So, I thought I had the hunger related bioluminescence for my Keplerians figured out. That once the hunger hormone reaches a certain threshold, the hormone receptors on some cells of a bioluminescent organ trigger the activation of a certain fluorescent protein which causes the baby's abdomen to glow. And I figured that an evolutionary reason to evolve bioluminescence would be to warn predators that they are poisonous or to mimic poisonous animals.
In other words, bioluminescence would both be a defense and a hunger cue simultaneously. And I figured that since the glow stops after 6 months of life, that maybe the mother's milk doesn't completely meet the nutritional needs and so it draws the rest of the needed nutrients from the bioluminescent organ, ultimately shrinking it and that in the place of this bioluminescent organ would be a more developed digestive tract and bigger lungs.
However, I got some feedback that the reason for the bioluminescent organ to shrink does not make sense and I got 2 alternatives in that feedback.
Alternative 1: Bioluminescent organ stays into adulthood, but the hormone it responds to changes
This is one of the alternatives that I got. In this alternative, the bioluminescent organ stays, but the hormone receptors on the cells change. So it goes from responding to the hunger hormone to signal that the baby is hungry to responding to adrenaline, the fight or flight hormone, later on in life. This would mean that whenever an adult Keplerian gets significantly stressed out, they would glow to signal to others that they are stressed.
I see a few problems with this though. For one thing, Keplerians are social, so having bioluminescence as a stress cue does not make any sense when vocalizations and physical movements can get across stress just as well on their own. Also, Keplerians have a human-like pregnancy. Pregnancy is going to push on the bioluminescent organ. What if that causes the main artery that supplies the organ with oxygen and nutrients to be partly occluded? That could potentially cause an infarction, especially in a multiple birth pregnancy. And that could lead to a life threatening infection. And pregnancy leads to stress as well, so it could mean an almost constant glow in those who are pregnant. Again, the physical and social changes are enough to know the Keplerian is pregnant, so bioluminescence in response to stress caused by pregnancy doesn't make sense either.
Alternative 2: Bioluminescent organ becomes poison glands
Now, this is what the person giving me feedback said would be a way to make the shrinking of the bioluminescent organ make sense. But, what would be the use of poison glands in an intelligent species? I mean, even as babies, Keplerians have quite a bit of intelligence and they develop mental, social, and physical skills fast. I could see poison glands being viable for say a reptilian species, but a humanoid species with a lot of intelligence? I don't see how both the intelligence and the poison glands would be viable.
So, clearly there are flaws in both proposed alternatives. I think the reason that the person giving feedback said that my original idea doesn't make sense has to do with the mother's milk not quite reaching the nutritional needs. Basically, the person giving me feedback was implying that the mother's milk not quite reaching nutritional needs would cause the Keplerian to have organ failure from autophagy and it would be fatal. But, what if all except the bioluminescent organ has receptors for a certain protective factor that prevents the breakdown of tissues? And what if this protective factor is produced in abundance in the fetus and lingers around for months after birth? That would solve the organ failure issue while also not preventing the bioluminescent organ from shrinking to nothing over 6 months, leaving room for a more developed digestive tract and bigger lungs.
So does my original idea make sense or does one of the proposed alternatives make more sense, despite the flaws I pointed out in both alternatives?