driving factor. pregnancy with this many resources going into it, even when you are a large, social predator who can afford it, is still an exhausting and risky affair, and the earliest moments of life are easily among the riskiest. merfolk have very good senses of smell and taste, making it easy for outside merfolk to find merfolk who were pupping, and if there's a strain in the social cohesion of the group they're already in, it would also be very easy for even merfolk in those early social groups to turn on one member and to enforce who is allowed to reproduce. merfolk also came from animals that lived along shorelines in loosely associated but dense colonies, and getting away from the others for vulnerable moments was already a factor.

so the answer evolution took with merfolk was to make the pupping merfolk experience a sudden massive drop in their need to socialize and bond with other merfolk, and a heightened sense of aggression towards other merfolk. this would occur around the last few weeks of their pregnancy, and would continue a few weeks after the birth, taking up a period of about a month. this would also involve usually only one other merfolk from the same social group experiencing the same shift, the hormones creating a positive feedback loop between each individual merfolk, who would essentially act as a midwife or carer for the pupping merfolk, and was enough of a guarantee that both were well-fed that it was selected for.

for modern merfolk: pupping is universally seen as the one time violence is "permitted" without question, as they experience it as nearly a fugue state where they are unable to control themselves and cannot stop the aggression they feel towards all other merfolk or other "intruders" (sharks being an example of something common for your usual merfolk that wouldn't be tolerated here). however, since they aren't violent all the time and calm down if they are allowed to be away and apart from other merfolk, the modern solution has usually been to create "pupping rooms", glorified apartments with no windows and intense soundproofing, where they can be alone and feel safe. other buildings can be converted into pupping spaces, or they can simply be places located far enough off from the main township to not set it off, but in all cases, there's a lot of warnings set up around them, with the symbols being very similar across cultures. a sort of "do not enter, do not disturb the peace, this is a nursery".

food and resources are delivered in as non-obstructive a way as possible, and usually some medical training/advice is given to the merfolk well ahead of time, since getting someone else into that space puts everyone at risk. some merfolk, however, out of cultural habit or due to having health issues, will select for "midwives" as their non-pregnant pupping partner to help care for them, a practice that is the default among the royals. its selected for primarily by time spent in close contact with each other, and involves a professional who has been trained in medicine pairing up with the pregnant merfolk for this time, going through the fugue state together, and broadly being able to better confirm the health of everyone involved.

where the war gods come in, is that merfolk often say that this sudden aggression and will to do violence comes from the (one of their) god of violence and warfare being given the domain of children and pregnancy as either a blessing or a punishment. a punishment usually involves the story of how the god came to earn the ire of the other gods, and was given this task to make up for the debt they owed, so they gave their bloodlust and terrible rage to young children and to new parents, in retribution for this insult. a blessing, however, involves them more voluntarily offering their services, and giving their battle lust and war rage to the young and vulnerable, in order to better keep them safe and to ensure they grow up into great hunters and protectors of their communities.

because of this, in areas where the pupping rooms are closed off from the outside instead of being isolated from other merfolk, shrines and tribute to said war god are set up. some of the nice royal pupping rooms have large frescos and statues outside of the area, both as a warning to keep away, and as a place where visitors will come by, unseen and unbothersome to the pupping merfolk inside, to offer tribute or make prayers or otherwise pay their respects to such a god, to ask for their blessings in warfare and honorable victory in battle or to soothe violence and rage where they see it. likewise, some military positions can only be held by merfolk who have been pregnant before.

this god, and other variations of gods of violence and warfare across merfolk cultures, often are depicted as being pregnant themselves, and/or with severe mutations that could not survive out of the womb. merfolk do know such mutations happen, due to autopsies given to pregnant merfolk who have passed away, and they're retroactively seen as being monstrous or demonic in nature, saying that they were what killed the pregnant merfolk, when often its more likely the other way around (the parent died, and because of this, this mutation wasn't just consumed by their siblings and could be discovered).

at the same time, merfolk also believe in a high plurality of even single individuals, with their spirituality suggesting that their sapience and intelligence is given through the gesalt of all these merfolk coming together as one even before birth, and seeing the intrauterine cannibalism as more spiritual and holy than how humans might see the same thing, being a combination of both merfolk's intense desire to socialize and needing their large social groups, and as a common philosophy towards hunting and the eating of other animals, which is that the animal is willingly giving their spirit and strength to the hunter in exchange for the hunter ensuring the health of all of said type of animal.

so these war gods are also, uniquely, said to be truly individual in a way that few merfolk deities are, and this being partially an explanation for how monstrous and terrifying they are, that they are removed from even the natural process that animals go through, let alone the dual process that merfolk go through. this too, also effects their policies and attitudes towards other species and why they view them as child-like and primitive, being that they are far too individual to make any accurate judgements about the world and cannot tend it like merfolk do.

[royalreef]

Anonymous inquired:  What are baby Merfolk like? How do they develop?

(( The first thing to remember is that merfolk are more closely related to amphibians than anything else alive today. 

While they aren’t modern amphibians proper, and belong to an entirely different clade all their own, with themselves and the leviathans being the only extant members remaining, there’s still a lot of similarities among them. Sure, they have more derived features, but that’s just due to them ending up with selective pressures to convergently evolve things like scales and claws. And their specific reproductive strategy is one of the places where this is the most obvious.

You know how amphibians will create many squishy eggs that entirely lack a shell and cannot be taken out of water? Merfolk do the same! However, they also encountered the same issue that other tetrapods also had. Namely, that the eggs could both dry out, but also that they were remarkably delicate. Amniotes solved this issue through the creation of the amniotic sac, hence the name, allowing them to create eggs ( and, later, switch to live birth ).

The clade merfolk belong to took a... different route. As in, they never actually switched to any kind of shelled egg! They looked at their squishy eggs that needed to be laid in water, and instead decided to begin just using themselves as their pool of water.

A given merfolk will release several dozen eggs at the same time, and they’ll still be contained within the body. If these eggs are fertilized, then they’ll begin to develop and go through roughly the equivalent stages of fetal development ( or, in this case, the comparison would directly go to things like tadpoles and metamorphosis ). Merfolk also have a form of histotrophy, which brings me to exactly what happens during development.

Namely, in that merfolk will begin to cannibalize each other in the womb. This wasn’t universal amongst their clade, some others would simply release the young as effectively-tadpoles and others would already be inclined towards larger numbers of offspring, but among all living members, only one pup will be born at a time. While it certainly does help with things like minimizing immediately-fatal birth defects, largely this is just because of space and resource constraints. Merfolk and leviathans both are K-selected species, and having carnivorous offspring that hatch, begin to kill and eat each other in the womb, and have one remaining at the end is a fairly easy way to do so. 

This is also why twins are so rare — because it requires for two pups to make it that far without killing each other in the womb, and that thinning-out happens rather early on in gestation. There can be problems, if one kills the other far later on than they were supposed to.

Merfolk similarly have long pregnancies for this reason, as well as just how their pups are born. Namely, they also needed their pups to be able to both swim and ( somewhat ) defend themselves from the moment of birth, plus they are simply large animals, so they need that extra time. 14 months is the universal average amongst merfolk.

The parents will also have a hormonal shift during that time. Merfolk, evolutionarily speaking, had an issue with other merfolk killing and sometimes cannibalizing pups, and for a lot of other marine predators, mer pups make for very easy meals. So, in order to prevent this, soon-to-be mer parents will have a dip in their social needs and will separate off to themselves, to have the pup in a safe, isolated location. Similarly, they will become more irritable and defensive, protective of their new pup and very, very stubborn in not letting anyone else near them. I’ve been waffling back and forth on how intense to exactly make it, whether it be just a more emotional time or if it’s outright more of a fugue state, but regardless, they will refuse to let anyone else close to the location or to the pup, and can be a lot more eager to try and physically deter anything that is not letting them have their space. As in, there are warning signs within the Merkingdom that mean that a couple with a new pup is there, and you should turn back now unless you possibly want to get bit.

You can think about merfolk as new parents in the same way you might consider a mother crocodile. Do not approach, they are territorial and aggressive and immensely protective, and you are not uniquely safe from it.

It fades back to normal after a few weeks or so, when the pup is considered “ready” to be safely brought into the community of other merfolk. In the past, some merfolk have counted the day where it fades enough to come back as the new pup’s birthday, but in the modern era, they will often count the actual day of birth ( since new parents can still easily mark that down so long as they have a clock with them and no one else is sending them into a frenzy ). The parents will still stick with the pup and care for them basically until their adulthood ( around the same time as it is for humans ), but they will also begin communally raising the pup with everyone else. Most communities will consider any children within them to be basically everyone’s children, with some special weight given to their blood family, but largely with expectations on everyone to play some part. This is why there’s actually very little pressure for any mer that is not a royal to become a parent, but LOTS of pressure for them to be good around kids. 

It’s also a good explanation for why merfolk compulsively adopt children that they might find, even if they aren’t actually other merfolk. If the Merkingdom didn’t refuse to let anyone past their borders, then merfolk would rather quickly form a reputation for massive mixed-species families, their urge to adopt is that strong.

But all of this comes back to merfolk pups in of themselves:

Pups are born already very developed and independent. They are capable of swimming with decently powerful tails, they have very strong vocal cords for chirping and shrieking, ability to chase after small fish ( and their parents ), claws, and a full set of teeth. While adult merfolk have their own dentition, as pups, all merfolk are born with a set of simple, needle-like teeth. They do not have the jaw power of adults yet, but they are perfectly adapted to eat and process soft-bodied prey and meat that has been stripped of bone, and will require being fed like this from the moment they are born. They also have a fairly strong grip — as merfolk will carry their pups a bit like sloths do. Chest-to-chest, both facing forward, with the pup’s hands beneath the adult’s arms, easily within reach to hold onto should something happen. For abyssals, they are born without bioluminescence and their fins cannot yet maintain the consistent shape of the adults’.

And, yes, if they are placed upon land at this early stage, mer pups can even begin walking from the moment of birth.

Taking care of them is, likewise, about as straining as you could imagine a baby that could run around on its own and open cabinets would be. They’re kinda feral.

[ocean-fact-of-the-week]

OFOTD #276

Histotrophy is a form of maternal care in the uterus exhibited by some live-bearing sharks and rays, in which the developing embryo receives additional nutrition from its mother in the form of uterine secretions, known as histotroph (or "uterine milk"). There are two types: mucoid and lipid histotrophy, mucoid histotrophy being the more widespread of the two.

[royalreef]

Anonymous inquired:  How would mermaid pregnancy work?

(( I’ve answered this question before! Several times, actually, because I have basically the full details on mer reproduction worked out. I think the only parts I haven’t written down on this blog are the matching protein casing on the outer shells of the egg/sperm to prevent self-fertilization and inbreeding, how that affects mer reproductive healthcare, their histotrophy, the exact interaction that causes the same hormonal reaction in the non-carrying partner or other closest merfolk to have that surge around the birth of the pup ( and if this could occur in non-merfolk at all ), and the exact developmental stages for pups. I should also update their reproductive anatomy posts, but otherwise, yeah it’s mostly all there!